ISSUE 10:  SCIENTIFIC LITERATURE (July - Mid-October, 2001)

The material in this section is selected from scientific and technical papers which became available during the reporting time period.   A brief synopsis of each paper is provided along to links to the full text of article abstracts available on the web.

·        Academy Sinica (China):Review of GaN-based materials, growth techn. and device tech.

·        Agilent :GaN-based LEDs with tunnel junctions.

·        Boston U : Current crowding in GaN/InGaN LEDs.

·        Cambridge U : Chemical mapping of InGaN.

·        Chonbuk U (Korea): Influences of AlGaN layer on UV LED structures.

·        CNRS (France): Wurtzite GaN epitaxial layers.

·        CNR S : Green InGaN LEDs on silicon by MVPE.

·        CNRS : Review of III-nitride QW and Q dots by MBE.

·        Dongguk U (Korea): DX center formation on unintentionally doped GaN epilayers on sapphire substrates.

·        Dublin City U : Study of structural and optical failure UB-LEDs under varying stress levels.

·        Hirosaki U (Japan): Application of current-modulated EL spectroscopy to InGaN SQW blue/green LEDs.

·        Ioffe Inst. (Russia): Theoretical analysis of electronic structure of truncated pyramidal GaN/AIN Q-dots.

·        Kyoto U (Japan): Inhomogeneity and emission characteristics of InGaN (blue/UV LEDs).

·        Mitsubishi: High output power InGaN UV LEDs on patterned substrates using MVPE.

·        Moscow State U (Russia): Current and voltage dependence of luminescence spectra and efficiency of GaN-based QW heterostructure LEDs.

·        Nagoya UJapan): Selective area growth of GaN on patterned 111 and 001 Si substrates.

·        Nichia: Review of progress in InGaN-based LEDs and improving external quantum efficiency of nitride LEDs.

·        Nichia : AlInGaN UV laser diodes.

·        Nichia: UV GaN SQW laser diodes.

·        NCSU: Minority-carrier diffusion lengths in GaN LEDs.

·        Northwestern U : Origin of 2.8 eV blue emission in p-type GaN:Mg.

·        Nottingham U (UK): Spectrally resolved electroluminescence microscopy and mu-electroluminescence investigation of GaN-based LEDs.

·        NMRC (Ireland): Failure mechanisms associated with InGaN-based LED fabrication.

·        NTT(Japan): Efficient, high-power AlGaN UV LED grown on bulk GaN.

·        Office of Naval Research: Review of wide bandgap III-nitride semiconductors and opportunities for the future.

·        OSRAM Opto: Influence of strain on growth and electro-optical properties of InGaN on Si HB-LEDs.

·        OSRAM Opto : Industrial production of GaN and InGaN LEDs on SiC substrates.

·        Pohang U(Korea): Interfacial microstructure in GaN nucleation layers investigated.

·        Polish Academy of Sciences : Photoemission studies on GaN (0001) surfaces.

·        Seoul U (Korea): Measurement of piezoelecric field and tunneling times in strongly biased InGaN/GaN quantum wells.

·        Sophia U (Japan): Reducing threading dislocations in migration enhanced epitaxy-grown GaN by use of AIN multiple interlayer.

·        Strathclyde U (UK): Structural analysis of InGaN epilayers.

·        Sunkyunkwan U (Korea): High rate etching of sapphire wafers.

·        Tampere U (Finland): RCLED grown by solid source MBE.

·        Tampere U: Emission studies of InGaN layers and LEDs grown by plasma-assisted MBE.

·        Texas Tech : Gas source MBE of high quality AlGaN on Si

·        U Compl. De Madrid (Spain): Lasing characteristics of low-threshold GaInNAs grown by MCVP.

·        U of Illinois Chonbuk U (Korea): Spatially resolved photoluminescence in InGaN/GaN quantum wells.

·        U of Surrey (UK): Optical transitions and radiative lifetime in GaN/AIN self-organized Q-dots.

·        U of Tsukuba (Japan): Defects in GaN grown by 2-flow MCVD.

