bluuebunny/crossref_metadata_2025_split huggingface dataset:
The influence of the sapphire substrate on the temperature dependence of the GaN bandgap
Authors: Krüiger Joachim , Shapiro Noad , Subramanya Sudhir , Kim Yihwan , Siegle Henrik , Perlin Piotr , Weber Eicke R. , Wong William S. , Sands Timothy , Cheung Nathan W. , Molnar Richard J. 
Published: April 2011

ABSTRACTThis paper analyses the influence of the sapphire substrate on stress in GaN epilayers in the temperature range between 4K and 600K. Removal of the substrate by a laser assisted liftoff technique allows, for the first time, to distinguish between stress and other material specific temperature dependencies. In contrast to the prevailing assumption in the literature, that the difference in the thermal expansion coefficients is the main cause for stress it is found that the substrate has a rather small influence in the examined temperature range. The measured temperature dependence of stress is in contradiction to the published values for the thermal expansion coefficients for sapphire and GaN.
Enhanced Optical Emission from GaN Film Grown on Composite Intermediate Layers
Authors: Zhang Xiong , Chua Soo-Jin , Li Peng , Chong Kok-Boon 
Published: April 2011

ABSTRACTGaN films have been grown on silicon-(001) substrate with specially designed composite intermediate layers consisting of an ultra-thin amorphous silicon layer and a GaN/AlxGa1−xN (x=0.2) multilayered buffer by metal-organic chemical vapor deposition and characterized by photoluminescence and x-ray diffraction spectroscopy. It was found that the GaN films grown on the composite intermediate layers gave comparable or slightly stronger optical emission than those grown on sapphire substrate under identical reactor configuration. Moreover, the full width at half maximum for the GaN band-edge-related emission is 40 meV at room temperature. This fact indicates that, by using the proposed composite intermediate layers, the crystalline quality of GaN-based nitride grown on a silicon substrate can be significantly improved.
Electron Transport in the III-V Nitride Alloys
Authors: Foutz B. E. , Otleary S. K. , Shur M. S. , Eastman L. F. 
Published: April 2011

ABSTRACTWe study electron transport in the alloys of aluminum nitride and gallium nitride and alloys of indium nitride and gallium nitride. In particular, employing Monte Carlo simulations we determine the velocity-field characteristics associated with these alloys for various alloy compositions. We also determine the dependence of the low-field mobility on the alloy composition. We find that while the low-field mobility is a strong function of the alloy composition, the peak and saturation drift velocities exhibit a more mild dependence. Transient electron transport is also considered. We find that the velocity overshoot characteristic is a strong function of the alloy composition. The device implications of these results are discussed.
High-Quality GaN Grown by Molecular Beam Epitaxy on Ge(001)
Authors: Siegle H. , Kim Y. , Sudhir G. S. , Kruger J. , Perlin P. , Ager J. W. , Kislelowski C. , Weber E. R. 
Published: April 2011

ABSTRACTWe report on growth of GaN on Germanium as an alternative substrate material. The GaN films were deposited on Ge(001) substrates by plasma-assisted molecular beam epitaxy. Atomic force microscopy, x-ray diffraction, photoluminescence, and Raman spectroscopy were used to characterize the structural and optical properties of the films. We observed that the Ga/N ratio plays a crucial role in determining the phase purity and crystal quality. Under N-rich conditions the films were phase-mixed, containing cubic and hexagonal GaN, while in the Ga-rich regime they were purily hexagonal. The latter samples show bandedge luminescence with linewidths as small as 31 meV at low temperatures.
Carrier Recombination Dynamics of AlxGa1−xN Epilayers Grown by MOCVD
Authors: Cho Yong-Hoon , Gainer G. H. , Lam J. B. , Song J. J. , Yang W. , McPherson S. A. 
Published: April 2011

