Brian K. Crone Los Alamos National Laboratory
Heng Liu eLite Corporation
E. Fred Schubert Rensselaer Polytechnic Institute
Fatemeh Shahedipour-Sandvik State University of New York-Albany
Yan-Kuin Su National Cheng Kung University
DD1: Organic Light Emitting Diodes and Quantum Dots
Tuesday PM, April 18, 2006
Room 2016 (Moscone West)
9:00 AM - **DD1.1
Organic Phosphine Oxides and Sulfides as Wide Bandgap Electron Transporting Materials.
Paul Burrows 1 , L.S. Sapochak 1 , A. Padmaperuma 1 , P. Vecchi 1 , A. Q. Hong 1 Show Abstract
1 , Pacific Northwest National Lab, Richland, Washington, United States
9:30 AM - **DD1.2
Chain Morphologies in Blue-Emitting Polyfluorenes: Impact on Light-Emitting Diodes.
Suchi Guha 1 Show Abstract
1 Physics, University of Missouri, Columbia, Missouri, United States
Blue-emitting polyfluorenes (PF) have emerged as especially attractive conjugated polymers due to their strong blue emission, high charge mobility, excellent chemical and thermal stability, and thus great prospects for device applications. Almost all PF derivatives utilize solubilizing side chain substituents anchored at the bridging carbon atom to mould the explicit molecular level properties. PFs exhibit optical properties that are extremely sensitive to changes in both side chain architecture and physiochemical processing. Structural studies of dioctyl-substituted polyfluorene (PF8) have identified at least five different crystalline phases including the liquid-crystalline nematic mesophase above 150 C. Additionally, PF8 has several conformational isomers depending upon the torsional angle between fluorene monomers. PF8 is especially well known for the presence of an unusual spectral feature identified as the beta phase, known to originate in regions of enhanced chain planarity. Although this phase appears as a minority constituent it dominates the emission resulting in a red shift of the luminescence. We present Raman scattering studies of PF8 as a function of thermal cycling that establish a connection between the conformational isomers and chain morphology. Density-functional calculations of the vibrational spectra of single chain oligomers in conjunction with our experimental results demonstrate the incompatibility of the beta phase with the overall alpha crystalline phase. Further, current-voltage and capacitance-voltage measurements have been carried out from PF-based metal-insulator-semiconductor (MIS) and light-emitting diodes. The acceptor dopant concentration and charge carrier mobility are deduced. These results will be discussed in terms of the crystalline phases of PFs.This work is supported by the National Science Foundation under grant nos. ECS-0523656 and DMR-0413601.
10:00 AM - **DD1.3
Dye-Dispersed Polymer Electrophosphorescent Devices for Solid State Lighting
Franky So 1 , Mathew Mathai 2 Show Abstract
1 Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 , Plextronics, Inc., Pittsburgh, Pennsylvania, United States
While there has been considerable progress made in small molecule based heterostructure phosphorescent OLEDs for solid state lighting applications, the progress in phosphorescent polymer OLEDs has been lagging. In small molecule devices, high performance devices are the direct results of carrier transport and confinement by the use of heterostructures and hetero-interfaces. On the other hand, polymer devices are based on the single layer device architecture and the light emitting polymers are responsible for both charge transport as well as emission. Designing a polymer with high luminescence efficiency while maintaining a balanced transport of electrons and holes is very challenging.An alternative approach to fabricate polymer based OLED devices is to disperse small molecule dyes into an inert polymer matrix. By controlling the composition of the small molecule- polymer matrix, the luminescent and the charge transport properties can be independently tuned and a single polymer layer can be optimized for luminescence and carrier transport. With this approach, high efficiency phosphorescent OLED devices with efficiencies close to small molecule heterostructure devices can be realized. For example, the efficiencies of green and blue phosphorescent devices can be as high as 55 cd/A and 22 cd/A respectively. In this paper, we will review the recent progress made in this class of devices. In particular, we will present how the charge transport and injection properties are affected by the composition of the dispersed dyes and discuss their implications on device performance.
10:30 AM - **DD1.4
Challenges and Progress in Developing OLEDs for Lighting
Anil Duggal 1 Show Abstract
1 , GE Corporate Research Center, Niskayuna, New York, United States
OLED technology has enormous potential as a low cost, diffuse light source which could enable more energy efficient lighting and enable new applications due to the unique OLED form factor. In this talk, the challenges to achieving this vision will be outlined and highlights of the worldwide progress aimed at enabling OLED lighting will be reviewed.
11:30 AM - DD1.5
Investigation of a Novel Light-blue-emitting Fluorescent Guest/Host System with Excellent Lifetime.
Philipp van Gemmern 1 , Stefan Grabowski 2 , Herbert Boerner 2 , Volker van Elsbergen 2 , Hans-Peter Loebl 2 , Edward Young 2 , Holger Heil 3 , Rocco Fortte 3 , Heinrich Becker 3 , Holger Kalisch 1 , Michael Heuken 1 4 , Rolf Jansen 1 Show Abstract
1 Institut fuer Theoretische Elektrotechnik, RWTH Aachen, Aachen Germany, 2 , Philips Research Laboratories, Aachen Germany, 3 , Merck OLED Materials GmbH, Frankfurt/Main Germany, 4 , AIXTRON AG, Aachen Germany
White organic light-emitting diodes (OLEDs) are promising candidates to substitute conventional light sources like incandescent bulbs and fluorescent tubes. Excellent color rendering is a key issue for lighting applications, which can only be achieved by mixing red, green and blue emission. While highly efficient organic emitters are available for the generation of green and red light, materials for blue emission with acceptable lifetimes are a topic of current research.We have investigated the light-blue-emitting fluorescent guest/host system SEB-20:SEB-10 from Merck OLED Materials GmbH. OLED devices were prepared by vacuum thermal evaporation on ITO-coated glass substrates comprising a hole transport layer (HTL), the emissive film SEB-20:SEB-10, a hole-blocking film and an electron transport layer (ETL). The cathode contact was formed by a LiF/Al metallization. Samples with N,N'-diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4,4'-diamine (α-NPD) as HTL and tris-(8-hydroxyquinoline) aluminum (Alq3) as ETL were fabricated. The hole blocking capabilities of aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate (BAlq) in this device structure were investigated. Additionally, it was found that deposition of an undoped layer of the matrix material SEB-10 as blocking layer enables the omittance of the BAlq.Furthermore, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4-TCNQ) doping of the HTL was investigated. Devices with 4,7-diphenyl-1,10-phenanthroline (BPhen) or 1,3,5-Tris-(N-phenylbenzimidazol-2-yl)benzene (TPBI) as alternative ETLs were fabricated and the resulting electrical properties, efficiencies and lifetimes of devices were compared. A strong influence of the charge carrier balance on the emission characteristics has been found. The highest power efficiencies of 5.7 lm/W at a brightness of 15 cd/m2 and 4.5 lm/W at 1000 cd/m2 were achieved with a combination of F4-TCNQ-doped α-NPD as HTL and BPhen as ETL. Employing undoped α-NPD and Alq3 leads to lower power efficiencies of 3.8 lm/W max. at 60 cd/m2 and 3.3 lm/W at 1000 cd/m2. The emission color was in the light-blue regime with color coordinates of x = 0.16, y = 0.23.Lifetime tests were conducted at a constant current density of 25 mA/cm2. While devices with BPhen as ETL reached 50% of the initial light output after 120 hours only, those with Alq3 as ETL exhibited extrapolated lifetimes of 2000 hours. Both devices were tested at an initial brightness of about 1700 cd/m2.We assume that excitons form on the host material SEB-10 before a Förster energy transfer to the dopant SEB-20 takes place. This assumption is supported by the overlap of the emission spectrum of the host SEB-10 with the absorption spectrum of the dopant.In conclusion, the fluorescent guest/host system SEB-20:SEB-10 enables the fabrication of light-blue-emitting OLEDs with excellent lifetimes and good efficiencies.