·        Xiamen U (China): Nanopipes in undoped AlGaN epilayers.

·        Academy Sinica (China). Exotic family of semiconductor materials-brief introduction to GaN based materials. Sun Dian-Zhao in Wuli [Chinese Physics Journal] ; July 2001; vol.30, no.7, p.413-19. [No online abstract available]
A review is given of GaN-based materials, growth techniques, and device (optoelectronic, high-temperature, and high-power microwave) technologies.

·        Agilent/LumiLeds. “GaN-based light emitting diodes with tunnel junctions.”  T. Takeuchi et al in Japanese Journal of Applied Physics,Part 2 (Letters) ; 15 Aug. 2001; vol.40, no.8B, p.L861-3.  [ Abstract]
GaN-based LEDs have been fabricated using a tunnel junction to enable replacement of high-resistance p-contacts and current spreading p-layers by lower-resistance n-contacts and current spreading n-layers.  The light output of the LEDs is comparable to that of conventional LEDs, but with a higher voltage drop (4.1V rather than 3.5V at an injection current density of 50A/cm2).

·        Boston Univ.  “Current crowding in GaN/InGaN light emitting diodes on insulating substrates.” X. Guo and EF Shubert in Journal of Applied Physics, October 15, 2001, Volume 90, Issue 8 pp. 4191-4195.  [ Abstract]
Current crowding has beenmeasured and modeled for p-side-up mesa-structure GaN-based LEDs with various p-contact and p-layer resistances.  For high-resistance p-type layers and contacts, very little current crowding occurs, and the current distribution is relatively uniform across the LED.  For low-resistance p-type layers and contacts, significant current crowding occurs, and the current distribution is non-uniform across the LED.

·        Cambridge University (UK)/Gent U/Thomas Swan.  “Chemical mapping of InGaN MQWs.”  N. Sharma et al in Journal of Crystal Growth ; Sept. 2001; vol.230, no.3-4, p.438-41.  (Gallium nitride EGW-4: 2000. Fourth European Workshop on Gallium nitride, 2-5 July 2000, Nottingham, UK).  [ Abstract]
Combined structural and chemical imaging using TEM and X-Ray scattering was used to characterize typical defects in InGaN layers capped by GaN.  So-called V-defects containing pure edge dislocations were identified, and found to be composed of pure GaN, without InGaN.

·        Chonbuk University (Korea). “The influences of AlxGa1-xN layer on the characteristics of UV LED structure.” CR Lee et al in Journal Of Crystal Growth V. 226(#2-3) p. 215-222 Jun 2001.  [ Abstract]
Dislocation densities and X-ray linewidths of AlGaN layers grown on GaN were found to increase with Al fraction, due to lattice mismatch and strain.  The optical power of LEDs fabricated using these AlGaN cladding layers was found to decrease with the increasing dislocation density, while electrical characteristics such as turn-on voltage were relatively unaffected.

·        CNRS (France). “The atomic structure and properties of wurtzite GaN epitaxial layers.”P Ruterana et al in Materials Science And Engineering B-SolidState Materials For Advanced Technology v. 82(#1-3) pp. 123-127 MAY 22, 2001.  [ Abstract ]
The microstructures ofline and planar defects in wurtzite GaN epilayers were investigated.  Pure edge threading dislocations exhibited varying atomic (5/7, 4, 8) periodicities along their lengths.  Basal and prismatic stacking faults, and inversion domains, also exhibit a range of atomic configurations, reconstructions, and associated surface morphologies.

·        CNRS (France).  “Green InGaN light-emitting diodes grown on silicon (111) by metalorganic vapor phase epitaxy.” E. Feltin et al in Japanese Journal of Applied Physics, Part 2 (Letters) ; 15 July 2001; vol.40, no.7B, p.L738-40.  [Abstract]
Green (508nm) LEDS were fabricated from InGaN single-quantum-well layers grown by OMVPE on Si (111) substrates.  Optical output powers of 6 microW were achieved a an operating current and voltage of 20mA and 10.7V.

