Leonid Tsybeskov New Jersey Institute of Technology
David J. Lockwood National Research Council
Christophe Delerue IEMN
Masakazu Ichikawa The University of Tokyo
Anthony W. van Buuren Lawrence Livermore National Laboratory
L1: Light Emission and Photonic Devices I
Monday PM, November 27, 2006
Room 207 (Hynes)
9:30 AM - **L1.1
Group IV Semiconductor Light Emitting Nanostructures: Which can be Bright? Which can Yield Gain?
Harry Atwater 1 Show Abstract
1 Applied Physics, California Institute of Technology, Pasadena, California, United States
In this talk, I will describe progress in light emission from both Si and non-Si Group IV semiconductor nanostructures and alloy materials with potential for visible and near-infrared imaging emission. Column IV elements can be combined to form alloys (e.g., SixSn1-x and GexSn1-x) with tunable infrared optical properties in the infrared, and have yielded the first known example of a direct bandgap Column IV semiconductor. Progress on GexSn1-x alloy growth and key requirements for light-emitting devices will be discussed. Plasmon-enhanced photoluminescence and electroluminescence has been observed from silicon quantum dot (QD) emitters interacting with the enhanced local field when in close proximity to noble metal nanostructures. This enhanced luminescence is attributed to an increase in quantum efficiency, radiative decay rate, and absorbance cross section. Moreover, the enhancement is a resonant process, and this frequency-specific interaction can be used to tune the spectral emission of the Si QDs.Metal-oxide semiconductor (MOS) structures containing Si nanocrystals that exhibit field effect electroluminescence have potential to enable electrically-pumped Si-based optical gain media based nc-Si:Er media. Design requirements for achieving net gain in electrically-pumped nc-Si:Er and recent experimental results will be discussed.
10:00 AM - L1.2
Experimental Measurement of the Dielectric Constant of Nanometer-size Silicon Structures
Han Yoo 1 , Rishi Krishnan 2 , Christopher Striemer 2 , Philippe Fauchet 2 Show Abstract
1 Department of Physics and Astronomy, University of Rochester, Rochester, New York, United States, 2 Department of Electrical and Computer Engineering, University of Rochester, Rochester, New York, United States
During the design of devices using Si nanostructures, it is often important to precisely know the dielectric function ε, since it determines many of their electrical and optical properties. Several theoretical studies [1 – 5] have predicted a reduction in ε as the nanostructure size decreases. However different physical mechanisms have been proposed for the reduction. In one model, the decrease is due to quantum confinement effects [1 – 3], whereas a more recent model attributes it to a breaking of polarizable bonds—a surface effect [4, 5].
There have been only a few experimental works on the size dependence of ε [6, 7]. In these studies ε was measured only for one particular size and no confirmation of a particular theory was possible. In our work, we have measured the size-dependent ε of both silicon nanocrystals and thin crystalline slabs at different sizes using spectroscopic ellipsometry from 0.73 eV (1700 nm) to 4.58 eV (270 nm).
In one of the two types of samples we studied, alternating layers of a-Si and a-SiO2 were deposited on a Si substrate by RF magnetron reactive sputtering. The thickness of the a-SiO2 layer was kept fixed at 5 nm, whereas the a-Si layer thickness was varied from 1 nm to 15 nm. Rapid thermal annealing initiated crystallization of the a-Si layers and furnace annealing completed it, creating a dense array of nc-Si . In the second type, the thickness of the top Si layer of SOI wafers was first reduced to ~ 13 nm by a wet thermal oxidation process and the oxidized Si layer was removed by HF etching. The Si layer was then thinned down by repeated oxidation and etching to produce nano-sized Si slabs of different thicknesses. Ellipsometry and surface profile measurements were performed between each etching step.
We focused on ε in the transparent region. At 1.7 µm wavelength where the bulk ε ~ 11.7, we found that ε was reduced by ~ 40% (from 11.6 to 7.0) in the case of dense arrays of nc-Si with 2.6 nm diameters, whereas it was reduced by ~ 36% (from 11.7 to 7.5) for a 2.4 nm thick Si slab. For the nano-sized slabs, the decrease in ε with size was gradual and could be said to follow the model presented in reference . For the dense arrays of nc-Si, the decrease was initially slower until around a size of 2.7 nm, when the decrease became much more rapid, which might be explained by a recent model . Our results represent the first systematic measurement of the dielectric function of Si nanostructures as a function of size and represent the first test of theory.
 L, Wang and A. Zunger, Phys. Rev. Lett. 73, 1039 (1994);  M. Lannoo, et. al., Phys. Rev. Lett. 74, 3415 (1995);  R. Tsu, et. al., J. Appl. Phys. 82, 1327 (1997);  C. Delerue, et. al., Phys. Rev. B 68, 115411 (2003);  C. Delerue and G. Allan, Appl. Phys. Lett. 88, 173117 (2006);  C. Ng, et. al., Appl. Phys. Lett. 88, 063103 (2006);  K. Lee, et. al., Thin Solid Films 476, 196 (2005);  G. Grom, et. al., Nature 407, 358 (2000)
10:15 AM - L1.3
Effect of Surface Termination on Electronic Structure of Silicon Nanoparticles.
