bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photoluminescence Excitation Study of Lo-Phonon Assisted Excitonic Transitions in Gan
Authors: Hwang S. J. , Cho Y. H. , Song J. J. , Shan W. , Chang Y. C. 
Published: April 2011

AbstractWe report the results of a photoluminescence excitation (PLE) study on excitonic transitions in GaN. PLE measurements were carried out as a function of temperature to investigate exciton formation, thermalization, and annihilation processes in GaN. The PLE spectra detected at free-exciton resonance were found to exhibit a large number of oscillatory emission structures with an energy spacing of LO-phonon (92 meV), and such emission persisted up to 400K. The observation suggests that a phonon-assisted indirect exciton formation process, which simultaneously generates a free-exciton and an LO-phonon, is very significant and efficient in GaN, and the lifetime of the free-exciton is longer than the relaxation time of LO-phonon emission but much shorter than that of acoustic-phonon emission. The appearance of the broad spectral features at the PLE spectrum detected at free-exciton resonance, similar to those measured at the boundexciton resonance, is attributed to the higher order transition processes which involve acousticphonon scattering and thermal repopulation of free-excitons. In addition, we observed up to the 12th LO-phonon emission in PLE spectrum around 120 K, indicating the existence of the excitons with a large kinetic energy in GaN.
Carbon And Hydrogen Induced Yellow Luminescence In Gallium Nitride Grown By Halide Vapor Phase Epitaxy
Authors: Zhang R. , Kuech T. F. 
Published: April 2011

AbstractYellow luminescence (YL) from GaN was systematically investigated through the intentional introduction of carbon, from propane, and excess H2 during growth by the halide vapor phase epitaxy technique. All GaN films were studied by photoluminescence, X-ray diffraction and Hall measurements. The unintentionally doped GaN showed undetectable or very weak YL signal, while both C-doping and H2 addition resulted in a significant enhancement of YL. The blue- and red-shift of the YL band of the C-doped and ‘H2-grown’ GaN with the increasing temperature indicated that different mechanisms existed in these two cases. The temperature dependence of the integrated intensity of the YL band of both groups implicated that shallow donors, not ‘shallow’ acceptors participated the YL transition and that there were more than one radiative recombination channel within the YL band.
Temperature Dependence Of The Fundamental Band Gap In Hexagonal GaN
Authors: Herr H. , Alex V. , Weber J. 
Published: April 2011

AbstractPhotoluminescence spectra of hexagonal GaN were measured in the temperature range T= 2 – 1200 K. We identify the Free Exciton (FX) as the dominant recombination process in our high quality samples for temperatures above 200 K. From the line shape fit of the FX we determine the excitonic band gap shift with temperature. An analysis according to the empirical Varshni equation gives Eg (T)-Eg(0 K) = (-α T2)/(T + β), with α = (7.3 ± 0.3)·10−4 eV/K and β = (594 ± 54) K. We have detected significant differences in the band gap energy at low and higher temperatures for GaN layers grown on different substrate materials. Heating GaN above 1200 K leads to irreversible changes in the near band gap photoluminescence spectra.
Structural And Electronic Properties of GaN/AL Interfaces
Authors: Picozzi S. , Continenza A. , Massidda S. , Freeman A. J. 
Published: April 2011

AbstractThe structural and electronic properties of the GaN/Al interface are determined from first principles local density full potential linearized augmented plane wave (FLAPW) calculations. The charge distribution of the gap states as a function of the distance from the interface shows that the gap states induced into the semiconductor by the presence of Al are strongly localized in the junction region. Furthermore, we find that Al does not provide good ohmic contacts on thecleannitrides considered, in contrast with experimental results on chemically treated GaN, but in agreement with recent measurements on the clean surface[1]. We also study some auxiliary systems (all grown on a GaN substrate), i.e. the Al/AlN interface, the GaN/AlN heterojunction and the GaN/Al with an AlN intralayer (GaN-AlN/Al). The transitivity rule for the GaN/Al, AlN/Al and GaN/AlN interfaces is fairly well satisfied and small differences must be ascribed to differences in the interface morphology. Finally, we find that the AIN intralayer does not significantly affect thep-type Schottky barrier height of the GaN/Al interface.
The Velocity-Field Characteristic Of Indium Nitride
Authors: O'Leary S. K. , Foutz B. E. , Shur M. S. , Eastman L. F. , Bhapkar U. V. 
Published: April 2011