·        CNRS (France).  “Group-III nitride quantum heterostructures grown by molecular beam epitaxy.”  N. Grandjean et al in Journal of Physics: Condensed Matter ; 13 Aug. 2001; vol.13, no.32, p.6945-60.  [ Abstract]
A review is given of ammonia-based MBE-growth of group-III nitride heterostructures, including vertically-tailored quantum wells and laterally-tailored quantum dots.  Special emphasis is given to the use of in situ measurement tools such as RHEED, and to the effects of polarization fields and carrier localization.  The use of InGaN/GaN quantum wells for white light LEDs is also discussed.

·        Dongguk University (Korea) / Kwangwoon Univ.  “The origins of the DX center formation in unintentionally doped GaN epilayers grown on sapphire substrates.” TW Kang et al in Applied Surface Science ; 1 Aug. 2001; vol.180, no.1-2, p.81-6.  [ Abstract]
Temperature-dependent PL measurements were made of the DX center in GaN grown by plasma-assisted MBE.  The barrier heights between the charged and uncharged shallow donor levels and between the shallow and deep donor levels were deduced, and indicate that the DX center originates in oxygen impurities.

·        Dublin City University (Ireland) /Plasma Ireland/Helsinki U. “Examination of the structural and optical failure of ultra-bright LEDs under varying degrees of electrical stress using synchrotron X-ray topography and optical emission spectroscopy.”  D. Lowney et al in Journal of Materials Science: Materials in Electronics ; April-June 2001; vol.12, no.4-6, p.249-53.  [ Abstract
X-ray topography images were made of ultra-bright green (565nm), red (660nm) and IR (890nm) LEDs as they failed due to very high injected currents.  The failure mechanism was local thermal stress near the ball-bonded regions of the devices; this led, in the case of red LEDs, to the development of a polycrystalline microstructure with misoriented sub-grains.

·        Hirosaki University (Japan) / U of Tsukuba/Waseda U/Nichia.  “Current-modulated electroluminescence spectroscopy and its application to InGaN single-quantum-well blue and green light-emitting diodes.” T. Azuhata et al in Applied Physics Letters ; 20 Aug. 2001; vol.79, no.8, p.1100-2.  [Abstract]
Modulatedelectroluminescence spectroscopy was used to study the spectral blue-shift which is observed with increasing current injection in InGaN SQW blue and green LEDs.  The dominant mechanism for the blue-shift is attributed to the filling of tail states.

·        Ioffe Inst. (Russia) / University of Surrey .  “Theoretical analysis of the electronic structure of truncated-pyramidal GaN/AlN quantum dots.” AD Andreev  and EP O'Reilly in PHYSICA E v. 10(#4) pp. 553-560 JUN 2001.  [Abstract
The electronic structure of hexagonal, truncated-pyramidal GaN quantum dots was calculated using a Fourier-transform technique for the 3D strain and built-in electric fields, and using an 8-band k-p plane-wave-expansion method for the electron and hole energy levels and wave functions.  The transition energies were found to depend, via the large built-in piezoelectric and spontaneous polarization fields, sensitively on the pyramid geometry – including the thickness of the wetting layer underneath the quantum dots and the pyramid top diameter.

·        Kyoto University (Japan) / Nichia. “Inhomogeneity and emission characteristics of InGaN.”  Y. Kawakami et al in Journal of Physics: Condensed Matter ; 13 Aug. 2001; vol.13, no.32, p.6993-7010.  [ Abstract]
Time-resolved photoluminescence and photoluminescence excitation spectroscopy were used to study the levels (and transfer of electrons between levels) responsible for light emission in InGaN UV, violet and blue LEDs and laser diodes.
-- In low-In-content LEDs,excitons are weakly localized at low temperature, and free at room temperature.  In high-In-content LEDs, internal strain-induced electric fields modify the excitons considerably, but are insufficient to explain observations such as temperature-dependent spectral shifts, and temperature-independent radiative lifetimes and mobility-edge behavior.
-- In low-In-content LDs, optical gain was found to be due to the lowest delocalized quantum-well level, which is populated within 1ps by photogenerated carriers.  In high-In-content LDs, optical gain was found to be due to localized levels, which are populated within a few ps from the delocalized quantum-well level.