ABSTRACTWe present a comprehensive study of the optical characteristics of AlxGa1−xN epilayers by means of photoluminescence (PL), PL excitation, and time-resolved PL spectroscopy. All AlxGa1−xN epilayers were grown by metalorganic chemical vapor deposition and the Al mole fraction (x) was varied from 0 to 0.6. We observed that (i) the full width at half maximum of the PL emission, (ii) the energy difference between the PL emission peak energy and the PLE absorption edge, and (iii) the effective lifetime increase with increasing x. These facts indicate that degree of band-gap fluctuation due to a spatially inhomogeneous Al alloy content distribution increases with increasing x. We observed anomalous temperature-induced emission shift behavior for AlxGa1−xN epilayers, specifically, an S-shaped (decrease-increase-decrease) temperature dependence of the peak energy with increasing temperature. This anomalous temperature-dependent emission behavior was enhanced as the Al mole fraction was increased. Since the band-gap fluctuation in AlxGa1−xN epilayers due to inhomogeneous spatial variations of the Al content increases with increasing Al content, we believe that band-gap fluctuation causes the PL peak energy to deviate from the typical temperature dependence of the energy gap shrinkage. Therefore, the anomalous temperature-induced emission shift can be attributed to energy tail states due to alloy potential inhomogeneities in the AlxGa1−xN epilayers with large Al content.
Recessed gate GaN MESFETs fabricated by the photoelectrochemical etching process
Authors: Lee Won Sang , Choi Yoon Ho , Chung Ki Woong , Shin Moo Whan , Moon Dong Chan 
Published: April 2011

ABSTRACTA new photo-electrochemical etching method was developed and used to fabricate GaN MESFETs. The etching process uses photoresist for masking illumination and the etchant is KOH based. The etching rate with 1.0 mol% of KOH for n-GaN is as high as 1600 Å/min under the Hg illumination of 35 mW/cm/2. The MESFET saturates at VDS = 4 V and pinches off at VGS = −3 V. The maximum drain current of the device is 230 mA/mmn at 300 K and the value is remained almost same for 500 K operation. The characteristic frequencies, fT and fmax, are 6.35 GHz and 10.25 GHz, respectively. Insensitivity of the device performance to temperature was attributed to the defect-related high activation energy of dopants for ionization and band-bending at the subgrain boundaries in GaN thin films.
High Barrier Height n-GaN Schottky diodes with a barrier height of 1.3 eV by using sputtered copper metal
Authors: Lai W. C. , Yokoyama M. , Chang C. Y. , Guo J. D. , Tsang J. S. , Chan S. H. , Sze S. M. 
Published: April 2011

ABSTRACTCopper Schottky diodes on n-type GaN grown by metal-organic chemical vapor deposition were achieved and investigated. Ti/Al was used as the ohmic contact. The copper metal is deposited by the Sputter system. The barrier height was determined to be as high as (ΦB =1.13eV by current-voltage (I-V) method and corrected to be ΦB =1.35eV as considered the ideality factor, n, with the value of 1.2. By the capacitance-voltage (C-V) method, the barrier height is determined to be ΦB =1.41eV. Both results indicate that the sputtered copper metal is a high barrier height Schottky metal for n-type GaN.
Photoionization Spectra of Traps Responsible for Current Collapse in GaN MESFETs
Authors: Klein P. B. , FreitasJr J. A. , Binari S. C. 
Published: April 2011

ABSTRACTCurrent collapse in GaN MESFETS is believed to result from the trapping of carriers in the high resistivity GaN layer, and can be reversed by the application of light. Light photoionizes (or photoneutralizes) the carriers, releasing them from the traps and restoring all or part of the original I-V characteristics of the device. In these investigations we have taken advantage of this effect to characterize the traps responsible for current collapse in an n-channel GaN MESFET. At fixed source-drain voltage, the incremental light-induced drain current, above that measured in the dark, and normalized per incident photon, is measured as a function of wavelength. The resulting photoionization spectrum reflects two absorption thresholds corresponding to two distinct electron traps. Because of the nature of the measurement, these traps can be identified as those responsible for current collapse in the device.
Carbon and Silicon Related Surface Compounds of Palladium Ultrathin Films on SiC After Different Annealing Temperatures
Authors: Lu W. J. , Shi D. T. , Crenshaw T. , Burger A. , Collins W. E. 
Published: April 2011