April Montoya Vaverka 1 2 , Robert Meulenburg 2 , Trevor Willey 2 , Subhash Risbud 1 , Louis Terminello 2 , Anthony van Buuren 2 3 Show Abstract
1 Chemical Engineering and Materials Science, University of California, Davis, Davis, California, United States, 2 Chemistry and Materials Science, Lawrence Livermore National Laboratory, Livermore, California, United States, 3 , University of California, Merced, Merced, California, United States
10:30 AM - **L1.4
Quasi-Direct Transition due to Proximity Effects in GaSb-Si Anti-Electron Type-II Quantum Dots.
Susumu Fukatsu 1 2 Show Abstract
1 Graduate School of Arts and Sciences, University of Tokyo, Meguro, Tokyo, Japan, 2 PRESTO, Japan Science and Technology Agency, Saitama Japan
To create an efficient Si-based light emitter is essential to the realization of Si-photonics and has been challenged over decades. To this end, many approaches have been proposed and extensively studied: these include π-Si and Si-nanocrystals emitting in the visible, and column-IV-based nanostructures such as Ge quantum dots and short-period Si/Ge superlattices emitting in the near-infrared. However, there has appeared no successful demonstration of either efficient light emission or gain due to interband transitions over the technologically important wavelengths, 1.1-1.7µm, where Si is not strongly absorbing. The conventional wisdom to tailor the dispersion of the otherwise indirect-gap Si relies solely on the principle of the zone-folding that takes advantage of an artificial periodicity due to short-period superlattices. This has, however, turned out to be elusive for practical but technical reasons: three-dimensional superlattices are hard to achieve, and even worse an inborn tendency of spontaneous disordering due to interface mixing disrupts the superlattice coherence. Recently, we have come up with a new concept of band-gap-type conversion utilizing proximity coupling of electronic wavefuctions, as opposed to standard band-gap engineering. The idea is to utilize quantum mechanical tunneling of electron wave function of indirect Si into the forbidden gap of direct-gap QDs standing as an anti-electron barrier. This takes effect once electrons are localized sharply at the interface. The electron trapping potential arises from anion-Si bond polarization while carrier capture over macroscopic distances is facilitated by band warping which occurs due to anisotropically distributed local strain encompassing QDs. Among allied III-V compounds, GaSb has turned out to provide the best results. As a matter of fact, efficient light emission as evidenced by 0.3-% power efficiency and room-temperature light-emitting-diode, and even near-infrared gain were obtained from 10 monolayers-equivalent GaSb-Si QDs grown by solid source molecular beam epitaxy. The proximity effects allow electrons in Si to behave more like those in direct-gap GaSb, leading to the development of on-off gain well over 10dB/cm for a 5-mm long waveguide sample in dual-chip pump-and-probe geometry both under optical and current pumping at a cryogenic temperature of 5 K. The results promise a Si-based semiconductor optical amplifier, Si-SOA. Gain saturation, probe-intensity dependent gain, and clear threshold behaviors are indicative of population-inversion in a three-level system. It has been found that as the whole system is spontaneously n-type doped, free-carrier recombination diminishes gain at a high pumping level in a slab waveguide geometry. Possible lasing is expected in view of a clear kink in the growth curve of the light output of a single chip under optical pumping, which coincides well with the kink on gain curve in the dual-chip experiment.
11:00 AM - L1: LEPD1
11:30 AM - **L1.5
Epitaxial Growth and Luminescence Characterization of Si-based Double Heterostructures Light-emitting Diodes with Iron Disilicide Active Region.
Takashi Suemasu 1 , Tsuyoshi Sunohara 1 , Yuya Ugajin 1 , Ken'ichi Kobayashi 1 , Shigemitsu Murase 1 Show Abstract
1 Institute of Applied Physics, University of Tsukuba, Tsukuba Japan
Since the demonstration of EL in β-FeSi2, β-FeSi2 has been attracting much attention as a material for a Si-based light emitter. We have succeeded in obtaining 1.6µm EL at RT from β-FeSi2 particles embedded in Si p-n diodes on Si(001)[2-4], and very recently from p-Si/β-FeSi2/n-Si (SFS) double heterostructures (DH) on Si(111) by MBE . In this paper, we report recent experimental results on the formation of SFS DH on both Si(001) and Si(111) substrates and their PL and EL properties.A SFS DH was prepared as follows. For Si(001) substrates, 8-nm-thick -oriented β-FeSi2 was grown by reactive deposition epitaxy, followed by undoped Si by MBE. For Si(111) substrates, 250-nm-thick -oriented β-FeSi2 was grown by codeposition of Fe and Si on RDE-grown β-FeSi2 template, followed by undoped Si by MBE. For fabrication of LEDs, a p+-Si top layer was grown. Details of the growth procedure have been already described in our previous papers. 1.6µm EL was realized at RT from SFS DH LEDs formed on both Si(001) and Si(111). For LEDs on Si(001), the current density necessary for EL at RT, which was approximately 20A/cm2, was suppressed by a factor of 3 compared to previous LEDs on Si(001) with β-FeSi2-particles active region. Time-resolved PL measurements elucidated that the luminescence originated from two sources, one with a short decay time (10 ns) and the other with a longer decay time (100 ns) at 8K. In contrast, a short decay time (10 ns) was found to be dominant for previous Si/β-FeSi2 particles/Si(001) structures. The short decay time was thought to be due to carrier recombination in β-FeSi2. On the other hand, the long decay time was due probably to a dislocation-related D1 line in Si. The luminescence intensity ratio of β-FeSi2 to D1 line was approximately 2 at 8K, and it increased with temperature (6 at 130K) since the D1 line is more rapidly quenched. Similar results were obtained for SFS DH on Si(111). For LEDs on Si(111), EL was obtained at a current density higher than 80A/cm2. The lattice mismatch between β-FeSi2 and Si is approximately 1% and 5% for β-FeSi2 formed on Si(001) and Si(111), respectively. Thus, we think that more defects working as nonradiative recombination centers exist at the SFS on Si(111). When current passing through the defects saturated, bias current began to contribute to the radiative recombination and a reasonable EL output was obtained. Thus, by increasing carrier injection into β-FeSi2 by reducing the defect densities at the β-FeSi2/Si hetero interfaces, practical Si-based LEDs will be obtained in the near future.  Leong et al., Nature 387 (1997) 686., Suemasu et al. , Jpn. J. Appl. Phys.39 (2000) L1013.,  Li et al., J. Appl. Phys. 97 (2005) 043529.,  Sunohara et al., Jpn. J. Appl. Phys. 44 (2005) 3951.,  Takauji, et al., Jpn. J. Appl. Phys. 44 (2005) 2483.