·        Mitsubishi (Japan) / Stanley Electr./Yamaguchi U.   “High output power InGaN ultraviolet light-emitting diodes fabricated on patterned substrates using metalorganic vapor phase epitaxy.”  K. Tadatomo et al in Japanese Journal of Applied Physics, Part 2 (Letters) ; 15 June 2001; vol.40, no.6B, p.L583-5.  [ Abstract]
UV (ultraviolet) LEDs (light-emitting diodes) have been fabricated from LEPS (lateral epitaxy on a patterned substrate) InGaN grown on sapphire by OMVPE.  The LEPS material had a dislocation density of 1.5E8/cm2.  The output power of the 382nm-wavelength LEDs was 15.6mW at 20mA, with an external quantum efficiency of 24%, and was 38mW at 50mA.

·        Moscow State University (Russia) / Moscow Inst. of Steels & Alloys.  “Luminescence spectra and efficiency of GaN-based quantum-wellheterostructure light emitting diodes: current and voltage dependence.” KE Kudryashov et al in Fizika i Tekhnika Poluprovodnikov ; July 2001; vol.35, no.7, p.861-8. (Translation in Semiconductors, July 2001; vol.35, no.7, p.827-34).  [ Abstract]
PL spectra from commercial InGaN/AlGaN/GaN multi-quantum-well LEDs were measured and modeled over a large range of injected currents.  At low voltages and ultralow (< 100 microAmps) currents, emission is due to tunneling across the space-charge region, and is in the 1.92-2.05eV range.  At medium voltages and low (0.05-0.5 mA) currents, emission is due to radiative transitions between localized states and is in the 2.35-2.36eV range.  At high voltages and medium (>1mA) currents, emission is due to radiative transitions between a range of occupied states in the 2D energy band tail, and is in the 2.36-2.52eV range.

·        Nagoya University (Japan). “Selective area growth of GaN microstructures on patterned (111) and (001) Si substrates.”  Y Honda et al in Journal Of Crystal Growth V. 230(#3-4) pp. 346-350 Sept 2001.  [ Abstract]
Selective-area OMVPE was used to grow GaN on SiO2-patterned Si (111) surfaces, both with Si (111) starting substrates, as well as with Si (001) starting substrates which had been groove-etched to form (111) facets.  In both cases the wurtzite crystallography was found, but the details of the microstructure and the PL spectra depended on the details of the growth conditions.

·        Nichia Corp. (Japan).  “Nitride light-emitting diodes.” T. Mukai et al in Journal of Physics: Condensed Matter ; 13 Aug. 2001; vol.13, no.32, p.7089-98.  [ Abstract]
A review is given of InGaN-based LEDs, with special emphasis on the issue of high luminous efficiencies despite the presence of high threading-dislocation densities, believed to be due to spatial fluctuations in In composition.  A discussion is also given of possibilities for further improvement of the efficiencies of nitride-based LEDs.

·        Nichia Corp. (Japan).  “Characteristics of ultraviolet laser diodes composed of quaternary Al_xIn_yGa_(1-x-y)N.”S. Nagahama et al in Japanese Journal of Applied Physics, Part 2 (Letters) ; 1 Aug. 2001; vol.40, no.8A, p.L788-91.  [ Abstract]
UV laser diodes were fabricated from quaternary InGaAlN layers grown by OMVPE on ELO (epitaxially-laterally-overgrown) GaN substrates.  For active layers composed of 3% Al and 3% In (with the remaining 94% Ga) composition, cw room-temperature operation with 3.5kA/cm2 threshold current density and 2mW output power was demonstrated.  For slightly lower (2%) In composition performance was poorer, but a record-short lasing wavelength of 366.4nm was achieved under pulsed operation.