ABSTRACTPd/SiC Schottky diode has triggered interest as a chemical sensor to be operated at high temperatures. Various surface compounds formed at high temperatures are known to alter the device performance. In this work, the carbon and silicon related compounds and morphology of Pd ultra-thin film on 6H-SiC and 4H-SiC are investigated after thermal annealing using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The Pd ultra-thin films of about 3 nm in thickness are deposited by RF sputtering. The XPS analysis reveals the presence of silicon oxycarbides (SiCxOy) as deposited. After being annealed above 300°C, the atomic ratio of C to 0 in SiCxOy decreases with increasing the annealing temperatures, and the Pd film becomes a Pd silicide nanofeatured layer on SiC. When the annealing temperature is at 500°C, the majority of the SiCxOy is converted into SiO2. An amorphous Si phase exists after annealing at 200 to 400°C, which indicates that the Si-C bonds in SiC are broken at lower temperatures due to the presence of Pd. Graphite and C=O are found on the as deposited samples and also after annealing at temperatures up to 600°C. The formations of the carbon and silicon related compounds on Pd/4H-SiC are very similar to those on Pd/6H-SiC.
Production of InSb Thin Films Through Annealing Sb2S3-In Thin Films
Authors: Nair M. T. S. , Rodríguez-Lazcano Y. , Nair P. K. 
Published: April 2011

ABSTRACTA method to produce large area indium antimonide thin films through a reaction, Sb2S3 + 2 In → 2 InSb + 3 S↑ is presented. A thin film of Sb2S3 with typically 0.2 μm thickness is produced on glass substrate by chemical bath deposition (CBD) at 10°C using thiosulfatoantimonate(III) complex. Subsequently, a thin film of indium is deposited on the Sb2S3 film by thermal evaporation. Annealing the thin film stack of Sb2S3-In at 300°C in a nitrogen atmosphere produces the InSb thin film. The formation of this film is confirmed by x-ray diffraction studies. We would discuss the optimization of the individual film thickness in the Sb2S3-In stack to produce a thin film of single phase InSb or a heterostructure, Sb2S3-InSb. The electrical and optical properties of the films are presented.
Low Energy, High Density Plasma (ICP) for Low Defect Etching and Deposition Applications on Compound Semiconductors
Authors: Etrillard J. , Maher H. , Medjdoub M. , Courant J. L. , Nissim Y. I. 
Published: April 2011

ABSTRACTThe use of a low ion energy of an extremely dense plasma has been studied as a dry etching as well as a thin film deposition tool (same source, two different reactors) for InP and GaAs device processing. Under these working conditions it is expected to control well the etch depth or in the case of deposition to obtain high deposition rates. In all cases minimun ion damages are induced on the processed substrate. Both technologies are presented here from the point of view of material analysis as well as device processing demonstration. For etching, the gate recess of an InP-based HEMT has been addressed as one of the key technological step that requires such properties for good device performances. InGaAs/InAlAs HEMT like structures have been grown and the recess of the InGaAs layer has been conducted with a 13eV SiCl4 inductively coupled plasma (ICP). DLTS and AFM measurements made on the exposed AlinAs surface after InGaAs removal indicate that device quality on its electrical and structural properties are achieved. Passivation of fully processed HEMT devices with a ICP enhanced chemical vapor deposition (ICPECVD) silicon nitride film is being studied.
Wet and Dry Etching Characteristics of Electron Beam Deposited SiO and SiO2
Authors: LaRoche J. R. , Ren F. , Lothian J. R. , Hong J. , Pearton S. J. , Lambers E. 
Published: April 2011

ABSTRACTWe have studied the thermal stability and etching characteristics of E-beam deposited SiO and SiO2. Dry etch rates were studied using SF6 and NF3 discharges in a Plasma Therm inductively coupled plasma system. Wet etch rates were assessed with buffered HF and HF/H2O solutions. SiO2 etched faster than SiO under all etch conditions. Dry etch rate of SiO2 was comparable with PECVD SiO2. Auger analysis indicated that SiO2 maintained excellent thermal stability after annealing to 700°C. The Si/O ratio of SiO in the film increased when annealed to 700°C. Ellipsometry also revealed greater refractive index variance across the sample for SiO, as compared to SiO2. However, thickness variation of both films was ≤ 2% across the wafer. Ellipsometry data also showed great thermal stability of SiO and SiO2. There was <4% change after 700°C annealing.
Structure of Chemically Passivated Semiconductor Surfaces Determined Using X-Ray Absorption Spectroscopy
Authors: Hitchcock A. P. , Tyliszczak T. , Lu Z. H. , Brodersen P. , Dharmawardana M. W. C. 
Published: April 2011