12:00 PM - L1.6
Quantum-confinement Effect in β-FeSi2 Flat Nanoislands on Si (111) Substrates.
Yoshiaki Nakamura 1 2 , Ryota Suzuki 1 , Masafumi Umeno 1 , Sung Cho 3 2 , Nobuo Tanaka 3 2 , Masakazu Ichikawa 1 2 Show Abstract
1 Dept. of applied physics, The University of Tokyo, Tokyo Japan, 2 CREST, Japan Science and Technology Agency, Tokyo Japan, 3 EcoTopia Science Institute, Nagoya University, Nagoya Japan
Semiconducting β-FeSi2 is attractive as a Si-based light emitting material for an optical fiber communication. Nanostructures of β-FeSi2  have drawn much attention due to their quantum-confinement effects which can change material properties. However, the quantum-confinement effect in β-FeSi2 has not been elucidated yet. In this study, we investigated the quantum-confinement effect of individual β-FeSi2 nanoislands with quantum well structures using scanning tunneling spectroscopy (STS).Si (111) samples cleaned by flashing in the ultrahigh vacuum chamber at the base pressure of ~1×10-8 Pa were oxidized at 600°C for 10 min at the oxygen pressure of ~2×10-4 Pa to form ultrathin SiO2 films. We predeposited Si with an amount of 1 monolayer (ML) on the ultrathin SiO2 films and codeposited Fe and Si at 500°C at a stoichiometric ratio of deposition rates (~0.5). This deposition formed 3-nm hemispherical β-FeSi2 nanodots with ultrahigh density (>1012 cm-2). Annealing of the β-FeSi2 nanodots at 650°C for 30 min changed hemispherical dot shape to flat nanoisland one by diffusion and coalescence of iron silicide.STM images showed that flat nanoislands were formed with a lateral size of ~10-20 nm and a height of ~2-5 nm. 7×7 Si surfaces were observed in the surface areas among the nanoislands revealing that the SiO2 was decomposed during annealing process. RHEED patterns of the samples indicated that β-FeSi2 was epitaxially grown on Si (111). We measured the energy bandgaps of the individual hydrogen-terminated β-FeSi2 nanoislands using STS. The energy bandgaps were found to increase with the decrease in the island heights while the energy bandgaps were independent of the lateral island sizes. This indicated that the β-FeSi2 nanoislands had quantum well structures. This size dependence of the energy bandgaps was fitted with the L-2 curve based on the hard wall square potential model with well width L, where the reduced mass was adjusted to be (0.25±0.07)m0 with m0 free electron mass. This is consistent with the value (0.21–0.25m0) estimated from electron and hole effective masses calculated by Martinelli .In summary, we measured the energy bandgaps of individual β-FeSi2 nanoislands using STS. The island-height dependence of the energy bandgaps was explained by the quantum-confinement effect in β-FeSi2 nanoislands with quantum well structures. This work was partly supported by JSPS.KAKENHI (15201023 and 17710093).References Y. Nakamura, Y. Nagadomi, S.-P. Cho, N. Tanaka, and M. Ichikawa, Phys. Rev. B 72, 075404 (2005). L. Martinelli, E. Grilli, D. B. Migas, L. Miglio, F. Marabelli, C. Soci, M. Geddo, M. G. Grimaldi, and C. Spinella., Phys. Rev. B 66, 085320 (2002).
12:15 PM - L1.7
Theoretical study of Si-rich transition-metal silicides with double-graphene-like structures.
