Symposium Organizers
Juergen Christen Universität Magdeburg
Chennupati Jagadish Australian National University
David C. Look Wright State University
Takafumi Yao Tohoku University
K3: Defects
Session Chairs
Jürgen Christen
Masashi Kawasaki
Tuesday AM, November 28, 2006
Room 200 (Hynes)
9:30 AM - **K3.1
First-Principles Defect Theory for Zinc Oxide.
Shengbai Zhang 1
1 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractIn some sense, defect study is at the heart of ZnO research for the utilization of its vast potential in electronic and optoelectronic applications. Over the years, we have carried out systematic first-principles calculations on the various defect properties of ZnO ranging from native point defects [1], to the enhancement of nitrogen incorporation [2], to the behavior of elemental p-type dopants [3], to the theory of large lattice-mismatched impurities [4], and most recently to the formation of complexes for unintentional free electrons [5]. We now know that oxygen vacancy (VO) is an important deep-level defect, possibly giving rise to the green band and persistent photoconductivity. Zinc interstitial (Zni) is, on the other hand, an important shallow donor. Zinc oxide is a typical large gap semiconductor with doping asymmetry, and is hence difficult to dope p-type. To remove this obstacle, non-equilibrium doping is required. We predicted that by using metastable molecular doping sources such as NO or NO2 and a control of growth kinetics, one could significantly increase the solubility of substitutional NO in ZnO, as having been confirmed by several later experiments. We have systematically studied the various potential p-type dopants. While substitutional group-I dopants produce relatively shallow acceptors, to be successful one needs to overcome their intrinsic tendency for Jahn-Teller distortion and to form interstitial donors. We show that most of the perceived group-V acceptors (P, As, and Sb) have very low solubility and very high ionization energy. It is therefore a real puzzle why recent experiments have succeeded in using these dopants for p-type ZnO. To solve the puzzle, an antisite model was proposed, in which the dopant substitutes Zn, instead of O, and acts as a gettering center for zinc divacancies (2VZn). It is this complex that is responsible for the observed p-type conductivity. We will analyze the recent XANES study on arsenic-doped p-type ZnO, as it questions the validity of the AsZn-2VZn model. We will show that in fact their raw data support the model. Finally, we show that in ionic crystals such as ZnO the complexing of native defects with impurities could be a more general phenomenon. For example, residual NO can bind the otherwise mobile Zni during post-growth cooling, causing intrinsic n-type behavior of ZnO in good agreement with recent experiment. Work supported by the U.S. DOE/BES and EERE under contract No. DE-AC36-99GO10337.[1] S. B. Zhang, S.-H. Wei, and A. Zunger, Phys. Rev. B 63, 075205 (2001).[2] Y. Yan, S. B. Zhang, and S. T. Pantelides, Phys. Rev. Lett. 86, 5723 (2001).[3] C. H. Park, S. B. Zhang, and S.-H. Wei, Phys. Rev. B 66, 073202 (2002).[4] S. Limpijumnong, S. B. Zhang, S.-H. Wei, and C. H. Park, Phys. Rev. Lett. 92, 155504 (2004).[5] D. C. Look, G. C. Farlow, P. Reunchan, S. Limpijumnong, S. B. Zhang, and K. Nordlund, Phys. Rev. Lett. 95, 225502(2005).
10:00 AM - K3.2
Electrical Characterization of Deep Acceptor States in ZnO.
Holger von Wenckstern 1 , Heidemarie Schmidt 1 , Rainer Pickenhain 1 , Gisela Biehne 1 , Matthias Brandt 1 , Michael Lorenz 1 , Gerhard Brauer 2 , Armin Dadgar 3 , Alois Krost 3 , Marius Grundmann 1
1 Institut für Experimentelle Physik II, Semiconductor Physics, Universtät Leipzig, Leipzig Germany, 2 Institut für Ionenstrahlphysik und Materialforschung, Forschungszentrum Rossendorf, Dresden Germany, 3 Institut für Experimentelle Physik, Otto-von-Guericke-Universität Magdeburg, Magdeburg Germany
Show Abstract10:15 AM - K3.3
Defect physics in ZnO
Anderson Janotti 1 , Chris Van de Walle 1
1 Materials Department, University of California - Santa Barbara, Santa Barbara, California, United States
Show AbstractAs with any semiconductor material, understanding the role of impurities and native defects is essential for controlling the electronic and optical properties of ZnO. We have performed a comprehensive investigation of native point defects in ZnO using first-principles methods based on density functional theory. Excess zinc, manifested in the form of oxygen vacancies and zinc interstitials, has long been invoked as the source of the commonly observed unintentional n-type conductivity in ZnO. However, contrary to the conventional wisdom, we find that native point defects are very unlikely to be the cause of unintentional n-type conductivity [1]. Oxygen vacancies, which have most often been invoked as shallow donors, have high formation energies in n-type ZnO, and are deep rather than shallow donors [2]. Zinc interstitials also have high formation energies in n-type ZnO, and are fast diffusers with migration barriers as low as 0.57 eV; hence zinc interstitials are unlikely to be stable. Zinc antisites are also shallow donors, but have even higher formation energies. Zinc vacancies are the deep acceptors possibly related to the green luminescence, and act as compensating centers in n-type ZnO. Oxygen interstitials have high formation energies. They can occur in the form of electrically neutral split interstitials, but also as a double acceptor at octahedral interstitial sites in n-type ZnO. Oxygen antisites have very high formation energies and are unlikely to exist in measurable concentrations under equilibrium conditions. Our calculated migration barriers are in good agreement with experimental data where available and may provide a guide to more refined experimental studies of point defects in ZnO. We also explore possible sources of the unintentional n-type conductivity and the consequences of point-defect behavior for the control of p-type doping.[1] A. Janotti and C.G. Van de Walle. J. Cryst. Growth 287, 58 (2006)[2] A. Janotti and C.G. Van de Walle, Appl. Phys. Lett. 87, 122102 (2005).
10:30 AM - K3.4
Persistent Photoinduced Changes in Charge States of Donors and Acceptors in Hydrothermally Grown ZnO.
Nancy Giles 1 , Yongquan Jiang 1 , Larry Halliburton 1
1 Physics Department, West Virginia University, Morgantown, West Virginia, United States
Show AbstractZinc oxide (ZnO) bulk single crystals grown by the hydrothermal technique are being developed for use as substrates for thin film growth. In this work, a bulk single crystal obtained from Tokyo Denpa (Japan) was investigated using electron paramagnetic resonance (EPR), photoluminescence (PL), and infrared absorption (FTIR) techniques. The sample is low n-type with a room-temperature Hall carrier concentration of about 2 x 1014 cm-3. EPR spectra from Mn, Co, Ni, Fe, shallow Group III donors (Al, Ga), and substitutional lithium acceptors were easily observed. PL revealed the presence of trace amounts of copper impurities (the characteristic spectrum associated with Cu2+ ions was present). Lithium, which is present during the hydrothermal growth process as a mineralizer, was the only major acceptor impurity detected in this material, and substitutes for zinc on the cation site. Lithium can be present in ZnO as an isolated substitutional singly ionized acceptor in n-type material. Also, as shown using the FTIR data, a significant portion of the lithium impurities are compensated by a nearby hydrogen in the form of a neutral Li-OH complex [1]. Photoinduced changes in the charge states of the different deep and shallow centers were monitored using 325 nm light from a He-Cd laser. Before illumination, all the lithium acceptors are compensated (i.e., are non-paramagnetic). After illumination, the neutral Li acceptor is detected using EPR, and the electrons have been redistributed among the various deep and shallow donor levels. All the trivalent nickel and iron centers initially present are converted to their divalent forms, and increases in divalent Co and Mn are observed. When the laser light is shuttered, the changes in charge states are persistent and stable at liquid helium temperatures. The thermal stability of the various centers is determined by monitoring the recovery of their EPR signals to the pre-illumination state. The EPR signals are monitored at a fixed temperature (which was optimum for each defect spectrum), as a function of sequential steps of heating to progressively higher temperatures and then cooling back to the measurement temperature. The thermal release of charge from the deep transition-metal donors occurs in the 100 to 150 K range. This work was supported by the National Science Foundation under Grant DMR-0508140. [1]. L. E. Halliburton et al., J. Appl. Phys. 96, 7168 (2004).
10:45 AM - K3.5
Diffusion of Intrinsic Point Defects in Zinc Oxide.
Paul Erhart 1 , Karsten Albe 1
1 Institut für Materialwissenschaft, Technische Universität Darmstadt, Darmstadt Germany
Show AbstractFor the fabrication of zinc oxide devices the mobilities of point defects are of crucial importance. Unfortunately, experiments have produced very scattered data for the self-diffusion coefficients in ZnO and did not succeed in resolving the mechanisms by which intrinsic defects migrate.In order to obtain a more profound understanding of self-diffusion density-functional theory calculations were carried out using the generalized gradients approximation with semi-empirical self-interaction corrections (GGA+U). The migration barriers for vacancy and interstitial motion for oxygen as well as zinc were obtained. The lowest barriers (0.2-0.3 eV) are found for zinc interstitials moving via a second neighbor interstitialcy mechanism. They become mobile at temperatures between 80 and 130 K, which conincides with the range of experimentally determined onset temperatures for annealing due to intrinsic defects. The migration enthalpies for oxygen interstitials are strongly dependent on the charge state ranging between 0.3 and 1.0 eV. The barriers for vacancy migration on the other hand are only weakly dependent on the charge state and somewhat higher. The influence of Fermi level and chemical environment on the self-diffusion coefficients is discussed. Depending on the conditions both vacancy and interstitialcy mechanisms can be operational. For conditions, however, under which oxygen diffusion experiments are carried out, interstitial migration dominates.
11:30 AM - **K3.6
ZnO Near-Interface Defects and Control of Schottky Barriers.
Leonard Brillson 1 2 , H. Mosbacker 2 , Michael Hetzer 2 , Yuri Strzhemechny 3 , David Look 4 , Stephen Ringel 1 2 , Maria Gonzalez 1 , Gene Cantwell 5 , Jizhi Zhang 5 , Jin Joo Song 5 6
1 Electrical & Computer Engineering, The Ohio State University, Columbus, Ohio, United States, 2 Department of Physics, The Ohio State University, Columbus, Ohio, United States, 3 Department of Physics & Astronomy, Texas Christian University, Fort Worth, Texas, United States, 4 Semiconductor Research Center, Wright State University, Dayton, Ohio, United States, 5 , ZN Technology, Inc., La Brea, California, United States, 6 Department of Electrical & Computer Engineeing, University of California, San Diego, California, United States
Show AbstractAs ZnO becomes a leading candidate for next generation semiconductor electronics, the ability to control its electrical contacts with metals becomes critical. Until now, there have been no ZnO Schottky barrier studies that isolate the effects of surface contamination, lattice defects, impurity dopants, and interface chemical reactions. We have used low energy depth-resolved cathodoluminescence spectroscopy (DRCLS) at 10 K in a UHV scanning electron microscope and macroscopic current-voltage (I-V) measurements to study Schottky barrier (SB) formation at metal interfaces to clean, ordered ZnO(000-1). We fabricated sets of 30 nm-thick, 0.4 mm diameter Au, Al, Ni, Pt, Pd, Mo, Ta and Ir diodes on the same single crystal surfaces from different growers. Prior to metallization, DRCLS revealed orders-of-magnitude difference in native bulk defect densities for crystals grown by different techniques, and these defect densities varied substantially between the crystals’ bulk and surface. For all crystals, surfaces treated with a remote oxygen (20% O2/80% He) plasma created clean, ordered surfaces and reduced defect emissions in the surface region.[1] Micro-DRCLS taken through the metal diodes revealed defect transitions at 2.1, 2.5, and 3.0 eV that change dramatically with process steps and metal. These transitions are associated with native point defects predicted theoretically [2] and identified experimentally via positron annihilation spectroscopy.[3] Deep-level optical and transient spectroscopies found corresponding bulk defects at EC-2.54 eV and EC-0.53 eV. DRCLS from bulk and shallower depths reveal that these densities can increase by > 100x at the surface. Near-interface defect accumulation depends on the ZnO-metal chemical interaction and crystal quality. Plasma cleaning strongly affects which interface defects form. Metals on low defect ZnO more than double near-interface densities, while the same metals on high defect ZnO increase densities by 10-100x – indicating both defect creation and diffusion of existing defects. These metal-induced defects impact device performance. I-V characteristics changed from Ohmic to Schottky and idealities decreased for Pt, Au, Ir, and Pd with plasma treatment. SBs increased and idealities lowered as near-surface defect densities decreased by orders of magnitude with a combination of higher crystal quality and remote O2 plasma treatment. The magnitude of the metal’s influence on Schottky barriers measured electrically correlates directly to the metal reactivity and the DRCLS- measured defect densities at the surface and ZnO bulk. Similar gap state-limited SBs for other compound semiconductors indicate that the impact of near-interface native defects on ZnO Schottky barriers is more general in nature.[1] H.L. Mosbacker et al., Appl. Phys. Lett. 87, 012102 (2005).[2] A. Janotti and C.G.Van de Walle, Appl. Phys. Lett. 87, 122102 (2005).[3] F. Tuomisto et al., Phys. Rev. B 72, 085206 (2005).
12:00 PM - K3.7
Field-Emitter SEM based Cathodoluminescence Characterization of ZnO Nanostructures and Films
Martin Schirra 1 , Anton Reiser 1 , Raoul Schneider 1 , Günther Prinz 1 , Martin Feneberg 1 , Tobias Röder 1 , Klaus Thonke 1 , Rolf Sauer 1
1 Institut für Halbleiterphysik, Universität Ulm, Ulm Germany
Show AbstractThe wide-gap semiconductor ZnO is a promising candidate for a new generation of optical and electronic devices including small structures down to the nanometer scale. Prior to successful application of this material system adequate preparation of both bulk material and nanostructures is mandatory requiring also a detailed characterization of such structures. Using an optimized field-emitter type electron microscope (SEM), cathodoluminescence measurements with very high spatial and spectral resolution were performed on ZnO films and ZnO nanostructures to assess material quality, doping, and strain on a scale of a few tens of nanometers. ZnO nanopillars on different substrates were investigated exhibiting intrinsic and extrinsic luminescent features. Pillars on a-plane sapphire show increasingly dominant near-band edge luminescence when cathodoluminescence spectra are mapped from the bottom close to the substrate up to the top of the pillars indicating optimum crystal quality in these top regions. There are indications that aluminum from the sapphire substrate is incorporated in the lower parts of the pillars. Also single ZnO pillars grown homoepitaxially on ZnO films deposited before pillar growth on a GaN substrate were studied. These pillars show very high luminescence intensities at narrow linewidths in the region of donor bound excitonic recombination, demonstrating very high material quality.For ZnO films grown on various substrates, the influence of the substrate material was investigated by performing line scans on cleaved samples from the ZnO/substrate interface to the ZnO film surface. In addition, monochromatic CL images were recorded from ZnO films and the results correlated with the surface morphology and strain.
12:15 PM - K3.8
Electrical Characterization of Proton Irradiated n-Type ZnO.
Danie Auret 1 , Michael Hayes 1 , Jackie Nel 1 , Walter Meyer 1 , Werner Wesch 2 , Elke Wendler 2
1 Physics, University of Pretoria, Pretoria, Gauteng, South Africa, 2 Institut für Festkörperphysik, Friedrich-Schiller-Universität, Jena Germany
Show AbstractDue to its direct wide bandgap of 3.37eV, Zinc oxide (ZnO) has become the focus of many studies. Devices such as detectors, lasers and diodes operating in the ultra-violet (UV) and blue regions of the spectrum have been reported. Furthermore, the large band gap of ZnO renders it suitable as window or buffer layers in the fabrication of solar cells and as a substrate or buffer layer for the group III – nitride based devices. Further practical advantages of ZnO include bulk-growth capability, amenability to conventional wet chemistry etching, which is compatible with Si technology and convenient cleavage planes. It has previously been reported by us that the defect introduction rate in ZnO by MeV protons at room temperature is almost two orders of magnitude lower than that in GaN. To investigate if this is due to a material property of the ZnO, or perhaps a case of radiation enhanced annealing, low temperature proton irradiation were performed in this study. ZnO Schottky barrier diodes (SBD’s) were fabricated with 20/80/40/80 nm Ti/Al/Pt/Au ohmic contacts on the O-face and circular 0.5 mm in diameter 500 nm thick Ru Schottky contacts in the Zn face. The carrier concentration of the ZnO prior to irradiation was approximately 5x1016 cm-3. These diodes were irradiated with 1.8 MeV protons at a temperature of –140 °C with fluences ranging from 5x1012 cm-2 to 5x1013 cm-2. Current (I) deep level transient spectroscopy (I-DLTS) was used to study the shallow level defects introduced during the proton-irradiation of the ZnO SBD’s. These measurements revealed that this implantation introduced a defect with an energy level at 0.04 eV below the conduction band and with an electron capture cross section of about 10-15 cm2. There are at least two possible origins of this defect. Firstly, it may be that it is hydrogen-related and is the consequence of the hydrogen implantation performed for this study. Theory has predicted that hydrogen forms a shallow donor in ZnO. Secondly, it was reported that electron irradiation with an energy of >1.6 MeV produces the ZnI in ZnO which is a shallow level defect at 0.03 eV below the conduction band. The defect we measure here may therefore also be the ZnI.
12:30 PM - K3.9
Optical Quenching of Hydrogen Shallow Donors in Zinc Oxide.
Norbert Nickel 1
1 , Hahn-Meitner-Institut Berlin, Berlin Germany
Show AbstractResearch on zinc oxide (ZnO) is driven by a strong desire for blue and ultraviolet light emitting devices. So far, however, the major shortcomming is the lack of reliable p-type doping. Interestingly, the unique properties of hydrogen have been identified as a significant problem that interferes with effective p-type doping. Hydrogen forms a complex with oxygen that gives rise to a local vibrational mode at 3326.4 cm-1. In this paper we will show that the intensity of the O-H vibrational modes is very sensitive to sub bandgap light. For this purpose single crystal ZnO samples with a c-axis orientation were hydrogenated by the following procedure. The samples were sealed into quartz ampoules with 800 mbar of hydrogen gas. Then the ampoules were put in a furnace and annealed for 2.5 hours at 830 °C. Subsequently, the ampoules were rapidly quenched to room temperature by immersion in water. The hydrogenated ZnO samples were characterized with Fourier transform infrared spectroscopy. All measurements and illumination sequences were performed at a temperature of 5 K. Upon illumination the intensity of the O-H vibrational line decreases significantly. This effect is completely reversible and annealing at temperatures above 30 K restores the O-H vibrational mode to its initial intensity. Isochronal annealing experiments indicate the presence of a second shallow donor state with larger ionization energy than that of the hydrogen donor state. The observed changes of the O-H vibrational mode will be discussed in terms of changes of the effective charge of the O-H complex due to capture and release of electrons.
12:45 PM - K3.10
Defect Characterization of Zinc Oxide Bulk Crystals
Govindhan Dhanaraj 1 , Balaji Raghothamachar 1 , Michael Dudley 1 , Michael Callahan 2 , Buguo Wang 2 , David Bliss 2
1 Dept. of Materials Science, Stony Brook University, Stony Brook, New York, United States, 2 Sensors Directorate, Air Force Research Labs., Hanscom AFB, Massachusetts, United States
Show AbstractZinc oxide (ZnO) is a wide band-gap semiconductor with an energy gap of 3.37eV. It has a potential for applications as emitter devices in the blue to ultraviolet region and as a substrate material for GaN based devices. It also has the highest shear modulus and stable lattice because of the very small inter-atomic distance among the II-VI semiconductors. Its large exciton binding energy is useful for efficient UV laser applications. In our research effort, ZnO crystals were grown in autoclaves made of high strength steel, with a sealed platinum liner. The mineralizer solution was a mixture of Li2CO3, KOH, and NaOH, with the fill quantity at 80%. During growth, the nutrient zone was at 355°C with a temperature gradient of 10°C. These ZnO crystals obtained from many growth runs were characterized using synchrotron x-ray topography to find the suitability of these crystals as substrates for epitaxy. ZnO crystal plates of (10-10) orientation, cut perpendicular to the seed, were prepared for X-ray topographic characterization. These crystal plates contained the seed crystal and the bulk grown from the seed to show the growth history. Also, c-cut plates were used for the defect evaluation. X-ray topographs were recorded using synchrotron white beam radiation. The systematic study revealed the presence dislocations penetrating into the bulk from the seed, dislocation refraction, growth sector boundaries, inclusions, planar inclusion defects etc. Process induced dislocations such as dislocation loops around the seed suspension as well as slip bands could be observed. The role of edge dislocations in the growth process could also be seen. The defect structures were compared with the structural quality of the ZnO crystals grown from other techniques. Details of the synchrotron X-ray topographic defect characterization will be presented.
K4: Spintronics and magnetism
Session Chairs
Alex Hoffmann
Andreas Waag
Tuesday PM, November 28, 2006
Room 200 (Hynes)
2:30 PM - **K4.1
Spin-Exchange Interaction in ZnO-based Quantum Wells.
Bernard Gil 1 , P. Lefebvre 1 , T. Bretagnon 1 , T. Guillet 1 , T. Taliercio 1 , C. Morhain 2
1 Groupe d'etude des Semiconducteurs, University of Montpellier, Montpellier cedex 5 France, 2 , Centre de Recherche sur l'Hetero-Epitaxie et Applications, Valobonne France
Show AbstractContinuous-wave, time-integrated, and time-resolved photoluminescence experiments are used to study the excitonic optical recombinations in wurtzite ZnO/Zn0.78Mg0.22O quantum wells of varying widths. By comparing experimental results with a variational calculation of excitonic energies and oscillator strengths, we determine the magnitude (0.9 MV/cm) of the longitudinal electric field that is induced by both spontaneous and piezoelectric polarizations. The quantum-confined Stark effect counteracts quantum confinement effects for well widths larger than 3 nm, leading to emission energies that can lie 0.5 eV below the ZnO excitonic gap. Wurtzitic ZnO/(Zn,Mg)O quantum wells grown along the (0001) direction permit unprecedented tunability of the short-range spin exchange interaction. In the context of large exciton binding energies and electron-hole exchange interaction in ZnO, this tunability results from the competition between quantum confinement and giant quantum confined Stark effect. By using time-resolved photoluminescence we identify, for well widths under 3 nm, the redistribution of oscillator strengths between the A and B excitonic transitions, due to the enhancement of the exchange interaction. Conversely, for wider wells, the redistribution is cancelled by the dominant effect of internal electric fields, which dramatically reduce the exchange energy.
3:00 PM - K4.2
Reconsidering Magnetic Exchange in Oxide-based DMS.