ABSTRACTThe structure of monolayer-passivated single crystal semiconductor surfaces has been studied using synchrotron radiation X-ray absorption fine structure spectroscopy (XAFS). The near edge and extended fine structure signals, supported in some cases by first-principles calculations, have been used to investigate Ge(111)-Cl; GaAs(111)-Cl; GaAs(111)A-S, GaAs(111)B-S and GaAs(001)-S. The use of a solid state Ge X-ray fluorescence array detector has led to significant improvements in data quality and thus structural accuracy. The relationship between the derived surface structures and the development of improved passivated surfaces is discussed.
Li Ion diffusion measurements in crystalline and amorphous V2O5 thin-film battery cathodes
Authors: McGraw Jeanne M. , Bahn Christian S. , Parilla Philip A. , Perkins John D. , Readey Dennis W. , Ginley David S. 
Published: April 2011

ABSTRACTThin films of crystalline and amorphous V2O5 were deposited by pulsed laser deposition (PLD) and the chemical diffusion coefficients, , were measured by the potentiostatic intermittent titration technique (PITT). In crystalline V2O5 films, the maximum and minimum were found to be 1.7 × 10−2 cm2/s and 5.8 × 10−15 cm2/s respectively, with a general trend for to rise in single-phase regions. The changes in correlated well to the known phases in LiV2O5. In amorphous V2O5 films, exhibited a smooth, continuous decrease as the Li concentration increased.
Structural study of lithium insertion in vanadium oxides used as cathode materials
Authors: Rozier Patrick , Savariault Jean Michel , Galy Jean 
Published: April 2011

ABSTRACTCombined soft and solid state chemistry followed by precise XRD investigations allow us to determine the Li-V-O system as well as the structural modifications induced by Li insertion in silver vanadates. On the base of these studies we propose an interpretation of both Li//V2O5 and Li//Ag2V4O11 batteries electrochemical behavior. In the I<x<3 domain, disproportionation of V4+, occurs leading to the formation of different mixtures between lithium vanadates and vanadium oxides. The different domains are related to the different steps observed in the Li//V2O5 discharge curve. It is also demonstrated that the sprouting phenomenon occurring in the Ag1+xV3O8 vanadate induces the formation of a new phase Ag2V4O11 instead of the oxygen deficient form Ag2V4O11-y. According single crystal XRD structural determination this phase is shown to be isostructural with Li1+xV3O8. Electrochemical Li insertion starts with the reduction of Ag+ leading to the lithiated phase meaning that whatever the starting phase used, the main insertion process occurs in Li1+xV3O8.
High Performance Zr-based Metal Hydride Alloys For Nickel Metal Hydride Batteries
Authors: Young R. C. , OVSHINSKY S. R. , HUANG B. , CHAO B S. , LI Y. 
Published: April 2011

ABSTRACTBased upon Ovonic's multi-element, atomic engineering approach, two families of alloys are being used in commercial Nickel Metal Hydride (NiMH) rechargeable batteries, i.e. the mischmetal (Mm) based AB5 and Zr based AB2 alloys. While Mm based alloys are faster to activate, are limited by a discharge capacity of only 320–340 mAh/g. The Zr based alloy, although slightly slower to activate, provides a much higher discharge capacity. In this paper, we first discuss the use of Ovonic's multi-element approach to generate a spectrum of disordered local environments. We then present experimental data to illustrate that through these atomically engineered local environments, we are able to control the hydrogen site occupancy, discharge capacity, kinetics, and surface states. The Zr based alloy with a specific discharge capacity of 465 mAh/g and excellent rate capability has been demonstrated.
Development of Composite Materials for Pefc bipolar Plates
Authors: Busick Deanna , Wilson Mahlon 
Published: April 2011

ABSTRACTThe most costly and problematic components of fuel cell stacks may be bipolar plates. Besides meeting cost constraints, bipolar plates must possess a host of other properties including low gas permeability, corrosion resistance, low weight, high strength, and manufacturability. While we have developed a baseline composite material that meets these requirements, further optimization and development have resulted in significant improvements in properties and processability.
Heat-Resistant, Electrically Conducting Joint Between Ceramic end Plates and Metallic Conductors in Solid Oxide Fuel Cell
Authors: Wilkenhoener R. , Buchkremer H. P. , Stoever D. , Stolten D. , Koch A. 
Published: April 2011