Takehide Miyazaki 1 , Toshihiko Kanayama 2 Show Abstract
1 RICS, AIST, Tsukuba Japan, 2 ASRC, AIST, Tsukuba Japan
Recently, there has been an enthusiasm for fabrication of graphene[1,2]. A reason is that graphene with the thickness of a few atomic layers shows the outstanding transport properties[3,4]. Regarding this excitement about graphene, it would be very intriguing to synthesize the silicon (Si) counterpart of graphene, because the use of Si in constructing those nanometer-size objects should be much more compatible with the current VLSI technology than introduction of carbon (C) systems. However, it has been argued that it is very difficult to construct Si atoms in a single stable graphene sheet[5-8] without mixing elements other than Si such as C [9,10]. In this presentation, we propose a completely novel form of graphene-like Si nanostructure based on ab initio total-energy calculation and geometry optimization. It has a three-layer structure, where the two layers of Si atoms positioned in graphene-like geometries sandwich another layer of transition metal atoms. It is possible to tune the electronic structure of this layered material from metal to semiconductor by changing the element of the transition metal atoms. Our new material can be regarded as a Si- rich phase of transition-metal (TM) silicide with a large Si-to-TM composition ratio being around ~10, which may be suitable for a material to smoothly connect the interfaces between electrodes made of conventional TM disilicide and Si substrates in transistors. We will further discuss how the novel material in question could be synthesized.References S. Horiuchi, T. Gotou, M. Fujiwara, T. Asaka, T. Yokosawa and Y. Matsui, Appl. Phys. Lett. 84, 2403 (2004). J.-L. Li, K. N. Kudin, M. J. McAllister, R. K. Prud’homme, I. A. Aksay, and R. Car, Phys. Rev. Lett. 96, 176101-1 (2006). K. S. Novoselov, A. K. Geimm, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva and A. A. Firsov, Science 306, 666 (2004). K. S. Novoselov, A. K. Geimm, S. V. Morozov, D. Jiang, M. I. Katsnelson, S. V. Dubonos, I. V. Grigorieva and A. A. Firsov, Nature 438, 197 (2005). M. T. Yin and M. L. Cohen, Phys. Rev. B29, 6996 (1984). K. Takeda and K. Shiraishi, Phys. Rev. B50, 14916 (1994). Y.-C. Wang and K. Sheerschmidt and U. Gosele, Phys. Rev. B61, 12864 (2000). E. Durgun, S. Tongay and S. Ciraci, Phys. Rev. B72, 075420 (2005). Y. Miyamoto and B. D. Yu, Appl. Phys. Lett. 80, 586 (2002). C. L. Freeman, F. Claeyssens, N. L. Allan and J. H. Harding, Phys. Rev. Lett. 96, 066102 (2006).
12:30 PM - **L1.8
Advances in SiGeSn/Ge Technology
Richard Soref 1 , John Kouvetakis 2 , Jose Menendez 2 Show Abstract
1 , Air Force Research Laboratory, Hanscom AFB, Massachusetts, United States, 2 , Arizona State University, Tempe, Arizona, United States
We have recently reported the CVD growth of binary Ge1-ySny and ternary Ge1-ySixSny alloys directly on Si wafers using SnD4, GeH4, SiH3GeH3, and (GeH3)2SiH2 sources. Ge1-ySny is an intriguing infrared material that undergoes an indirect-to-direct bandgap transition for y > 0.09. In addition, we have found that Ge1-ySny layers have ideal properties as templates for the subsequent deposition of other semiconductors: (a) they are strain-relaxed and have low threading defect densities (105 cm-2) even for films thinner than 1 µm; (b) their low growth temperatures between 250°C and 350°C are compatible with selective growth, and the films possess the necessary thermal stability for conventional semiconductor processing (up to 750°C depending on composition); (c) they exhibit tunable lattice constants betwen 5.65 Å and at least 5.8 Å, matching InGaAs and related III-V systems; (d) their surfaces are extremely flat; (e) they grow selectively on Si and not on SiO2; and (f) the film surface can be prepared by simple chemical cleaning for subsequent ex-situ epitaxy.The incorporation of Sn lowers the absorption edges of Ge. Therefore, Ge1-ySny is attractive for detector and photovoltaic applications that require band gaps lower than that of Ge. Spectroscopic ellipsometry and photoreflectance experiments show that the direct band gap is halved for as little as y = 0.15. Studies of a Ge0.98Sn0.02 sample yield an absorption coefficient of 3500 cm-1 at 1675 nm (0.74 eV). Thus infrared detectors based on Ge0.98Sn0.02 could easily cover the U-(1565 nm-1625 nm), L-(1565 nm-1625 nm), and C-(1530 nm-1565 nm) telecomm bands. We have made advances in P and N doping of GeSn and shall present results on infrared detection using GeSn/SiGeSn PIN heterodiodes. GeSn also has application in band-to-band laser heterodiodes.The ternary system Ge1-x-ySixSny grows on Ge1-ySny-buffered Si. It represents the first practical group-IV ternary alloy, since C can only be incorporated in minute amounts to the Ge-Si network. The most significant feature of Ge1-x-ySixSny is the possibility of independent adjustment of lattice constant and band gap. For the same value of the lattice constant one can obtain band gaps differing by more than 0.2 eV, even if the Sn-concentration is limited to the range y < 0.2. This property can be used to develop a variety of novel devices, from multicolor detectors to multiple junction photovoltaic cells. A linear interpolation of band gaps and lattice constants between Si, Ge and α-Sn shows that it is possible to obtain SiGeSn with a band gap and a lattice constant larger than that of Ge. We shall use this feature to make a tensile-strained Ge-on-SiGeSn telecomm detector with improved performance. The tensile-strain-induced direct gap of Ge can be used also for electroptical modulators and lasers.
L2: Light Emission and Photonic Devices II
Monday PM, November 27, 2006
Room 207 (Hynes)
2:30 PM - **L2.1
Sub-micron Silicon Photonic Devices.
Graham Reed 1 , Goran Mashanovich 1 , Frederic Gardes 1 , Branislav Timotijevic 1 , William Headley 1 Show Abstract
1 , University of Surrey, Guildford United Kingdom
3:00 PM - L2.2
Fabrication of Extreme aspect Ratio Tubes and Wires of Silicon and Germanium Within Microstructured Optical Fibers.