Rebecca Janisch 1 2 , Priya Gopal 2 , Nicola Spaldin 2
1 Electrical and Information Engineering, Chemnitz University of Technology, Chemnitz Germany, 2 Materials Department, University of California, Santa Barbara, California, United States
Show AbstractMany transition metal (TM) doped oxides, such as TMxTi1-xO2 and TMxZn1-xO, are considered to be robust room temperature diluted magnetic semiconductors (DMS) and therefore promising materials for spintronic devices. However, for most oxide-based DMS there is still controversy over the origin of the magnetism as well as the factors influencing its magnitude and ordering temperature. In recent ab initio density-functional studies [1,2] we showed that in defect-free systems the magnetic interaction is very short ranged and strongly dependent on the TM-O-TMbond angle. In this presentation we will show our results on Co-doped TiO as well as ZnO doped with a range of transition metals. Based on our results the influence of the host crystal structure as well as of point and extended defects in the oxide host on the magnetic interaction will be discussed. Finally, we will demonstrate theextreme sensitivity of the sign and the magnitude of the magnetic interaction not only on the choice of the exchange correlation functional, but also on structural relaxations, and the convergence parameters of the calculation.[1] R. Janisch and N. A. Spaldin, PRB 73, 035201 (2006)[2] P. Gopal and N. A. Spaldin, cond-mat/0605543 (2006)
3:15 PM - K4.3
Demonstration of Spin Injection into ZnO using ZnO Based Diluted Magnetic Semiconductors.
Shivaraman Ramachandran 1 , Jonh Prater 2 1 , Jagdish Narayan 1
1 , NCSU, Raleigh, North Carolina, United States, 2 Materials Science Division, Army Research Office, Raleigh, North Carolina, United States
Show Abstract3:30 PM - K4.4
Room Temperature ZnO Nanostructures For SpintronicsApplication.
Weilie Zhou 1 , Jingjing Liu 1 , Jiajun Chen 1 , Minghui Yu 1
1 Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractMn and Co doped ZnO diluted magnetic semiconductor nanostructures, such as bowls, cages, nanorodes, and nanowire arrays have been successfully fabricated through chemical vapor deposition and pulsed laser deposition, respectively. The nanostructures were characterized using X-ray diffractometer (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The doped elements were detected by electron energy dispersive X-ray analysis (EDS), electron energy loss spectroscopy (EELS), and X-ray photoelectron spectroscopy (XPS). Superconducting quantum interference device (SQUID) magnetometer was employed to measure ferromagnetism of the DMS nanostructures and room temperature ferromagnetism was observed. The DMS nanostructures with room temperature ferromagnetic ordering have strong applications in spintronic nanodevices.
3:45 PM - K4.5
ZnO Based Diluted Magnetic Semiconductors: Novel Materials and Devices.
Shivaraman Ramachandran 1 , John Prater 2 1 , Jagdish Narayan 1
1 , NCSU, Raleigh, North Carolina, United States, 2 Materials Science Division , Army Research Office, Raleigh, North Carolina, United States
Show AbstractSpintronics is the emerging field where the spin of the charge carrier is utilized in addition to the charge to bring about novel functionalities for ultra-low power devices, non-volatile memories, magnetic recording and optical polarizers. One of the prime requirements for practical applications is that these materials be ferromagnetic above room temperature.Zinc oxide has been studied extensively to synthesize what are known as diluted magnetic semiconductors, where a transition metal dopant is used to substitute a fraction of the host atoms. We have doped various dopants such as cobalt (Co)1, manganese (Mn)2 and vanadium(V)3 in ZnO in varying concentrations and synthesized thin films of these DMS materials by pulsed laser deposition technique to study the effect on the magnetic properties. In addition we have done extensive annealing studies to correlate the properties of these thin films with the free carrier concentration that is generated due to intrinsic defects in the as grown films. Microstructural characterization of these materials is done using cross sectional transmission electron microscopy (TEM) including high resolution TEM and electron energy loss spectroscopy (EELS). We have established that ZnO-Co and ZnO-Mn systems are ferromagnetic up to room temperature whereas ZnO-V system is not. We have recently shown that ferromagnetism in ZnO-Mn can be controlled by varying free-carrier concentration2. Upon annealing in oxygen the conductivity decreases and the moments per atom of the dopant reduces considerably and in some cases the DMS ceases to be ferromagnetic. In other cases the annealed films are ferromagnetic at very low temperatures. We conclude from these results that a mixture of carrier induced ferromagnetism and the bound polaron exchange mechanisms are operative in these materials. From a materials perspective to device perspective, it is important to study the efficiency of such DMS materials to inject spin polarized electrons into a semiconductor. We have used such materials in conjunction with ZnO itself to make novel device structures to accomplish this objective. Preliminary results are very encouraging to the mark that we can achieve highly efficient spin injection at least up to temperatures of the order of 50K.These ZnO based materials could pave the way for a new generation of novel devices based on the concept of spintronics.1S.Ramachandran et al, App.Phys.Lett, 84 , 5255-5257(2004) 2S.Ramachandran et al, App.Phys.Lett, 87, 172502 (2005) 3S.Ramachandran et al, App.Phys.Lett, 88, 242503 (2006)
4:30 PM - K4.6
Electrical and Magnetic Properties of Doped ZnO Nanowires.
Gennady Panin 1 2 , Andrey Baranov 3 , Tae Kang 1 , Oleg Kononenko 2 , Dubonos Sergey 2 , S. Min 4 , H. Kim 4
1 Physics, QSRC, Dongguk University, Seoul Korea (the Republic of), 2 , Institute of Microelectronics Technology, RAS, Chernogolovka, Moscow distr. Russian Federation, 3 Chemistry, Moscow State University, Moscow Russian Federation, 4 Semiconductors, QSRC, Dongguk University, Seoul Korea (the Republic of)
Show AbstractZinc oxide doped by different impurities has a unique combination of electrical, magnetic and optical properties (Eg. = 3.37 eV, Eeb = 60 meV) which can be used in a variety of novel devices such as UV light emitting diodes, lasers, spin and dipole controlled switches, chemical and biosensors. Here we report on magnetic properties of single doped ZnO nanowires and a persisting highly reproducible resistance modulation of the wires by a dc voltage at room temperature.ZnO nanowires were synthesized by heating the mixture of solution processed Zn precursor with NaCl Li2CO3 salt at 700°C [1] and were doped by different electric-active and magnetic impurities. The size of wires was in the range of 40-150 nm in diameter and 1000-5000 nm in length. The nanowires characterized by high resolution transmission microscopy showed a single crystal wurtzite structure and were free from second phase. For transport measurements the individual nanowires were configured as two terminal device with electrode-ZnO-electrode structure on silicon substrate capped with thick SiO2 layer. E-beam lithography was used to pattern aluminum electrodes contacting individual nanowires. Structure of the device was controlled by high-resolution scanning electron microscopy. Electrical transport properties of the two-terminal device were investigated by applying quasi-dc voltage with a constant sweep velocity. Magnetic susceptibility of the samples as a function of temperature demonstrated Curie–Weiss behavior. Hysteresis with the coercive field <200 Oe was clearly observed in magnetization versus field curves at 5 and 300K. Increasing the Mn concentration increases significantly the magnetic hysteresis indicating ferromagnetic properties of single nanowires. Magnetic force microscopy measurements of single nanowires with spatial resolution revealed the local magnetic polarization. The domain nanomagnet structure aligns perpendicular to the surface and can be controlled by magnetic field.The effects of ZnO surface band-bending due to formation of charged traps [2] as well as trapping effects and charge transfer process via impurity and intrinsic point defects with changes of polarization and sensitivity to oxygen are discussed. [1] A.N. Baranov, G.N. Panin T.W. Kang and Y.-J. Oh, Nanotechnology 16, 1918 (2005).[2] G.N. Panin, T.W. Kang, A. N. Aleshin, A. N. Baranov, Y.-J. Oh, I. A. Khotina, Appl. Phys. Lett. 86, 113114(2005)
4:45 PM - K4.7
Structural and Magnetic Properties of Iron and Cobalt Implanted ZnO Thin Films.
Wing Yan Luk 3 , S. P. Wong 1 3 , Ning Ke 1 , Quan Li 2 3
3 Materials Science and Technology Research Centre, Chinese University of Hong Kong, Shatin Hong Kong, 1 Dept of Electronic Engineering, Chinese University of Hong Kong, Shatin Hong Kong, 2 Dept of Physics, Chinese University of Hong Kong, Shatin Hong Kong
Show Abstract5:00 PM - K4.8
Nano-scale Spinodal Decomposition Phase in ZnO-based Dilute Magnetic Semiconductors.
Masayuki Toyoda 1 , Kazunori Sato 1 , Hiroshi Katayama-Yoshida 1
1 , The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka, Japan
Show Abstract5:15 PM - K4.9
Ferromagnetism in Cu doped ZnO Based Diluted Magnetic Semiconductors.
Deepayan Chakraborti 1 , John Prater 1 2 , Jagdish Narayan 1
1 Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Materials Science Division, Army Research Office, Research Triangle Park, North Carolina, United States
Show Abstract5:30 PM - K4.10
Transition Metal-doped ZnO: A Comparison of Optical, Magnetic, and Structural Properties of Bulk and Thin Films.
Matthew Kane 1 2 , William Fenwick 1 , Rengarajan Varatharajan 3 , Martin Strassburg 1 , Bill Nemeth 3 , David Keeble 4 , Hassane El-Mkami 5 , Graham Smith 5 , Jeff Nause 3 , Christopher Summers 2 , Ian Ferguson 1 2
1 Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 , Cermet, Inc., Atlanta, Georgia, United States, 4 Carnegie Laboratory of Physics, Faculty of Engineering and Physical Sciences, University of Dundee, Dundee United Kingdom, 5 School of Physics and Astronomy, University of St. Andrews, St. Andrews United Kingdom
Show Abstract5:45 PM - K4.11
Ferromagnetic Mn-Mn Interactions in Low Doped Zn1-xMnxO Thin Films.
Aroussi Ben Mahmoud 2 , H.Jurgen von Bardeleben 1 , Alain Mauger 3 , Jean-Louis Cantin 1 , Ekaterina Chikoidze 4
2 , Faculté des Sciences de Gabès, Gabès Tunisia, 1 , University Paris 6, CNRS, Paris France, 3 , MIPPU CNRS, Paris France, 4 , GEMC CNRS, Meudon France
Show Abstract
Symposium Organizers
Juergen Christen Universität Magdeburg
Chennupati Jagadish Australian National University
David C. Look Wright State University
Takafumi Yao Tohoku University
K5: Growth
Session Chairs
R.D. Vispute
Takafumi Yao
Wednesday AM, November 29, 2006
Room 200 (Hynes)
9:30 AM - **K5.1
Growth of Large Size ZnO Bulk Crystals by Hydrothermal Method.
Tsuguo Fukuda 1 2 , Y. Kagamitani 1 , D. Ehrentraut 1 , Y. Mikawa 2 , K. Maeda 3 , T. Ono 3
1 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai Japan, 2 , Fukuda Crystal Laboratory, Sendai Japan, 3 , Tokyo Denpa Co., LTD., Tokyo Japan
Show AbstractZnO is a wide band-gap semiconductor (Eg = 3.37 eV) with a large exciton binding of 60 meV. ZnO has a high potential for broad applications in optoelectronics, piezoelectronics and UV-blue LED device. Since exciton luminescence of ZnO shows very short decay time of < 1 ns, it is attractive as ultra-fast scintillator. In this research, 3-inch size undoped bulk ZnO was grown by the hydrothermal method and its basic properties were characterized. Also, indium-doped ZnO crystal was grown and scintillation properties were measured.The hydrothermal method has been used for industrial growth of quartz crystals for more than 50 years. The advantages of this method are (1) growth at low temperature, (2) suitable for mass production and large size crystals by scaling up the equipment, (3) high crystal quality because of the extremely small temperature gradient at the growing interface. However, the hydrothermal method never before was applied to the growth of semiconductor crystals. The technique had to be developed to control electrical properties by impurity control and accomplish doping of ZnO for use in semiconductor devices. The growth of 3-inch ZnO crystals was achieved by the modified hydrothermal method, which is based on the conventional technique for quartz mass production. A high pressure vessel (autoclave) of 250 mm ID and 4.5m in height is used. A platinum inner container was installed inside the autoclave to prevent impurity incorporation from autoclave wall. Alkaline aqueous solution (3M KOH and 1M LiOH) is filled into the inner container whereas the outside of the container is filled with pure water for pressure balance. ZnO single crystal wafers were set in the upper half zone (growth zone) as seed crystals and ZnO poly crystals, sintered at 1000-1200°C, were placed in the lower half zone (dissolving zone) as raw materials. The inside of the container was separated by a baffle plate into the two zones. The crystals were grown at 300-400°C and 80-100MPa. The growth rate was 0.1-0.3mm/day along c-axis. The crystallinity of 3-inch undoped ZnO is characterized by X-ray rocking curve measurements and the FWHM of 0002 reflection is 18 arcsec. To our knowledge this is the best value of FWHM ever reported for large bulk ZnO. For scintillator application, indium-doped ZnO crystals were grown so as to increase the luminescence intensity at longer wavelength by avoiding the self absorption. Exciton luminescence of In:ZnO was observed at 398 nm (undoped ZnO: 387 nm) at room temperature. The decay time was measured using a femtosecond laser at λ = 260 nm. Ultrashort decay of 40 ps and 650ps was observed.
10:00 AM - K5.2
Hydrothermal Growth of Various Doped ZnO Crystals.
Michael Callahan 1 , Buguo Wang 2 , Lionel Bouthillette 1 , David Bliss 1
1 , Sensor Directorate, Air Force Research Laboratory, Massachusetts, United States, 2 , Solid State Scientific Corporation, Nashua, New Hampshire, United States
Show Abstract10:15 AM - K5.3
Growth an Characterization of Homoepitaxial ZnO Thin Films Grown by CVD.
Joachim Sann 1 , Christian Neumann 1 , Bruno Meyer 1 , Frank Bertram 2 , Jürgen Christen 2
1 1st Physics Institute, Justus Liebig University Giessen, Giessen Germany, 2 Institute for Experimental Physics, Otto-von-Guericke University Magdeburg, Magdeburg Germany
Show Abstract10:30 AM - K5.4
Orders of Magnitude Reduction in Threading Dislocations in ZnO Grown on Facet-controlled GaN.
Soo Jin Chua 1 2 , Hai Long Zhou 3 , Hui Pan 3 , Thomas Osipowicz 3 , Jian Yi Lin 3
1 , Institute of Materials Research and Engineering, Singapore Singapore, 2 Department of Electrical and Computer Engineering, National University of Singapore, Singapore Singapore, 3 Department of Physics, National University of Singapore, Singapore Singapore
Show AbstractGaN is grown by Metal Organic Chemical Deposition on oxide masked GaN with stripe window openings of 6μm in width. Growth conditions were selected to achieve trapezoidal shaped cross section of GaN with {11-22} sidewalls and (0001) top surface. ZnO is next epitaxially overgrown (EO) on these facets by Chemical Vapour Deposition (CVD). SiO2 is chosen as the masking material to prevent nucleation of ZnO on it. For different CVD growth parameters, the growth morphology of EO ZnO changes from long, needle-shaped nanorods to rectangular stripes with (0001) top facet and {11-20} sidewalls and finally to triangular stripes with {11-22} sidewalls. It is also demonstrated that the EO ZnO growth facets can be controlled and the overgrown region can achieve two orders of magnitude reduction in dislocation density in the entire epitaxial film as measured by the X-ray diffraction (XRD), Rutherford Backscattering (RBS), high resolution transmission electron microscopy (HRTEM) and room temperature photoluminescence (PL). The strongest PL intensity of the EO ZnO is observed from samples grown at 800oC with the full width at half maximum (FWHM) of the ZnO photoluminescence peak of about 5.5 nm. The spectra of 820C EO ZnO/GaN shows the declining crystallinity, with the broadening of ZnO peaks to around 23 nm. Laterally resolved channeling data have been extracted from the Rutherford Back Scattering spectra in near-surface regions. The random and channeled spectra of the band of the EO ZnO grown at 800C showed the greatest contrast. This is further evidence of better quality of the EO ZnO grown at 800C. This growth method can be used to fabricate ZnO/GaN heterostructures with low dislocation densities, which will find important applications in future electronic and UV laser devices.
10:45 AM - K5.5
Electrochemically Induced Growth of ZnO on (0001) GaN.
Thomas Loewenstein 1 , Joachim Sann 2 , Christian Neumann 2 , Bruno K. Meyer 2 , Tsukasa Yoshida 3 , Derck Schlettwein 1
1 Institute of Applied Physics, Justus-Liebig-University Giessen, Giessen Germany, 2 Institute of Experimental Physics I, Justus-Liebig-University Giessen, Giessen Germany, 3 Graduate School of Engineering, Gifu University, Gifu Japan
Show Abstract11:30 AM - **K5.6
Effects of Polarity on MBE Growth of Undoped, Ga- and N-doped ZnO Films.
Hiroyuki Kato 1 , Akio Ogawa 1 , Hiroshi Kotani 1 , Michihiro Sano 1 , Takafumi Yao 2
1 , Stanley Electric Co., Ltd., Yokohama Japan, 2 , Tohoku Univ., Sendai Japan
Show Abstract12:00 PM - K5.7
Solution Growth and Luminescence Characteristics of Undoped, In- and Ge-doped ZnO Thin Films.
Dirk Ehrentraut 1 , Jan Pejchal 2 , Martin Nikl 2 , Hideto Sato 3 , Yuji Kagamitani 1 , Hiroshi Fukumura 4 , Tsuguo Fukuda 1
1 , IMRAM, Tohoku University, Sendai Japan, 2 , Institute of Physics, AS CR, Prague Czech Republic, 3 , Murata Mfg. Co. Ltd., Shiga Japan, 4 , Dept. Chemistry, Faculty of Sciences, Tohoku University, Sendai Japan
Show Abstract12:15 PM - K5.8
ZnCdMgO-based Quantum Well Structures Grown by Molecular Beam Epitaxy for Light-emitting Applications.
Sergey Sadofev 1 , Sylke Blumstengel 1 , Jian Cui 1 , Joachim Puls 1 , Fritz Henneberger 1
1 Institut für Physik, Humboldt-Universität, Berlin Germany
Show Abstract12:30 PM - K5.9
Epitaxial growth of ZnO on (0001) 6H SiC
Christian Pettenkofer 1 , Stefan Andres 1 , Thomas Seyller 2
1 SE6, HMI, Berlin Germany, 2 Institut für Technische Physik, Universität Erlangen, Erlangen Germany
Show AbstractZnO is deposited by MOMBE on H-terminated 6H-SiC substrates. In situ XPS reveals that the interface is abrupt and non reactive. The growth mode is FvdM type (layer by layer). LEED data show a clear LEED pattern for the substrate and the grown film confirming the epitaxial growth. A detailed analysis of the LEED data show beside the (0001) plane a facetting into the (10-12) plane for thicker films. Ex situ AFM shows considerable surface roughness and supports the morphology deduced from the LEED data. The interface energetics are determined by XPS and UPS. The obtained heterojunction is of type II with a valence-band offset of 1.25 eV and an bandbending of 0.5 ev on both sides of the junction. Interesting is the observation of an interfacial dipole considerably smaller than 0.1 eV for the prepared junction.
12:45 PM - K5.10
The Growth of ZnO on CrN Buffer Layer Using Surface Phase Control by Plasma Assisted Molecular-beam Epitaxy.
Jinsub Park 1 , Tsutomu Minegishi 1 , Seunghwan Park 1 , Inho Im 1 , Meoungwhan Cho 1 2 , Takafumi Yao 1 2
1 , Institute for Materials Research, Sendai Japan, 2 , Center for Interdisciplinary Research, Sendai Japan
Show Abstract We propose CrN as a new buffer material for the growth of high-quality ZnO on Al2O3(0001).Since CrN has a rock salt crystal structure with lattice parameter of 0.293 nm, the epitaxy relationship for the heterostructure of ZnO/CrN/ Al2O3(0001) is expected to be as follows: ZnO(0002)//CrN(111)// Al2O3(0001). Assuming this epitaxy relationship, the 18% lattice misfit between ZnO/Al2O3(0001) can be split into two heterostructures with smaller lattice misfits: ZnO/CrN (11%) and CrN/Al2O3(6.6%)[1]. Since the thermal expansion coefficient (TEC) of CrN is 6X10-6/K, the difference in TEC between ZnO and CrN is 16.7%, while that between CrN and Al2O3(0001) is 20%. Hence ZnO will suffer from tensile stress by ZnO/CrN thermal mismatch, while CrN layers will be compressive strained by CrN/Al2O3(0001). These situations will help grow high-quality ZnO onAl2O3(0001). On top of those advantages, the surface treatments of CrN surface by oxygen plasma will produce various surface phases including Cr2O3(rhombohedral crystal structure), and CrO2(tetragonal crystal structure), which may result in combined CrxOy/CrN double buffer layers. Such novel buffers will play crucial roles in controlling crystal polarity of ZnO, since crystal polarity of ZnO layers are quite dependent on the crystal structure of buffer layers. This paper will report :(1) Although CrN buffer deposited on Al2O3 shows twinning, ZnO layers grown on CrN buffer are single crystalline without rotational twinning.(2) RHEED investigation indicates that ZnO grows in a two dimensional mode on CrxOy/CrN double buffer formed by oxygen plasma treatment on CrN. The surface of ZnO layers is smooth which is consistent with the RHEED observation.(3) ZnO layers grown directly on CrN show O-polarity with small anti-phase domain density, while those grown on CrxOy/CrN double buffer show a mixture of O-polar region and Zn-polar anti-phase domains. We are optimizing the oxygen treatment conditions to obtain complete Zn-polar ZnO layers.(4) X-ray rocking curve of ZnO layers grown on CrxOy/CrN double buffer shows a narrower FWHM value compare to ZnO directly on CrN buffer. Therefore, we believe that cubic CrN layer is an appropriate material as a buffer layer for ZnO grown on Al2O3 and that the control of surface phase of CrxOy/CrN double buffer will play a crucial role in growing high-quality ZnO layers with controlled crystal polarity.
K6: Optical Properties, Nanostructures
Session Chairs
Bernard Gil
Seong-Ju Park
Wednesday PM, November 29, 2006
Room 200 (Hynes)
2:30 PM - **K6.1
Optical Properties of ZnO Epilayers.