11:45 AM - DD1.6
Electroluminescent Devices from Ionic Transition Metal Complexes for Lighting Applications.
Jason Slinker 1 , Jonathan Rivnay 1 , John DeFranco 1 , Samuel Flores-Torres 2 , Michael Lowry 3 , Leonard Soltzberg 4 , Ji-Seon Kim 5 , Stefan Bernhard 3 , Richard Friend 5 , Hector Abruna 2 , George Malliaras 1 Show Abstract
1 Materials Science and Engineering, Cornell University, Ithaca, New York, United States, 2 Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States, 3 Department of Chemistry, Princeton University, Princeton, New Jersey, United States, 4 Department of Chemistry, Simmons College, Boston, Massachusetts, United States, 5 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom
12:00 PM - DD1.7
Fabrication and Development of Low-voltage Thin Films Quantum-dot Light-emitting Devices.
Cristina Bertoni 1 , Diego Gallardo 1 , Steve Dunn 1 Show Abstract
1 Advanced Materials, Cranfield University, Cranfield, BEDFORDSHIRE, United Kingdom
12:15 PM - DD1.8
Spatial Confinement of Optical Phonon in ZnO Quantum Dots.
Wen-Feng Hsieh 1 , Kuo-Feng Lin 1 , Hsin-Ming Cheng 2 , Hsu-Cheng Hsu 1 Show Abstract
1 National Chiao Tung Univ., Department of Phoonics, Hsinchu Taiwan, 2 Material Research Laboratories, Industrial Technology Research Institute, Hsinchu Taiwan
12:30 PM - DD1.9
Light Emission Properties of ZnO Quantum Dots and Nanocrystals
Khan Alim 1 , Vladimir Fonoberov 1 , Alexander Balandin 1 2 , Alex Rozhin 2 , Andrea Fasoli 2 , Andrea Ferrari 2 Show Abstract
1 Nano-Device Laboratory, Department of Electrical Engineering, University of California - Riverside, Riverside, California, United States, 2 Department of Engineering, University of Cambridge, Cambridge United Kingdom
12:45 PM - DD1.10
Metal-nano-antenna-enhanced Luminescence of Solid-state Light Emitters.
Hans Mertens 1 , Julie Biteen 2 , Harry Atwater 2 , Albert Polman 1 Show Abstract
1 Center for Nanophotonics, FOM-Institute AMOLF, Amsterdam Netherlands, 2 , California Institute of Technology, Pasadena, California, United States
DD2: Phosphors and Oxides
Tuesday PM, April 18, 2006
Room 2016 (Moscone West)
2:30 PM - DD2.1
Novel SiAlON-based Oxynitride Phosphors and their Applications in White Light-emitting Diodes.
Rong-Jun Xie 1 , Naoto Hirosaki 1 , Mamoru Mitomo 1 , Ken Sakuma 2 Show Abstract
1 , National Institute for Materials Science, Tsukuba Japan, 2 , Fujikura Ltd, Sakura Japan
In the last few years, white light-emitting diodes (LEDs) have been the subject of increasing interest due to their potential applications in indicators, backlights, automobile headlights, and general illumination. In the case of the phosphor-converted LED (pc-LED), rare-earth doped oxynitride/nitride phosphors have been attracted great attention as down-conversion materials because they have excellent luminescence efficiency, high thermal and chemical stability, as well as they are environmental friendly materials.In this work we will report on several SiAlON-based oxynitride phosphors that are suitable for use as wavelength-conversion materials in white light-emitting diodes. These materials were prepared from silicon nitride, aluminum nitride, alumina, alkaline carbonates, and rare-earth metal oxides, then synthesized by firing at 1600-1900oC for 2-12h under 0.5-1.0 MPa N2. The photoluminescence spectra and diffuse reflectance spectrum were measured at room temperature. The temperature dependence of the luminescence efficiency was investigated in the range of 25-300oC. The results show that intense blue, green, yellow and red emissions are observed in these oxynitride phosphors under the near ultraviolet or blue light irradiation. The oxynitride samples exhibit high stability of luminescence against temperature. We have attempted to use these phosphors to manufacture white LED lamps using a blue LED as a primary light source. A wide range of white light with high efficiency can be achieved using oxynitride phosphors.
2:45 PM - DD2.2
Sulfide Phosphors for LED White Light Sources.