AbstractWe determine the velocity-field characteristic of wurtzite indium nitride using an ensemble Monte Carlo approach. It is found that indium nitride exhibits an extremely high room temperature peak drift velocity, 4.2 × 107 cm/s, at a doping concentration of 1 × 1017 cm−3. This exceeds that of gallium nitride, 2.9 × 107 cm/s, by approximately 40 %. For our nominal parameter selections, the saturation drift velocity of indium nitride is found to be 1.8 × 107 cm/s. The device performance of this material, as characterized by the cut-off frequency, is found to superior to that of gallium nitride, gallium arsenide, and silicon.
AB-Initio Calculations Of Second Order Optical Response Functions In Wurtzite GAN and ALN, And Their Short Period Superlattices
Authors: Rashkeev Sergey N. , Lambrecht Walter R. L. , Segall B. 
Published: April 2011

AbstractSecond harmonic generation coefficients were calculated from first-principles for wurtzite GaN, AlN and the (0001) superlattices (SL) (GaN)n,(AlN)n for n = 2, 4. The effects of the LDA gap underestimate are discussed. The SLs are found to have a strongly reduced static SHG response. The frequency dependent SHG coefficients are found to be sensitive to the SL band structure and to differ significantly form a superposition of the bulk components, indicating a strong intermixing of the bands.
Thermal Expansion Of GaN And Ain
Authors: Wang Kai , Reeber Robert R. 
Published: April 2011

AbstractThe temperature dependence of the thermal expansion and the bulk modulus are critical for predicting the residual stress distribution in epitaxial films and provides information relevant for interatomic potentials and equations of state. The thermal expansions of aluminum nitride (AIN) and gallium nitride (GaN) are calculated with two models that employ the limited elastic and lattice parameter data. These semiempirical models allow prediction of the thermal expansions to higher temperatures. Calculated results are compared with experimental data.
Simulation of Vacancy Pairs in GaN Using Tight-Binding Molecular Dynamics
Authors: Boucher Derrick E. , Gál Zoltán A. , DeLeo Gary G. , Fowler W. Beall 
Published: April 2011

AbstractThe electronic structure, geometry and energetics of Ga vacancy pairs and N vacancy pairs in both wurtzite and zincblende GaN are investigated via molecular dynamics (MD) simulations using an empirical tight-binding (TB) model with total energy capabilities and supercells containing up to 216 atoms. Our calculations suggest that, by pairing, N vacancies, which in isolation act as shallow donors, can lower their collective formation energy by about 5 eV. In doing so, however, these N vacancies lose their shallow-donor character as the lattice relaxes in response to this aggregation. Contrasting with the N vacancies, the Ga vacancies are found to retain their isolated shallow acceptor behavior and do not gain significant energy upon aggregation. The possible implications for larger aggregate defects are discussed.
Hydrogen Passivation Of Er-Doped AIN
Authors: Pearton S. J. , Abernathy C. R. , MacKenzie J. D. , Hömmerich U. , Zavada J. M. , Rent F. , Wilson R. G. , Schwartz R. N. 
Published: April 2011

AbstractAIN(Er) doped with Er during Metal Organic Molecular Beam Epitaxy has been plasma hydrogenated in-situ at 200–250°C using an Electron Cyclotron Resonance source. By isotopic substitution of 2H for 1H, we have found from Secondary Ion Mass Spectrometry profiling that a 30 min hydrogenation treatment can incorporate ˜2×1019cm−3 deuterium atoms to depths ≥1μm. The intensity of the 1.54μm Er3+ luminescence is increased by a factor of ˜5 by the 200°C hydrogenation, and this effect is thermally stable to 300°C, indicating a binding energy of >1.5eV for hydrogen at defects in the AIN. These defects would normally either be recombination centers or provide an alternative de-excitation path for the Er. We have previously found that AIN provides the best resistance to thermal quenching of Er luminescence of any semiconductor due to its wide bandgap. Together, these results suggest that AIN(Er) may be a promising material for optical control of devices such as light-triggered SiC or GaN thyristors for power switching applications, where a fiber-transmitted signal from temperaturetolerant material is necessary in controlling power distribution grids. Hydrogen does not leave the AIN until ˜800°C and presumably forms an intermediate state such as H2 or larger clusters prior to evolution from the surface, and again this stability is among the best for any semiconductor.
Residual Oxygen Determination In Silicon Epilayer, Comparison With Ftir Measurements
Authors: Degas F. , Blondiaux G. , Pichaud B. 
Published: April 2011