·        Nichia Corp. (Japan). “Ultraviolet GaN single quantum well laser diodes.” S. Nagahama et al in Japanese Journal of Applied Physics, Part 2 (Letters) ; 1 Aug. 2001; vol.40, no.8A, p.L785-7.  [ Abstract]
UV laser diodes were fabricated from binary GaN grown by OMVPE on ELO (epitaxially-laterally-overgrown) GaN substrates.  CW room-temperature operation with 3.5kA/cm2 threshold current density and 2mW output power was demonstrated, at a wavlength of 360.0nm.

·        North Carolina State Univ. “Minority-carrier diffusion length in a GaN-based light-emitting diode.”  JC Gonzalez et al in Applied Physics Letters ; 3 Sept. 2001; vol.79, no.10, p.1567-9. Abstract]
Using electron-beam-induced current (EBIC) techniques and spatially dependent generation/recombination models, minority-carrier currents diffusion lengths were measured in GaN and AlGaN layers.   The minority carrier diffusion length for electrons in p-GaN was 80nm; for holes in n-GaN was 70nm; and for electrons in p-AlGaN was 55nm.

·        Northwestern University.  “On the origin of the 2.8 eV blue emission in p-type GaN:Mg : A time-resolved photoluminescence investigation.” F.Shahedipour, et al. MRS Internet J of Nitride Research 6, 12, August 17, 2001.  [Full text].
Using time-resolved PL, the dynamics of the carrier recombination that gives rise to 2.8eV blue luminescence in bulk p-GaN was measured and modeled.  The dynamics was found to be non-exponential, and was consistent with recombination via deep donors and shallow acceptors.

·        Nottingham University (UK) / CNRS. Spectrally resolved electroluminescence microscopy and mu -electroluminescence investigation of GaN-based LEDs.  R. Xia et al in Journal of Crystal Growth ; Sept. 2001; vol.230, no.3-4, p.467-72.  (Gallium nitride EGW-4: 2000. Fourth European Workshop on Gallium Nitride, 2-5 July 2000, Nottingham, UK).  [Abstract]
Using electroluminescence microscopy and spectroscopy, spectrally resolved EL images were made of GaN LEDs.  The deep-level, defect-related emission in the range 1.95-2.45eV was found to be anticorrelated with the band-edge emission at 3.18eV.

·        NMRC (Ireland). “Failure mechanisms associated with the fabrication of InGaN-based LEDs.”   P.Maaskant et al in IEEE Transactions on Electron Devices ; Aug. 2001; vol.48, no.8, p.1822-5.  (ESSDERC 2000. 30th European Solid-State Device Research Conference, 11-13 Sept. 2000, Cork, Ireland.) [ Pointer to issue table of contents page – IEEE membership required]
Fabrication-related failure modes of LEDs fabricated from InGaN/GaN grown on sapphire have been studied.  One mode leads to non-rectifying behavior; it is suggested that it is caused by metal migration along defect tubes, and that it may be avoided through lower p-contact metal alloying temperatures.  Deposition and removal of sputtered oxides were also found to affect the quality of the p-contact.

·        NTT (Japan).  “Efficient and high-power AlGaN-based ultraviolet light-emitting diode grown on bulk GaN.” Toshio Nishida, et al in Applied Physics Letters -- August 6, 2001 -- Volume 79, Issue 6 pp. 711-712.  [Abstract]
UV LEDs were fabricated from AlGaN grown on thick bulk GaN substrates.  Output powers of 3mW at a wavelength of 352nm and an injected current of 100mA were achieved, with internal quantum efficiencies estimated to be 80% or higher.

·        Office of Naval Research.  “Wide bandgap III-Nitride semiconductors: opportunities for future optoelectronics.”  YS Park in Opto-Electronics Review v. 9(#2) pp. 117-124 Jun 2001.  [ Abstract]
Opportunities for future optoelectronics based on wide-bandgap III-nitride semiconductors are reviewed.  These include the areas of energy efficiency (solid-state lighting), information technology (high-density optical storage), and environmental sensing (UV/visible detectors and sensors).