Weiyi Jia 1 , Dongdong Jia 2 , Anura Goonewardene 2 , Xiaomei Guo 3 , Yingyin Zou 3 , Kewen Li 3 Show Abstract
1 Physics, University of Puerto Rico, Mayaguez, Puerto Rico, United States, 2 Department of Physics and Geology, National Tsing Hua University, Lock haven, Pennsylvania, United States, 3 , Boston Applied Technology,Inc., Woburn, Massachusetts, United States
In LED-phosphor white light devices, Y3Al5O12:Ce3+ is currently widely used. In this paper we present our investigation on using sulfides, such as CaS:Ce3+,Na+ and CaS:Eu2+ to convert blue LED emission to yellow and red emission bands. The sulfides were synthesized through solid-state chemical reaction with the starting materials CaS, Ce2(CO3)3.5H2O, Na2S and Eu2O3. NH4Cl was used as a sintering flux and Na was used for charge compensation to improve luminescent efficiency. CaS:Ce,Na showed strong emission bands at 505 and 565 nm, while CaS:Eu gave a red emission band at 650 nm. Both sulfides can be efficiently excited at 460 nm. It is expected that a proper mixing ratio of these two sulfides will provide a flat emission spectrum from 480 nm to 660 nm, and the corresponding LED-phosphor devices may have a higher color rendering index. Co-doped calcium sulfide, CaS:Ce,Eu, was also studied. It was found that very efficient energy transfer occurred from Ce3+ to Eu2+. As a result, no emission from Ce3+ was observed in the samples even with a very low concentration of Eu2+ (Eu/Ce<0.10). Nevertheless, the luminescent efficiency in the co-doped samples was found increased effectively. Therefore, CaS:Ce3+,Eu2+ is a good phosphor to be used as a red component for LED light sources.In addition, the ZnS system was also investigated. ZnS:Ce,Li showed emission bands at 510 nm and 560 nm, similar to those of CaS:Ce,Na. Unfortunately, its first absorption band was located at 410 nm, and therefore cannot be used in current regime of LED devices. ZnS:Te,Mn was found to have strong emission band at 640 nm, and ZnS:Se,Mn shows strong emission band at 570 nm and 638 nm. The emission wavelength of the sulfides could be tailored slightly by adjusting the relative concentrations of Te (or Se) and Mn. Both sulfides could be excited at 460 nm with reasonable pump efficiency.Work is supported in part by US Department of Energy under Grant No. DE-FG02-05ER84314.
3:00 PM - DD2.3
Synthesis, Structure and Luminescent Properties of Selenogallate phosphors
Amitava Choudhury 1 , Peter Dorhout 1 Show Abstract
1 Department Of Chemistry, Colorado State University, Fort Collins, Colorado, United States
The ternary thiogallate compounds represented by the formula MGa2S4 (M= Ca, Sr, Ba) can be doped with various rare-earth ions thus producing an important class of phosphors for many luminescence applications . Rare earth ions readily substitute the alkaline earth in the host lattice, thus resulting in phosphors that fluoresce strongly under ultraviolet and cathode rays. For example Eu2+ and Ce3+ doped MGa2S4 provide green and blue emissions for the thin film electroluminescent materials (EL) . The MGa2S4 (M=Ca, Sr, Eu) phases crystallize in the orthorhombic system with space group Fddd or in the cubic system in the Pa3 space group (M=Ba). The alkaline earth metal can also be replaced by trivalent lanthanide ions with alkali metals as charge compensators giving rise to the composition NaxLnx(M1-2x)Ga2S4, (Ln = lanthanides). In the limit composition of x= 0.5 a stoichiometric quaternary sulfide of the composition NaLnGa4S8 (Ln= Ce, Nd) can be obtained where alkaline earth has been entirely substituted by the +3 rare-earth and alkali metals. However, till date there are almost no reports of the Se analogue of these compounds, i.e the selenogallates except for a brief report on CaGa2Se4:Eu . In this regard, we have successfully synthesized the limit composition of NaLnGa4Se8 [Ln=Nd, Ce] employing solid state reaction routes, where synthesis is carried out in sealed quartz ampoules in presence of alkali selenide reactive flux. The structures have been solved employing single crystal X-ray diffraction data. Both these compounds crystallize in the orthorhombic system with Fddd space group similar to their sulfide analogues. These compounds are quite stable similar to their S-analogues. Since the luminescence property depends on the ligand field strength and the extent of covalency in the bonding, the replacement of S by Se may enhance the luminescence property of these materials. The measurement of the luminescent property of these compounds is in progress.References: T. E. Peters and J. A. Baglio, J. Electrochem. Soc.,1972, 119, 230; T. E. Peters, ibid, 1972, 119, 1720; R. Ibanez, P. Garavereau, A. Garcia, C. Fouassier, J. Solid State Chem., 1988, 73, 252. P. Benalloul, C. Barthou, J. Benoit, L. Eichenauer and A. Zeinert, Appl. Phys. Lett., 1993, 63, 1954; I. Ronot-Limousin, A. Garcia, C. Fouassier, C. Barthou, P. Benalloul, J. Benoit, J. Electrochem. Soc., 1997, 144, 687. P. C. Donahue and J. E. Hanlon, J. Electrochem. Soc., 1974, 121, 230.
3:15 PM - DD2.4
Effect of Rapid Thermal Annealing on the Correlation of Strain and Optical Properties of Self-assembled InAs Quantum Dots.
Hsing-Yeh Wang 1 , H. Niu 2 , C.H Chen 3 , S.C. Wu 3 , C.P. Lee 1 Show Abstract
1 Electronics Engineering, National Chiao Tung University, Hsinchu Taiwan, 2 Nuclear Science and Technology Development Center, National Tsing Hua University, Hsinchu Taiwan, 3 Physics, National Tsing Hua University, Hsinchu Taiwan
4:00 PM - DD2.5
Pulsed Laser Deposited YAG:Ce and Ba3MgSi2O4:Eu,Mn Thin Films for Phosphor Converted White Light Emitting Diodes.
M Kottiasamy 2 , P Thiyagarajan 1 2 , Mamidanna Ramachandra Rao 1 2 Show Abstract
2 Materials Science Research Centre, Indian Institute of Technology Madras, Chennai, Tamilnadu, India, 1 Department of Physics, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India
4:15 PM - DD2.6
UV and VUV Luminescence Properties of Eu2+ in Ba2MSi2O7 (M=Mg, Zn).
ZhiYa Zhang 1 , YH Wang 1 Show Abstract
1 Department of Materials Science, Department of Materials Science, School of Physical Science and Technology, Lanzhou University, Lanzhou China
4:30 PM - DD2.7
Pulsed Laser Deposited ZnGa2O4:Mn and Zn2SiO4:Mn Phosphor Thin Films for Display Applications.