AbstractFor power devices the use of silicon epilayer on CZ substrate is a solution to make devices with a low oxygen concentration in the active zone. Oxygen is probably one of the most important residual impurities in silicon samples. Usualy the determination of the interstitial oxygen is done by Fourier Transform Infra Red spectroscopy (FTIR). In this work we have determined oxygen by Charged Particle Activation Analysis (CPAA). The main difference between these two techniques is that CPAA gives the total oxygen concentration whereas FTIR gives interstitial oxygen.We have determined the oxygen in 200μm thick silicon epilayer and studied its behavior during thermal treatments. Oxygen concentration is found in the range of 1015/cm3 just after the epitaxial process. After thermal treatment the concentration in the epilayer rose to several 1016/cm3 to 1017/cm3, depending on the treatment. A comparison with FTIR experiment is done and the amount of oxygen precipitate is determined.
In-Situ Monitoring Of Etch By-Products During Reactive Ion Beam Etching Of Gaas In Chlorine/Argon
Authors: Lee J. W. , Pearton S. J. , Abernathy C. R. , Vawter G. A. , Shul R. J. , Bridges M. M. , Willison C. G. 
Published: April 2011

AbstractMass spectrometry of the plasma effluent during Reactive Ion Beam Etching (RIBE) of GaAs using an Inductively Coupled Plasma (ICP) source and a Cl2/Ar gas chemistry shows that AsCl3, AsCl2 and AsCl are all detected as etch products for As, while GaCl2 is the main signal detected for the Ga products. The variation in selective ion currents for the various etch products has been examined as a function of chuck temperature (30–100°C), percentage Cl2 in the gas flow, beam current (60–180 mA) and beam voltage (200–800 V). The results are consistent with AsCl3 and GaCl3 being the main etch product species under our conditions, with fragmentation being responsible for the observed mass spectra.
Understanding The Role Of Defects In Limiting The Minority Carrier Lifetime In Sic
Authors: Doolittle W. A. , Rohatgi A. , Ahrenkiel R. , Levi D. , Augustine G. , Hopkins R. H. 
Published: April 2011

AbstractDeep level Transient Spectroscopy (DLTS), Electron Beam Induced Current (EBIC), EBIC Diffusion Length Mapping (EBIC-DLM) and contactless Photoconductive Decay (PCD) were used to characterize both bulk substrates and epitaxially grown Silicon Carbide films. Traps as deep as 0.93 eV were observed via DLTS. These traps may play a role in the persistent photoconductivity effect. EBIC reveals the electrical activity of the well known triangular defects. However, only some of these defects display electrical activity consistent with that of 3C-SiC inclusions, others do not. Additionally, not all defects identified in the EBIC images are observable in the topographic SEM image, possibly indicating a new, yet unidentified defect. EBIC revealed the electrical activity of defects including micro-pipes, dislocations (or possibly growth step edge decoration), surface polish damage, and bulk defects. Diffusion length maps of SiC indicate wide variations in diffusion length on both microscopic and macroscopic scales. EBIC-DLMindicatedepitaxial 4H SiC resulted in diffusion lengths from 0.1 to 3 μm, while bulk values were less than 0.07 μm. PCD measurements indicate tens of nanosecond to microsecond variations in lifetime. Lifetime verses injection level variations are observed and explained on the basis of trap energy. The injection level dependence of lifetime was observed at various nitrogen doping concentrations. Finally, electron beam annealing is found to dramatically improve the minority carrier lifetime in epitaxial SiC.
Theoretical Model And Computer Simulation Results Of Enhanced Diffusion Of High-Temperature Implanted Aluminum In Silicon Carbide
Authors: Gadiyak G. V. 
Published: April 2011

AbstractWide applications of silicon carbide (SiC) films in microelectronics devices make especially important predictions of the doping profiles during and/or after thermal treatment. A macroscopic kinetic model of enhanced diffusion of aluminum in SiC films during ion bombardment at high temperatures has been considered. The set of equations describing the kinetic model takes into account generation Vc and Csi vacancies during bombardment, migration of mobile species (Al) toward the surface and reactions of Al atoms with Vc and Vsi vacancies, as well as Al evolution from the film. The calculations were carried out for the flux of Al ions with energy 40 keV and current density 20 μA/cm2 to a dose 2 1016 cm−2 at 1800° C. The calculations have shown that the Al content in SiC at these condition does not exceed 40%. The calculation profile of Al is in a good agreement with experimental data [1].
Pld Epitaxial Tin Contacts To 6H-Sic And Gan
Authors: Talyansky V. , Vispute R. D. , Andronescu S. N. , Iliadis A. A. , Jones K. A. , Choopun S. , Dowries M. J. , Sharma R. P. , Venkatesan T. , Li Y. X. , Salamanca-Riba L. G , Wood M. C. , Lareau R. A. 
Published: April 2011