·        OSRAM Opto Semiconductor (Germany).  “Influence of strain on growth mode and electro-optical properties of high-brightness InGaN-LEDs on SiC.”  J. Baur et al in Journal of Crystal Growth ; Sept. 2001; vol.230, no.3-4, p.507-11.  (Gallium nitride EGW-4: 2000. Fourth European Workshop on Gallium nitride, 2-5 July 2000, Nottingham, UK).  [ Abstract]
High-brightness LEDs were fabricated from InGaN heterostructures grown on various types of buffer layers on SiC substrates.  Highly-strained buffer layers resulted in homogeneous In distributions and lower quantum efficiencies; reduced-strain buffer layers resulted in inhomogeneous dot-like In distributions and higher quantum efficiencies.  Optimally-strained buffer layers resulted in extremely bright 460nm LEDs with output powers of 7mW at  20mA.

·        OSRAM Opto Semiconductor (Germany).  “Industrial production of GaN and InGaN-light emitting diodes on SiC-substrates.”  U. Zehnder et al in Journal of Crystal Growth ; Sept. 2001; vol.230, no.3-4, p.497-502.  (Gallium nitride EGW-4: 2000. Fourth European Workshop on Gallium nitride, 2-5 July 2000, Nottingham, UK).  [Abstract]
A review is given of the fabrication of blue LEDs from GaN and InGaN grown on SiC substrates.  Emphasis is given to the critical steps and methods required for meeting performance (output powers at 20mA, reverse currents, stability, robustness against electrostatic discharge) specifications over the wide operating temperature range (-55 to +85C) and high (85%) humidities necessary for the automotive market.  For example, the accurate control, testing, and optimization of the p-contact process has been partly responsible for the steady increase from 1mW in 1998 to more than 6mW at present of the light output power from 5 mm radial lamps.

·        Pohang University (Korea) / Kwangju Inst. of Sci. & Tech./ CNRS.  “In-plane tensile-strained interfacial structure in a GaN nucleation layer on sapphire(0001)”  CC Kim et al in Journal Of Applied Physics V. 90(#5) p. 2191-2194 Sep 1, 2001.  [ Abstract]
Using synchrotron x-ray scattering and transmission electron microscopy, the microstructure at the interface of GaN layers nucleated on sapphire (0001) has been studied.  The interfacial layers are mostly cubic, composed of a coexistence of (a) aligned tensile-strained domains with an interfacial coincidence-site lattice of six atoms on the GaN side and seven atoms on the sapphire side, and (b) misaligned low-stress domains.  Upon annealing, stacking faults are generated in the aligned domains, which causes a cubic to hexagonal transformation, and a shortening of the correlation length of the coincidence-site lattice.

·        Polish Academy of Sciences / U Hamburg. Photoemission studies on GaN (0001) surfaces.  BJ Kowalski et al in Surface Science ; 20 June 2001; vol.482-485, pt.1, p.740-5.  [ Abstract]
Angle-resolved photoemission spectroscopy with synchrotron radiation was used to determine the electronic valence-band structure of bulk GaN along particular directions in the Brillouin zone.  A comparison is made with recent electronic band structure calculations.

·        Seoul University (Korea). “Measurement of piezoelectric field and tunneling times in strongly biased InGaN/GaN quantum wells.”  YD Jho et al in Applied Physics Letters ; 20 Aug. 2001; vol.79, no.8, p.1130-2.  [ Abstract]
Using spectrally-resolved and time-resolved photoluminescence (PL), the dependence of light emission from InGaN/GaN LEDs on external bias was measured.  As the bias changes, the internal piezoelectric field is modified and/or compensated, and the luminescence properties change.  Blue and red shifts are observed, as well as decreases in recombination times attributed to carrier escape by tunneling through tilted barriers.