P Thiyagarajan 1 2 , M Kottiasamy 2 , Mamidanna Ramachandra Rao 1 2 Show Abstract
1 Department of Physics, Indian Institute of Technology Madras, Chennai, Tamil Nadu, India, 2 Materials Science Research Centre, Indian Instituteof Technology Madras, Chennai, Tamilnadu, India
4:45 PM - DD2.8
Pb2+ and Ce3+ Doped SrZnO2: New Blue Luminescent Phosphors
Alp Manavbasi 1 , Jeffrey LaCombe 1 Show Abstract
1 Materials Engineering, University of Nevada Reno, Reno, Nevada, United States
Two new blue emitting phosphors, SrZnO2:Pb2+ and Ce3+ were synthesized by adipic acid and sucrose templated sol-gel routes, respectively. The resulting phosphor particles were fine, nanocrystalline and pure. The photoluminescence (PL) excitation and emission characteristics of phosphors with different concentrations of Pb2+ and Ce3+ ions doped into the host lattice are reported. The optimum activator concentrations for the highest emission intensities were found to be 1 mol% Pb2+ and 12 mol% Ce3+. Two excitation bands centered at 283 and 317 nm were observed for Pb2+ doped samples, however only one broad excitation band with a maximum at 294 nm was observed for Ce3+ doped samples. The emission spectra of SrZnO2:Pb2+ showed a very broad band extending from 374 to 615 nm with a maximum at 455 nm which was ascribed to the 3P1 → 1S0 transition on the Pb2+ ions allowed by the strong spin-orbit (SO) coupling. Similarly, SrZnO2:Ce3+ showed a broad emission band extending from 374 to 609 nm and centered at 467 nm. This broad emission was attributed to the 5d1 → 4f1 transition of Ce3+ ions. The lower level 2F5/2 of the 4f1 is populated but the level 2F7/2 is almost empty at room temperature where all measurements were taken. The photoluminescence properties and crystallinity of these phosphors were also studied with varying calcination temperatures between 800 and 1200 °C for 2 h. SrZnO2 phase was observed to start to form at 900 °C (after 2 hrs), with single phase SrZnO2 obtained at calcination temperatures starting at 1000 °C. Observations of the phosphors by scanning electron microscopy have shown that both phosphors have a rounded and filled morphology for individual particles with an approximate diameter of 50-250 nm in diameter. These individual particles agglomerated to form larger-sized micron scale particles. Additional work is continuing, and will be reported on.
5:00 PM - DD2.9
Role of Threading Dislocations on Domain-epitaxially Grown ZnO Films Using XRD and TEM.
Wei-Rein Liu 1 2 , Chiang-Hung Hsu 1 2 , F. S.-S Chien 3 , Keng.S Liang 2 , Wen-Feng Hsieh 1 Show Abstract
1 Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu Taiwan, 2 , National Synchrotron Radiation Research Center, Hsinchu Taiwan, 3 Department of Physics, Tunghai University, Taichung Taiwan
5:15 PM - DD2.10
Correlated Scanning Capacitance and Conductive Atomic Force Microscopy Studies of Dislocations in ZnO film.
Shih-Yang Huang 1 , Wei-Rein Liu 2 4 , F.S.-S Chien 3 , Chiang-Hung Hsu 2 4 , Keng.S Liang 4 , Wen-Feng Hsieh 2 , Tzeng-Feng Liu 1 Show Abstract
1 Institute of Nanotechnology, National Chiao Tung University, Hsinchu Taiwan, 2 Department of Photonics and institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu Taiwan, 4 , National Synchrotron Radiation Research Center, Hsinchu Taiwan, 3 Department of Physics, Tunghai University, Taichung Taiwan
5:30 PM - DD2.11
Cathodoluminescence and Optical Modeling of AlGaN Nano-crystals for Biofluorescence Applications.
Steven LeBoeuf 1 , Radislav Potyrailo 1 , Todd Tolliver 1 , Alexei Vertiatchikh 1 , Sheila Tandon 1 , Joleyn Balch 1 , Rui Chen 1 , Fatima Shahedipour-Sandvik 2 , James Grandusky 2 , Vibhu Jindal 2 Show Abstract
1 , GE Global Research, Niskayuna, New York, United States, 2 College of Nanoscale Science and Engineering, UAlbany-SUNY, Albany, New York, United States
DD3: Poster Session: OLEDs, Quantum Dots, Phosphors and Oxides
Wednesday AM, April 19, 2006
Salons 8-15 (Marriott)
9:00 PM - DD3.1
UV and VUV Spectroscopy of ns2-type Ions Co-doped YBO3:Eu3+ Red Phosphor.
L.L. Wang 1 , Y.H. Wang 1 , W.X. Hua 2 Show Abstract
1 , Department of Material Science, School of Physical Science and Technology, Lanzhou University, Lanzhou China, 2 , Continuing Education School, Lanzhou University, Lanzhou China
The photoluminescence of trivalent europium ion doped yttrium borate are of most interest. Especially, (Y,Gd)BO3:Eu3+ is widely utilized as red phosphor in plasma display panels(PDPs) and Hg-free lamps. However, the efficiency of this phosphor under 147nm excitation is not satisfied. In this presentation, YBO3:5% Eu3+ with the incorporation of some ns2-type ions were synthesized by solid-state reaction and their luminescence properties under ultraviolet (UV) and vacuum ultraviolet (VUV) region were investigated. The results indicated that in the excitation spectrum of YBO3:5%Eu3+, the strong charge transfer (CT) band of Eu3+ was located in the UV region and the absorption band of the host lattice lay in the VUV region. When the ns2-type ions, such as Sn2+ and Sb3+(n=5), and Tl+, Pb2+ and Bi3+(n=6) were co-doped into the host lattice of YBO3:5%Eu3+, the CTS band of Eu3+ was improved and shifted, and the intensity of the absorption band of the host lattice was also improved. And the resulting luminescence of Eu3+ was significantly enhanced compared with that of YBO3:5%Eu3+. These luminescent phenomena were analyzed in detail and possible reasons were given.
9:00 PM - DD3.2
Photoluminescence Enhancement of PEG-modified YAG:Ce3+ Nanophosphor Prepared by Glycothermal Method.
Ryo Kasuya 1 , Tetsuhiko Isobe 1 , Hitoshi Kuma 2 , Junichi Katano 2 Show Abstract
1 Department of Applied Chemistry, Keio univ., Yokohama, Kanagawa, Japan, 2 , Idemitsu Kosan Co., Ltd., Sodegaura, Chiba, Japan
9:00 PM - DD3.3
Optical Properties of Alkali Doped Group 4 Nano Materials.