Axel Hoffmann 1
1 Inst. f. Fstkoerperphysik, TU Berlin, Berlin Germany
Show AbstractWe present time-resolved photoluminescence (PL) measurements of nitrogen implanted ZnO single crystals and lithium doped ZnO, grown by chemical vapor deposition. The samples revealed the presence of several bound exciton states as well as their two electron satellites (TES) and phonon replicas. The decay times of the observable exciton complexes and their associated emissions were studied for different excitation energies. The dynamics and energy transfer processes were analyzed by probing the free and bound exciton states, TES and phonon replicas, while varying the laser energy.Furthermore, magneto-optical PL and absorption spectroscopy has been performed. The electron and hole effective g-values are calculated from the Zeeman splitting at 5 T. Above 3 T an additional fine-splitting of peaks in magnetic fields was clearly apparent in the Li doped sample. The relaxation of selection rules by internal strain in combination with a non-zero an-isotropic hole effective g-value for B⊥c is discussed a the possible origin of the observed splitting. In this context, new evidence for the uppermost valence band having Γ7-symmetry are reasoned and clarified by angular and polarization dependent measurements. The donor or acceptor character of the bound exciton complexes is investigated through their thermalization behavior in magnetic fields.Finally, time resolved resonant and non-resonant photoluminescence measurements have been performed in externally applied magnetic fields. The interference of the coherently excited Zeeman states provides addition insight about the de-phasing mechanisms, influenced by the spin dynamics and energy relaxation processes.
3:00 PM - K6.2
Recombination Kinetics of Bound Excitons in ZnO: Carrier Capture by Ionized Impurities.
Frank Bertram 1 , Juergen Christen 1 , Armin Dadgar 1 , Alois Krost 1
1 Insitute of Expermental Physics, University Magdeburg, Magdeburg Germany
Show Abstract3:15 PM - K6.3
Cathodoluminescence Study of Indented ZnO Crystals.
J. Mass 1 5 , M. Avella 1 , Juan Jimenez 1 , T. Rodríguez 2 , M. Callahan 3 , E. Grant 3 , K. Rakes 3 , D. Bliss 3 , B. Wang 4
1 Dpto. Física de la Materia Condensada, Universidad de Valladolid, Valladolid Spain, 5 Dpto. Matemáticas y Física, UniNorte, Barranquilla Colombia, 2 Dpto. Tecnología Electrónica, Universidad Politécnica de Madrid, Madrid Spain, 3 Sensors Directorate, Air Force Research Laboratory, Hanscom AFB, Massachusetts, United States, 4 , Solid State Scientific Corporation, Hollis, New Hampshire, United States
Show AbstractZnO is a wide band gap semiconductor with high potential for UV optoelectronics applications due to its large free exciton binding energy (60 meV). The understanding of the mechanisms governing the luminescence emission is necessary to improve the emission properties of ZnO. The luminescence spectrum of ZnO consists of a complex spectrum in the near band gap (NBG) spectral region and a broad band composed of at least two subbands in the visible (green-orange) range. The origin of some of these bands remains to be a matter of controversy; in particular, the role of intrinsic defects is far to be understood. We present herein a cathodoluminescence study of ZnO crystals in which defects were created by Vickers indentations under different conditions. The influence of the indentations in the luminescence spectrum was studied by spectrally resolved cathodoluminescence, paying special emphasis to visible luminescence and the luminescence bands in the DAP spectral region. Thermal treatments in different atmospheres are carried out in order to study the evolution of the luminescence spectra and thepossible origin of the defects created by the indentations.
3:30 PM - K6.4
Valence Band Photoemission Spectroscopy of ZnO and CdO.
C. McConville 1 , T. Veal 1 , P. Jefferson 1 , L. Piper 1 , A. Schleife 2 , F. Fuchs 2 , J. Furthmüller 2 , F. Bechstedt 2 , J. Zúñiga-Pérez 3 , V. Muñoz-Sanjosé 3
1 Department of Physics, University of Warwick, Coventry United Kingdom, 2 Institut für Festkörpertheorie und Theoretische Optik, Friedrich-Schiller-Universität, Jena Germany, 3 Department Física Aplicada i Electromagnetisme, Universitat de València, València Spain
Show Abstract3:45 PM - K6.5
Photoluminescence and Phonon Properties of ZnO and MgZnO Nanocrystallites.
John Morrison 1 , Jesse Huso 1 , Heather Hoeck 1 , Erin Casey 1 , Xiang-Bai Chen 1 , Leah Bergman 1 , Tsvetanka Zheleva 2
1 Department of Physics, University of Idaho, Moscow, Idaho, United States, 2 , Army Research Laboratory, Adelphi, Maryland, United States
Show AbstractZnO and MgZnO alloys are promising wide-bandgap semiconductors for optoelectronic applications, and also of considerable interest from a fundamental viewpoint. The environmentally friendly chemical composition and the deep excitonic level ~ 60 meV of ZnO make it an excellent candidate for high-efficiency next generation ultraviolet light sources. Moreover, the MgZnO solid solution has been recently realized for thin films as well as for nanopowders. These optical alloys enable the tuning of the bandgap and the luminescence at the range of ~ 3.0 for ZnO of the wurtzite structure up to ~ 7 eV for the MgO of the rocksalt structure.We present studies on the ultraviolet photoluminescence and Raman properties of wurtzite MgZnO nanopowders of average size ~ 30 nm that were synthesized via the thermal decomposition method. For the studied composition range of 0-26% Mg, the room temperature UV-PL was found to be tuned by ~ 0.3 eV towards the UV-spectral range; the extent of the blueshift found to depend on the crystallite quality. For that composition range the first-order LO Raman mode was found to exhibit a significant blueshift of ~ 33 cm-1 and the second-order LO a shift of ~ 60 cm-1 indicating that a good solid solution was achieved at the nanoscale. Results and issues concerning the properties of the nanoalloys at above 26% of Mg concentrations; where structural phase transition takes place will be presented as well.
4:30 PM - **K6.6
Piezoelectric and Luminescent Properties of ZnO Nanostructures on Ag Films.
Julia Hsu 1 , David Scrymgeour 1 , David Tallant 1 , Nancy Missert 1 , David Look 2 , James Voigt 1 , Jun Liu 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 , Wright State University, Dayton, Ohio, United States
Show AbstractIn the past decade, significant advances have been made in the synthesis of ZnO nanostructures. The next step in making these nanomaterials useful is to assemble them on surfaces in a controlled and desired fashion. In this talk, I will discuss the growth of complex ZnO nanostructures via a solution method in which organic templates are used to control assembly of these nanostructures on substrate surfaces. The low temperature aqueous growth method used in this work is an environmentally benign process, which is compatible with organic templates and modifiers, can be used to grow large area uniformly, and has potential for inexpensive manufacturing. To control the assembly of these solution grown nanostructures, we modify the substrate surfaces with patterned self-assembled monolayers, which in turn determines the final spatial organization of the ZnO nanorods. This is a bottom-up approach in which materials are deposited only where they are needed. Using this approach, we have achieved excellent control in spatial placement, selectivity, crystal orientation, and nucleation density. In addition, complex, hierarchical structures have been synthesized by controlling solution chemistry and growth conditions. Due to lack of inversion symmetry in hexagonal crystal, ZnO is a piezoelectric material with Zn (0001) polar and O (0001-) polar surfaces exhibiting drastically different physical and chemical properties. Hence, it is important to determine the orientation of the ZnO nanorods on surfaces. Using piezoelectric force microscopy (PFM), we have determined that the nanorods are [0001] oriented. We also studied the luminescent properties of these solution-grown ZnO nanorods. As-grown nanorods displayed a broad yellow-orange sub-bandgap luminescence and a small near-bandgap emission peak. Scanning cathodoluminescence experiments showed that the width of the sub-bandgap luminescence is not due to an ensemble effect. Upon reduction, the sub-bandgap luminescence disappeared and the near-bandgap emission increased. Comparing to ZnO powders that are stoichiometric and oxygen deficient, we conclude that the yellow-orange sub-bandgap luminescence most likely arises from bulk defects that are associated with excess oxygen.
5:00 PM - K6.7
Fabrication of ZnO Based Multifunctional Nanostructures.
Shiva Hullavarad 1 , R. Vispute 1 , R. Heng 1 , T. Venkatesan 1
1 Center for Superconductivity Research, University of Maryland, College Park, Maryland, United States
Show Abstract5:15 PM - K6.8
Piezoelectric Nanogenerators Based on Zinc Oxide Nanowire Arrays.
Jinhui Song 1 , Zhong Wang 1
1 Materials Science & Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractDeveloping novel technologies for wireless nanodevices and nanosystems are of critical importance for in-situ, real-time and implantable biosensing, biomedical monitoring and biodetection. An implanted wireless biosensor requires a power source, which may be provided directly or indirectly by charging of a battery. It is highly desired for wireless devices and even required for implanted biomedical devices to be self-powered without using battery. Therefore, it is essential to explore innovative nanotechnologies for converting mechanical energy (such as body movement, muscle stretching), vibration energy (such as acoustic/ultrasonic wave), and hydraulic energy (such as body fluid and blood flow) into electric energy that will be used to power nanodevices without using battery. It also has a huge impact to miniaturizing the size of the integrated nanosystems by reducing the size of the power generator and improving its efficiency and power density. We have demonstrated an innovative approach for converting nano-scale mechanical energy into electric energy by piezoelectric zinc oxide nanowire (NW) arrays [1, 2]. By deflecting the aligned NWs using a conductive atomic force microscopy (AFM) tip in contact mode, the energy that was first created by the deflection force and later converted into electricity by piezoelectric effect has been measured for demonstrating nano-scale power generator. The operation mechanism of the electric generator relies on the unique coupling of piezoelectric and semiconducting dual properties of ZnO as well as the elegant rectifying function of the Schottky barrier formed between the metal tip and the NW. The efficiency of the NW based piezo-electric power generator is ~ 17-30%.
[1] Z.L. Wang and J.H. Song, Science, 312 (2006) 242-246.
[2] http://www.nanoscience.gatech.edu/zlwang/
5:30 PM - K6.9
Investigation of Optical and Electrical Properties of ZnO Nanowires Grown by Pulsed Laser Deposition.
Marius Grundmann 1 , Andreas Rahm 1 , Thomas Nobis 1 , Gregor Zimmermann 1 , Christian Czekalla 1 , Jörg Lenzner 1 , Holger von Wenckstern 1 , Michael Lorenz 1
1 Institut für Experimentelle Physik II, Semiconductor Physics, Universtät Leipzig, Leipzig Germany
Show Abstract5:45 PM - K6.10
Nonlinear I-V Characteristics of ZnO Nanoparticle Compacts and Nanocomposites.
Simone Herth 1 2 3 , Xiaoping Wang 1 2 , Teresa Hugener 1 2 , Henrik Hillborg 4 , Tommaso Auletta 4 , Linda Schadler 1 2 , Richard Siegel 1 2
1 Rensselaer Nanotechnology Center, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Materials Science and Engineering Department, Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Faculty of Physics, University Bielefeld, Bielefeld Germany, 4 , ABB Corporate Research, Västerås Sweden
Show AbstractK7: Poster Session I
Session Chairs
Jürgen Christen
Chennupati Jagadish
David Look
Takafumi Yao
Thursday AM, November 30, 2006
Exhibition Hall D (Hynes)
9:00 PM - K7.1
Vibrational Characterization of ZnO Nanostructures Revealing Phonon Confinement.
Sanju Gupta 1 , Rusen Yang 2 , Zhang Wang 2
1 Physics and Materials Science, Missouri State University, Springfield, Missouri, United States, 2 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractZinc oxide (ZnO) and related compound semiconductors (CdO, MgO) have drawn interest in recent years due to their suitability for visible and UV light emitters and detectors as well as high-temperature electronics. ZnO, in particular, can be utilized for technology of photonic and electronic devices including light-emitting diodes, gas, chemical, and biosensors and now spintronics (if doped with magnetic ions dilutely). ZnO nanostructures in forms like nanobelts, nanorods, and nanotubes were prepared using thermal evaporation of oxide powders inside an alumina tube in the absence of catalysts. One of the key issues of phonon/lattice dynamics of nano- and micrometer-scale is the identification of the observed Raman active modes. It is because, due to the tilted orientation of smaller crystallites and/or nanostructures, the usual Raman selection rules pertaining to the symmetry axes or in general no longer hold, and it is likely that mixed-symmetry modes need to be considered to explain the phonon properties. In addition, nanostructures in general give rise to phonon confinement which induces phonon peak shifts and the main mechanism are: (a) spatial confinement within the boundaries; (b) phonon localization by defects (oxygen deficiency, zinc excess, surface impurities etc.); or (c) laser-induced heating in nanostructure ensembles (which can be minimized or eliminated by using very low powers of excitation source). Usually, only the first mechanism, referred to as optical phonon confinement, is involved as an explanation of the phonon frequency shifts in ZnO nanostructures. Effect of confinement is investigated on optical phonons of different symmetries using nonresonant Raman spectroscopy. An optical phonon confinement model is used to calculate theoretical line shapes which exhibit different asymmetric broadening and shifts, depending upon the symmetries of phonon. *Supported by internal Funds.
9:00 PM - K7.10
Vertically Aligned Single Crystalline ZnO Nanorods Grown by Hydrothermal Synthesis and the Theoretical Model for Predicting the Dot Density.
Soo Jin Chua 1 3 , Hong Quang Le 3 , Kian Ping Loh 2
1 , Institute of Materials Research and Engineering, Singapore Singapore, 3 , Singapore-MIT Alliance, Singapore Singapore, 2 Department of Chemistry, National University of Singapore, Singapore Singapore
Show Abstract9:00 PM - K7.11
Study of the Temperature Dependence of E2 and A1(LO) Modes in ZnO.
Esther Alarcon-Llado 1 , Ramon Cusco 1 , Jordi Ibanez 1 , Luis Artus 1 , Juan Jimenez 2 , Michael Callahan 3
1 Inst. Jaume Almera, C.S.I.C., Barcelona Spain, 2 Fisica Materia Condensada, Universidad Valladolid, Valladolid Spain, 3 , Air Force Research Lab, Hanscom AFB, Massachusetts, United States
Show AbstractZnO is a wide band-gap semiconductor with great potential as an alternative to GaN for optoelectronic devices in the blue and UV spectral region, since it has a much higher free exciton binding energy (60 meV), it is more resistant to radiation damage and large native substrates are available. The possibility of growing large crystals of ZnO has renewed the interest in this material. High-quality large ZnO single crystals can now be obtained by the hydrothermal (HTT) growth method. These crystals exhibit optical properties similar to those of crystals grown by vapor-phase transport (VPT).Raman scattering provides useful information about sample quality as well as phonon interaction with free carriers, both of which have an impact on device performance. Here, we present Raman spectra of a high-quality HTT ZnO single crystal obtained over a wide temperature range, from 80 up to 750 K. All Raman-active modes are identified in polarized first-order spectra and their temperature dependence is determined. Second-order spectra show a rich structure that is discussed in the light of recently published ab-initio calculations of the ZnO phonon dispersion. The temperature dependence of the intensity of the second-order Raman modes allows us to establish the assignment of peaks that had been previously attributed to different possible combinations. The low temperature spectra reveal additional peaks that we tentatively assign to local impurity modes. On the other hand, the optical phonon lifetimes are important for the performance of ultra-fast devices because of their role in the energy relaxation of excited carriers. Raman scattering provides a way to measure phonon lifetimes as well as an insight into phonon decay mechanisms. We have carried out high resolution Raman spectra of the E2 and A1(LO) modes as a function of temperature in the 80-750 K range. The analysis of the observed line shapes allowed us to determine the phonon lifetimes as well as to discuss possible phonon decay channels for these modes. The temperature dependence of the A1(LO) mode linewidth is well accounted for by third-order anharmonic decay into a TO and a LA phonon (Ridley's channel). We find an A1(LO) lifetime of 0.5 ps at room temperature, which is one order of magnitude lower than the one reported for GaN. This value suggests that hot phonon effects should be expected to play a less relevant role in carrier relaxation in ZnO as compared to GaN.
9:00 PM - K7.12
In situ Electrochemical Deposition and Lithography of ZnO nanocrystals
Nicholas Polomoff 1 , Bryan Huey 1
1 Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States
Show AbstractThin films of polycrystalline ZnO nanocrystals have been deposited electrochemically. Deposition is possible near pH=7, therefore allowing in-situ observation of film evolution and growth in a liquid-cell equipped atomic force microscope. Through careful control of the electrochemical parameters and ionic concentrations, film growth rates on the order of 30nm per hour and higher have been achieved. The morphology of films grown with a variety of conditions have further been imaged by AFM and field emission SEM, and their piezoelectric properties have been characterized using piezo force microscopy. Finally, using a conducting AFM tip as the working electrode, individual ZnO islands can be lithographically deposited according to the tip position, contact force, dwell time, and electrochemical parameters, allowing a variety of nanoscale oxide features to be prepared.
9:00 PM - K7.13
Growth And Interface Microstructure Of Zinc Oxide Thin Film On Elinvar (Fe-Ni-Cr-Ti) Alloy By Radio Frequency Sputtering.
Yukio Yoshino 1 , Akira Saito 2
1 R&D Division, Murata Mfg. Co., Ltd, Yasu, Shiga, Japan, 2 Materials Research Division, Murata Mfg. Co., Ltd., Yasu, Shiga, Japan
Show Abstract Zinc Oxide (ZnO) thin film has been grown on ELINVAR (Fe-Ni-Cr-Ti alloy) substrate by RF magnetron sputtering. ZnO thin film has piezoelectricity. ELINVAR is a good elastic material. The temperature coefficient of sound velocity in ELINVAR can be controlled by the heat annealing temperature, so the sound velocity depends on Young’s modulus that is changed by ferromagnetic transition of ELINVAR [1]. We can fabricate piezoelectric devices to combine ZnO thin film and ELINVAR if we make a ZnO thin film which had good piezoelectricity on ELINVAR substrate [2]. The ZnO thin film on ELINVAR shows c-axis orientation confirmed by x-ray diffraction. The ZnO/ELINVAR interface has been observed by high resolution cross section transmission electron microscope. A polycrystalline layer grows on the ELINVAR substrate surface, and a c-axis oriented layer grows on the polycrystalline layer. This result is similar to ZnO thin film grown on glass substrate [3]. However, the interface microstructure between ZnO and ELINVAR is complicated. The c-axis orientation of ZnO is disordered near the ZnO/ELINVAR interface. Seeing the interface microstructure of ZnO on ELIVBAR, these results are caused by the rough polished surface of the ELINVAR substrates. The c-axis orientation of the ZnO thin film on ELINVAR is strongly dependent on the surface roughness of the substrate. [1] The Japan Institute of Metals, Metals data book, 1971, p.1050[in Japanese].[2] Y. Yoshino, M. Takeuchi, K. Inoue, T. Makino, S. Arai, T. Hata, Vacuum, 2002, Vol.66, p.467.[3] Y. Yoshino, S. Iwasa, H. Aoki, Y. Deguchi, Y. Yamamoto, K. Ohwada, 1996 Fall Meeting Proceedings, Mater. Res. Soc.1997, Vol. 441,p.241.
9:00 PM - K7.14
ZnO-Sn bilayer Ultraviolet (UV) Photon Detector with Improved Responsitivity.
Harish Yadav 1 , Kondepudy Sreenivas 1 , Vinay Gupta 1
1 Physics and Astrophysics, Delhi University, Delhi, Delhi, India
Show Abstract9:00 PM - K7.15
Two Dimensional Well Organized ZnO Nanowire Arrays for Photonic Applications.
Jingbiao Cui 1 , Ursula Gibson 1
1 , Dartmouth College, Hanover, New Hampshire, United States
Show AbstractRecently there has been a great interest in the investigation of ZnO nanowire arrays due to their potential applications in electronics, photonics and sensors. Dense randomly distributed ZnO nanowire arrays have been obtained using both catalytically activated vapor phase processes at high temperature and solution routes at low temperature. To date, however, it's still challenge to fabricate large scale well organized ZnO nanowire arrays for many applications such as photonic devices and displays, which require the ability to precisely control the placement of each individual nanowires. In this study, we developed a new technique to grow well organized ZnO nanowire arrays using a soft template created by e-beam lithography. The nanowires were grown in an aqueous solution at 90 degree using an electrochemical process, which ensures the suitability of using Polymethyl Methacrylate (PMMA) as template materials. We demonstrate that individual single crystal ZnO nanowires with diameter about 100 nm can be precisely placed in the desired location to form two dimensional ordered nanowire arrays. The structure, composition and optical diffraction of the ordered arrays were investigated. This approach provides a possibility to design and fabricate complicated structures of two dimensional ZnO nanowire arrays with variable periodicity. Importantly, the fabrication process is compatible with current micro-fabrication technique and promising for the fabrication of photonic and optoelectronic devices.
9:00 PM - K7.16
Electrical Characterization of Isotype n-ZnO/n-GaN Heterostructures.
Yahya Alivov 1 , Bo Xiao 1 , Sena Akarca-Biyikli 1 , Qian Fan 1 , Daniel Johnstone 2 , Cole Litton 3 , Hadis Morkoc 1
1 , VCU, Richmond, Virginia, United States, 2 , SEMETROL, Chesterfield, Virginia, United States, 3 , Air Force Research Laboratory , Dayton, Ohio, United States
Show Abstract9:00 PM - K7.17
Defect Engineering in ZnO.
Victoria Coleman 1 , Hark Tan 1 , Jodie Bradby 1 , Manuela Buda 1 , C. Jagadish 1 , Sergei Kucheyev 2 , Jin Zou 3 , Matthew Phillips 4
1 Research School of Physical Sciences and Engineering, Australian National University, Canberra, Australian Capital Territory, Australia, 2 , Lawrence Livermore National Laboratory, Livermore, California, United States, 3 School of Engineering, Division of Materials, University of Queensland, Brisbane, Queensland, Australia, 4 Microstructural Analysis Unit, University of Technology, Sydney, Sydney, New South Wales, Australia
Show Abstract9:00 PM - K7.18
Recombination Mechanism of Green Emission: Study of ZnO Nanocrystals.