·        Sophia University (Japan).  “Reduction of threading dislocations in migration enhanced epitaxy grown GaN with N-polarity by use of AIN multiple interlayer.” K. Iusakabe et al in Journal of Crystal Growth ; Sept. 2001; vol.230, no.3-4, p.387-91.  (Gallium nitride EGW-4: 2000. Fourth European Workshop on Gallium nitride, 2-5 July 2000, Nottingham, UK).  [Abstract]
AlN intermediate layers were found to decrease the dislocation densities of GaN grown by migration-enhanced RF-plasma-assisted MBE on sapphire (0001) substrates.  Edge dislocations were filtered at the AlN/GaN interfaces, and threading dislocations were bent in the GaN above the GaN/AlN interface.  Through the use of multiple AlN intermediate layers, an electron mobility of 668 cm2/Vs was obtained at a carrier density of 9.5E16/cm3 in a Si-doped GaN layer.

·        Strathclyde University (UK) / CLRC Daresbury Lab. / U de Aveiro.  “Structural analysis of InGaN epilayers.” KP O’Donnell et al in Journal of Physics: Condensed Matter ; 13 Aug. 2001; vol.13, no.32, p.6977-91.  [Abstract]
Extended x-ray absorption fine structure (EXAFS) measurements were made of the local nanostructure of InGaN layers with various (15% to 40%) In compositions.  The EXAFS-determined ratios of the numbers of In and Ga atoms in the first metal coordination shell changed with In/Ga ratio, in agreement with x-ray diffraction (XRD) measurements.  However, the EXAFS-determined local structure does not vary significantly with In/Ga ratio.

·        Sunkyunkwan Univ. (Korea) / Strathclyde U / Samsung. “High rate etching of sapphire wafer using Cl₂/BCl₃/Ar inductively coupled plasmas.” Sung YJ et al in Materials Science And Engineering B-Solid State Materials For Advanced Technology, V. 82(#1-3) Pp. 50-52 May 22, 2001.  [ Abstract] Dry etching of sapphire by Cl₂/BCl₃/Ar mixtures in inductively coupled plasmas was studied.  Increasing the BCl₃ composition increased the etch rates and the selectivity over photoresist.  At 50%Cl₂ / 50% BCl3, etch rates of 362.7 nm/min were obtained; with an additional 20% Ar in this mixture, etch rates of 377.5 nm/min were obtained.  The surfaces of lapped wafers also became  smooth (12.95 nm to 1.43 nm) -- even smoother than mechanically polished sapphire (5.38 nm).

·        Tampere Univ of Technology (Finland). “Resonant cavity light-emitting diodes grown by solid source MBE.”  S. Orsila et al in Journal Of Crystal Growth v. 227 pp. 346-351 JUL 2001.  [ Abstract]
650-nm-wavelength-range resonant-cavity LEDs were fabricated from AlInGaP active layers and AlGaAs DBRs grown by MBE on GaAs substrates.  Output powers of 2mW and external quantum efficiencies of 6.5% were obtained.

·        Tampere Univ of Technology (Finland) / U Helsinki.  “Emission studies of InGaN layers and LEDs grown by plasma-assisted MBE.” P. Laukkanen et al in Journal of Crystal Growth ; Sept. 2001; vol.230, no.3-4, p.503-6 (Gallium nitride EGW-4: 2000. Fourth European Workshop on Gallium nitride, 2-5 July 2000, Nottingham, UK).  [ Abstract]
InGaN layers were grown at various temperatures by RF-MBE on GaN/sapphire substrates.  As the growth temperature increases from 600C to 650C the InGaN layers tend to phase separate, the PL spectrum broadens and becomes more intense.  Blue (447nm) LEDs fabricated from these layers had emission linewidths of 37nm and output powers of 20 microWatts at 60mA.