Hal Gokturk 1 Show Abstract
1 , PEWLA, Mountain View, California, United States
Sodium is well known for its efficient optical transitions in the visible and it is utilized extensively in lighting applications. However the sodium used in lamps must be vaporized and excited by means of a plasma in order to emit light. In this research, optical properties of sodium and other alkali metals (lithium & potassium) incorporated into nano hosts of group 4 elements (carbon, silicon & germanium) were investigated as candidates for solid state light emitting materials. First, optical properties of of alkali dopants with Group 4 nano hosts were calculated by quantum mechanical simulations. The simulation model of the nano host was chosen as the smallest stable cage structure of the diamond type crystal (adamantane). Surface of the nano host was passivated with hydrogen atoms. Alkali dopants were incorporated onto the surface of the nano host, replacing one or more of the hydrogen atoms. Optical properties were calculated by TDDFT method of Gaussian 03 software. Results of the simulations indicated that alkali doped Group 4 nano hosts exhibited optical transitions in and around the visible range whereas, undoped nano hosts did not have any at similar wavelengths. Some combinations of alkali dopant and nano host (for example Na and Si nano host) gave rise to multiple transitions in the visible. Li and K, which do not have visible lines in gaseous form, began to exhibit visible transitions when combined with Group 4 nano hosts such as Ge. Next, one of the above combinations, Li dopant and carbon nano host was chosen to be synthesized in the exact molecular structure which was simulated. Chloro adamantane (C10H15Cl) was used as the starting material and Li was introduced to the nano host by a replacement reaction of Cl with Li, to obtain Li adamantane (C10H15Li). Optical absorption and emission characteristics of the synthesized material was measured and compared with those obtained from quantum mechanical calculations. It was found that both the wavelength and the relative intensity of the measured optical transitions were in good agreement with the results of the calculations. Overall one can conclude that alkali metals which have good light emission characteristics can be combined with Group 4 indirect semiconductors to obtain new nano materials which have interesting optical properties in the visible range.
9:00 PM - DD3.4
Improving Performance of Organic Light-emitting Devices Based on Flexible Substrates
Guangfeng Wang 1 , Xiaoming TAO 2 , Wei CHEN 3 Show Abstract
1 , The HongKong Polytechinic University, Hong Kong Hong Kong, 2 , The Hong Kong Polytechnic University, Hong Kong Hong Kong, 3 , The Hong Kong Polytechnic University, Hong Kong Hong Kong
Brian K. Crone Los Alamos National Laboratory
Heng Liu eLite Corporation
E. Fred Schubert Rensselaer Polytechnic Institute
Fatemeh Shahedipour-Sandvik State University of New York-Albany
Yan-Kuin Su National Cheng Kung University
DD4: Light Emitting Diodes for Solid State Lighting I
Wednesday AM, April 19, 2006
Room 2016 (Moscone West)
9:00 AM - **DD4.1
Nanoheteroepitaxy for Efficient GaN LEDs on Silicon?
Steve Hersee 1 3 , Sang Han 2 3 , Xinyu Sun 1 3 , Xin Wang 1 3 , Mohammad Ferdous 1 3 , Qiming Li 2 3 Show Abstract
1 Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico, United States, 3 Center for High Technology Materials, University of New Mexico, Albuquerque, New Mexico, United States, 2 Department of Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, New Mexico, United States
9:30 AM - **DD4.2
Improvements in Light-extraction Efficiency of Light-emitting Diodes.
Jong Kyu Kim 1 , E. Fred Schubert 1 Show Abstract
1 Electrical, Computer and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
This talk discusses possible solutions to limitations in light-extraction efficiency of light-emitting diodes (LEDs) including highly efficient reflectors and optimized packaging configurations for white LED lamps. New types of omni-directional reflectors (ODRs) with lower mirror losses than metal reflectors and distributed Bragg reflectors (DBRs) have been developed and incorporated into AlGaInP LEDs and GaInN LEDs. It is shown that the ODR significantly increases light extraction from the LEDs as compared to reference LEDs employing DBRs or metal reflectors. Other examples of innovative concepts in ODRs to be presented include novel materials with unprecedented low refractive index, and partially diffuse reflectors. SiO2 nanorod-array films with very low refractive indices and their optical properties for reflectors will be discussed as well as an improvement of light extraction in LEDs employing diffuse ODRs. With the rapid development of phosphor-based high-power white LEDs, advances in packaging are required to further improve the light-extraction efficiency of white LED lamps. An optimized packaging configuration is presented along with experimental results and ray-tracing simulations. Enhancement of phosphorescence efficiency is obtained experimentally by employing diffuse reflector cups and a remote-phosphor configuration, which is consistent with ray tracing simulations. This improvement is attributed to reduced absorption of the phosphorescence by the LED chip and the reduction of deterministic optical modes trapped inside the encapsulant.
10:00 AM - DD4.3
Continuous Wave Lasing from Ground State of InAs Quantum Dots with GaInNAs Capping Layer Grown by MOCVD.
Rei Hashimoto 1 2 , Mitsuhiro Kushibe 1 2 , Mizunori Ezaki 1 2 , Genichi Hatakoshi 1 2 , Masao Nishioka 2 3 , Yasuhiko Arakawa 2 3 4 Show Abstract
1 EDL, Toshiba RDC, Tokyo Japan, 2 , Nanoelectronics Collaborative Research Center, Tokyo Japan, 3 IIS, University of Tokyo, Tokyo Japan, 4 RCAST, University of Tokyo, Tokyo Japan
10:15 AM - DD4.4
MOCVD Growth of Ordered GaN Nanopillar Arrays Without the use of Additional Catalysts
Xinyu Sun 1 , Xin Wang 1 , Mike Fairchild 1 , Stephen Hersee 1 Show Abstract
1 Center for High Technology Materials, University of New Mexico, Albuquerque, New Mexico, United States
10:45 AM - DD4.6
Epitaxial GaN Layer Growth Using Nitrogen Enriched TiN Buffer Layers.
Kazuhiro Ito 1 , Yu Uchida 1 , Susumu Tsukimoto 1 , Yuhei Ikemoto 2 , Koji Hirata 2 , Naoki Shibata 2 , Masanori Murakami 1 Show Abstract
1 Department of Materials Science and Engineering, Kyoto University, Kyoto Japan, 2 Optoelectronics Division, Toyoda Gosei Co. Ltd., Nakashima, Aichi Japan
11:30 AM - **DD4.7
High Power LEDs.