Yinyan Gong 1 , Tamar Andelman 1 , Gertrude Neumark 1 , Stephen O'Brien 1 , Igor Kuskovksy 2
1 Department of Applied Physics and Applied Mathematics, Columbia Unversity, New York, New York, United States, 2 Department of Physics, Queens College of CUNY, New York, New York, United States
Show AbstractZnO has long been regarded as a promising candidate for optoelectronics owing to its direct, wide, band gap and to its high exciton binding energy. It is known that the photoluminescence of most ZnO samples consist of a near band edge UV emission and a defect-related green emission. For many device applications, it is important to suppress the green emission, whose origin is still under debate and no consensus has been reached. Here we present results of photoluminescence (PL) and optical absorption measurements for ZnO nanocrystals of various morphologies as well as spherical nanoparticles of comparable size but with differently modified surface. All samples were prepared by a simple solution method [1, 2]. For optical characterization the nanocrystals were removed from their growth solution and redispersed in hexane. We found that although the PL from all our samples is dominated by the UV emission, the green emission is present most of the time, but it strongly depends on morphologies and sizes of the nanocrystals. Furthermore, for spherical nanoparticles we found that the green emission is largely suppressed by modifying surface states, for instance, by adding a small amount of trioctylamine or trioctylphosphine oxide to the original solvent. Based on the present study, as well as our previous results [2, 3], we suggest that the green emission is mainly due to radiative recombination between deep levels, formed by oxygen vacancies located on the surface, and free holes. Finally, we use the green luminescence to estimate the sizes of optically active spherical nanoparticles. The results are in excellent agreement with those of transmission electron microscopy. The proposed approach, estimating size based on green emission, is seemingly better than the use of excitonic emission, since it does not require the knowledge of the exciton binding energy, which depends on the degree of confinement in the nanoparticles. 1. M. Yin, et al., J. Am Chem. Soc. 126, 6206 (2004).2. T. Andelman, et al. J. Phys. Chem. B 109, 14314 (2005).3. Gu et al., Appl. Phys. Lett. 85, 3833 (2004).
9:00 PM - K7.19
Acceptors in ZnO Studied by Photoluminescence.
Michael Reshchikov 1 , Hadis Morkoc 2 1 , Bill Nemeth 3 , Jeff Nause 3
1 Physics Department, Virginia Commonwealth University, Richmond, Virginia, United States, 2 Electrical Engineering Dept., Virginia Commonwealth University, Richmond, Virginia, United States, 3 , Cermet, Inc., Atlanta, Georgia, United States
Show Abstract9:00 PM - K7.2
Surface Luminescence of Zinc Oxide Excited by Recombination of Hydrogen Atoms.
Vladimir Tyutyunnikov 1 , Michael Sushchikh 3 , Vladislav Styrov 1 2
1 Physics Department, Azov Sea State Technical University, Mariupol Ukraine, 3 Chemical Engineering, UCSB, Santa Barbara, California, United States, 2 , School of Physics and Mathematics, Mariupol Ukraine
Show AbstractExcitation of a luminescence by highly exothermic chemical reaction on the surface of a luminophore provides unique opportunity to separate surface luminescence from the bulk one. This enables studies of the electronic properties of the semiconductor surfaces even for the surfaces of complicate shapes. We have studied surface luminescenceof ZnO powders, films and single crystals excited by catalytic recombination of hydrogen atoms, i.e. heterogeneous chemiluminescence (HCL), and the HCL spectra were compared to the photoluminescence (PL) spectra. The HCL spectra were sensitive to the details of the sample preparation and treatment whereas PL spectra almost did not change. The HCL spectra of powdered samples exhibited long wavelength tail (up to 800 nm) and their maximum was blue-shifted by 5nm as compared with PL spectra. Different HCL bands forming long-wavelength tail were separated by changing the temperature of the samples and by varying the treatment conditions. Additional milling of ZnO led to amplification of the HCL-specific bands. Special pure grade ZnO showed neither PL nor HCL, however we were able to observe HCL bands with max at 610 nm and 730 nm after exposure the powder to H2+H atmosphere at 570K. Such treatment did not caused appearance of the PL.The HCL can be utilized for in situ monitoring of the growth and evolution of ZnO in controlled atmosphere including its nanoforms.
9:00 PM - K7.20
Controllable Synthesis of ZnO nanorod Arrays via Simple Solution-Based Method.
Patcharee Charoensirithavorn 1 , Susumu Yoshikawa 1
1 Institute of Advance Energy, Kyoto University, Uji, Kyoto, Japan
Show Abstract9:00 PM - K7.21
Selective Growth of Zn- and O-polar ZnO Films by P-MBE for Fabrication of Periodically Polarity-inverted Photonic Crystals.
Tsutomu Minegishi 1 , Takashi Hanada 2 , Rafal Boze 3 , Seunghwan Park 1 , Jinsub Park 1 , Kazushi Sumitani 4 , Osami Sakata 4 , Katsushi Fujii 1 , Meoungwhan Cho 2 , Takafumi Yao 1 2
1 Center for Interdisciplinary Research(CIR), Tohoku University, Sendai, Miyagi, Japan, 2 Institute for Materials Research(IMR), Tohoku University, Sendai, Miyagi, Japan, 3 Institute of Experimental Physics, Warsaw University, Warsaw Poland, 4 , Japan Synchritrin Radiation Research Institute(JASRI), Sayo-gun, Hyogo, Japan
Show Abstract9:00 PM - K7.22
Controlled Growth of ZnO micro- and Nanorod Arrays by the Wet Chemical Method.
Yong-Jin Kim 1 2 , Chul-Ho Lee 1 3 , Young Joon Hong 1 3 , Gyu-Chul Yi 1 2 3
1 , National CRI Center for semiconductor nanorods, Pohang, Gyeongbuk, Korea (the Republic of), 2 Environmental Science and Engineering, POSTECH, Pohang, Gyeongbuk, Korea (the Republic of), 3 Materials Science and Engineering, POSTECH, Pohang, Gyeongbuk, Korea (the Republic of)
Show Abstract9:00 PM - K7.23
Photoluminescence of MgxZn1-xO/ZnO Quantum Wells Grown by Pulsed Laser Deposition.
Susanne Heitsch 1 , Gregor Zimmermann 1 , Jörg Lenzner 1 , Holger Hochmuth 1 , Gabriele Benndorf 1 , Michael Lorenz 1 , Marius Grundmann 1
1 Institut fuer experimentelle Physik II, Universitaet Leipzig, Leipzig Germany
Show Abstract9:00 PM - K7.24
Raman Scattering Characterization of Implanted ZnO.
Esther Alarcon-Llado 1 , Ramon Cusco 1 , Luis Artus 1 , German Gonzalez-Diaz 2 , Ignacio Martil 2 , Juan Jimenez 3 , Michael Callahan 4
1 Inst. Jaume Almera, C.S.I.C., Barcelona Spain, 2 Fisica Aplicada III, Univ. Complutense, Madrid Spain, 3 Física Materia Condensada, Univ. Valladolid, Valladolid Spain, 4 , Air Force Research Lab, Hanscom AFB, Massachusetts, United States
Show Abstract9:00 PM - K7.25
Morphology and Electronic Structure of MOMBE Grown Epitaxial ZnO Surfaces.
Christian Pettenkofer 1 , Stefan Andres 1
1 SE6, HMI, Berlin Germany
Show Abstract9:00 PM - K7.26
Atomic Layer Deposition of ZnO for Display Applications.
Eun Ho Kim 1 , Chang Yeon Kim 1 , Doo Hyeong Lee 1 , Bo Hyun Chung 1 , Jae Ha Jeon 1 , Hee Soo Kim 1 , Jun Won Hyun 1 , Yongmin Kim 1 , Seung Jeong Noh 1
1 Applied Physics, Dankook University, Seoul Korea (the Republic of)
Show AbstractZnO has wurtzite structure exhibiting very excellent piezoelectric and optical properties. ZnO has rapidly emerged as a promising optoelectronical material due to its large band gap of 3.37 eV, low power threshold for optical pumping at room temperature, and highly efficient UV emission of a large exciton binding energy of 60 meV. Various deposition techniques, such as sputtering, pulsed laser deposition, chemical vapor deposition, spray pyrolysis, and molecular beam epitaxy have been widely employed for the growth of ZnO films. However, these processes have drawbacks of rough morphology, poor step coverage, etc. In atomic layer deposition(ALD), the deposited film has excellent conformality and uniformity down to an atomic scale thickness since surface reactions of metal precursor and reactant gas are complementary and self-limiting. In addition, ALD provides high quality films especially at low temperature. Thus, we have fabricated ZnO and ZnO:N thin films by ALD using diethylzinc(DEZn) and H2O for ZnO deposition and DEZn, H2O and N2 for ZnO:N deposition. Self-limiting growth was observed at substrate temperatures from 105 to 165 °C, in the different flow rates of DEZn, H2O and N2. The crystal growth orientation was investigated by x-ray diffraction and the characteristics were by Hall measurement, photoluminescence measurement, etc. This work was supported by Seoul R & BD Program (10555).
9:00 PM - K7.27
ZnMgO UV Photodetectors Fabricated By A Novel Method; Linear Source Mist CVD.
Yudai Kamada 1 , Tosiyuki Kawaharamura 1 , Hiroyuki Nishinaka 1 , Shizuo Fujita 2
1 Department of Electronic Engineering and Science, Kyoto University, Kyoto Japan, 2 International Innovation Center, Kyoto University, Kyoto Japan
Show AbstractIn order to meet the increasing demand for ZnO-based devices, we need to develop ZnMgO thin films which allow various heterostructures. A lot of technologies such as MBE, MOCVD, or PLD are reported to form ZnMgO thin films, but evolution of safe and economical deposition technologies is significant especially for utilizing the unique functions of ZnO-based materials on large-area substrates, that is, for such as transparent conductors, UV absorbers, and UV image sensors. For this reason, we developed a new method to fit the demand. An attention has been given to the mist CVD method where a liquid solution of constituent elements is ultrasonically atomized and the aerozol particles hence formed are transferred to the reaction area to form ZnO. We have established an improved system by utilizing a special nozzle composed with a linear aperture to flatten the flow to guarantee the formation of uniform and high quality films. This method possesses advantages of safety, cost-effective, light load to the environment, and multiplicity of applying to a lot of materials. Following to the successful deposition of highly uniform ZnO in our earlier works, in this presentation the fabrication of ZnMgO thin films and UV photodetectors will be reported.ZnMgO films were deposited on soda-glass substrates. The sources used were zincacetate and magnesium acetate which were diluted in deionized water with the concentrations of 0.050 mol/l and 0-0.050 mol/l, respectively. The carrier gas for the aerosol particles was N2, whose flow rate was 8 l/min. The temperatures of the substrate were set at 360-520 oC. ZnMgO thin films were successfully grown on glass substrates and these transmittances in visible range was more than 90%, showing good transparency. With increasing the source concentration ratios of [Mg]/([Zn]+[Mg]), the absorption edge shifted to the shorter wavelength and the band gap energy gradually increases. It was possible to control the band gap energy up to 3.75 eV. In order to demonstrate the optoelectronic performance of the ZnMgO films, we made a planar geometry Schottky type metal-semiconductor-metal UV photodetector using the ZnMgO film and measured the dark-current and photo-current characteristics. The 50 pairs of interdigital electrodes consisted with the Au (60 nm)/Cr (20 nm) bilayer with 2 mm long, 10 µm wide, and 15 µm spacing were formed by conventional photolithography and lifting off on the ZnMgO layer whose band gap was 3.5eV. No photoresponse was seen with illuminating the 400nm light. However, by illuminating the 300nm light, the photoresponsivity of 5.0A/W was obtained. Considering the Schottky characteristics of the electrodes, the large photoresponsivity may be attributed to the variation of Schottky barrier height under the illumination. Promising optoelectronic performance of the ZnMgO has been confirmed in spite of the simple and cost-effective deposition technique.
9:00 PM - K7.28
A Solution Method for Large-scale Selective Growth of Aligned ZnO Nanorods.
Q. Ahsanulhaq 1 , A. Umar 1 , Sang-Hoon Kim 1 , Yeon Ho Im 1 , Yoon-Bong Hahn 1
1 School of Chemical Engineering and Technology and Nanomaterials Processing Research Center, Chonbuk National University, Jeonju Korea (the Republic of)
Show Abstract9:00 PM - K7.3
ZnO and MgZnO Nanoalloys: Optical and Structural Properties.
Heather Hoeck 1 , John Morrison 1 , Jesse Huso 1 , Erin Casey 1 , Xiang-Bai Chen 1 , Leah Bergman 1 , Slade Jokela 2 , Matthew McCluskey 2 , Tsvetanka Zheleva 3
1 Department of Physics, University of Idaho, Moscow, Idaho, United States, 2 Department of Physics, Washington State University, Pullman, Washington, United States, 3 , Army Research Laboratory, Adelphi, Maryland, United States
Show AbstractZnO and MgZnO alloys are promising wide-bandgap semiconductors for optoelectronic applications, and also of considerable interest from a fundamental viewpoint. The environmentally friendly chemical composition and the deep excitonic level ~ 60 meV of ZnO make it an excellent candidate for high-efficiency next generation ultraviolet light sources. These optical alloys enable the tuning of the bandgap and the luminescence at the range of ~ 3.0 eV for ZnO of the wurtzite structure up to ~ 7 eV for the MgO of the rocksalt structure. The optical properties of bulk and nanoscale ZnO at ambient conditions have been extensively investigated. In contrast, less is known about ZnO bulk properties under the influence of applied pressure and still less so for ZnO nanomaterials.We present studies on the ultraviolet photoluminescence and Raman properties of wurtzite MgZnO nanopowders of average size ~ 30 nm that were synthesized via the thermal decomposition method. For the studied composition range between 0 and 26% the room temperature UV-PL was found to be tuned by ~ 0.3 eV towards the UV-spectral range; the extent of the blueshift found to depend on the crystallite quality. For that composition range the first-order LO Raman mode was found to exhibit a significant blueshift of ~ 33 cm-1 and the second-order LO a shift of ~ 60 cm-1 .Additionally we present studies on the pressure response of the ZnO and MgZnO nanocrystallites. We found that up to 6 GPa the pressure coefficients of ZnO and MgZnO are 23 and 27 meV/GPa, respectively. The pressure coefficient of the ZnO nanocrystallites is similar to that reported elsewhere for bulk ZnO material. The higher value found for MgZnO is discussed in terms of the difference in the atomic numbers of the cation constituents.
9:00 PM - K7.30
Controllable Synthesis of ZnO Nanonails by Vapor-solid Process: Growth Mechanism and Structural and Optical Properties.
Ahmad Umar 1 , Q. Q. Ahsanulhaq, 1 , Sang Hoon Kim 1 , Yeon Ho Im 1 , Yoon-Bong Hahn 1
1 School of Chemical Engineering and Technology and Nanomaterials Processing Research Center, Chonbuk National University, Jeonju Korea (the Republic of)
Show AbstractWith the controllable morphologies, wurtzite ZnO nanonails have been synthesized on steel alloy substrate without the use of any metal catalyst or additives by the thermal evaporation of metallic zinc powder at low temperature. Morphological studies revealed that different types of ZnO nanonails in terms of their diameters and lengths of caps versus shafts were obtained at different positions in the reactor chamber depending upon the distance of the substrates from the source material in different temperature zones. The deposited ZnO nanonails exhibited well defined morphologies with the clean surfaces without any surface contaminations. High resolution transmission electron microscopy (HRTEM), X-ray and selected area electron diffraction patterns indicated that the deposited nanostructures are single crystalline and grew along the [0001] direction. A sharp, strong and dominant E2 mode in Raman spectra, for all the cases, confirms the excellent crystallinity and wurtzite hexagonal phase for the grown ZnO nanonails. Additionally, the appearance of strong and sharp UV emission with the absence of green emission observed in the photoluminescence (PL) spectra at room temperature for the deposited products gives a strong evidence for their excellent optical properties.
9:00 PM - K7.31
Surface Preparation of Single Crystals for ZnO Homoepitaxy.
Christian Neumann 1 , Stefan Lautenschläger 1 , Swen Graubner 1 , Joachim Sann 1 , Niklas Volbers 1 , Bruno Meyer 1 , Jürgen Bläsing 2 , Alois Krost 2
1 I. Phys. Institute, Justus-Liebig-University, Giessen Germany, 2 Institute of Experimental Physics, Otto-von-Guericke-University, Magdeburg Germany
Show AbstractHere we report on a thermal surface preparation of commercial ZnO crystals. Usually the surface is severely damaged by cutting and polishing.Thus, an additional high temperature treatment is necessary to improve the morphology and surface crystallinity of the delivered crystals.The ZnO crystals were treated at different temperatures and characterized by atomic force microscopy, X-ray diffraction and reflection, photoluminescence, and hall measurements.Finally, we report on first results of a successful ZnO homoepitaxy.
9:00 PM - K7.32
Structural Properties of ZnO Nanowires Grown by Chemical Vapor Deposition on GaN/sapphire (0001).
F. Tsao 1 , P. Huang 1 , C. Pan 2 , C. Tun 2 3 , C. Kuo 4 , B. Pong 1 , G. Chi 1 2
1 Department of Physics, National Central University, Jhongli, Taoyuan, Taiwan, 2 Optical Sciences Center, National Central University, Jhongli, Taoyuan, Taiwan, 3 , National Synchrotron Radiation Research Center, Hsinchu Taiwan, 4 Institute of Optical Sciences, National Central University, Jhongli, Taoyuan, Taiwan
Show Abstract9:00 PM - K7.33
Conversion of Deep Level Emissions into Band-edge Emission from Au/ZnO by Using Plasmonic Mediation.
Weihai Ni 1 , Hock Chun Ong 1
1 Physics Dept., The Chinese Univ. of Hong Kong, Hong Kong China
Show Abstract9:00 PM - K7.34
RF Magnetron Sputtered ZnO Films for Flexural Plate Wave Devices.
Sang Yoon 1 , Dong-Joo Kim 1
1 Materials Engineering, Auburn University, Auburn, Alabama, United States
Show Abstract9:00 PM - K7.35
Hetero-Junction Diodes Composed of Undoped p-ZnO and n-SnO2 Thin Films.
Nick Brilis 1 , Dimitris Tsamakis 1 , Hasina Ali 2 , Soumya Krishnamoorthy 2 , Agis Iliadis 2 3
1 School of Electrical Engineering and Computer Science, National Technical University of Athens, Athens Greece, 2 Department of Electrical & Computer Engineering, University of Maryland, Maryland, District of Columbia, United States, 3 Department of Information and Communication Systems Engineering, University of the Aegean, Karlovasi, Samos, Samos Island, Greece
Show Abstract9:00 PM - K7.36
Cathodoluminescence Study of Hydrothermal Zn1-xMgxO Alloy Crystals.
J. Mass 1 4 , M. Avella 1 , Juan Jimenez 1 , M. Callahan 2 , E. Grant 2 , K. Rakes 2 , D. Bliss 2 , B. Wang 3
1 Dpto. Física de la Materia Condensada, Universidad de Valladolid, Valladolid Spain, 4 Dpto. Física y Matemáticas, UniNorte, Barranquilla Colombia, 2 Sensors Directorate, Air Force Research Laboratory, Hanscom, Massachusetts, United States, 3 , Solid State Scientific Corporation, Hollis, New Hampshire, United States
Show AbstractBand engineering of ZnO is necessary for UV optoelectronic applications. It can be achieved by alloying with MgO for increasing the band gap, and with CdO for decreasing the band gap. Alloying with MgO has been reported to reach 36% using epitaxial techniques. There are not reports about the growth of ZnMgO crystals by the hydrothermal route. The alloy composition should be limited by the solubility of MgO in wurtzite ZnO. One of the main challenges consists of obtaining crystals with homogeneous composition to be used as substrates for both ZnO and GaN based optoelectronic devices. We present herein a cathodoluminescence (CL) study of ZnMgO hydrothermal crystals. The incorporation of Mg was found to depend on the growth face using CL spectral imaging, however, the variations were very small, being the changes in the formation of defects responsible for the visible luminescence much more significant. On the other hand, varying the acceleration voltage of the excitation e-beam one observes a depth gradient in the incorporation of Mg. The Mg concentration was found to increase close to the surface. The crystals were previously etched in order to remove the thin ZnO layer grown on the surface during cooling.
9:00 PM - K7.37
Properties of Dominant Electron Trap Center in n-type SiC Epilayers by Means of Capacitance Spectroscopy.
Muhammad Asghar Hashmi 1 , Quamar ul Wahab 1 2 , Ijaz Hussain 1 , Hafiz Shahid Noor 1 , Faisal Iqbal 1 , Muhammad Shahid 1
1 Semiconductor Division, The Islamia University, Bahawalpur, Punjab, Pakistan, 2 Physics and Measurements Technology Materials Science, Linkoping University , Linkoping Sweden
Show Abstract9:00 PM - K7.38
Low Temperature Growth and Characterization of Mg0.15Zn0.85O Thin Film by Pulsed Laser Deposition.
Wei Wei 1 2 , Chunming Jin 2 , Andy Doraiswamy 2 , Roger Narayan 2 , Jagdish Narayan 1
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Joint Department of Biomedical Engineering, University of North Carolina and North Carolina State University, Chapel Hill, North Carolina, United States
Show Abstract9:00 PM - K7.39
Visible Luminescence from ZnO Nanostructures.
Minseo Park 2 , An-jen Cheng 1 2 , Dake Wang 2 , Yonhua Tzeng 1
2 Physics, Auburn University, Auburn, Alabama, United States, 1 Electrical Engineering, Auburn University, Auburn, Alabama, United States
Show Abstract9:00 PM - K7.4
Sonochemical Synthesis of Transition Metal-doped ZnO Nanorod Arrays on the Substrate.
Eugene Oh 1 , Seung-Ho Jung 2 , Kun-Hong Lee 2 , Soo-Hwan Jeong 1 , Moon-Hyung Lee 1 , Tae-Yong Kim 1 , Yu-Sung Jin 1
1 Chemical Engineering, Kyungpook National University, Daegu Korea (the Republic of), 2 Chemical Engineering, Pohang University of Science and Technology, Pohang Korea (the Republic of)
Show Abstract9:00 PM - K7.40
Magneto-optical Properties and Strain Evolution in Homoepitaxially Grown ZnO and ZnO:Li Layers.
Axel Hoffmann 1 , U. Haboeck 1 , M. Wagner 1 , R. Mc Kenna 1 , S. Lautenschläger 2 , J. Sann 2 , B. Meyer 2
1 Inst. f. Fstkoerperphysik, TU Berlin, Berlin Germany, 2 1. Physikalisches Institut, Justus Liebig University, Giessen Germany
Show Abstract9:00 PM - K7.41
Influence of Buffer Layers on the Structural Properties of ZnO Grown by Plasma Assisted Molecular Beam Epitaxy.
Thomas Wassner 1 , Bernhard Laumer 1 , Martin Stutzmann 1 , Martin Eickhoff 1
1 Walter Schottky Institut, Technische Universitaet Muenchen, Garching Germany
Show Abstract9:00 PM - K7.43
In-Situ Arsenic Doping of ZnO Grown on GaN/Sapphire and ZnO Substrates by Molecular Beam Epitaxy.