Neil Baril 1 4 , John Badding 1 4 , Vankatraman Gopalan 3 4 , Pier Sazio 5 , Thomas Scheidemantel 2 4 , Bryan Jackson 3 4 , Dong-Jin Won 3 4 , Adrian Amezcua Correa 5 , Chris Finlayson 5 Show Abstract
1 Chemistry, The Pennsylvania State University, University Park, Pennsylvania, United States, 4 The Center for Nanoscale Science, The Pennsylvania State University, University Park, Pennsylvania, United States, 3 Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania, United States, 5 Optoelectronics Research Centre, University of Southampton, Southampton United Kingdom, 2 Physics, The Pennsylvania State University, University Park, Pennsylvania, United States
Optical fibers are a natural conduit for light and semiconductors are the basis of modern optoelectronics. We have recently fabricated semiconducting micro- and nanowires with extreme aspect ratios in ordered arrays using microstructured optical fibers (MOF’s), as templates. These systems contain the highest aspect ratio semiconducting micro- and nanowires yet produced by any method. The micro wires are over a meter in length, and the nanowires are centimeters long and ~100nm in diameter. The technique for infiltration uses high-pressure gasses to carry chemical vapor deposition precursors through the capillaries of the MOFs, which are heated in a tube furnace to deposit the semiconductor materials. The semiconductors are deposited amorphous and are annealed after deposition to produce polycrystalline materials. MOFs are versatile templates allowing the deposition of high density arrays of micro to nano sized capillaries. They are optically transparent allowing in situ characterization of the wires with Raman spectroscopy. The semiconductor wires can be easily manipulated because they are encased in a silica optical fiber, the silica can also be removed giving access to the wires. The possibilities for the fabrication of in-fiber optoelectronic devices are numerous. These structures have many potential applications for in-fiber sensing, light modulation, and light generation.Sazio et al. Science 311, 1583 (2006)
3:15 PM - L2.3
Large Scale Formation of Y2SiO5:Er Oxyorthosilicate Nanocrystals using Si Nanowires for Efficient, High-gain Light Emitting Material at 1.5 μm.
Kiseok Suh 1 , Jung Shin 1 , Byeong-Soo Bae 2 Show Abstract
1 Physics, KAIST, Daejeon Korea (the Republic of), 2 Materials Science, KAIST, Daejeon Korea (the Republic of)
3:30 PM - L2: LEPD2
4:30 PM - **L2.4
Silicon Integrated Nanophotonics - Advances and Challenges.
Yurii Vlasov 1 , Fengnian Xia 1 , Lidija Sekaric 1 , Eric Dulkeith 1 , Solomon Assefa 1 , William Green 1 , Martin O'Boyle 1 , Hendrik Hamann 1 , Sharee McNab 1 Show Abstract
1 Physical Sciences Department, IBM T.J. Watson Research Center, Yorktown Heights, New York, United States
5:00 PM - L2.5
Three Dimensional Silicon Inverse Photonic Quasicrystals for Infrared Wavelengths.
Alexandra Ledermann 2 , Ludovico Cademartiri 1 , Martin Hermatschweiler 3 , Martin Wegener 2 , Geoffrey Ozin 1 , Diederik Wiersma 4 , Georg von Freymann 3 Show Abstract
2 , Institut für Angewandte Physik, Karlsruhe Germany, 1 Department of Chemistry, University of Toronto, Toronto, Ontario, Canada, 3 , Institut für Nanotechnologie, Karlsruhe Germany, 4 , European Laboratory for Nonlinear Spectroscopy, Firenze Italy
Photonic quasicrystals pose numerous challenges and promises both from the theoretical and the technological point of view. For example it is impossible to completely predict the optical properties of three-dimensional (3d) photonic quasicrystals for their lack of translational periodicity, most fabrication techniques available today are planar and so are optimized for fabrication of two-dimensional structures and only of limited use for arbitrary 3d structures.One of the interesting promises of 3d photonic quasicrystals are anomalous diffusion of light due to the long range order coupled with a lack of short range order, as well as opening complete photonic bandgaps due to their nearly spherical Brillouin zone, which is a consequence of their extremely high rotational symmetry.Photonic quasicrystals might also be considered as a testbed on which to verify theories developed for atomic quasicrystals. In contrast to atomic quasicrystals, photonic quasicrystals can be created by design. Thus, the influence of the symmetry on e.g. transport properties can be monitored more easily.We will here present results on the fabrication of oriented photonic quasicrystals in a polymeric photoresist via direct laser writing and their subsequent inversion with Si.The quality of the structures will be demonstrated via scanning-electron and laser-confocal microscopy while the preservation of the symmetry will be demonstrated with Laue diffraction experiments and their comparison with theory.
5:30 PM - L2.7
Ultra-high Resolution Imaging of Highly Confined Optical Modes in Sub-micron Scale SOI Waveguides.
Jacob Robinson 1 , Stefan Preble 1 , Michal Lipson 1 Show Abstract
1 Electrical and Computer Engineering, Cornell , Ithaca, New York, United States
5:45 PM - L2.8
Si3N4-SiO2-Si Slot-waveguide Disk Resonators in a Silicon Photonic Platform.
Bradley Schmidt 1 , Carlos Barrios 2 , Michal Lipson 1 Show Abstract
1 Electrical and Computer Engineering, Cornell University, Ithaca, New York, United States, 2 Instituto de Sistemas Optoelectrónicos y Microtecnología, Ciudad Universitaria, Madrid Spain
Leonid Tsybeskov New Jersey Institute of Technology
David J. Lockwood National Research Council
Christophe Delerue IEMN
Masakazu Ichikawa The University of Tokyo
Anthony W. van Buuren Lawrence Livermore National Laboratory
L3: Ge and SiGe Nanostructures I
Tuesday AM, November 28, 2006
Room 207 (Hynes)
9:30 AM - **L3.1
Templated Selfassembly of Ge Dot Arrays, Molecules and 3-dimensional Crystals on Si.