Robert Karlicek 1 Show Abstract
1 , Luminus Devices, Inc., Woburn, Massachusetts, United States
12:00 PM - DD4.8
AlGaN UV LEDs Emitting at 340 nm Grown on AlN Bulk Substrates.
Yangang Xi 1 2 , Thomas Gessmann 1 3 , Kaixuan Chen 1 2 , Xiaolu Li 1 2 , Jong Kyu Kim 1 3 , E. Fred Schubert 1 2 3 , Wayne Liu 4 , Joseph Smart 4 , Leo Schowalter 4 Show Abstract
1 Future Chips Constellation, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 4 , Crystal IS, Inc., Green Island, New York, United States
12:15 PM - DD4.9
Local Indium Segregation and Band Gap Variations in High Efficiency Green Light Emitting InGaN/GaN Diodes.
Joerg Jinschek 1 2 , Rolf Erni 3 4 , Christian Kisielowski 1 Show Abstract
1 National Center for Electron Microscopy (NCEM), Lawrence Berkeley National Laboratory (LBNL), Berkeley, California, United States, 2 Institute for Critical Technology and Applied Science (ICTAS) / Department of Materials Science and Engineering, Virginia Polytechnic Institute and State University (Virginia Tech), Blacksburg, Virginia, United States, 3 Department of Chemical Engineering and Materials Science, University of California Davis, Davis, California, United States, 4 Now at, FEI Electron Optics, Eindhoven Netherlands
GaN/InGaN light emitting diodes (LEDs) are commercialized for lighting applications because of the cost efficient way that they produce light of high brightness. Nevertheless, there is significant room for improving their external emission efficiency. The electronically active region consists of stacked, few nm wide InxGa1-xN (x ~ 0.2) quantum wells that are sandwiched between p- and n-doped GaN. The photon emission energy and external device efficiency depend on the device architecture, the fraction x of indium atoms substituting gallium sites in the quantum wells, the quantum well width, and the homogeneity of the indium distribution in the well. Parameters such as well width, device architecture, or the average indium content can be optimized relatively well to enhance the efficiency for a particular emission wavelength. The homogeneity of the indium distribution, on the other hand, is widely debated and it was argued that the miscibility gap limits the indium solubility in GaN leading to local segregation and the formation of “dot-like” structures within the quantum wells. In fact, it is uncertain how device efficiencies are affected by a particular indium distribution. This uncertainty arises from the limited experimental ability to map the indium concentration at atomic resolution and to link this information to the electronic structure in devices. Advanced transmission electron microscopy (HRTEM, annular dark field (ADF)-TEM, Z-contrast imaging) was used to characterize the indium segregation in commercially available high-efficient green-light LED devices. By additional direct measurements of the variations in the electronic structure by low-loss electron energy-loss spectroscopy (VEELS) in a monochromated S/TEM (dE < 200meV), it is shown for the first time a correlation between indium-rich nanoclusters and local energy band gap minima inside the quantum wells. Our investigations reveal the presence of 1-3 nm wide indium rich clusters with indium concentrations x as large as x ~ 0.30-0.40 that narrow the band gap locally to energies as small as 2.65 eV . These clusters are able to act as local traps for migrating photon-emitting carriers and seem to boost the overall device performance. Concerns are debated about the use of electron microscopy to investigate the non-equilibrium state of the InGaN system since the exposure of specimen to high-energy electron beams may enhance phase separation. The electron beam induced damage can be controlled. Even 800 keV electrons do not cause measurable damage during an illumination time of up to 2 minutes. . Jinschek, J. R. et al., Local indium segregation and band gap variations in high efficiency green light emitting InGaN/GaN diodes, Solid State Communications, in press Jinschek, J. R., Kisiewloski, C., Time, Energy, and Spatially Resolved TEM Investigations of Defects in InGaN, Physica B: Condensed Matter, in press
12:30 PM - **DD4.10
Ultrafast Carrier Transport and Recombination in III-N Heterostructures
Alexander Cartwright 1 , Fei Chen 1 , Maurice Cheung 1 , Madalina Furis 1 , Sung-Jin Kim 1 Show Abstract
1 Department of Electrical Engineering, University at Buffalo, The State University of New York, Buffalo, New York, United States
DD5: Light Emitting Diodes for Solid State Lighting II
Wednesday PM, April 19, 2006
Room 2016 (Moscone West)
3:00 PM - DD5.2
Effect of HVPE GaN Substrate Condition on the Characteristics and Performance of 405nm LEDs.
James Grandusky 1 , Muhammad Jamil 1 , Vibhu Jindal 1 , Fatemeh Shahedipour-Sandvik 1 , Hai Lu 2 , Xian-An Cao 2 , Edmund Kaminsky 2 Show Abstract
1 College of Nanoscale Science and Engineering, University at Albany, Albany, New York, United States, 2 , GE Global Research Center, Niskayuna, New York, United States
3:15 PM - DD5.3
Selective Area Heteroepitaxy of Nano-AlGaN UV Excitation Sources for Biofluorescence Application.
Fatemeh Shahedipour-Sandvik 1 , Vibhu Jindal 1 , James Grandusky 1 , Steven LeBoeuf 2 , Joleyn Balch 2 , Todd Tolliver 2 Show Abstract
1 , UAlbany-State Univ. of New York, Albany, New York, United States, 2 , General Electric Global Research Center, Niskayuna, New York, United States
We report on the selective area heteroepitaxy (SAE) and facet evolution of sub-micron AlGaN islands on GaN/sapphire, AlN/Sapphire and bare sapphire substrates using various mask materials. We also report on the challenges associated with selection of an appropriate mask material, and template/substrate material for SAE of AlGaN with varying Al composition. It is shown that strain due to the lattice mismatch between AlGaN and the underlying substrate has a significant influence on the final morphology and faceting of sub-micron islands. In our present studies we have observed that the composition of Al in nano-AlGaN islands is different significantly from that grown on a thin film as measured by high resolution x-ray diffraction. Under identical metalorganic chemical vapor deposition (MOCVD) growth parameters, island growth with low mismatch strain exhibit trapezoidal to pyramidal morphologies, while highly strained islands evolve into prismatic shapes. The shape and the growth rate of the nano-islands are seen to be greatly affected by the mask material itself. This is hypothesized to be due to the variation in the affinity of various mask materials for the incoming precursors. Results of our Cathodoluminescence (CL) clearly show presence of a peak due possibly to the nano structures. Various characterization techniques are used to evaluate the morphology evolution and composition of the nano-structures.