ABSTRACTCeramic parts made of doped lanthanum chromite are used as interconnects and end plates
in stacks for several solid oxide fuel cell (SOFC) designs. Metallic conductors have to be
attached to enable a low-resistance connection between individual stacks in each SOFC unit and
to permit power to be drawn from the SOFC. The resistances of the metal-ceramic bond and the
metallic conductors have to be stable under operating conditions, i.e., 1000°C in air.
Consequently, heat-resistant materials have to be used.
A two-step process has been developed to connect commercially available, Ni- or Febased
metallic conductors to ceramic SOFC end plates by vacuum furnace brazing. In the first
step, a metallic sheet, which acts as the current collector, is brazed onto the ceramic end plate.
Thereby, the much lower electrical conductivity of the ceramic part is compensated by that of
the metal. The chromium alloy CrFe5Y2O31 is suitable because it is heat-resistant, and its
thermal expansion coefficient is close to that of lanthanum chromite. In the second step, metallic
wires or strips are brazed on the current collector. Since this joint area is significantly smaller
than that of the first joint, materials with a different thermal expansion coefficient can be used,
such as conventional heat-resistant nickel alloys (Inconel 617) and ferritic stainless steels
(FeCrAl 25 5). Filler alloys for both brazing steps with matching melting points have been
found. Hence, both brazing steps can be performed cost-effectively in one heating step.
Suitable parameters for vacuum furnace brazing of both joints are presented, and the
composition of the filler alloys is given. Data concerning the long-term behavior of the joint
resistances in air at 1000'C are discussed.
Phase Relations and Conductivity in Ba2 (In2. xMx)O5, System
Authors: Yamaji Akihiko , Kawakami Kazuya , Arai Masahiro , Adachi Tadaharu 
Published: April 2011

ABSTRACTThe high temperature cubic phase of Ba2 nr2O5 shows large ion conductivity. It is interestingto examine, if the cubic phase can be stabilized in the low temperature region (920 C) by making solid solution of another element. In the present study, we investigated the ion conductivity and the crystal structure of Ba2(In2-x.Mx)O5 system by substituting In site for element M such as Sc, Y, La, Ce, Nb, Ta etc. By substituting 3 mole % Nb for In, the transition temperature decreased by about 300 C. High temperature X-ray diffraction analysis shows the crystal structure changes from orthorhombic to cubic at this transition temperature. The effective elements which decreased the transition temperature were pentavalent or tetra valent elements such as Nb or Si ,Ce. The substitution In site for 20 mole percentage Nb stabilizes the cubic structure down to room temperature. Considering the transport number, the tetravalent element doping is very effective to stabilize the cubic phase of Ba2In2O5 without lose of excellent characteristic of pure Ba2ln2O5.
Nanostructure Material for Supercapacitor Application
Authors: Huang Yuhong , Chu C. T. , Wei Qiang , Zheng Haixing 
Published: April 2011

ABSTRACTTransition metal nitrides and carbonitride materials were fabricated via sol-gel technology. The transition metal amides were sythesized by two methods: chemical route and electrolysis. The transition metal amides were then further polymerized, sintering to high temperature in an inert or reduced atmosphere. Transition metal nitrides and carbonitrides powders with surface area up to 160 m2/g were obtained. The resultant electrode material showed high specific capacitance as crystalline ruthenium oxide.
Dielectric Properties of Pd/Y8Z Composites
Authors: Hendriks Mark G.H.M. , Verwei Henk , Timmerman Manon P. 
Published: April 2011

ABSTRACTImpedance measurements are performed on Pd/Y8Z composites. At 500 'C a 2- 108 times enhancement of the permittivity of the composite at a Pd composition near the percolation threshold for electronic conductivity relative to Y8Z at room temperature is obtained. At high frequencies, the enhancement decreases to a value comparable to geometric capacity of the composite as the double-layer capacity diminishes. At relatively low temperatures the capacity of Y8Z, due to ionic polarisability, increases with temperature.
Synthesis and properties of a vanadium oxide based lithium ion Cathode
Authors: Chaloner-Gill Benjamin , Shackle Dale R. 
Published: April 2011

ABSTRACTThe development of high capacity cathode materials for lithium ion batteries has resulted in three materials dominating the market, lithiated manganese, cobalt and nickel oxides and mixtures thereof. In the search for greater energy storage, we have examined a number of vanadium oxides.Comparing the ratio of lithium to metal atom in the three compounds listed above allows for the extraction of one lithium atom per two metal atoms. If the cathode is vanadium based, the number of cycleable lithiums increases to a value closer to 0.75–1.00.Despite the fact that vanadium oxides operate at lower voltages, a net gain in energy is observed from the use of LixVyOz over the currently available materials. Lithiation of LiV3O7.9 for use in a lithium ion cell is the focus of this paper. Chemical lithiation by reducing lithium salt will be described.