Detlev Grutzmacher 1 , Christian Dais 1 , Elisabeth Müller 1 , Harun Solak 1 , Hans Sigg 1 , Julian Stangl 2 , Günther Bauer 2 Show Abstract
1 Laboratory for Micro- and Nanotechnology, Paul Scherrer Institut, Villigen-PSI Switzerland, 2 Inst. for semiconductor and solid state physics, Johannes Kepler University Linz, Linz Austria
Templated self-organization has been used to prepare samples with regimented arrays of Ge quantum dots. Si (100) substrates have been patterned with 2-dimensional hole gratings using multiple beam diffraction in the extreme UV (EUV). The setup of EUV interference lithography (EUV-IL) at the swiss synchrotron ligth source (SLS) permits exposure areas up to 2x2 mm in a single illumination. Different gratings have been used for masks, leading to patterns with an periodicity ranging from 50 to 250 nm. After the pattern had been transferred into the Si (100) substrate by reactive ion etching, molecular beam epitaxy was employed to grow Si/Ge quantum dot layers on the pre-patterned substrates. First a 20-100 nm thick Si buffer layer was deposited at 300°C followed by the Ge deposition for island formation. In the first Ge quantum dot layer the dots align with holes provided by the pre-patterning. Here we studied the impact of the microscopic shape and size of the pre-pattern using the mask design and the XIL exposure time and dose as parameters. Very regular array of Ge dots are formed with a densities up to 2.2x1010 cm-2. The density depends not only on the periodicity of the pattern fabricated, but also on the shape of the patterned formed at various exposure conditions. The formation of square like holes on the Si substrates lead to the nucleation of ordered quantum dot molecules on the Si surface. Typically 4 Ge dots are formed, nucleating at the corners of the square holes of the prepattern. Lowering the exposure dose and thus decreasing the size of the holes in the prepattern allows the deposition of one Ge dot per hole. Atomic force microscopy has been employed to determine the size distribution of the Ge dots in the arrays. Narrow size distribution of 4% and 7% for dome and hut cluster of 80 and 40 nm diameter have been found on arrays with 250 nm and 100 nm periodicity, respectively.Continuation of depositing Si/Ge layer sequences on top of the ordered dot arrays leads to alignment of dots to the first layer due to strain fields. The alignment has been observed for quantum dot molecules as well. AFM surface scans as well as crossectional TEM micrographs reveal the formation of highly ordered 3-dimensional quantum dot crystals. Typically, the vertical periodicity amounts to ~8nm, whereas the lateral periodicity is 90 x 100 nm. The dots have a diameter of 34±3 nm, thus Ge dots exhibit a remarkably narrow size distribution and close to perfect ordering. This is confirmed by X-ray diffraction experiments at symmetric and asymmetric diffraction peaks. Moreover, photoluminescence and optically pumped absorption measurements have been performed giving insights into the bandstructure of the 2-d and 3-d quantum dot crystals. Our results on the fabrication and properties of 2- and 3-dimensional Ge quantum dot crystals may open a new routes towards the realization of nanoelectronic and spintronic devices as well as for quantum computing.
10:00 AM - L3.2
Stranski–Krastanov Growth of Tensely Strained Si on Ge (001) Substrates.
Dietmar Pachinger 1 , Gang Chen 1 , Herbert Lichtenberger 1 , Friedrich Schäffler 1 Show Abstract
1 Semiconductor Physics, Institute of Semiconductor and solid state physics, Linz Austria
10:15 AM - L3.3
Electric Field Controlled Directional Growth in Metal-Induced Lateral Crystallization of Amorphous SiGe on Insulating Films.
Masanobu Miyao 1 , Hiroshi Kanno 1 , Taizoh Sadoh 1 Show Abstract
1 Department of Electronics, Kyushu University, Fukuoka Japan
The low-temperature (<500oC) formation of high quality polycrystalline SiGe (poly-SiGe) on insulating substrates has been expected to realize advanced system-in-displays. In line with this, we have been developing metal-induced lateral crystallization (MILC) of a-Si1-XGeX (X:0-1) by using Ni as catalyst metal, and found that growth morphology strongly depends on Ge fraction., i.e plane crystallization for samples with low Ge-fraction (X<0.3), dendrite growth for intermediate Ge fraction (X:0.35-0.65) and no crystallization for high Ge fraction (X above 0.7). To solve these problems, present paper examines the electric-field stimulated MILC of a-Si1-XGeX (X:0-1). This enables uniform crystal growth of SiGe with all Ge fractions.In the experiment, a-Si1-XGeX (X:0-1, 50 nm thickness) were deposited on quartz substrate using a solid-source MBE system. Then, Ni films (15 nm thickness) were deposited selectively on a-SiGe layers. This Ni films were used as the catalyst atom source and electrodes for bias voltage. The spacing between anodes and cathodes were 40~6000 micron. Finally, the samples were annealed at 400~500oC with applying electric fields (0~5000 V/cm) between the electrodes. The lateral growth lengths and crystal qualities of SiGe were evaluated by using Nomarski optical microscopy, scanning electron microscopy, and Raman spectroscopy.When the electric fields were applied (<200V/cm) during MILC, lateral growth velocity at the cathode side became faster by 10 times than that at the anode side. This indicates that Ni atoms are charged negatively in SiGe, and their migration is enhanced by electric fields. In addition, the dendrite growth obtained by conventional MILC was almost vanished away and very large uniform growth regions (>50 micron) appeared at the cathode sides even for both samples with intermediate and high Ge fractions. Raman spectroscopy measurements showed that grown layers were completely strain free. Under the extremely high electric fields (>2000 V/cm), crystal growth propagated straight from the Ni patterns, where the growth direction was completely aligned to the electric fields. These phenomena are attributed to the facts that kinetic energy of Ni atoms transferred from the high electric fields (>2000 V/cm) exceeds thermal energy at 500oC. These results indicate that flow direction of catalyst atoms (Ni) during annealing can be controlled by the electric fields. This advantage of aligned growth of poly-SiGe on the insulating films should be used for advanced TFT with high speed operation. We are now fabricating thin-film transistors (TFT) with Schottky source and drain structures. Preliminary results indicated that TFTs showed good ambipolar operation characteristics. In addition, a kink effect due to the floating body effects, which were observed in the conventional doping source/drain TFTs, was successfully suppressed. The possible application of these TFTs to advanced system-in-displays will be discussed.