·        Texas Tech Univ/ Ioffe Institute / CINVESTAV.   “Gas source molecular beam epitaxy of high quality Al_xGa _1-xN (0 £ x £ 1) on Si(111).”  S. Nikishin et al in Journal of Vacuum Science & Technology B (Microelectronics and Nanometer Structures) ; July 2001; vol.19, no.4, p.1409-12.  [ Abstract ]
The formation and properties of AlGaN layers grown by gas-source MBE on Si (111) substrates was studied.  The transition to 2D-growth was very rapid at a growth temperature of 1130-1190K, and was essential to subsequent growth of high-quality heterostructures.  In nominally undoped GaN, background electron concentrations and mobilities were 2-3E16/cm3 and 700-900 cm2/Vs; for nominally undoped AlGaN with Al fraction 0.2-0.6, electron concentrations were 2-3E16/cm3.  From cathodoluminescence and optical reflectance spectroscopy, the bandgap dependence on Al composition was found to be Eg(x) = 3.42+1.21x+1.5x2.

·        Univ Complutense de Madrid (Spain). “Study of growth hillocks in GaN : Si films by electron beam induced current imaging.”  MH Zaldivar et al in Journal Of Applied Physics v. 90(#2) pp. 1058-1060 JUL 15, 2001.  [ Abstract]
Remote electron beam induced current (REBIC) measurements have been used to study electrically active regions associated with hillocks in Si-doped GaN films.  The measurements could be interpreted as due to an inhomogeneous distribution of charged point defects and impurities at the hillocks.

·        Univ of Illinois/Chonbuk University (Korea).  “Spatially resolved photoluminescence in InGaN/GaN quantum wells by near-field scanning optical microscopy.”   MS Jeong et al in Applied Physics Letters V. 79(#7) p. 976-978 Aug 13, 2001.  [Abstract]
Using near-field scanning optical microscopy (NSOM), spectrally resolved photoluminescence (PL) images were made of InGaN/GaN quantum well material.  It was found that for “bright” samples, the PL was highly nonuniform laterally, possible due to a nonuniform lateral distribution of nonradiative recombination centers such as dislocations or other defects.  Using transmission electron microscopy (TEM), quantum dots were also observed, which probably enable efficient localization of excitons into regions with fewer dislocations.

·        University of Surrey (UK). “Optical transitions and radiative lifetime in GaN/AlN self-organized quantum dots.”  AD Andreev et al in Applied Physics Letters v. 79(#4) pp. 521-523 JUL 23, 2001.  [ Abstract]
The radiative lifetime of carriers in hexagonal truncated-pyramidal GaN quantum dots was calculated taking into account the quantum-dot energy levels, wave functions, and strain-induced internal electric fields.  The strain-induced electric fields are found to increase the radiative lifetime, which increases strongly with an increase in quantum dot size.

·        University of Tsukuba (Japan) / Shizuoka U. “Study of defects in GaN grown by the two-flow metalorganic chemical vapor deposition technique using monoenergetic positron beams.” A. Uedono et al (including S. Nakamura) in Journal of Applied Physics; July 1, 2001; vol.90, no.1, p.181-6.  [Abstract]
Monoenergetic positron beams were used to study point defects in Mg and Si doped GaN grown by two-flow MOCVD; the results were compared with photoluminescence and transmission spectroscopy measurements.

·        Xiamen University (China) / Tohoku U / Nanjing U / Chinese Acad. Of Sci. /Gakushuin U. ”Nanopipes in undoped AlGaNepilayers.”  JY Kang et al in Journal Of Crystal Growth v. 229(#1) pp. 58-62 July 2001.  [ Abstract]
Scanning electron and atomic force microscopies were used to study the surface morphology associated with nanopipes in undoped AlGaN grown by OMVPE.  Larger nanopipes appear as dodecagonal, and smaller nanopipes appear as hexagonal, pyramidal indentations at the surface.  Energy dispersive x-ray spectroscopy was used to show a higher concentration of Al on the facets of the nanopipes; and cathodoluminescence imaging was used to show luminescence signatures around the indentations.

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The information presented in this section has been developed by Perspectives, a firm that specializes in technical and market intelligence, with assistance from Sandia National Labs.
NOTE:  The provision of summaries and mention of specific manufacturers or products does not constitute an endorsement by Sandia National Laboratories or Perspectives; nor is the information presented warranted or guaranteed by either Sandia National Laboratories or Perspectives.

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Last modified:
09/27/04

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