Weiming Wang 1 , Emine Cagin 1 , Willie Bowen 1 , Jamie Phillips 1
1 , University of Michigan, Ann arbor, Michigan, United States
Show AbstractZinc oxide and related oxide semiconductor alloys are emerging as important materials for active electronic and optoelectronic devices due to their desirable growth parameters, availability of native ZnO substrates, excellent optical properties, and near lattice-matched alloy system. High quality ZnO materials have been achieved using molecular beam epitaxy (MBE) with a plasma source to provide atomic oxygen. However, many challenges remain with respect to the repeatable growth of high quality material, and the ability to achieve reliable p-type doping. In this work, the epitaxial growth of arsenic doped ZnO and resulting electronic properties are presented. ZnO was grown on GaN/sapphire (0001) substrates and on native c-plane ZnO (0001) bulk substrates. GaN/sapphire (0001) substrates consisted of several microns of GaN grown by MOCVD to provide a substrate with a near lattice match (1.8% mismatch) and semi-insulating properties. Growth on ZnO substrates were conducted on both Zn-face and O-face of high resistivity bulk ZnO for comparison. The background n-type carrier concentration for these epilayers was found to span the range of 1017 cm-3 to 1019 cm-3, and to be highly dependent on VI/II flux ratio. The incorporation and activation of acceptors related to arsenic doping were found to have a strong dependence on both the arsenic flux and the VI/II flux ratio. The electronic properties of undoped and arsenic doped ZnO will be presented. Challenges associated with the achievement of stable p-type behavior will be discussed.
9:00 PM - K7.44
Manipulation of Chemical and Optical Properties of MgO Nanocubes via Surface Functionalization.
Slavica Stankic 1 , T. Berger 1 , Oliver Diwald 1 , J. Bernardi 1 , Erich Knözinger 1
1 Institute of Materials Chemistry, Vienna University of Technology, Vienna Austria
Show Abstract9:00 PM - K7.45
A Study of Nano-phased ZnO Thin Film Grown by Pulsed Laser Deposition.
Wonwoo Lee 1
1 Materials Science, University of alabama at birmingham, Fultondale, Alabama, United States
Show Abstract9:00 PM - K7.46
Effects of Homogeneous Buffer and Annealing on the Low Temperature Optical Properties of ZnO Films Grown by PLD
Xiyao Zhang 1 , Anuj Dhawan 1 , Patrick Wellenius 1 , John F Muth 1
1 , North Carolina State University, Raleigh, North Carolina, United States
Show Abstract9:00 PM - K7.47
Growth of ZnO Thin Films by Metalorganic Chemical Vapor Deposition for Optoelectronic and Spintronic Applications.
William Fenwick 1 , Tahir Zaidi 1 , Vincent Woods 1 , Nola Li 1 , Matthew Kane 1 2 , Shalini Gupta 1 , Ian Ferguson 1 2
1 Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show Abstract9:00 PM - K7.48
A Comparative Study of MOCVD Produced ZnO Films Doped with N, As, P and Sb.
Gary Tompa 1 , S. Sun 1 , C. Rice 1 , L. Provost 1 , D. Mentel 1
1 , Structured Materials Industries, Inc., Piscataway, New Jersey, United States
Show Abstract9:00 PM - K7.49
Electrical Properties of Solution Grown Piezoelectric ZnO Nanorods.
David Scrymgeour 1 , Dana Olson 1 , Julia Hsu 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractNanoscale semiconducting zinc oxide has been regarded a one of the most promising materials for the next generation sensors, UV lasers, solar cells, and nanoscale electronic devices. This is because of its important physical properties that include a wide band gap (~3.44 eV) and interesting optoelectronic, pyroelectric, and piezoelectric properties. However, despite advances in the growth and fabrication of nanostructures, reliable nanoscale metal-semiconducting oxide contacts are required for utilization of ZnO nanostructures for device applications. Understanding the nature of this contact is a critical step in incorporation of nanostructures.
Piezoelectric zinc oxide nanocrystals are grown by solution techniques on highly textured Ag (111) films in patterned arrays. These ZnO nanocrystals form hexagonal crystal rods with diameters of 100-600 nm and heights of 400-1200 nm with their [0001] polar axis growing from the substrate. The nature of the electrical contact on a nanorod will be studied by contact atomic force microscopy (C-AFM) where the metallic coating on the probe tip forms the metal contact. This contact will be investigated on different rods as a function of tip coating work function, as well as rod surface treatments such as vacuum and UV ozone exposure. These measurements will be compared to work function measurements on assemblages of nanorod. From the results of these studies, we will discuss the mechanisms that control the contact properties and I-V characteristics of the ZnO nanorods.
Additionally, the piezoelectric response of the individual nanorods has been determined by piezoelectric force microscopy (PFM). The rods have a response of ~5.6 pm/V that can vary from rod to rod and is not correlated to nanorod height or radius, which indicates another factor is responsible for the variation. It is known from studies of other semiconductor piezoelectric crystals that the conductive properties can have a strong influence on the strength of the measured piezoelectric coefficient. Correlations between the conductive properties and the variation rod-to-rod of the measured piezoelectric coefficient will be presented.
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
9:00 PM - K7.5
Erbium Doped ZnO Thin Films Synthesized using Glycerol as Chelating Agent in Modified Pechini Process.
Uma Choppali 1 , Brian Gorman 1
1 Materials Science and Engineering, University of North Texas, Denton , Texas, United States
Show Abstract9:00 PM - K7.50
Photodetectors Based on Ti/Al Contacts to Sb-doped p-ZnO/n-Si.
Leelaprasanna Mandalapu 1 , Faxian Xiu 1 , Zheng Yang 1 , Jianlin Liu 1
1 Department of Electrical Engineering, University of California, Riverside, Riverside, California, United States
Show Abstract9:00 PM - K7.51
Zinc Oxide Fiber-like and Whisker Formations by Electrospinning.
Onur Yordem 1 , Erdem Ogut 1 , Mehmet Gulgun 1 , Melih Papila 1
1 , Sabanci University, Istanbul Turkey
Show AbstractZinc Oxide (ZnO) has been focus of many researchers for its electronic and optical properties. Its wide direct band gap value of 3.32eV, is attractive for the potential applications such as functional electrical devices, gas sensors and solar cells. Among several processing techniques such as chemical vapor deposition, thermal evaporation, electrodeposition, sputtering, and pattern growth techniques; electrospinning process is utilized in this study to form nano-scale Zinc Oxide fibers. Zinc Oxide fibers attract our attention particularly in terms of piezoelectric characteristics, actuation and sensing capabilities. Although the fiber formation with electrospinning has been in use for the last decade, control of ceramic fiber formation in order to yield single crystal structures by electrospinning is relatively a fresh field of interest. The polymer system poly(vinyl alcohol) (PVA) in an aqueous solution is mixed with the aqueous zinc acetate (Zn(CH3COO)2.2H2O) solution at 80C and gently stirred for five hours for the sol-gel reaction. The so-called precursor solution is electrospun under a high DC voltage and the precursor fibers are collected as a mat of fibers. Randomly oriented and aligned precursor fibers of PVA/(Zn(CH3COO)2) in ~600nm diameter are produced. TGA analysis of the precursor mats revealed the significant heating regime for the calcination and sintering procedure of the mats. The precursor fibers are first dried at 120C for 1hour and then calcinated at different temperatures above 500C for various durations at several heating rates. The resultant samples exhibit the significance of the process parameters in the ZnO formation. Better process schemes produced porous ZnO fibers of 100nm to 200nm in diameter. The porous fibers which are composed of hexagonal ZnO particles are further made uniform by a sintering process at temperatures higher than the calcination temperature. XRD results suggested the electrospun ZnO fibers have a hexagonal wurtzite structure which is favorable due to its piezoelectric property. Further sintering procedure revealed the micron scale single crystal ZnO whisker formation throughout the mat.
9:00 PM - K7.52
Carrier-Dependence Photoluminescence Study of Ga-doped ZnO Thin Films
Zheng Yang 1 , Faxian Xiu 1 , Leelaprasanna Mandalapu 1 , Jianlin Liu 1
1 Electrical Engineering, Univ of California, Riverside, Riverside, California, United States
Show AbstractGa-doped ZnO has been considered as one of the potential candidates of transparent conducting oxide (TCO) thin films to substitute for the conventional TCO such as indium tin oxide. Additionally, higher electron concentrations can be achieved in ZnO through Ga doping than those in undoped n-type ZnO thin films as a result of intrinsic defects. Ga-doped ZnO films with electron concentrations in the region of 10^17 to 10^18 cm^-3 are important for UV optoelectronic applications. High carrier concentration (>10^19 cm^-3) is necessary for ZnO-based diluted magnetic semiconductors (DMS) from theoretical predictions. Therefore, it is important to systematically study the optical and electrical properties of the Ga-doped ZnO.A series of Ga-doped ZnO thin films were grown on sapphire substrates using an SVTA plasma-assisted molecular beam epitaxy (P-MBE) system. Different electron carrier concentrations were achieved by controlling Ga effusion cell temperature. Reflection high Energy Electron Diffraction (RHEED), X-ray diffraction (XRD), Hall effect, and photoluminescence (PL) measurements were performed on as-grown Ga-doped ZnO thin films. RHEED and XRD results show that these films are of good crystalline quality. Hall effect measurements show that the sample with higher Ga cell temperature has higher electron concentration, which can be controlled precisely. Well-resolved low-temperature (9K) PL spectra were obtained from these ZnO:Ga samples, the Ga-related donor-bound exciton (D^0X) peak does not appear until the Ga cell temperature reaches 550 °C. The Ga-DY^0X peak dominates in the spectra when the Ga cell temperature reaches 600 °C. The temperature-dependent and power-dependent PL spectra were used to investigate the detailed information on the donors in the ZnO:Ga samples.
9:00 PM - K7.53
Growth in Aqueous Solution and Characterization of ZnO Whiskers Bridging Between Micron-gap Electrodes.
Keisuke Kametani 1 , Hiroshi Imamoto 2 , Herve Dumot 3 , Shizuo Fujita 1
1 International Innovation Center, Kyoto University, Kyoto Japan, 2 Advance Device Laboratory, OMRON Co. Ltd, Kyoto Japan, 3 Venture Business Laboratory, Kyoto University, Kyoto Japan
Show Abstract9:00 PM - K7.54
A Photoluminance (PL) Study on LPCVD ZnO Assisted by RF sputtered Buffers.
Yuneng Chang 1
1 Chemical and Materials engineering, Lunghwa university of science and technology, Taoyuan, Taiwan, Taiwan
Show Abstract9:00 PM - K7.55
Low Temperature Atmospheric Pressure CVD of ZnO Films at 150oC using Zinc acetylacetonate as precursor
Yuneng Chang 1
1 Chemical and Materials engineering, Lunghwa university of science and technology, Taoyuan, Taiwan, Taiwan
Show Abstract9:00 PM - K7.56
Gas Phase Fourier Transform Infrared Spectroscopy (Ftir) Analysis of ZnO APCVD at 150-300°C.
Yuneng Chang 1
1 Chemical and Materials engineering, Lunghwa university of science and technology, Taoyuan, Taiwan, Taiwan
Show Abstract9:00 PM - K7.57
Visible-Light Sensitivity for N-Doped ZnO Films Prepared by Reactive Magnetron Sputtering.
Yoshitaka Nakano 1 , Takeshi Morikawa 1 , Takeshi Ohwaki 1
1 , Toyota Central R&D Labs., Aichi Japan
Show Abstract9:00 PM - K7.6
Bulk Acoustic Resonator Based on ZnO Belts
Brent Buchine 1 , William Hughes 1 , Fahrettin Degertekin 2 , Zhong Wang 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show Abstract9:00 PM - K7.7
Unambiguous Identification of the PL-I9-line in Zinc Oxide.
Sven Müller 1 , Daniel Stichtenoth 1 , Michael Uhrmacher 1 , Hans Hofsäss 1 , Jens Röder 2 , Carsten Ronning 1
1 II. Institute of Physics, University of Göttingen, Göttingen Germany, 2 Institute of Physical and Theoretical Chemistry, Technical University of Braunschweig, Braunschweig Germany
Show AbstractThe intense luminescence of zinc oxide (ZnO) is usually dominated by transitions of donor bound excitons, which are commonly labelled from I1 to I11. The identity of the respective causing donors is in the most cases unknown, but some of them were assigned to specific elements like hydrogen, aluminium, gallium, or indium; mainly based on doping studies during growth and/or ion implantation [1]. However, an unambiguous identification is in both cases difficult due to the accompanying co-doping effects during growth and creation of defects during ion implantation, respectively. A clear identification can be achieved using radioactive dopants, which undergo an element transition upon decay. Thus, luminescence lines, which vary their intensities with the specific half-life of the respective isotope with increasing measuring time, can be unambiguous assigned to specific elements. In recent literature such an experiment has been described for ZnO resulting into a clear assignment of the I1 & I8-line to Ga [2].We have implanted radioactive 111In with an ion energy of 400 keV into commercial available ZnO single crystals. The isotope 111In decays into stable 111Cd with an half-time of 2.8 days; thus, an element transition from a donor to an isoelectronic element within the ZnO crystal occurs upon time. The samples were annealed at 700°C for 15 minutes under vacuum, and the annealing process was monitored by perturbed angular-γγ-spectroscopy (PAC). Here, a recovery of the lattice and no out-diffusion of the implanted 111In atoms were observed. The samples were finally characterised by photoluminescence spectroscopy over a time period of 3 weeks. The obtained results together with additional ion implantation studies with stable 115In and varying ion fluences will be discussed in respected to the existing literature in this presentation.[1] B.K. Meyer et al.; Physica Status Solidi B, 2004 , 241 , 231-260 [2] K. Johnston et al.; Physical Review B, 2006 , 73 , 165212
9:00 PM - K7.8
Synthesis and Growth Mechanism of Zinc Oxide Multi-needles in Arc Discharge.
Vladimir Pokropivny 1 3 , Mais Kasumov 2
1 , Frantsevich Institute for Problems of Materials Science of NASU, Kiev Ukraine, 3 , Institute of Physics of Tartu University, Tartu Estonia, 2 , Vernadsky Institute of General and Inorganic Chemistry of NASU, Kiev Ukraine
Show Abstract9:00 PM - K7.9
Growth Behaviors of ZnO Nanostructures on SrTiO3 Substrates.
Dong-Wook Kim 1 , Heejun Jeong 1 , Heung-Suk Oh 1 , Seo-Hyung Chang 2 , Young-Jun Chang 2
1 Dept. of Applied Physics, Hanyang University, Ansan, Kyunggi-do, Korea (the Republic of), 2 Department of Physics, Seoul National University, Seoul Korea (the Republic of)
Show Abstract
Symposium Organizers
Juergen Christen Universität Magdeburg
Chennupati Jagadish Australian National University
David C. Look Wright State University
Takafumi Yao Tohoku University
K8: Doping
Session Chairs
Leonard Brillson
Yicheng Lu
Thursday AM, November 30, 2006
Room 200 (Hynes)
9:30 AM - **K8.1
p-type Doping in ZnO and ZnO-based LED realized by MOCVD.
Zhizhen Ye 1 , Weizhong Xu 1 , Yujia Zeng 1 , Liping Zhu 1 , Haiping He 1 , Binghui Zhao 1
1 , Zhejiang University, Hangzhou , Zhejiang, China
Show Abstract10:00 AM - K8.2
Systhesis of p-type ZnO Thin Films by (N,Ga) Co-doping using DMHy Dopant.
Hui Wang 1 , Ho-pui Ho 1
1 Dept. of Electronic Engineering, The Chinese University of Hong Kong, Hong Kong China
Show Abstract10:15 AM - K8.3
Electrical Characterization of Defect States in Local Conductivity Domains in ZnO:N,As Layers.
Andre Krtschil 1 , Armin Dadgar 1 , Anette Diez 1 , Alois Krost 1
1 Institute of Experimental Physics, Otto-von-Guericke-University of Magdeburg, Magdeburg Germany
Show Abstract10:30 AM - K8.4
Properties of p-type ZnO Grown by Oxidation of Zn-group-V Compounds.
Eliana Kaminska 1 , Ewa Przezdziecka 2 , Anna Piotrowska 1 , Jacek Kossut 3 , Piotr Boguslawski 2 , Elzbieta Dynowska 2 , Witold Dobrowolski 2 , Rafal Jakiela 2 , Iwona Pasternak 1 , Elzbieta Lusakowska 2
1 , Institute of Electron Technology, Warsaw Poland, 2 , Institute of Physics, PAS, Warsaw Poland, 3 , Institute of Physics, PAS and ERATO Semiconductor Spintronics Project , Warsaw Poland
Show Abstract10:45 AM - K8.5
Donors and Acceptors in Bulk ZnO Grown by Vapor-phase, Melt, and Hydrothermal Processes.
David Look 1 2
1 Semicondcutor Research Center, Wright State University, Dayton, Ohio, United States, 2 Materials and Manufacturing Directorate, Air Force Research Laboratory, Dayton, Ohio, United States
Show AbstractOne of the advantages of ZnO as a material for photonic and electronic devices is the availability of large-area wafers from bulk crystals. Such crystals can be grown by vapor-phase (VP), melt, or hydrothermal processes, and each type of material has unique structural, optical, and electrical characteristics. Here we will discuss important similarities and differences in their donor and acceptor properties, as determined by low-temperature photoluminescence (PL) and temperature-dependent Hall-effect (TDH) measurements.All three growth techniques produce material with sharp (FWHM ≤ 0.3 meV), intense donor-bound-exciton (D0X) lines in the UV region (3.357 – 3.365 eV), but much broader spectra in the visible region (1.7 – 2.5 eV). However, there are interesting growth-dependent differences. For example, I4, arising from interstitial H, is usually the strongest line in VP material, whereas it is weak or nonexistent in melt or hydrothermal samples. On the other hand, the lines due to Group III elements, I6(Al), I8(Ga), and I9(In), are all found in VP and melt ZnO, but only I6 and I8 appear in hydrothermal ZnO. These donors, H, Al, Ga, and In, are all shallow, with energies in the 45 – 60 meV range. Besides the D0X transistions, there are also much weaker visible emissions. The VP samples are distinguished by a 2.5-eV green band and sometimes a small 1.7-eV red band, whereas the melt and hydrothermal samples show a strong 2.4-eV band with a much weaker shoulder at 2.2 eV. The 2.4/2.5-eV band is variously assigned to CuZn, VZn, or VO, and may have more than one origin. The 1.7-eV band is associated with an interstitial, according to a recent study.The TDH measurements in the VP and melt samples always show a dominance of shallow donors, of total concentration in the low-mid 1016-cm-3 range, while the hydrothermal samples are controlled by much deeper donors, but of similar concentrations. In VP material three donors, at energies of 30, 45, and 75 meV, and assigned to ZnI-NO, HI, and AlZn/GaZn, respectively, are sometimes necessary to accurately fit the n vs. T data. However, in melt ZnO, a single donor at about 50 meV is usually sufficient, and in hydrothermal ZnO, a deeper donor, at 200 – 400 meV, is nearly always dominant at room temperature. With regard to acceptors, the VP ZnO has the lowest concentration, ~ 2 x 1015 cm-3, and thus the highest peak mobility, up to 2500 cm2/V-s. The dominant acceptor in VP material is known to be VZn, but other acceptors, such as NO, may also be present but passivated by H. Hydrothermal ZnO has a much higher acceptor concentration, ~ 1 x 1016 cm-3, probably due to LiZn, and melt ZnO has an intermediate concentration. Further insights can be gained from electron irradiation, forming-gas anneals, and SIMS. Surface conduction will also be discussed.
11:30 AM - **K8.6
Phosphorus Doped ZnO Light-emitting Diodes.
Jae-Hong Lim 1 , Kyoung-Kook Kim 1 , Dae-Kue Hwang 1 , Seong-Ju Park 1
1 Department of Materials Science and Engineering, Gwangju Institute of Science & Technology, Gwangju Korea (the Republic of)
Show AbstractAmong the available wide bandgap semiconductors, zinc oxide (ZnO) of a large direct bandgap of 3.37 eV is a promising candidate for use as an efficient UV light emitter due to the characteristic features of ZnO. Homojunction ZnO light-emitting diode(LED) was successfully fabricated by using phosphorus oxide doped p-type ZnO films. Photoluminescence spectra of p-type ZnO:P thin films showed an acceptor bound excitonic and phosphorus related peaks at low temperature and strong band edge emission peak at 380nm at room temperature. A p-n homojunction ZnO LED with a structure of p-ZnO:P/n-ZnO:Ga was fabricated and it showed a clear emission peak at 380 nm which corresponds to the near band edge of ZnO. The I-V characteristics of ZnO LED showed a low threshold voltage of 3.2 V. The intensity of near bandedge emission was further increased and the deep-level emission was greatly suppressed by using Mg0.1Zn0.9O layers as energy barrier layers to confine the carriers to the high quality n-type ZnO. The fabrication and the characteristics of heterojunction ZnO light-emitting diode (LED) which consists of p-type ZnO:P and n-type GaN:Si layers are also reported. The current-voltage (I-V) and electroluminescence measurements of ZnO LED showed a threshold voltage of 5.4 V and a red-shifted band-edge emission of 409 nm due to the band offset.
12:00 PM - K8.7
A Promising p-type Doping Method in ZnO Thin Film Using Li–N Dual-acceptor Dopant Source.
Liping Zhu 1 , Zhizhen Ye 1 , Jianguo Lu 1 , Yinzhu Zhang 1 , Binghui Zhao 1
1 State Key Laboratory of Silicon Materials, Zhejiang University, Hangzhou, Zhejiang, China
Show Abstract12:15 PM - K8.8
Effect of Annealing Temperature and Ambient Gases on the Phosphorus Doped p-type ZnO.
Dae-Kue Hwang 1 , Mis-Suk Oh 1 , Jae-Hong Lim 1 , Chang-Goo Kang 1 , Young-Seok Choi 1 , Seong-Ju Park 1
1 , Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
Show AbstractIt is well known that the ZnO films grown in an O2 rich condition have a better chance to show p-type conductivity compared to those grown in the Zn rich growth condition due to the decrease of native defects acting as compensation centers in ZnO films. Recently, we reported that the phosphorus doped n-type ZnO can also be converted to p-type ZnO by a post annealing process. However, there is no report on the effect of various ambient gases on the post annealing of phosphorus doped ZnO. In this study, we report on the thermal activation of phosphorus doped ZnO thin films grown by radio frequency (RF) magnetron sputtering. Phosphorus doped ZnO thin films were activated to obtain p-type ZnO in the N2, Ar, and O2 ambient at different annealing temperatures. The hole concentration of p-type ZnO in an O2 ambient showed a lower hole concentration (2.01×10^17 cm-3 at 850 °C) compared to those of samples annealed in N2 (4.8×10^18 cm-3 at 850 °C) and/or Ar (4.5×10^18 cm-3 at 850 °C) ambient. The measurement of activation energy of phosphorus dopant in the ZnO film and the study on the effect of ambient gases on the hole concentration suggested that the dissociation of Zn-O and P-O are suppressed in the O2 ambient and the phosphorus replaces oxygen atoms in the ZnO film to increase the hole concentration in the phosphorus doped ZnO film.