10:30 AM - L3.4
Spin Relaxation in SiGe Islands.
Hans Malissa 1 , Wolfgang Jantsch 1 , Gang Chen 1 , Herbert Lichtenberger 1 , Thomas Fromherz 1 , Friedrich Schäffler 1 , Günther Bauer 1 , Alexei Tyryshkin 2 , Stephen Lyon 2 , Zbyslaw Wilamowski 3 Show Abstract
1 Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Linz Austria, 2 Department of Electrical Engineering, Princeton University, Princeton, New Jersey, United States, 3 Institute of Physics, Polish Academy of Sciences, Warsaw Poland
10:45 AM - L3.5
Photoluminescence Excitation Dependencein Three-dimensional Si/SiGe Nanostructures.
Eun Kyu Lee 1 , Boris Kamenev 1 , Theodore Kamins 2 , Jean-Mark Baribeau 3 , David Lockwood 3 , Leonid Tsybeskov 1 Show Abstract
1 ECE, New Jersey Institute of Technology, Newark, New Jersey, United States, 2 Quantum Science Research, Hwelett-Packard Laboratories, Palo Alto, California, United States, 3 National Research Council, Institute for Microstructural Sciences, Ottawa, Ontario, Canada
We find that in Ge (SiGe) clusters grown on Si using Stranski-Krastanov (SK) growth mode, (i) photoluminescence (PL) spectra, (ii) PL lifetime and (iii) PL thermal quench activation energies exhibit strong dependence on the excitation intensity. Under PL excitation intensity increasing from 1 to 104 W/cm2, the PL spectra exhibit blue shift from below Ge bandgap up to ~ 970 meV. The PL lifetime shows strong dependence on the excitation wavelength, decreasing from 20 microseconds at ~ 0.8 eV to 200 nanoseconds at ~ 0.9 eV. The process of PL thermal quench has two clearly distinguished activation energies. At low temperature, small (~ 15 meV) and excitation-independent activation energy is attributed to exciton thermal dissociation. At higher temperature, excitation-dependent PL thermal quench activation energy (increasing from ~ 120 to 340 meV as excitation intensity increases) is found, and it is attributed to hole redistribution via tunneling and/or thermal ionization over the Ge (SiGe)/Si valence band confinement barrier.
11:00 AM - L3: Ge/SiGe
11:30 AM - **L3.6
Ge/Si self-assembled Islands for Photonics Applications.
Philippe Boucaud 1 , Xiang Li 1 , Moustafa El Kurdi 1 , Sébastien Sauvage 1 , Xavier Checoury 1 , Sylvain David 1 , Navy Yam 1 , Frédéric Fossard 1 , Daniel Bouchier 1 , Guy Fishman 1 Show Abstract
1 , CNRS-IEF, Orsay France
12:00 PM - L3.7
Ordering and Shape Tuning of Ge Islands on Metal-patterned Si.
Jeremy Robinson 1 2 , Donald Walko 3 , Dohn Arms 3 , Daniel Tinberg 4 , Paul Evans 4 , Yifan Cao 1 , J. Liddle 2 , Oscar Dubon 1 2 Show Abstract
1 Materials Science and Engineering, University of California, Berkeley, California, United States, 2 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States, 4 Materials Science and Engineering, University of Wisconsin, Madison, Wisconsin, United States
12:15 PM - L3.8
Photo-oxidation of Ge Nanocrystals: Kinetic Measurements by In Situ Raman Spectroscopy
Ian Sharp 1 2 , Qing Xu 1 2 , Chun Yuan 1 2 , Joel Ager III 1 , Daryl Chrzan 1 2 , Eugene Haller 1 2 Show Abstract
1 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Materials Science and Engineering Department, University of California, Berkeley, Berkeley, California, United States
Ge nanocrystals are formed in silica by ion beam synthesis and are subsequently exposed by selective HF etching of the silica. Under ambient conditions, the exposed nanocrystals are stable after formation of a protective native oxide shell of no more than a few monolayers . However, under visible laser illumination at room temperature and in the presence of O2, the nanocrystals rapidly oxidize. The oxidation rate was monitored by measuring the Raman spectra of the Ge nanocrystals in situ. The intensity ratio of the anti-Stokes to the Stokes line indicated that no significant laser-induced heating of illuminated nanocrystals occurs. Therefore, the oxidation reaction rate enhancement is due to a photo-chemical process. Under certain conditions laser illumination can lead to complete oxidation of nanocrystals, whereas those that are not illuminated are stable after formation of a thin native oxide. The oxidation rate varies linearly with the logarithm of the laser intensity, and at constant laser intensity the rate increases with increasing photon energy. These kinetic measurements, along with the power and energy dependencies, are described quantitatively by an electron active oxidation mechanism involving tunneling of optically excited electrons through the forming oxide skin and subsequent transport of oxygen ions to the Ge nanocrystal surface. This work was supported in part by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 and in part by U.S. NSF Grant No. DMR-0405472. Sharp, I.D. et al., J. Appl. Phys. 97, 124316 (2005).