3:30 PM - DD5.4
Investigation of Piezoelectric Field Effects on Emission Spectra of GaN QDs Grown on AlN.
Nanying Yang 1 , Dimitris Korakakis 1 Show Abstract
1 , West Virginia Univ., Morgantown, West Virginia, United States
Wednesday, 4/19Transferred from DD6.6 (poster) to DD5.4 (oral)2:30 pm DD5.4Investigation of Piezoelectric Field Effects on Emission Spectra of GaN QDs Grown on AlN. Nanying Yang
3:45 PM - DD5.5
Infrared Reflectance of Optic Phonon Modes in AlGaN Epitaxial Layers Grown on Sapphire Substrates.
Gensheng Huang 1 , H. H. Yao 1 , Y. T. Wang 1 , T. C. Lu 1 , H. C. Kuo 1 , S. C. Wang 1 , L. -H. Peng 1 Show Abstract
1 , Department of Photonics & Institute of Electro-Optical Engineering, , Hsinchu, Taiwan
AlGaN and AlGaN/GaN heterostructures are widely in the production of high-temperature\high-power\high-frequency electronic and optoelectronic devices, e.g. heterostructure field-effect transistors (HFETs) and UV light-emitting diodes (LEDs) and laser diodes (LDs). The series of high quality alloy layers was grown on (0001)-oriented sapphire substrates using metalorganic chemical vapor deposition. Fourier transform infrared (FTIR) was employed to study AlxGa1-xN alloy layers across the full composition range. From FTIR reflectance measurements, we determine the composition dependence of phonons having A1 (TO), E1 (TO), A1 (LO), and E1 (LO) symmetry. The silent B1 mode also was observable during to partial or complete relaxation of selection rule in our case. Two-mode alloy behavior is observed for A1 (LO) longitudinal optic and each mode has AlN-like and GaN-like branches. GaN like A1(TO) and E1(LO) phonons are seen to blueshift with increasing x. The influence of biaxial tensile strain on GaN like A1(TO) and E1 (LO) phonon energies and density of state is discussed. The AlN like E1 (TO) and A1(LO) phonon frequencies exhibit the downward and upward bowings, respectively. The detail discussion will be presented.
4:30 PM - **DD5.6
A Novel Non-Imaging Optic for Multi-Color, Multi-Die, LED Arrays.
Jim Mazzochette 1 , Edward Bailey 1 Show Abstract
1 , Lamina Ceramics, Inc., Westampton, New Jersey, United States
LED arrays are used today to create bright (1000 lumen +) light sources for a variety of applications including, medical, automotive, architectural, and entertainment. This paper describes the design and performance of a new, non-imaging optic that is integrated with the array package and individual LED sources to create a unified optical system. The system can achieve extremely narrow (< 10°) radiation patterns, with tailored cut-off performance, and excellent color mixing from multiple LED sources. Design simulation, constraints, measured performance, and thermal analysis will be given. Multiple designs will be presented and demonstrated along with current work under development.
5:00 PM - DD5.7
Reliability study of GaN-based UV LEDs
Alexei Vertiatchikh 1 , Xian-An Cao 1 , Steven LeBoeuf 1 , Richard Gawrelski 2 , Maxine Gibeau 2 , Thomas Stecher 3 Show Abstract
1 Semiconductor Technology Lab, GE GRC, Niskayuna, New York, United States, 2 RF and Photonics Laboratory, GE GRC, Niskayuna, New York, United States, 3 MicroSystems & MicroFluidics Laboratory, GE GRC, Niskayuna, New York, United States
GaN-based UV light emitting diodes (LEDs) become promising for bio-fluorescence and purification applications as their output optical power density and reliability being improved. Light emission at wavelengths as short as 280nm and 265nm was demonstrated. Reliability of 280nm LEDs was studied. It was found that degradation mechanism is related to the bias voltage and electric field in the device. Defects charging and migration within structure might be responsible for the short lifetime. Reliability and total optical power of pulsed and continuously operated LEDs was evaluated. Modified pulsing technique allowed increasing LEDs lifetime by several times.
5:15 PM - DD5.8
Growth of cubic GaN on Si (100) Substrates.
Suzuka Nishimura 1 , Tomohiko Takeuchi 2 , Sigeya Naritsuka 3 , Kazutaka Terashima 1 Show Abstract
1 , Shonan Institute of Technology, Kanagawa Japan, 2 Electrical Engineering, Keio University, Hiyoshi Yokohama, Kanagawa Japan, 3 , Meijyo University, Nagoya Japan
The cubic type GaN has attracted many researchers attention due to its high carrier mobility and low piezo coefficient for use in high power optical devices. It has been reported to grow GaN on GaAs substrates [1,2], but the lattice mismatch problem made the high concentrated defect in grown crystals. In addition the chemical reaction between GaN and the substrates makes many problems. On the other hand, silicon substrates are the most useful materials with large diameter and high crystal perfection. We have focused to grow cubic GaN on silicon (100) substrates using boronmonophosphide (BP) buffer crystals. We have successfully grown BP crystals by MOVPE technique with electrically n-type and thickness deviation is within several % along 2inch wafer under undoped conditions. The electrical conductivity is less than 0.5mohmcm [3,4]. We have preliminary grown GaN by MBE technique, before we carry out mass producing MOVPE on larger diameter silicon substrates. It has been found the cubic type GaN epitaxial layer has been successfully grown on the substrates by observing X-ray (Diffraction, Phi) evaluation and PL studies. The crystal quality and defect generation will be discussed.
5:30 PM - DD5.9
Integrated Fresnel Microlenses for Deep UV Applications.