AbstractWe have investigated the influence of TiN growth temperature on the contact resistance in TiN/SiC and TiN/GaN heterostructures. Epitaxial TiN layers grown at temperatures above 600°C formed low resistance contacts to n-type 6H-SiC and GaN of 1.1× 10−3 Ωcm2 and 7.9 ×10−5 Ωcm2, respectively. Structural and electrical characterization of TiN thin films is discussed.
Wet Chemical Etching Survey Of III-Nitrides
Authors: Cho Hyun , Hays D. C. , Vartuli C. B. , Pearton S. J. , Abemathy C. R. , MacKenzie J. D. , Ren F. , Zolper J. C. 
Published: April 2011

AbstractWet chemical etching of GaN, InN, AIN, InAlN and InGaN was investigated in various acid and base solutions at temperatures up to 75°C. Only KOH-based solutions were found to etch AIN and InAlN. No etchants were found for the other nitrides, emphasizing their extreme lack of chemical reactivity. The native oxide on most of the nitrides could be removed in potassium tetraborate at 75°C, or HCl/H2O at 25°C.
Applications Of High Power Electronic Switches In The Electric Power Utility Industry And The Needs For High Power Switching Devices
Authors: Heydt G. T. , Skromme B. J. 
Published: April 2011

AbstractThis paper is a review of the main issues relating to power electronic devices as used (or proposed) for the electric power engineering area. Several applications are described. Costs of the devices are discussed. The future of the area is conjectured in terms of the needed breakthroughs in power electronic devices.
Bulk Growth Of Silicon Carbide Crystals: Analysis Of Growth Rate And Crystal Quality
Authors: Hofmann D. , Eckstein R. , Kadinski L. , Kölbl M. , Müller M. , Müller St. G. , Schmitt E. , Weber A. , Winnacker A. 
Published: April 2011

AbstractThe process conditions during SiC bulk crystal growth by physical vapor transport (PVT) are studied both theoretically and experimentally focussing on the magnitude of achievable growth rates V and possible correlations with defect formation. An increase of micropipe density with crystallization rate is observed. Growth parameters determining V are identified allowing a general non-dimensional representation of the dependencies of growth rate from kinetics, mass transport and heat transfer. It can be shown that at conventional process conditions of SiC growth by sublimation in graphite environment (5 mbar ≤p≤ 100 mbar, 2400K ≤T≤ 2600K) growth is limited by diffusion and kinetics for very short crystal lengths L and by heat transfer for geometries L> 1 mm. Including possible destabilizing effects due to constitutional supercooling an augmentation of V without deteriorating crystal quality should be conducted by stochiometry control for supression of graphitization and control of the thermal field tailoring the axial heat transfer with process time. Finally SiC growth from the liquid phase is introduced to promise a growth technique for specific SiC material as, in contrast to PVT growth, the closing of micropipes is demonstrated to be feasible.
Uniformity, High Temperature Performance And Reliability Of X-Band Nitride Power Hemts Fabricated From 2-Inch Epitaxy
Authors: Hickman R. , Hove J. M. Van , Chow P. P. , Klaassen J. J. , Wowchack A. M. , Polley C. J. 
Published: April 2011

AbstractX-band performance, high temperature DC operation, and uniformity have been evaluated for 1 μm gate AlGaN/GaN HEMTs grown by RF atomic nitrogen plasma MBE. Deposition and fabrication were performed on 2-inch (0001) saphirre substrates to determine process uniformity. HEMTs with 300 μm total gate width and dual gate finger geometry have been fabricated with 650–700 cm2/V s mobility. Maximum frequency cut-offs on the order of of 8–10 were achieved. DC performance at room temperature was >500 mA/mm, and external transconductance was >70mS/mn. The transistors operated at test temperatures of 425°C.
Novel Fabrication of C-Doped Base InGaAs/InP DHBT Structures For High Speed Circuit Applications
Authors: Kopf R.F. , Hamm R.A. , Malik R.J. , Ryan R.W. , Burm J. , Tate A. , Chen Y-K. , Georgiou G. , Lang D.V. , Geva M. , Ren F. 
Published: April 2011