12:30 PM - L3.9
Influence of Nanoimprinted and Etched Surface Relief on Nucleation and Ordering of Si and Ge on Amorphous Silicon Dioxide.
Ted Kamins 1 , Amir Yasseri 1 , Shashank Sharma 1 , Fabian Pease 2 , Qiangfei Xia 3 , Stephen Chou 3 Show Abstract
1 Quantum Science Research, Hewlett-Packard Laboratories, Palo Alto, California, United States, 2 Dept. of Electrical Engineering, Stanford University, Stanford, California, United States, 3 Nanostructure Lab, Dept. of Electrical Engineering, Princeton University, Princeton, New Jersey, United States
12:45 PM - L3.10
Control of Valley Splitting in a Si/SiGe 2DEG Quantum Point Contact.
Lisa McGuire 1 , K. Slinker 1 , S. Goswami 1 , J. Chu 2 , Mark Friesen 1 , S. Coppersmith 1 , M. Eriksson 1 Show Abstract
1 , University of Wisconsin, Madison, Wisconsin, United States, 2 , IBM Research Division, T. J. Watson Research Center, Yorktown Heights, New York, United States
Valley splitting in Si quantum wells is an important component of Si-based quantum computing. If valley splitting is large, the spin degree of freedom forms the basis for a robust two-level qubit. If valley splitting is small, different valley states will interfere with this qubit basis. Here we report the measurement and control of valley splitting in a Si/SiGe quantum point contact. In contrast with previous results on large Hall bars, which have shown small valley splitting, we find that the valley splitting in a quantum point contact is large, approaching the maximum theoretical estimates1. To measure the valley splitting, we perform a point contact spectroscopy by recording the point contact conductance as function of magnetic field and gate voltage at an electron temperature T~100 mK. The results show that the point contact geometry enables control of the valley splitting as a function of both gate voltage and magnetic field in individual subbands. Research supported by ARO, NSA, and NSF. 1Valley splitting in strained silicon quantum wells, Timothy B. Boykin, Gerhard Klimeck, M.A. Eriksson, Mark Friesen, S. N. Coppersmith, Paul von Allmen, Fabiano Oyafuso, and Seungwon Lee, Appl. Phys. Lett. 84, 115 (2004).
L4: Ge and SiGe Nanostructures II / MEMS and Strained Si
Tuesday PM, November 28, 2006
Room 207 (Hynes)
2:30 PM - **L4.1
Optoelectronic Properties and Bandstructure of SiGe Quantum Dot and Cascade Structures.
Thomas Fromherz 1 , Moritz Brehm 1 , Patrick Rauter 1 , Nguyen Vinh 2 , Ben Murdin 3 , Jonathan Phillips 4 , Carl Pidgeon 4 , Zhenyang Zhong 1 , Gang Chen 1 , Jiri Novak 1 , Julian Stangl 1 , Detlev Gruetzmacher 5 , Guenther Bauer 1 Show Abstract
1 Semiconductor Physics, University Linz, Linz Austria, 2 , FOM Institute for Plasma Physics Rijnhuizen , Nieuwegein Netherlands, 3 , University of Surrey, Guildford United Kingdom, 4 , Heriot-Watt University, Edinburgh United Kingdom, 5 , Paul Scherrer Institut, Villigen Switzerland
Due to its indirect fundamental bandgap in k-space, bulk silicon - the dominating material for microelectronics - is not suitable for optoelectronic applications. Nevertheless, the demand for processing and transmitting a large amount of data in very short times is steadily increasing and intra-chip optical communication links will become more and more important in the near future. Evidently, a Si based optoelectronic platform compatible with modern CMOS technology is highly desirable. While several levels of integrating electronics and optics are followed in research, for wide-spread applications in consumer electronics the most attractive and probably cost-efficient level would be a monolithic optoelectronic integration.The central building block of any Si based optoelectonic platform is an electrically pumped emitter. In order to circumvent small optical matrix elements typically for interband transitions in an indirect semiconductor, large efforts are devoted to the development of a SiGe based quantum cascade emitter, since in these unipolar devices, no transitions across the fundamental bandgap are involved in the generation of light. After an initial rapid success in the demonstration of electroluminescence emitted by quantum cascade (QC) structures, lasing has still to be demonstrated. For a proper design of laser structures, a critical parameter is the excited state lifetime of the laser transition. In our work, we have for the first time directly measured the optical-phonon limited heavy hole (HH) excited state lifetime of a quantum well (QW) sequence designed for MIR emission. For these measurements, time resolved pump-pump photocurrent experiments under various applied biases have been performed. A lifetime of 550 fs was determined, significantly longer than reported in literature