12:30 PM - K8.9
Bipolar Phosphorus-doping of ZnO Thin Films Fabricated by Pulsed Laser Deposition.
Xiaoqing Pan 1 , Arnold Allenic 1 , Guangyuan Zhao 1 , Yong Che 2 , Zhendong Hu 2 , Bing Liu 2
1 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Research Group, IMRA America Inc., Ann Arbor, Michigan, United States
Show AbstractSemiconductor-based light-emitting devices require n-type and p-type materials. ZnO can readily be doped n-type, however it shows strong resistance to shallow acceptor doping. In this work, epitaxial phosphorus-doped ZnO (PZO) films were grown on sapphire by pulsed laser deposition. The full width at half maximum (FWHM) value of the rocking curve of the (0002) ZnO peak is as low as 0.08°. The surface of PZO films is smooth with rms values smaller than 1 nm. The film microstructure and film/substrate interface structure were characterized by transmission electron microscopy. As-grown PZO films are n-type with n~1019 cm-3 and ρ~10-3 Ω.cm. On the other hand, PZO films grown between 400 °C and 600 °C and subsequently annealed are p-type with p~5.0×1017 cm-3 and ρ~40 Ω.cm. PL spectra at 10 K of p-type PZO show a dominant phosphorus-related peak at 3.3417 eV and a broad red band peaking at 1.93 eV.
12:45 PM - K8.10
Microwave Enhanced Nitrogen Plasma Doping of ZnO Crystals.
Yi-Chun Liu 1 , Jiping Cheng 1 , Ruyan Guo 1
1 , Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania, United States
Show AbstractK9: Processing, TFT
Session Chairs
Thursday PM, November 30, 2006
Room 200 (Hynes)
2:30 PM - K9.1
Formation of Nanovoids and Nanocolumns in High Dose Hydrogen Implanted ZnO Bulk Crystals.
Rajendra Singh 1 , Roland Scholz 1 , Ulrich Gösele 1 , Silke Christiansen 1 2
1 Experimental Deptt. 2, Max Planck Institute of Microstructure Physics, Halle, Sachsen Anhalt, Germany, 2 Physics Department, Martin Luther University Halle-Wittenberg, Halle, Sachsen Anhalt, Germany
Show AbstractZnO(0001) bulk crystals grown by a hydrothermal synthesis method were implanted by 100 keV H2+ ions with various doses in the range of 5x1016 to 3x1017 cm-2. The ZnO crystals implanted up to a dose of 2.2x1017 cm-2 did not show any surface exfoliation after post-implantation annealing of a variety of time/temperature combinations while those crystals implanted with a dose of 2.8x1017 cm-2 or higher exhibited exfoliated surfaces already in the as-implanted state. In a narrow dose window in between, controlled exfoliation can be obtained upon annealing. Cross-sectional transmission electron microscopy (XTEM) of the implanted ZnO wafers showed that a large number of nanovoids, having dimensions of about 10 nm, formed within the implanted zone of ZnO. These nanovoids obviously serve as precursors for the formation of microcracks leading to the exfoliation of ZnO surfaces. In addition to the nanovoids, nanocolumns perpendicular to the substrate surface form, having diameters of up to about 10 nm and lengths of up to a few hundreds of nanometers. These nanocolumns are found in the ZnO lattice even well beyond the projected range of hydrogen ions. Moreover, the micro-roughness, as given by the root-mean-square (RMS) roughness, of the hydrogen implanted and exfoliated ZnO surface, as measured by atomic force microscopy (AFM) yields a particularly high value of about 24 nm in a 10x10 µm2 scan and a peak-to-valley height of about 100 nm, which is much higher compared to other hydrogen implanted and exfoliated semiconductors such as Si, InP, GaAs and GaN, where an RMS roughness value of less than 8 nm is usually found. These findings of nanostructural pecularities in ZnO are discussed with respect to successfully using a high dose hydrogen implantation to initiate ZnO layer transfer after direct wafer bonding to a variety of desired handle wafers.
2:45 PM - K9.2
Effect of Cryogenic Temperature Deposition of Various Metal Contacts to Bulk, Single-Crystal n-type ZnO.
Jon Wright 1 , L. Stafford 1 , B. Gila 1 , D. Norton 1 , S. Pearton 1 , Hung-Ta Wang 2 , F. Ren 2
1 Materials Science and Engineering, The University of Florida, Gainesville, Florida, United States, 2 Chemical Engineering, The University of Florida, Gainesville, Florida, United States
Show AbstractThe development of reliable and thermally stable Ohmic and Schottky contacts to ZnO is one of the critical issues related to the fabrication of ZnO-based UV light emitters/detectors and field effect transistors. To date, a number of different metallization schemes and surface cleaning procedures prior to metal deposition have been examined for rectifying contacts on n-ZnO. While these reports have shown that low reactive metals such as Au, Ag and Pd form rectifying contacts with Schottky barrier heights in the 0.6-0.8 eV range, the thermal stability of these contacts is usually extremely poor, with degradation occurring even at 60 C for Au/n-ZnO. One approach to achieving increased barrier heights that has proven successful for GaAs, InP, InGaAs and other compound semiconductors is the use of cryogenic deposition temperatures. In this context, we report in this work on the effect of cryogenic temperature metal deposition on the contact properties of Pd, Pt, Ti, and Ni on single-crystal n-type ZnO. Deposition at both room and low temperature produced contacts with Ohmic characteristics for Ti and Ni metallizations. In comparison, both Pd and Pt contacts showed rectifying characteristics after deposition. All rectifying contacts exhibited barrier heights around 1-2 eV and idealities between 1 and 2. Low temperature deposition gave higher resistances in comparison to room temperature deposition for all cases. Larger contacts also corresponded to an increase in resistance. Changes in contact behavior were measured on Pd to anneal temperatures of ~300 C, showing an increase in barrier height along with a decrease in ideality with increasing temperature. This difference with annealing temperature is in sharp contrast to previous results for Au contacts to ZnO. There were no differences in near-surface stoichiometry for the different deposition temperatures; however low temperature contacts demonstrated some cracking in Pt and Pd, probably due to surface stress.
3:00 PM - K9.3
Schottky Contact Behaviour as a Function of Metal and ZnO Surface Polarity
Martin Allen 1 2 , Paul Miller 3 2 , Jessica Chai 1 2 , James Metson 4 2 , Roger Reeves 3 2 , Maan Alkaisi 1 2 , Steven Durbin 1 2
1 Dept. of Electrical and Computer Eng., University of Canterbury, Christchurch New Zealand, 2 , MacDiarmid Institute for Advanced Materials and Nanotechnology, Christchurch New Zealand, 3 Dept. of Physics and Astronomy, University of Canterbury, Christchurch New Zealand, 4 Dept. of Chemistry, University of Auckland, Auckland New Zealand
Show AbstractAlthough significant advances have been made in recent years concerning the heteroepitaxial growth of high-quality single crystal ZnO, many of the best reported electrical properties are for bulk crystals, and p-type material remains elusive. For visible-blind UV detectors and related applications, Schottky as opposed to pn junction devices may prove the most desirable, anyway, although control over the electrical properties is still important in such situations. There are numerous reports of high-quality Schottky contacts to ZnO, particularly in the case of bulk crystals. Among the many metals investigated, Ag, Au, Pd and Pt are the most common, although few reports include results for each of these materials on the same samples, and there remains a need for further study of the role surfaces (in particular, surface polarity) play in determining contact properties.High-quality bulk ZnO single crystals are available commercially and have been for some time, although the electrical characteristics vary somewhat from vendor to vendor. We have recently investigated the comparative performance of Ag, Au, Pd and Pt contacts to “epi-polished” bulk ZnO single crystals from three separate vendors (Cermet, MTI, and Tokyo Denpa Co., Ltd.) for both polar and non-polar surfaces. In each case, arrays of ring-dot contacts of each metal were lithographically patterned onto the same wafer sample which was first cleaned using solvents. No etching, annealing or surface treatment of the wafers was performed. A separate piece of each wafer was characterised using photoluminescence at 4 K and 300 K, and room-temperature Hall effect measurements were conducted. Diodes were characterised at room temperature by both current-voltage and capacitance-voltage techniques, the results of which were generally found in good agreement with one another, indicating a reasonable degree of homogeneity/uniformity over the contact area.The most striking result is that the best diodes tested to date were based on Ag, with barrier heights slightly greater than 1 eV – despite the fact that Ag has the lowest workfunction of the four metals considered. No significant polarity effect was observed for these diodes, nor for corresponding devices based on Au. Intriguingly, a measurable difference in barrier height was observed for both Pd and Pt based diodes fabricated on Zn-polar (0001 oriented) and O-polar (000–1) faces, with the higher quality devices being those on O-polar surfaces. Analysis of the Ag-based devices indicated that the best rectification behaviour corresponded to contacts exhibiting clear signs of oxidation under an optical microscope, confirmed by X-ray photoelectron spectroscopy to include Ag2O – a material which has been suggested by others to have a work function as high as 7 eV. We have confirmed this correlation by intentionally fabricating Ag2O contacts via RF sputtering using an elemental Ag target in conjunction with a 50 W O2/Ar plasma.
3:15 PM - K9.4
Microstructure and Electrical Property Correlations in Ga:ZnO Transparent Conducting Thin Films.
Vikram Bhosle 1 , Jagdish Narayan 1
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show Abstract3:30 PM - K9.5
Large Area Multi-wafer MOCVD of Transparent and Conducting ZnO Films.
Gary Tompa 1 , S. Sun 1 , L. Provost 1 , D. Mentel 1 , D. Sugrim 1 , Philip Chan 2 , Keny Tong 2 , Raymond Wong 2 , A. Lee 2
1 , Structured Materials Industries, Inc., Piscataway, New Jersey, United States, 2 , Podium Photonics, Ltd., Kowloon Hong Kong
Show Abstract3:45 PM - K9.6
One-step Non-Lithographic Microetching of Transparent Conductive Oxides and Semiconductors.
Stoyan Smoukov 1 , Bartosz Grzybowski 1
1 Chem. & Biol. Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractA benchtop, one-step, maskless-but-parallel method of etching micropatterns is described. Transparent conducting oxides (ZnO, ITO) and semiconductors (GaAs) are etched with lateral resolution down to 200nm using a reaction-diffusion process. Patterned hydrogel stamps act as a reservoir and a two-way "pump" transporting etchant onto the substrate while removing reaction products into its bulk. This low-cost method is suitable for rapid prototyping of bulk and thin film materials, minimizing the need for multistep lithographic processing.
4:30 PM - **K9.7
The (R)Evolution of Thin Film Transistors.
Elvira Fortunato 1 , P. Barquinha 1 , A. Pimentel 1 , A. Goncalves 1 , L. Pereira 1 , R. Martins 1
1 Materials Science, CENIMAT, Caparica Portugal
Show AbstractTransparent electronics are nowadays an emerging technology for the next generation of optoelectronic devices. Oxide semiconductors are very interesting materials because they combine simultaneously high/low conductivity with high visual transparency and have been widely used in a variety of applications (e.g. antistatic coatings, touch display panels, solar cells, flat panel displays, heaters, defrosters, optical coatings, among others) for more than a half-century.Transparent oxide semiconductor based transistors have recently been proposed using as active channel intrinsic zinc oxide (ZnO) [1,2]. The main advantage of using ZnO deals with the fact that it is possible to growth at/near room temperature high quality polycrystalline ZnO, which is a particular advantage for electronic drivers, where the response speed is of major importance. Besides that, since ZnO is a wide band gap material (3.4 eV), it is transparent in the visible region of the spectra and therefore, also less light sensitive. In this work after a short overview about the history of TFTs, we report some of our recent results concerning the fabrication and characterization of high field-effect mobility ZnO and ZnO based-thin film transistor deposited at room temperature by rf magnetron sputtering.[1]E. Fortunato, P. Barquinha, A. Pimentel, A. Gonçalves, A. Marques, L. Pereira, R. Martins, Appl. Phys. Lett. 85, 2451 (2004).[2]E. Fortunato, P. Barquinha, A. Pimentel, A. Gonçalves, A. Marques, L. Pereira, R. Martins, Advanced Materials 17, 590 (2005).
5:00 PM - K9.8
Electrical Stability of Low-Temperature Amorphous Gallium-Indium-Zinc-Oxide Thin Film Transistors under Constant Current Stress for AM-OLED Application.
Ihun Song 1 , Chang Jung Kim 1 , Donghun Kang 1 , Jae Chul Park 1 , Hyuck Lim 1 , Sunil Kim 1 , Youngsoo Park 1 , RanJu Jung 2 , Jae Cheol Lee 2 , Eunha Lee 2
1 SDM Lab, SAIT, Suwon Korea (the Republic of), 2 AE Center, SAIT, Suwon Korea (the Republic of)
Show AbstractThe transistors which drive AM-OLED circuits should be operated under a constant current stress condition. Previous studies showed that the threshold voltage of amorphous silicon thin film transistor shifted by several volts under current stress condition due to charge trapping and dangling-bond defect state creation. Recently, there have been reports that oxide based thin film transistors could be better choice for the purpose of reducing charge trapping in the channel materials. Especially, amorphous oxide thin film transistors take advantages of the good uniformity and smooth surface morphology. In this study, we have developed very stable amorphous Gallium-Indium-Zinc-Oxide(a-GIZO) thin film transistors under constant current stress operations. The a-GIZO films were deposited by rf magnetron sputtering at room temperature and confirmed to be amorphous by X-ray diffraction. We also examined the effect of the thickness of channel layer and the chemical composition of GIZO thin films on the stability of the a-GIZO thin film transistors. The a-GIZO thin film transistors showed a high mobility of 40 cm2/Vs with a high on-to-off current ratio of 108. Gate leakage and the sub-threshold voltage swing were about 2 pA and 0.23 V/decade, respectively. Surprisingly, the a-GIZO thin film transistors exhibited the threshold voltage shifts less than 0.2 V for 100 hours at 60°C under constant current stress. These promising results indicate that the a-GIZO thin film transistors could be a candidate for driving transistors of large area AM-OLED display.
5:15 PM - K9.9
Atomic Layer Deposition ZnO as an Active Channel Layer of Transparent Thin Film Transistor.
Seongjoon Lim 1 , Soonju Kwon 1 , Hyungjoon Kim 1
1 Materials Science and Engineering, POSTECH, Pohang, Gyungbuk, Korea (the Republic of)
Show AbstractRecently, the application of ZnO as an active channel layer of transparent thin film transistor (TTFT) has become of great interests. However, ZnO prepared by deposition methods other than sputtering has rarely been studied for this application. Atomic layer deposition (ALD) is an attractive deposition method for display device due to large area uniformity and low process temperature. In this study, ZnO thin films were deposited by ALD using diethyl Zn (DEZ) as a precursor. To optimize the electrical properties of ALD ZnO as an active layer of TTFT, the ALD ZnO thin films were deposited with various reactants. By this approach, ALD ZnO thin films with carrier concentration as low as 1014 cm-3 were obtained at low growth temperature, producing TTFT with low off current. For comparison, ZnO thin films were also prepared by RF sputtering. For both ALD and RF sputtered ZnO, key electrical properties including resistivity, mobility, and carrier concentration were characterized and the microstructure and chemical properties of were analyzed by x-ray diffraction, transmission electron microscopy, X-ray photoemission spectroscopy, and Rutherford back scattering. TTFTs with high k gate insulator, also prepared by ALD, were fabricated and the device properties were characterized. The device characteristics of TTFT will be discussed focusing on the comparison between ALD and RF sputtered ZnO active layer.
5:45 PM - K9.11
Scaling and Parasitic Effects on ZnO Transparent Thin Film Transistors.
Hsing-Hung Hsieh 1 3 , Chung-Chih Wu 1 2 3
1 Graduate Institute of Electronics Engineering, National Taiwan University , Taipei, Taiwan, Taiwan, 3 Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan, Taiwan, 2 Graduate Institute of Electro-Optical Engineering, National Taiwan University, Taipei, Taiwan, Taiwan
Show Abstract Recent development of transparent TFTs (TTFTs) using large bandgap (Eg>3eV) semiconductors such as ZnO and related metal oxides is of particular interest. Such TTFTs could render a nearly 100% aperture ratio or even fully transparent active-matrix displays. To meet the requirements for real high-resolution display applications, we fabricated miniaturized ZnO TTFTs by using the lithographic method and studied the scaling and parasitic effects of these devices. Inverted staggered type ZnO TTFTs with varied dimensions were fabricated at room temperature. The channel length was varied from 2 to 50 um, and the channel width was varied from 20 to 200 um. ITO was used as gate, source, and drain electrode. ZnO was used as active layer and deposited by RF sputtering in Ar/O2, with gas flow rates of 45 sccm/5 sccm, chamber pressure of 5 mtorr, and RF power of 200 W. Double layer gate insulators consisting of Al2O3 and HfO2 were used due to their large bandgap and high dielectric constant, respectively. Post-fabrication annealing at 265 C in nitrogen was performed in order to improve the crystallinity and device performances. The ZnO TTFTs operated in the n-type enhancement mode, and exhibited hard saturation in long-channel devices (> 5 um). Mobility larger than 8 cm2/Vs and on/off ratio up to 10^7 were achieved with these devices. The transmission was more than 80% in the whole visible band. The device characteristics were rather immune to ambient illumination, which implies an advantage of needing no black matrices or light-shielding structure in active-matrix applications. Our results showed that these ZnO TTFTs retain well-behaved transistor characteristics down to channel length of ~5 um, rendering possible high-resolution applications. Apparent short channel effects (e.g., lowering of threshold voltages, degradation of subthreshold slope with the decrease of the channel length and the increase of drain voltage, and loss of hard saturation, etc.) were observed in our devices when the channel length was reduced below 5 um. These short channel effects can be explained by the charge sharing or drain-induced barrier lowering. Influences of parasitic series resistance on TFT characteristics were also studied. Parasitic series resistance and channel resistance were extracted using devices of various dimensions. The parasitic series resistance Rp*W was typically on the order of 10^2 ~ 10^3 ohm-cm, depending on the gate voltages. The ratio of parasitic series resistance to channel resistance at Vg = 10 V was increased from 0.04 to 0.36, when the channel length decreased from 20 um to 2 um. This indicates that parasitic series resistance has substantial influences on device performances when the channel length is reduced, and better contact techniques may be required.
K10: Poster Session II
Session Chairs
Jürgen Christen
Chennupati Jagadish
David Look
Takafumi Yao
Friday AM, December 01, 2006
Exhibition Hall D (Hynes)
9:00 PM - K10.1
Ferromagnetic Ordering at Room Temperature in Co:ZnO Nanoparticles.
Sujeet Chaudhary 1 , Kanwalpreet Bhatti 1 , Shankhamala Kundu 1 , Subhash Kashyap 1 , Dinesh Pandya 1
1 Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110 016 India
Show AbstractThe progress in the emerging field of spintronics is inherently associated with the search for newer semiconductor materials which should exhibit ferromagnetic behavior at room temperature. Such semiconductors are proposed to add new functionalities to the existing electronic and photonic devices. The challenge is to modify the oxides of Zn, Sn, Ti, etc., so that they exhibit intrinsic and stable room temperature ferromagnetism (RTFM), and a high Curie temperature, (T_c>300K). In past few years, various II-VI semiconducting materials, such as transition metal doped ZnO exhibiting RTFM, gained worldwide research interest. The case of Co:ZnO system is particularly interesting since most of the reports on bulk samples did not corroborate RTFM, though invariably evidenced in several reports on the thin films.In the present work, we report the results of the effect of processing parameters on the magnetization (M), structural property and phase purity investigations of the cobalt substituted nanocrystalline bulk samples of ZnO. The bulk samples have been synthesized by using acetates and poly vinyl pyrrolidane as precursors. The pallets were made from calcined powders. Both the 5% and 10% Co-substituted ZnO samples exhibited RTFM and had an estimated particle size in the range of 50-60 nm. These pellets were successively sintered upto 900C in steps of 100C, after which the particle size became ~80 nm. The sintering in air ambient at 700C for 6h resulted in formation of Co_3O_4 phase causing a sizable reduction in the saturation magnetic moment (M^sat). With further sintering at 800C, CoO also started forming. Further reduction in M^sat, however, was only small. When sintered at 900C for 6h, no further change in M^sat was detected in either of the samples. No noticeable change in the intensity of diffraction peaks due to either CoO or Co_3O_4 was seen even when the samples were sintered at 900C for additional 6h. The observed M-H behavior can be understood on the bases of ferromagnetic and paramagnetic contributions. The para contribution is attributed to Co_3O_4 and CoO phases, which are known to be paramagnetic at RT. The origin of FM can definitely not be attributed to metallic Co-clustures since these were not found in our samples prepared in air ambience. Based on the detailed M-H and Reitveld refinement studies, it is found that although the RTFM in Co:ZnO system gets affected by processing conditions, it can not be totally destroyed even after the prolonged sintering of the samples at higher temperatures. The observed RTFM in Co:ZnO system is explained on the basis of defect mediated bound magnetic polaron model.
9:00 PM - K10.10
Ferromagnetism in Co-doped ZnON Nanocrystals.
Xuefeng Wang 1 , Jian Bin Xu 1 , Wing Yiu Cheung 1 , Sai Peng Wong 1
1 Department of Electronic Engineering, The Chinese University of Hong Kong, New Territories Hong Kong
Show AbstractDiluted magnetic semiconductors (DMSs) are of particular current interest since they are believed to be potentially suitable for future spintronics (spin-based electronics) applications. Although recent reports of carrier-mediated ferromagnetism in oxide-based DMSs shed the light on the practical spintronics applications, the complete understanding of the latent microscopic mechanism of high-temperature ferromagnetism in oxide-based DMSs still remains a technical challenge. In this presentation, we demonstrate a novel solution-based crystal growth strategy to clarify the ferromagnetism in oxide-based DMSs, by exploiting the n-type cobalt-doped ZnO DMS nanocrystals as an example. The observed high-temperature ferromagnetism is established to be intrinsic using a couple of characterization techniques. An intimate correlation between self-orientation crystal growth and high-temperature ferromagnetism is observed, further supporting the recent proposal. It is the shallow donorlike electrons (as the legacy of aggregation-based growth) that are strongly bound on cobalt sites, yielding bound magnetic polarons and thus activating ferromagnetism. The complicated status of shallow defects upon different treatment conditions may lead to the highly controversial reports in oxide DMSs.
9:00 PM - K10.11
Thickness Dependent Strain Studies on Optical Properties of Low Temperature Processed Polymeric Precursor Derived ZnO Thin Films.
Uma Choppali 1 , Brian Gorman 1
1 Materials Science and Engineering, University of North Texas, Denton , Texas, United States
Show Abstract9:00 PM - K10.12
Optical Properties of Porous ZnO Nanorods Grown by Aqueous Solution Method.