Mikhail Gaevski 1 , Shuai Wu 1 , Maxim Shatalov 1 , M.Asif Khan 1 Show Abstract
1 Electrical Engineering, University of South Carolina, Columbia, South Carolina, United States
Deep UV emitting devices based on III nitride materials were shown to be promising light sources for biodetection systems, smart chips, storage devices, lithography tools. To improve performance one has to integrate optical elements into these devices that will focus the beam to small spot increasing lithography resolution and power density for detection or will make beam parallel to avoid cross-talk effect in smart chip microarrays. Polymer optics used for visible and soft UV light can not withstand deep UV irradiation and usually strongly absorbs UV light with wavelength shorter than 300 nm. Deep etching of UV transparent crystalline materials like sapphire or quartz results in lenses with rough surfaces which are not acceptable for short wave length optics. Fresnel phase plate or Fresnel lenses provide low losses and high flexibility for deep UV applications. In this paper we report on integration of Fresnel microlenses into AlGaN based 280 nm light emitting diodes (LED). Lenses were fabricated on the back side of the sapphire substrates from flowable oxide material using direct electron beam writing technique. Eight concentric rings with different width and variable thickness were designed for 360 degree phase correction. Within each ring the thickness varied in four steps to approximate linear profile. The width of each thickness step varied from 100 nm to several microns with a maximum thickness of 560 nm. Outer lens diameter was 65 μm. Optical properties of lenses were studied using UV microscope equipped with deep UV CCD camera from Hamamatsu Photonics. The focal distance of 68 μm was measured. Lenses integrated with 30 μm diameter LED give about 10 μm FWHM of intensity profile at focal plane. Maximum intensity at focal plane exceeds background radiation of about 50 times. Measurements of LED optical power using integrating sphere before and after lens fabrication did not show any power degradation. In fact, power increases slightly due to the improved light extraction from sapphire substrate.Obtained results demonstrate that flowable oxide integrated Fresnel microlenses are suitable to focus deep UV light and therefore can be used for complex UV optical systems.
5:45 PM - DD5.10
Design of High Efficiency Packages for White-light-emitting Diode Lamps.
Hong Luo 1 2 , Jong Kyu Kim 1 3 , E. Fred Schubert 1 2 3 , Jaehee Cho 4 , Cheolsoo Sone 4 , Yongjo Park 4 Show Abstract
1 Future Chips Constellation, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Electrical, Computer, and Systems Engineering Department, Rensselaer Polytechnic Institute, Troy, New York, United States, 4 Photonics Program Team, Samsung Advanced Institute of Technology, Suwon Korea (the Republic of)
DD6: Poster Session: Light Emitting Diodes for Solid State Lighting Posters
Thursday AM, April 20, 2006
Salons 8-15 (Marriott)
9:00 PM - DD6.1
Thermoreflectance Measurements of the Temperature Distributions in Laser Diodes with Non Absorbing Mirror.
Tomasz Ochalski 1 , Dorota Pierscinska 1 , Kamil Pierscinski 1 , Andrzej Malag 2 , Agata Jasik 2 , Anna Kozlowska 2 , Maciej Bugajski 1 Show Abstract
1 , Institute of Electron Technology, Warszawa Poland, 2 , Institute of Electronic Materials Technology, Warszawa Poland
9:00 PM - DD6.2
Luminescent Properties of Mn-Si-O Thin Films Grown by Pulsed Laser Deposition
Takashi Hirate 1 , Kazumoto Takizawa 1 , Tomomasa Satoh 1 Show Abstract
1 , Kanagawa University, Yokohama Japan
9:00 PM - DD6.3
Characterization and Elimination of the Dry Etching-damaged Layer in GaN-based LED.
Sang Jun Lee 1 , Su Gwang Son 1 , Sun Heu Kim 1 , Hyo Jung Kim 1 , Si Hyun Park 2 , June Key Lee 1 Show Abstract
1 School of Material Science and Engineering, Chonnam National University, Gwangju Korea (the Republic of), 2 Department of Photonic Engineering, Chosun University, Gwangju Korea (the Republic of)
9:00 PM - DD6.4
Effect of Dislocations on Contact Potential in Epitaxial ZnO Thin Films Studied by Electricostatic Force Microscopy.
F. S.-S Chien 1 , Wei-Rein Liu 2 4 , C. C. Tsai 2 , Chih-Yuan Li 3 , Chia-Chen Hsu 3 , C.S. Chang 2 , Chia-Huang Hsu 2 4 Show Abstract
1 Department of Physics, Tunghai University, Taichung Taiwan, 2 Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu Taiwan, 4 , National Synchrotron Radiation Research Center, Hsinchu Taiwan, 3 Department of Physics, National Chung-Cheng University, Chiayi Taiwan
9:00 PM - DD6.5
Design of p-type Reflectors for GaInN Flip-chip Light-Emitting Diodes.
Hyunsoo Kim 1 , Jin Seo Im 1 , Kwang Hyeon Baik 1 , Jaehee Cho 1 , Jeong Wook Lee 1 , Sukho Yoon 1 , JooSung Kim 1 , Hyungkun Kim 1 , Yu-Sik Kim 1 , JaeWook Jeong 1 , Cheolsoo Sone 1 , Yongjo Park 1 Show Abstract
1 , Samsung Advanced Institute of Technology, Yongin, Gyeonggi-do Korea (the Republic of)
Recently, GaN-based flip-chip light emitting diodes (FCLEDs) have been extensively investigated for use in high power applications. For high extraction efficiency of FCLEDs, it is important to obtain a good p-type reflector with a high reflectivity as well as a low contact resistance. In this study, we attempted to design efficient p-type reflectors via integrating the highly reflective layer into the Ohmic contact region. For the formation of highly reflective region, a quarter-wave thickness dielectric (SiO2)/ metallic Al layer, namely, omni-directional reflective structure was used. Since the omni-directional reflective region is an electrical insulator, more considerate electrode design was taken into account based on the current distribution and the overall device resistance. Theoretical calculation clearly showed that the effective active area determined from the current spreading length played an important role of optimizing the device resistance. In terms of noble electrical operation, calculated results also showed that the omni-directional reflective region could be successfully formed on the center of mesa beyond the current spreading length from the mesa edge. Experimentally, in this case, the optical output power of LED increased by above 10 % without significant change in the device resistance. This indicates that the proposed design of p-reflectors holds promise for practical application of omni-directional reflectors.
9:00 PM - DD6.6
Effect of Edge Dislocation Defect Reduction in GaN on Silicon Template on Performance of Overgrown Violet Light Emitting Diode.
Fatemeh Shahedipour-Sandvik 1 , Muhammad Jamil 1 , James Grandusky 1 , Vibhu Jindal 1 , Neeraj Tripathi 1 Show Abstract
1 , UAlbany-State Univ. of New York, Albany, New York, United States
Wednesday, 4/19Transferred from DD5.4 (oral) to DD6.6 (poster)Effect of Edge Dislocation Defect Reduction in GaN on Silicon Template on Performance of Overgrown Violet Light Emitting Diode. Fatemeh Shahedipour-Sandvik