AbstractWe have fabricated InGaAs/InP based DHBTs for high speed circuit applications. A process involving both wet chemical and ECR plasma etching was developed. Carbon was employed as the p-type dopant of the base layer for excellent device stability. Both the emitter-base and base-collector regions were graded using quaternary InGaAsP alloys. The extrinsic emitter-base junction is buried for junction passivation to improve device reliability. The use of an InP collector structure with the graded region results in high breakdown voltages of 8V to IOV, with no current blocking. The entire structure is encapsulated with spin-on-glass. These devices show no degradation in DC characteristics after operation at an emitter current density of 90kA/cm2 and a collector bias, VCE, of 2V at room temperature for over 500 hours. Typical common emitter current gain was 50. An ft of 80 and fmax of 155 GHz were achieved for 2 × 4 μm2 emitter size devices.
Wide Bandgap Semiconductor Power Devices
Authors: Chow T. P. , Ramungul N. , Ghezzo M. 
Published: April 2011

AbstractThe present status of high-voltage power semiconductor switching devices is reviewed. The choice and design of device structures are presented. The simulated performance of the key devices in 4H-SiC is described. The progress in high-voltage power device experimental demonstration is described. The material and process technology issues that need to be addressed for device commercialization are discussed.
Atomic-Scale Analysis of the Reactivity of Radicals from Silane/Hydrogen Plasmas with Silicon Surfaces
Authors: Ramalingam Shyam , Maroudas Dimitrios , Aydil Eray S. 
Published: April 2011

AbstractA systematic atomic-scale analysis is presented of the interactions of chemically reactive radicals originating in silane/hydrogen discharges with surfaces of hydrogenated amorphous silicon (a-Si:H) films. The hydrogen concentration on the surface is identified as the major factor that controls both the reactivity of the radicals and the surface reaction mechanism; other important factors include the location of impingement of the radical on the surface and the molecular orientation of the radical with respect to the surface. SiH is found to react with a-Si:H surfaces independent of location of impingement and radical orientation; the reaction mechanism, however, depends strongly on the hydrogen coverage of the surface and impingement location. Our results are in excellent agreement with experimental data for the reaction probability of SiH with a-Si:H film surfaces.
Ion Beam Deposition of Epitaxial Silicon Films
Authors: Khan H. R. , Frey H. 
Published: April 2011

AbstractSilicon films of thicknesses (100 – 800 nm) are deposited on Si[111] substrate at 490°C using Si+ ions of energies (20 – 70 eV) from Silane plasma. The structure of the films depends on the energy of Si+ ions and the film grows epitaxially for ion energy <20 eV. Si films are analyzed by X-ray diffraction technique.
Novel Multilayer Process for CuInSe2 Thin Film Formation by Rapid Thermal Processing
Authors: Chang Chih-hung , Stanbery Billy , Morrone Augusto , Davydov Albert , Anderson Tim 
Published: April 2011

AbstractCuInSe2 thin films have been synthesized from binary precursors by Rapid Thermal Processing (RTP) at a set-point temperature of 290°C for 70 s. With appropriate processing conditions no detrimental Cu2-xSe phase was detected in the CIS films. The novel binary precursor approach consisted of a bilayer structure of In-Se and Cu-Se compounds. This bilayer structure was deposited by migration enhanced physical vapor deposition at a low temperature (200°C) and the influence of deposition parameters on the precursor film composition was determined. The bilayer structure was then processed by RTP and characterized for constitution by X-ray diffraction and for composition by Wavelength Dispersive X-ray Spectroscopy.
Effects of Back Contact Treatments on Junction Photoluminescence in CdTe/CdS Solar Cells
Authors: Levi D. H. , Woods L. M. , Albin D. S. , Gessert T. A. , Niles D. W. , Swartzlander A. , Rose D. H. , Ahrenkiel R. K. , Sheldon P. 
Published: April 2011

AbstractDevice performance in CdTe/CdS solar cells is critically linked to the quality of the back contact. In this paper we report on a phenomenon wherein application of the back contact significantly alters the electro-optical properties of the absorber near the junction. We have studied the photoluminescence (PL) spectrum of the near-junction CdTe region in CdTe/CdS solar cells before and after contact application. It is found that the elemental Tellurium layer formed on the CdTe surface by the standard nitric-phosphoric etch process results in a dramatic qualitative change in the junction PL spectrum. Prior to NP etch, the spectrum has two peaks at energies of 1.50 eV and 1.45 eV, corresponding to recombination in bulk CdTe, and in a CdTeS alloy with 9% sulfur content, respectively. After NP etch, the relative intensity of the low-energy peak is reduced, and the peak shifts towards higher energy. These changes are consistent with a model of increased band-bending at the grain boundaries near the CdTe/CdS heterojunction.