Lee Sang Hyun 1 , Lee Hyun Jung 3 , Goto Takenari 1 , Cho Meoung-Whan 1 2 , Yao Takafumi 1 2
1 Center for Interdisciplinary Research, Tohoku Univ., Sendai Japan, 3 Graduate School of EnVironmental Studies, Tohoku Univ., Sendai Japan, 2 Institute for Materials Research, Tohoku Univ., Sendai Japan
Show Abstract9:00 PM - K10.13
High-density Plasma Etching of Zinc-Oxide and Indium-Zinc-Oxide in Cl2/Ar and CH4/H2/Ar Chemistires.
Wantae Lim 1 , Luc Stafford 1 , Rohit Khanna 1 , Lars Voss 1 , Jon Wright 1 , Brent Gila 1 , David Norton 1 , Stephen Pearton 1 , Fan Ren 2
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 Chemical Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractThe dry etching characteristics of bulk single-crystal Znic-Oxide(ZnO) and RF-sputtered indium-zinc-oxide (IZO) films have been investigated using an inductively coupled high-density plasma. The Cl2-based plasma mixture showed little enhancement over physical sputtering in a pure argon atmosphere, and the etch rate of ZnO is very similar to that of IZO, which indicates that Zinc and Indium atoms are driven by a similar plasma etching dynamics. The CH4/H2/Ar chemistry produced an increase of the IZO etch rate. The surface morphologies of bulk ZnO and IZO films after etching in Cl2/Ar discharges are smooth, whereas that of IZO after etching in CH4/H2/Ar presents particle-like features resulting from the preferential desorption of In- and O-containing products. Etching in CH4/H2/Ar also produces formation of a Zn-rich surface layer, whose thickness (~40 nm) is well-above the expected range of incident ions in the material (~1 nm). Such alteration of the IZO layer after etching in CH4/H2/Ar plasmas is expected to have a significant impact on the transparent electrode properties in optoelectronic device fabrication.
9:00 PM - K10.14
Epitaxial Growth of ZnO Thin Films on SiC Prepared by Chemical Solution Deposition.
Kyu-Seog Hwang 1 , Young-Sik Park 2 , Young-Sun Jeon 2 1 , Kyung-Ok Jeon 2 1 , Young-Hwan Lee 3 1
1 Dept. of Applied Optics and Institute of Photoelectronic Tech., Nambu University, Gwangju Korea (the Republic of), 2 Camera Module Team, Korea Photonics Technology Institute, Gwangju Korea (the Republic of), 3 Department of Automobile, Chunnam Techno College, Chonnam Korea (the Republic of)
Show AbstractZinc oxide (ZnO) thin films have emerged as one of the most promising oxide materials owing to their optical and electrical properties, together with their high chemical and mechanical stability. Chemical solution deposition (CSD) is attractive technique for obtaining ZnO thin films and has the advantages of easy control of the film composition and easy fabrication of a larger-area thin film at low cost. In this work, epitaxial ZnO thin films on SiC substrate were prepared by using a CSD method with a zinc naphthenate precursor. Precursor films were pyrolyzed at 500°C for 10 min in air and finally annealed at 600, 700, 800 and 900°C for 30 min in air. Crystallinity and in-plane alignment of the films were investigated by X-ray diffraction θ-2θ scan and β scan(pole-figure analysis). Field emission - scanning electron microscope, scanning probe microscope, and He-Cd laser (325 nm) are used to detect the surface morphology and photoluminescence of the films. The effects of annealing temperature on crystallinity and epitaxy of the films will be fully discussed on the basis of the results of X-ray diffraction analysis.
9:00 PM - K10.15
Improvement in Moisture Durability of ZnO Transparent Conductive Films with Ga Heavy Doping Process.
Osamu Nakagawara 1 , Yutaka Kishimoto 1 , Hiroyuki Seto 1 , Yoshihiro Koshido 1 , Yukio Yoshino 1 , Takahiro Makino 1
1 R&D Division, Murata Manufacturing Co., Ltd., Nagaokakyoshi, Kyoto Japan
Show AbstractMany researchers have investigated ZnO as a depletion-free and cost-effective substitute of ITO. For product commercialization, we assure that the improvement in reliability of ZnO films is very important as well as the progress in their electrical properties. The increase in resistivity occurs in the presence of moisture due to the H2O reaction with oxygen vacancy and grain boundary region in the ZnO film. Almost every researcher in this field recognizes this instability discourages the ZnO from practical applications for a transparent conductive oxide (TCO) material. Accordingly, we focused on the improvement of ZnO conductive films in their moisture durability. The increase in resistivity can be attributed to carrier decrease owing to re-oxidization of oxygen vacancies reacted with ambient moisture. We intend to make the site replacement play as a dominant role in supplying carriers, which motivates Ga heavy doping process. As opposed to previous papers focusing on the Ga content ranging from 2 to 4 wt% to obtain the lowest initial resistivity 1), ZnO films with heavier Ga doping up to 23.1 wt% are purposely prepared in our research. In consequence, moisture-resistant ZnO transparent conductive films were formed with Ga heavy doping by off-axis type rf magnetron sputtering. The resistivity of 12.4 wt% Ga-doped ZnO is 1.3×10-3Ωcm and changes less than 3 % over a 2000-hour reliability test at the temperature of 85 degrees Centigrade and the humidity of 85 degrees Centigrade. X-ray diffraction analysis shows the peak broadening of FWHM up to 16.9 degrees in a (002) rocking curve profile of 12.4 wt% Ga-doped ZnO and the decentering of the intensity distribution in 23.1 wt% Ga-doped ZnO in a (002) incident pole figure profile. The cross-sectional transmission electron microscope images of the heavily Ga-doped ZnO films indicate that the c-axis grows along with various directions as well as the normal line to the substrate surface. This is quite a different crystal structure from the conventional c-axis orientated growth, for example, observed at the 4.3 wt% Ga-doped ZnO films. The effect of heavy doping is discussed based on the grain boundary distribution and carrier compensation by excess Ga segregated in the film. This heavy doping process is remarkably effective for the improvement in reliability requisite for practical application of ZnO transparent conducting films.1) T. Minami, H. Nanto, and S. Takata, Appl. Phys. Lett., 41 (1982) 958.
9:00 PM - K10.16
Elaboration and Characterization of ZnO Transition Metal (Co, Mn, Ni, Fe) Doped Aerogel Nanoparticles.
Lassaad El Mir 1 , Aroussi BenMahmoud 1 , H.Jurgen von Bardeleben 2 , Jean Louis Cantin 2
1 , Faculté des Sciences de Gabès, Gabès Tunisia, 2 , University Paris 6, CNRS, Paris France
Show Abstract9:00 PM - K10.17
Magnetic Properties of ZnO:Ni Aerogel Nanopowders: Effect of Thermal Treatments.
Lassaad El Mir 2 , H.Jurgen von Bardeleben 1 , M. Saadoun 2 , Aroussi Ben Mahmoud 2 , Jean-Louis Cantin 1
2 , Faculté des Sciences de Gabès, Gabès Tunisia, 1 , University Paris 6, CNRS, Paris France
Show AbstractFerromagnetic phases in transition metal doped ZnO have been reported in various publications but their origin remains controversial. We report the elaboration of Ni doped ZnO nanoparticles prepared by a sol-gel processing technique. In this technique the water for hydrolyse was slowly released by esterification with methanol of the metal acetate followed by a supercritical drying in ethyl alcohol. Doping concentrations between 5 and 25 at% have been investigated. In the as-prepared state the powders with an average particle size of 30nm present ferromagnetic properties; thermal annealings in the 500°C to 700°C temperature range in air or oxygen modify the magnetic properties. We ascribe the observed ferromagnetism to the presence and transformation of Ni based secondary phases.
9:00 PM - K10.18
Photoluminescence Characteristics of ZnO Nanorods Fabricated by Different Methods.
Tobias Voss 1 , Chegnui Bekeny 1 , Lars Wischmeier 1 , Birgit Hilker 1 , Sandra Boerner 2 , Wolfgang Schade 2 , Bianca Postels 3 , Augustin Mofor 3 , Andrey Bakin 3 , Andreas Waag 3
1 Institute of Solid State Physics, University of Bremen, Bremen Germany, 2 Institute of Physics and Physical Technologies, Clausthal University of Technology, Clausthal-Zellerfeld Germany, 3 Institute of Semiconductor Technology, Braunschweig University of Technology, Braunschweig Germany
Show AbstractIn the last years remarkable progress has been achieved in reproducibly fabricating ZnO nanorods and nanowires of high crystalline and optical quality. Well-established high-temperature approaches like the catalyst-mediated vapour-liquid-solid (VLS) growth and the vapour-phase epitaxy (VPE) have been successfully optimized, and new low-temperature techniques like the aqueous-chemical growth (ACG) method have been extended to yield large-scale ZnO nanorod arrays with a highly preferential c-axis orientation. To finally integrate these nanostructures into optoelectronic devices it is mandatory to carefully analyze their specific optical properties and to look for possibilities to further improve their quality.Here, we present a systematic comparison of the fundamental optical properties of ZnO nanorods fabricated by the VLS, VPE, and ACG processes. For all three growth techniques we analyze the near-band-edge emission as well as the deep-level emission and discuss the underlying microscopic processes. Photoluminescence (PL) studies in the temperature range between 4 and 300K have been carried out supplemented by time-resolved studies and high-excitation-density measurements of the near band-edge luminescence. At low temperatures, the VLS and VPE nanorods show well-resolved donor-bound-exciton (D0X) related emission lines accompanied by their phonon replica. For samples grown at different temperatures a significant shift of the room-temperature PL is observed and can be clearly attributed to different ratios of the zero-, one-, and two-LO-phonon emission replica of the free exciton.In contrast, ACG nanorods exhibit rather broad near band-edge emission lines even at low temperatures (>7meV). First experiments demonstrate that their linewidths and the ratio of the deep-level to the near-band-edge emission can be significantly decreased by annealing in argon or oxygen atmosphere at moderate temperatures (500-600°C). First high-excitation-density measurements on ACG nanorods show emission from an electron-hole plasma at elevated excitation densities.To clarify the microscopic origin of the broad near-band-edge emission lines in the ACG nanorods, temperature dependent and time-resolved PL measurements have been carried out before and after annealing of the samples. The results reveal an energy shift of the main emission peak with temperature being different from that observed for the D0X and FX in the VLS and VPE samples. Additionally, in the as-grown samples a rather short recombination time of the carriers has been found (<100ps) which distinctly increases to about 200ps after the annealing procedure. These results point to the presence of large donor densities in the as-grown ACG nanorods which could even form a band of donor states and which are distinctly reduced through the annealing procedure.
9:00 PM - K10.19
Surfactant-assisted Alignment of ZnO Nanocryatals to Superstructures.
Hao Tang 1 2 , Shuit-Tong Lee 1 2
1 Centre of Super-Diamond and Advanced Films (COSDAF) , City University of Hong Kong, hongkong, Hong Kong, Hong Kong, 2 Physics and Materials Science, City University of Hong Kong, hongkong, Hong Kong, Hong Kong
Show Abstract9:00 PM - K10.20
Characterization of ZnO Nanostructure Networks Grown on AZO/Si Substrate.
Chung Ting Fung 1
1 Physics and Materials Science, City University of Hong Kong, Hong Kong Hong Kong
Show Abstract9:00 PM - K10.21
Transport Properties and Conduction Band Offset of n-ZnO/n-6H-SiC Heterostructures.
Yahya Alivov 1 , Bo Xiao 1 , Qian Fan 1 , Daniel Johnstone 2 , Hadic Morkoc 1 , Cole Litton 3
1 Electrical Engineering, VCU, Richmond, Virginia, United States, 2 , SEMETROL, Chesterfield, Virginia, United States, 3 , Air Force Research Lab, Dayton, Ohio, United States
Show Abstract9:00 PM - K10.22
Low Voltage Operating ZnO Thin-film Transistors with Ni Doped BaSrTiO3 high-K gate Insulator for Transparent and Flexible Electronics.
Jeong Ung Kim 1 , Jae-Kyu Lee 1 , Young-Woong Kim 1 , Duck-Kyun Choi 1 , Il-Doo Kim 2 , Jae-Min Hong 2
1 Ceramic engineering, Hanyang University, Seoul Korea (the Republic of), 2 Optoelectronic Materials Reserch Center, KIST, Seoul Korea (the Republic of)
Show AbstractTransparent ZnO based thin film transistors (TFTs) have received intensive interest due to their potential of replacing hydrogenated amorphous or polycrystalline silicon (a-Si:H or poly-Si) TFTs. Zinc oxide (ZnO) is a transparent compound semiconductor with a wide band gap (3.37 eV) which can be grown as a polycrystalline film at low or even room temperature. ZnO is, therefore, considered to be an ideal material for serving as the channel layer in transparent and flexible TFTs. As an important element, gate insulators for ZnO based TFTs have received increasing attention because ZnO-TFTs switching voltage can be reduced by using high-K gate dielectrics which can lead to high capacitance value. In this presentation, we report on the role of Ni doping in markedly reducing leakage currents in Ba0.6Sr0.4TiO3 (BST) high-K gate insulator. The 1% Ni-doped BST thin films, deposited by rf magnetron sputtering at room temperature on Pt/Ti/SiO2/Si substrates, exhibited a relatively dielectric constant of ~15. The 1% Ni-doped BST films exhibited remarkably improved leakage current densities less than 6x10-9 A/cm2 as compared to that of (5x10-4 A/cm2) of undoped BST films at an applied voltage of 7 V. All room temperature processed ZnO based TFTs using the 1% Ni-doped BST gate insulator exhibited a high optical transparency (> 80%, for wavelength > 400 nm), a high field effect mobility and low voltage device performance of less than 6 V. This result demonstrates that ZnO based TFTs with 1% Ni-doped BST gate insulator will open up a promising route for a wide variety range of applications in transparent, flexible, and portable electronic devices.
9:00 PM - K10.23
Characteristics of ZnO-TFTs with SiO2and Al2O3 Gate Dielectrics.
Chan Jun Park 1 , Jae-Kyu Lee 1 , Jeong-Ung Kim 1 , Young-Woong Kim 1 , Duck-Kyun Choi 1
1 Division of Materials Science and Engineering, Hanyang university, Seoul Korea (the Republic of)
Show AbstractZnO thin-film transistors (ZnO-TFT) have attracted much attention due to its optical transparency, wide band gap energy, and possibility of room temperature poly-crystalline formation. ZnO based thin-film transistors can be incorporated into next generation electronic devices such as transparent electronics, opto-electronics, and flexible electronics. ZnO-TFTs have been shown to perform better than hydrogenated amorphous silicon or organic materials based thin-film transistors. In spite of its advantages as an active layer, relatively low field effect mobility, low on/off ratio, and inadequate threshold voltage hinder the extensive usage of ZnO-TFTs. Electrical properties of a transistor are affected by various factors. Among them, the gate dielectric is the most important component because it determines the leakage current, threshold voltage, and operation voltage. In addition, unstable characteristics of a field-effect transistir are closely related to the interface between semiconductor and gate dielectric layers and trap density in the dielectrics. In this study, we investigated the dependence of gate dielectrics such as SiO2 and Al2O3 on the ZnO-transistor characteristics. All the component layers in ZnO-TFTs with bottom gate configuration were deposited by rf magnetron sputtering except for the SiO2 (100 nm) and Al2O3 (50 nm) gate dielectric layers which were deposited by the inductively coupled plasma chemical vapor deposition (ICP-CVD) and atomic layer deposition (ALD), respectively. The process temperature of ZnO-TFT on glass substrate was limited to 270 oC, for potential extension of this process to plastic substrates such as polyimide or polynorbornene. All of the fabricated ZnO-TFTs with SiO2 or Al2O3 dielectric layer showed high optical transmittance above 80 % in the visible light wavelengths between 400 and 700 nm. Field effect mobility and on/off ratio of ZnO-TFTs (W/L = 100μm/30μm) on Al2O3 were 6.98 cm2/Vs and 5×106, respectively. It is much higher than those of ZnO-TFT on SiO2. In addition, ZnO-TFT with Al2O3 showed lower threshold voltage of 4.2 V and smaller swing voltage of 0.60 V/decade compared to that with SiO2 with threshold voltage of 8 V and swing voltage of 2.13 V/decade. It is well known that ALD is a method for growing dense, pinhole-free films. Therefore, it is indicated from the current results that quality ALD Al2O3 film with higher dielectric constant induced good electrical properties such as low operation voltage and swing voltage as well as the better physical state in the ZnO channel region.
9:00 PM - K10.24
Synthesis and Characterization of Nickel-Doped ZnO Nanocrystals.
Xiao Li Zhang 1 , Yan Li 1 , Ru Qiao 1 , Ri Qiu 1 , Young Hwan Kim 1 , Young Soo Kang 1
1 Department of Chemistry, Pukyong National University, Pusan Korea (the Republic of)
Show AbstractZnO-based dilute magnetic semiconductors (DMSs) that are doped with nickel impurities via a solvothermal method in alcohol solution. Compared with those previous reported methods with the evaporation processes, the synthesis method we reported here is really facile and economical. Moreover, the percentage of doped nickel can be easily controlled. The X-ray diffraction, transmission electron micrograph, luminescence and magnetization hysteresis loops of nickel-doped ZnO nanocrystals were presented to confirm that the nickel impurities are embedded inside the nanocrystal. Optical measurements show that by exciting the nanocrystal, a green-light emission is observed, and efficient emission from Ni is not obtained, which further suggests that the nickel ions only substitutes for zinc ions sites.
9:00 PM - K10.25
Highly Transparent and Conductive Ga-doped ZnO Electrodes for High-performance GaN-based Green Light-emitting Diode.
Min-suk Oh 1 , Dae-Kue Hwang 1 , Jae-Hong Leem 1 , Young-Seok Choi 1 , Ja-Yeon Kim 1 , Seong-Ju Park 1
1 MSE, Gwangju Institute of Science and Technology, Gwangju Korea (the Republic of)
Show AbstractRecently, transparent conductive oxide (TCO) thin films draw a great attention and they are broadly used in many fields such as flat-panel displays, solar cells, and optoelectronic devices. Many conventional TCOs such as In2O3:Sn, SnO2, CdO and other related-materials have been reported to meet the various requirements for those devices. However, high-cost and toxicity make them difficult to be persistently used in industry. In contrast, ZnO is a harmless and low-cost material. In this study, we report on the growth of 200 nm thick Ga-doped ZnO (GZO) thin films deposited at a low temperature of 100 °C by oxygen radical-assisted pulsed-laser deposition (RA-PLD). The structural, electrical, and optical properties of the GZO films have been investigated as a function of rf power levels for the application of GZO thin film as a transparent and highly conductive current spreading layer on the green light-emitting diode(LEDs) which should be processed at low temperatures due to the high indium contents in the InGaN active layer. The X-ray reflectometry showed that the density of the GZO films grown by RA-PLD increases up to 5.32 g/cm3. An average optical transmittance of 97 % in the long wavelength range (500~600 nm) and resistivity as low as 3.5×10-4 Ω-cm were achieved in the GZO films deposited at an rf power of 100 W. The luminescence emission intensity of the GaN-based green LEDs fabricated with an optimized GZO electrode was improved by as high as 76 % at 20 mA as compared to those fabricated with conventional Ni/Au layers.
9:00 PM - K10.26
Preparation of Zinc Oxide Nanorods by Cost-effective Catalyst Free Chemical Spray Pyrolysis Technique.
Tatjana Dedova 1 , Malle Krunks 1 , Olga Volobujeva 1 , Jelena Aparina 1 , Maarja Grossberg 1 , Valdek Mikli 1
1 Department of Materials Science, Tallinn University of Technology, Tallinn, Harjumaa, Estonia
Show Abstract9:00 PM - K10.27
Influence of the Particle Size on Acoustic Phonon Modes of ZnO Nanocrystals.
Harish Yadav 1 , Vinay Gupta 1
1 Physics and Astrophysics, Delhi University, Delhi, Delhi, India
Show Abstract9:00 PM - K10.28
Room Temperature Ferromagnetism in Co-substituted ZnO.
Kousik Samanta 1 , Pijush Bhattacharya 1 , Ram Katiyar 1 , W. Iwamoto 2 , P. Pagliuso 2 , C. Rettori 2
1 Physics, Univ. of Puerto Rico, San Juan, Puerto Rico, United States, 2 Physics, Instituto de Fisica DEQ-UNICAMP Cidade Universitaria- Barao Geraldo 13083-970 , Campinas, SP, Brazil
Show Abstract9:00 PM - K10.3
Structure-Property Relationships in the xZnO-(1-x)alpha-Fe2O3 Nanoparticle System.
Monica Sorescu 1 , Lucian Diamandescu 2
1 Physics, Duquesne University, Pittsburgh, Pennsylvania, United States, 2 Materials Science, National Institute for Materials Physics, Bucharest Romania
Show AbstractThe xZnO-(1-x)alpha-Fe2O3 nanoparticles system has been obtained by mechanochemical activation for x=0.1, 0.3 and 0.5 and for ball milling times ranging from 2 to 24 hours. Structural and morphological characteristics of the zinc-doped hematite system were investigated by X-ray diffraction (XRD) and Mossbauer spectroscopy. The Rietveld structure refinements of the XRD spectra yielded the dependence of the particle size and lattice constant on the amount x of Zn substitutions and as function of the ball milling time. The x=0.1 XRD spectra are consistent with line broadening as Zn substitutes Fe in the hematite structure and the appearance of the zinc ferrite phase at milling times longer than 4 hours. Similar results were obtained for x=0.3, while for x=0.5 the zinc ferrite phase occurred at 2 hours and entirely dominated the spectrum at 24 hours milling time. The Mossbauer spectra corresponding to x=0.1 exhibit line broadening as the ball milling time increases, in agreement with the model of local atomic environment. Because of this reason, the Mossbauer spectrum for 12 hours of milling had to be fitted with two sextets. For x=0.3 and 12 milling hours, the Mossbauer spectrum reveals the occurrence of a quadrupole-split doublet, with the hyperfine parameters characteristics to zinc ferrite, ZnFe2O4. This doublet clearly dominates the Mossbauer spectrum for x=0.5 and 24 hours of milling, demonstrating that the entire system of nanoparticles consists finally of zinc ferrite. As ZnO is not soluble in hematite in the bulk form, the present study clearly demonstrates that the solubility limits of an immiscible system can be extended beyond the limits in the solid state by mechanochemical activation. Moreover, this synthesis route allowed us to reach nanometric particle dimensions, which would make the materials very important for gas sensing applications.
9:00 PM - K10.30
Self-assembled ZnO Nanostructure Characteristics in [PS]m/[PAA]n Diblock Copolymers with Varying Block Lengths on p and n-type (100) Si Substrates.
Hasina Ali 1 , Agis Iliadis 1 2 , Luz Martinez-Miranda 3 , Unchul Lee 4
1 Department of Electrical and Computer Engineering, University of Maryland, College Park, College Park, Maryland, United States, 2 Department of Information and Communication Systems Engineering, University of the Aegean, Mytilene Greece, 3 Department of Material Science and Engineering, University of Maryland, College Park, College Park, Maryland, United States, 4 , Army Research Laboratory, Adelphi, Maryland, United States
Show Abstract9:00 PM - K10.31
Self Assembly of Zinc Oxide Hollow Spheres on Single-walled Carbon Nanotube Templates.
Cengiz Ozkan 1
1 Mechanical Engineering, University of California at Riverside, Riverside, California, United States
Show Abstract9:00 PM - K10.33
ZnO Thin Films Prepared by a Single Step Sol-gel Process.
Shane O'Brien 1 , Lee Koh 1 , Gabriel Crean 1 2
1 , Tyndall National Institute, Cork Ireland, 2 Dept. Of Microelectronic Engineering, University College Cork, Cork Ireland
Show Abstract9:00 PM - K10.35
Electrical Properties and Interface Structures of Binary-alloy Schottky Contacts on ZnO Fabricated by a Combinatorial Ion Beam Sputtering.
Takahiro Nagata 1 2 , Janos Volk 1 , Michiko Yoshitake 2 , Ahmet Parhat 2 , Chikyow Toyohiro 2
1 International Center for Yong Scientists, National Institute for Material Science, Tsukuba Japan, 2 Advanced Electric Materials Center, National Institute for Material Science, Tsukuba Japan
Show Abstract9:00 PM - K10.36
Fabrication Of Textured Zinc Oxide By Electrophoretic Deposition In A Strong Magnetic Field.
Tetsuo Uchikoshi 1 , Tohru Suzuki 1 , Hideo Okuyama 1 , Fumiko Kimura 1 , Yoshio Sakka 1
1 Nano Ceramics Center, National Institute for Materials Science, Tsukuba, Ibaraki, Japan
Show AbstractMany materials in asymmetric (non-cubic) crystalline structures have anisotropic magnetic susceptibilities. When a single crystal of these materials is placed in a magnetic field, the crystal is rotated and the crystallographic axis of high magnetic susceptibility is aligned in the direction of the magnetic field. Zinc oxide has a hexagonal crystal structure and anisotropic magnetic susceptibility. As this anisotropy is quite small, no magnetic orientation is observed in a conventional magnetic field generated by a permanent magnet. However, the energy of anisotropy in a strong magnetic field generated by a superconducting magnet can be higher than the energy of thermal motion at room temperature. Therefore, when zinc oxide particles are placed in a strong magnetic field as high as about 10 T, they rotate to an angle minimizing the system energy. We demonstrate in this paper that a crystalline-textured zinc oxide ceramics are fabricated using the property of magnetic alignment.Commercial zinc oxide powder was dispersed in ethanol with dispersing agents and deflocculated stable suspension was prepared. The suspension was placed in a superconducting magnet and then a strong magnetic field of 12 T was applied to rotate each particle. Consolidation of the particles was carried out by electrophoretic deposition (EPD). The magnetic field was kept on applying to the suspension during EPD at a constant voltage condition at room temperature. The angle of the substrate against the magnetic field was altered to control the crystal faces of the particles. The zinc oxide particles in the deflocculated suspension were aligned due to their anisotropic magnetic susceptibility and then deposited on a cathodic substrate. The green compacts were dried, separated from the substrate, and then sintered at fixed temperatures. The sintering of the deposits was conducted at fixed temperatures for 2 h in air out of the magnetic field. The orientation of the zinc oxide crystallites was confirmed by XRD. It was confirmed that the a- or b-axis is easily aligned along the magnetic field. Orientation of the crystallites was dependent on the angle between the directions of magnetic and electric fields applied to the particles.
9:00 PM - K10.37
Electroplating of ZnO Using Nanohole Arrays of Anodized Aluminum Oxide.
Ken-ichi Ogata 1 , Shoso Shingubara 1 , Hiromi Yorozu 2 , Tadahiko Nakanishi 2
1 , Kansai University, Suita, Osaka, Japan, 2 , Shin-Chuo Kogyo, Higashihiroshima Japan
Show AbstractMuch attention is paid to zinc oxide (ZnO) nanostructure since the increase of the exciton binding energy occurs. Until now, lots of works related to the growth of ZnO nanostructure were reported, however, control of the size and position is still difficult. In this contribution, electroplating of ZnO was performed using nanohole arrays of anodized aluminum oxide (AAO) toward the fabrication of ZnO nanowires or nanodots. Nanohole arrays of AAO were prepared by anodization of Al foils (5N purity) or Al films sputtered on Si (100) substrates. 0.3M of H2SO4 or H2C2O4 was utilized as electrolytes, where the average nanohole sizes can be controlled in the range of 20 - 60nm by changing applied voltage. Depths of nanohole can be also variable by anodization time and their typical values are 2μm. In order to reduce the barrier layers that exist at the bottom of nanohole arrays, AAO arrays were immersed in 5wt% H3PO4 at 30oC for 3-5min. Then, they were annealed at 500-900oC for the enhancement of the chemical resistivity. Before electroplating of ZnO using a 0.1M of Zn(NO3)2, embedment of Au at the bottom of nanoholes was carried out using a solution contained Na3[Au(SO3)2]. Embedment of Au was available in the wide range of electroplating conditions, namely, that could be conducted at various applied voltage, AC frequency and annealing condition of AAO arrays. On the contrary, embedment of ZnO was done only when AAO arrays were annealed at 900oC, otherwise ZnO nanoparticles on the top surface of AAO arrays were observed.
9:00 PM - K10.38
Enhancement of Field Emission Current from ZnO Nanorods Fabricated by Two Step Chemical Vapor Deposition with Laser Ablation of ZnO.
Takashi Hirate 1 , Takashi Kimpara 1 , Kazumoto Takizawa 1 , Tomomasa Satoh 1
1 Faculty of Engineering, Kanagawa University, Yokohama Japan
Show Abstract9:00 PM - K10.39
High Mobility Ga Doped ZnO Thin Films on Flexible Substrate.
Ved Verma 1 , Do Hyun Kim 1 , Wonbong Choi 1
1 Mechanical & Materials Eng., Florida International University, MIAMI, Florida, United States
Show AbstractZinc oxide (ZnO) based transparent thin film transistors (TFTs) have been studied intensively as transparent FETs due to their potential of replacing hydrogenated amorphous or polycrystalline silicon (a-Si:H or poly-Si) TFTs which in present serve as the backplane for active matrix displays such as liquid crystal displays and organic light emitting diodes. ZnO is a transparent compound semiconductor with a wide band gap (3.37 eV) which can be grown as a polycrystalline film at low or even room temperature. ZnO is therefore considered to be an ideal material for serving as the channel layer in transparent and flexible FETs.The Ga doped ZnO thin film, which can be used as field-effect transistor or optoelectronics, have attracted much attention because of their potential for future nanoelectronics applications. In present study ZnO:Ga thin films were successfully deposited on flexible substrates at various temperatures ranging from room temperature to 300°C by RF plasma sputtering in pure oxygen environment. EPMA (Electron Probe Micro Analysis) and SEM analysis shows high quality Ga doped ZnO thin film can be grown on flexible polymer substrate. To enhance the electrical properties, especially for the high carrier mobility, thin film was treated by rapid thermal annealing in N2 atmosphere. ZnO: Ga thin film transistors were fabricated using 100nm ZnO/SiO2 as gate insulator by e-beam lithography and plasma sputtering. These thin films show a high carrier mobility of ~1.0 cm2/V.s and on/off ratio of ~105.
9:00 PM - K10.4
Opto-Electronic Properties and Stability of Artificial Zinc Oxide Molecules.
Liudmila Pozhar 1 , Gail Brown 2
1 Chemistry, Western Kentucky University, Bowling Green, Kentucky, United States, 2 Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, Ohio, United States
Show Abstract9:00 PM - K10.40
The Impact of Hydrogen Plasma Treatments at Moderate Temperatures on Sintered Zinc Oxide Samples – Evidence for Hydrogen Induced Nano-Void Formation.
Reinhart Job 1
1 Mathematics and Computer Science, University of Hagen, Hagen Germany
Show Abstract9:00 PM - K10.41
Electrical and Optical Properties of Ga2O3–ZnO Films Deposited by Room-temperature Sputtering.
Han-Chang Pan 1 , Chien-Ying Su 1 , Chien-Nan Hsiao 1 , Si-Pin Lin 2 , Chuan-Sheng Chiou 2
1 Vacuum Technology Division, Instrument Technology Research Center, Hsinchu Taiwan, 2 Department of Mechanical Engineering, Yuan Ze University, Taoyuan Taiwan
Show Abstract9:00 PM - K10.43
Transport Studies of Transition Metal Ion Doped ZnO: Bulk and Thin Films.
Shubra Singh 1 , Mahidanna Rao 1
1 Physics, Indian Institute of Technology, Chennai, TamilNadu, India
Show Abstract9:00 PM - K10.44
Investigating the Instability of ZnO Thin Film Transistors.
Richard Cross 1 , Maria De Souza 1
1 Emerging Technologies Research Centre, De Montfort University, Leicester United Kingdom
Show Abstract9:00 PM - K10.46
Growth and Characterization of Conducting and Transparent ZnO Films Doped with Ga and Al.
Sean Cherry 1 , D. Hunter 2 , H. Mustafa 2 , S. Jones 1 , A. Pradhan 2
1 Optical Engineering, Norfolk State University, Norfolk, Virginia, United States, 2 Center for Materials Research, Norfolk State University, Norfolk, Virginia, United States
Show Abstract9:00 PM - K10.47
The Growth and Characterization of Ga-doped Mg0.15Zn0.85O Thin Film by Pulsed Laser Deposition.
Chunming Jin 1 , Wei Wei 2 1 , Vikram Bhosle 2 , Andy Doraiswamy 1 , Roger Narayan 1 , Jagdish Narayan 2
1 1Joint Department of Biomedical Engineering, University of North Carolina and North Carolina State University, Chapel Hill, North Carolina, United States, 2 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show Abstract9:00 PM - K10.49
ZnO Nanofibers Doped with Ga, In and Er Fabricated with Electrospinning Technique.
Aurangzeb Khan 1 , Saima Khan 1 , Wojciech Jadwisienczak 2 , Martin Kordesch 1
1 Physics& Astronomy and CMSS Program, Ohio University, Athens, Ohio, United States, 2 School of Electrical Engineering and Computer Science, Ohio University, Athens, Ohio, United States
Show Abstract9:00 PM - K10.5
Analysis and Applications of ZnO Semiconductor Films Deposited by Laser and Sputtering Techniques.
Tingfang Yen 1 , Meiya Li 1 , Nehal Chokshi 2 , Yongwoo Jeong 1 , Sung Jin Kim 1 , Alexander Cartwright 1 , Wayne Anderson 1
1 EE, SUNY-Buffalo, Amherst, New York, United States, 2 , AMBP Tech, Tonawanda, New York, United States
Show Abstract9:00 PM - K10.50
Doped ZnO Nanoclusters: Ferromagnetism and UV Photoluminescence at Room Temperature
You Qiang 1 , Jiji Antony 1 , Amit Sharma 1 , Muhammad Faheem 1 , Daniel Meyer 1 , Michael Campanell 1
1 Physics, University of Idaho, Moscow, Idaho, United States
Show Abstract9:00 PM - K10.51
Structural, Optical and Magnetic Properties of Co and Fe doped ZnO Thin Films Growth by Radio-frequency Magnetron Sputtering
Luis Angelats 1 , Maharaj Tomar 1 , Oscar Perales-Perez 1 , Ricardo Melgarejo 1 , Hector Jiménez 1 , Ricardo Martinez 1
1 Physic, University of Puerto Rico, Mayaguez, Puerto Rico, United States
Show AbstractCo-doped and CoFe-doped ZnO films were growth onto quartz fused from ceramic targets using the magnetron sputtering technique under the following sputtering conditions: rf power 125 W, argon working pressure 8.5 x 10 -3 Torr and substrate temperature 300°C. The X-ray diffraction patterns of Zn0.90Co0.10O and Zn0.85[Co0.50Fe0.50]0.15O films showed only (002) peak indicating the strong preferred orientation along these planes. Raman spectra for thin films did not any significant additional modes for Co and Fe. Zn0.90Co0.10O film showed transmittance above 70% with three absorption peaks attributed to d-d transitions of tetrahedrally coordinated Co2+. Transmittance optic of Zn0.85[Co0.50Fe0.50]0.15O film was less than Zn0.90Co0.10O film in the visible range. The band gap values for Zn0.90Co0.10O and Zn0.85[Co0.50Fe0.50]0.15O films were 2.95 and 2.70 eV respectively, which are slightly less than ZnO films found in this work. The Zn0.90Co0.10O film showed a relatively large positive magnetoresistance (MR) at the high magnetic field in the temperature range from 7 to 50K, which reached 11.9% a 7K for the magnetoresistance. The lowest MR was found at 100K. From M-H curve of Zn0.90Co0.10O and Zn0.85[Co0.50Fe0.50]0.15O films measured at room temperature shown a coercive field of 30 and 40 Oe respectively.
9:00 PM - K10.53
Electrical and Optical Properties of Al-doped ZnO Thin Films Prepared by Magnetron Co-sputtering
Tin Yan Kwok 1 , Ning Ke 1 , Wing Yiu Cheung 1 , S. P. Wong 1 2
1 Dept of Electronic Engineering, Chinese University of Hong Kong, Shatin Hong Kong, 2 Materials Science and Technology Research Centre, Chinese University of Hong Kong, Shatin Hong Kong
Show AbstractWhile indium tin oxide has been widely used as transparent electrodes for many optoelectronic devices, to match the optical properties of various semiconductor materials systems in order to achieve better device performance, there are increasing interest to develop new materials with various optical properties for transparent electrode applications. In this work, we performed a systematic study of the electrical and optical properties of transparent conductive Al-doped ZnO (AZO) thin films prepared by magnetron co-sputtering with an RF source for ZnO and a DC source for Al. The Al doping composition was varied by adjusting the power of the two sources and was determined by Rutherford backscattering spectrometry. The thickness of the films was determined by an alpha-step surface profiler. The electrical properties were studied by resistivity and Hall effect measurements from 40K to 300K using the van der Pauw method. The optical properties were studied by optical transmittance spectroscopy and spectroscopic ellipsometry. The results showed that for samples with an Al atomic percentage falling between 3 to 4.5 %, they were optically transparent in the visible range with sufficiently low resistivity values suitable for transparent electrode applications. The thickness of these films ranged from about 150 nm to 300 nm. The transmittance values were observed to be larger than 80% in the wavelength range from 400 to 800 nm and the resistivity values varied from about 6x10-3 to 8x10-3 ohm-cm. The band gap energy was observed to increase slightly with increasing Al composition from 3.36 eV to 3.54 eV for the Al atomic percentage range from 2 to 4.5%. The refractive index n and extinction coefficient k of these films in the wavelength range from 400 nm to 700 nm were also determined by fitting of the spectroscopic ellipsometry spectra. A general decreasing trend of n values with increasing Al composition was observed. This work is supported in part by a direct grant for research from the Faculty of Engineering of CUHK.
9:00 PM - K10.55
Lasing Characteristics of Nano-structured Zinc Oxide
Shou-Yi Kuo 1 , Wei-Chun Chen 1 , Fang-I Lai 2
1 , Instrument Technology Research Center, National Applied Research Laboratories, Hsinchu Taiwan, 2 , Department of Electronic Engineering, Ching Yun University,, Taoyuan Taiwan
Show AbstractHighy-quality nano-structured ZnO samples, including thin films and nanorods, have been synthesized by simple chemical solution and thermal evaporation methods without any catalysts. The samples were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), temperature-dependent photoluminescence (PL) spectra measurements. XRD patterns illustrated that there were no second phases in these ZnO samples, and the TEM results indicated that the well-aligned ZnO nanorods are single crystalline with a hexagonal structure and grow along the [001] direction. Room-temperature PL spectra of ZnO thin films showed a strong UV near-band-edge (NBE) emission located at about 390 nm and a green defect-related (G) emissions, where the intensity ratio of NBE-to-G emission varies with the annealing temperatures. Meanwhile, the ZnO nanorods only revealed strong UV emission. The ZnO samples exhibited free exciton and very sharp exciton emissions at low temperatures. Particularly, room-temperature UV random lasing characteristic of ZnO films and nanorods has been observed as well. It is shown that these nano-structured ZnO samples can exhibit random laser action depending on the growth condition. The threshold intensity for the lasing is comparable to earlier reported data. These results indicate that nano-structured ZnO samples prepared by both simple techniques may be a promising material for further photonic devices. Possible lasing mechanism is discussed and further investigation to clarify the mechanism between the nano-structured ZnO samples is still underway.
9:00 PM - K10.57
Modelling the Preferred Shape and Orientation of ZnO Nanowires and Nanobelts.
Amanda Barnard 1 , Yanan Xiao 2
1 Department of Materials, University of Oxford, Oxford United Kingdom, 2 , Advanced Photon Source, Argonne, Illinois, United States
Show Abstract9:00 PM - K10.6
Investigation of Growth Mechanism of Aligned ZnO Nanowires.
Sharvari Dalal 1 , Richard Morris 2 , Daniel Baptista 1 , Ken Teo 1 , David Jefferson 1 , Rodrigo Lacerda 3 , Michael Dowsett 2 , William Milne 1
1 , Cambridge University, Cambridge, Cambridgeshire, United Kingdom, 2 Physics, University of Warwick, Coventry, West Midlands, United Kingdom, 3 Physics, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
Show AbstractZinc oxide is a II-VI wide bandgap (3.37eV) semiconductor that has many interesting optical and mechanical properties making it a promising material for various optical and electronic devices. Using a simple vapor deposition process and by controlling the growth kinetics, a wide range of 1D nanostructures have been synthesized. Vertically aligned ZnO nanowires have been grown which could be used in bottom-up devices for applications in sensing, optoelectronics and field emission. The present work reports an alternate view of the mechanism involved in the catalytic growth of aligned ZnO nanowires/rods. The nanowires are grown in a horizontal tube furnace by evaporation of 1:1 ZnO:C mixture at 1000 °C onto 1 to 10 nm Au coated sapphire substrates using a N2/O2(20%) gas flow. The deposition temperature and pressure varied from 680 to 890 °C and 1 to 9 mbar respectively. Although a catalyst was used, no traces of the metal have been detected in the nanowires. HRTEM analysis showed flat 0001 ends with no metal visible or detected with EDS. Secondary ion mass spectrometry (SIMS) was used for its more sensitive detection limits (ppm-ppb) and the ability to build up a depth profile.Two types of SIMS experiments were performed: mass spectral analysis to study the composition of the nanowire tips and depth profile analysis to investigate the bulk. The surface mass spectra showed no Au peak implying Au is not present at the tips of the nanowires. Since nanowires form a non-uniform, disconnected surface, a low angle of incidence was used during depth profiling to limit sputtering to the uppermost part of the sample and reduce the detection of secondary ions from deeper in the sample. The resulting profile showed that the initial Au level remained at the background detection limit before rising to a peak, and then gradually decreasing. Due to the sample morphology, the erosion during profiling is non-uniform, hence depth interpretation is difficult, but simultaneous measurement of the O level showed a jump followed by instability indicating the possible transition into the sapphire substrate. This jump occured just after the gold peak indicating the gold remained near the nanowire-substrate interface. The VLS mechanism is often cited as being responsible for vapor phase growth using a catalyst. This mechanism involves a vapor species supersaturating a liquid catalyst and later precipitating to form part of a crystal1. Since the gold catalyst is not detected in the nanowire, the mechanism may be different from the standard VLS process necessitating an alternative growth mechanism. The gold catalyst may be necessary only in the initial stage of growth, giving place to a posterior self-catalytic growth. Further investigations are crucial to elucidate these results. The ability to control the growth mechanism is integral to the use of ZnO nanowires for many technological applications. 1R. S. Wagner, et al., Journal of Applied Physics 35 (10), 2993 (1964).
9:00 PM - K10.7
Effect of Co-doping Co and Cu on the Properties of ZnO Based Diluted Magnetic Semiconductor Thin Films.
Deepayan Chakraborti 1 , Shivaraman Ramachandran 1 , John Prater 1 2 , Jagdish Narayan 1
1 Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Materials Science Division, Army Research Office, Research Triangle Park, North Carolina, United States
Show Abstract9:00 PM - K10.8
The Study of the Effect of Al-doped ZnO Surface Treatment for Organic Light Emitting Diode.
Jong Kook Jung 1 , Sil-Mook Lee 1 , Seong Eui Lee 1 , Ho Nyeon Lee 2
1 Department of Advanced Materials Engineering, Korea Polytechinc Univ, kyonggi-Do Korea (the Republic of), 2 Samsung Advanced Institute of Technology, Display Lab., kyonggi-do Korea (the Republic of)
Show AbstractTCOs (transparent conducting oxides) possess a wide range of applications in a variety of opto-electronic devices such as flat-panel displays or thin-film solar cells. By the present time, ITO is used almost electronic display devices, but its very expensive and it very high temperature to make ITO. So we made AZO (ZnO 98wt%: Al 2wt%) transparent electrode in RF magnetron sputtering method. To assess the credibility, we made sure of the electrical characteristics along the different temperature conditions. Also we wanted to fabricate high quality AZO thin films in order to apply to anode for OLED (Organic light emitting diode), and to improve OLED efficiency. Device structure of SM-OLEDs grown by vacuum thermal deposition is Anode(300nm AZO)/60nm Alq3/2nm LiF/75nm Al. The comparison of UV-Ozone and Electrolysis AZO thin films were studied, mainly, in the aspect of electrical stability and work function. The improved efficiency could be understood to be due to the change in work function at surface of AZO after UV-Ozone treatment. Additionally, the effects of surface roughness of AZO thin films were studied at various thermal conditions. We are now trying to find out the mechanism of this enhanced efficiency.
9:00 PM - K10.9
Synthesis, Morphological Control, and Photoluminescence Properties of Zinc Oxide Nanoparticles.
Tamar Andelman 1 , Yinyan Gong 1 , Igor Kuskovsky 2 , Dalia Yablon 3 , Alan Schilowitz 3 , Stephen O'Brien 1
1 Applied Physics and Applied Math, Columbia University, New York, New York, United States, 2 Physics, Queens College of CUNY, Queens, New York, United States, 3 , ExxonMobile Research, Annandale, New Jersey, United States
Show Abstract