bluuebunny/crossref_metadata_2025_split huggingface dataset:
Isoelectronic Trap Like Luminescence Centers Of Ingan
Authors: Kanie H. , Koami H. , Kawano T. , Totsuka T. 
Published: April 2011

AbstractThis paper describes the characteristics of the luminescence centers observed in the various photoluminescence (PL) and photoluminescence excitation (PLE) spectra of hexagonal InxGa1−xN microcrystals, synthesized by the nitridation of sulfide in the In concentration range of 2%<x<6%. The grown crystals showed macroscopic and microscopic inhomogeneity. A series of component bands expressed by Gaussian functions with discrete peak energies selected from the frequently observed peaks in the PL spectra and full width at half maximum obtained from the narrowest PL bands were fitted well to observed broad emission bands. As some of the peak energies of the component bands coincide with those of the bands that are attributed to the decay of excitons at the localized states caused by the In content fluctuation in the literature, we concluded the luminescence center for the component bands also originates from the fluctuation of the In contents. Although the In contents of the samples determined by the X ray diffraction method were compatible the gap energies from the PLE measurements were different. The PLE spectra showed that the Stokes shifts were large and the gap energies were irrelevant to the emission band peaks. The excitation bands for the emission bands in the range of 2.8 to 2.48 eV were located at 3.36, 3.26, and 3.21 eV. These results indicate that the states of the luminescence center are localized and the energy levels are discrete. To obtain the microscopic structure of the localized states in InxGa1−xN, we propose the isoelectronic atom cluster model comparable with Te clusters in ZnSeTe.
Ingan Quantum Dots Fabricated On Aigan Surfaces -Growth Mechanism And Optical Propertiesh-
Authors: Hirayama H. , Tanaka S. , Ramvall P. , Aoyagi Y. 
Published: April 2011

AbstractWe demonstrate photoluminescence from self- assembling InGaN quantum dots (QDs), which are artificially fabricated on AlGaN surfaces via metal- organic chemical vapor deposition. InGaN QDs are successfully fabricated by the growth mode transition from step- flow to three dimensional island formation by using anti-surfactant silicon on AlGaN surface. The diameter and height of the fabricated InGaN QDs are estimated to be ˜10nm and ˜5nm, respectively, by an atomic- force- microscope (AFM). Indium mole fraction of InxGal−x N QDs is controlled from x=˜0.22 to ˜0.52 by varying the growth temperature of QDs. Intense photoluminescence is observed even at room temperature from InGaN QDs embedded with the GaN capping layers. In addition, the temperature- dependent energy shift of the photoluminescence peak- energy shows a localization behavior.
Elemental Analysis On Group-Hi Nitrides Using Heavy Ion Erd
Authors: Dollinger G. , Karsch S. , Ambacher O. , Angerer H. , Bergmaier A. , Schmelmer O. , Stutzmann M. 
Published: April 2011

AbstractElastic recoil detection (ERD) using energetic heavy ion beams (e.g. 170 MeV 127I) is a suitable method to measure depth profiles of light and medium heavy elements in thin films. The main advantages of ERD, which makes it favorable over many other techniques for elemental analysis, is the possibility to obtain reliable and quantitative results, a sensitivity in the ppm region or a depth resolution even better than 1 nm.ERD analysis was employed to obtain quantitative information about the aluminium content x in MBE grown AlxGa1−xN layers on Al2O3 substrates. Using this stoichiometry information and the lattice constants obtained from high resolution X-ray diffraction, Vegard's law could be confirmed with high accuracy. Secondly, nitridation of heated Al2O3 substrates in NH3 atmosphere was investigated using high resolution ERD. A substantial nitrogen content on the surface of the substrate was detected which means a nearly complete AIN layer grown on the Al2O3 surface by a heat treatment only. Such a nitridation layer can be the base for further growth of nitrides on Al2O3 surfaces. As a third, the impurity content of group III nitrides was investigated in dependence on deposition conditions for both, MBE and MOCVD grown samples. In all samples investigated an oxygen concentration larger than 100 ppm was detected which is much higher than the intrinsic charge carrier density of these samples. In addition it is shown that the efficiency of p-doping by Mg may not only be hindered by hydrogen but also by carbon impurities.
Direct Observations Of Atomic Structures Of Defects In Gan By High Resolution Z-Contrast Stem
Authors: Xin Y. , Pennycook S.J. , Browning N.D. , Nellist P. D. , Sivananthan S. , Beaumont B. , Fauriel J-P , Gibart P. 
Published: April 2011

AbstractGaN/(0001)Sapphire grown by low pressure MOVPE is studied by high resolution Z-contrast imaging using STEM. First direct observation of the threading dislocation with edge character shows the atomic core structure, which appears to have a similar configuration to the {10–10} surface. The surfaces of the nanopipe walls are on {10–10} with the terminating layer between the atoms with one bond per pair. In addition, the high resolution Z-contrast image of the prismatic stacking fault confirms the results by conventional HRTEM.
Monte Carlo Calculation Of High- And Low-Field AlxGa1−xN Electron Transport Characteristics
Authors: Albrecht J.D. , Wang R. , Ruden P.P. , Farahmand M. , Bellotti E. , Brennan K.F. 
Published: April 2011

AbstractThe Monte Carlo technique is used to simulate electron transport in bulk, wurtzite phase AlxGa1−xN. A multi-valley analytical band model consisting of five spherical, non-parabolic conduction band valleys at the Γ, U, M, and K symmetry points of the Brillouin zone is matched to band structures of GaN and AlN. Parameters for the AlxGa1−xN alloy are obtained by linear interpolation. The Monte Carlo simulations are performed for ambient temperatures in the range of 300K to 600K. Scattering mechanisms taken into account include ionized impurity scattering and alloy scattering, in addition to deformation potential scattering (intra- and inter-valley), and polar optical phonon scattering. We present results for the electron steady-state drift velocity and the valley occupancy for electric fields up to 500 kV/cm. Low-field drift mobilities are extracted from the Monte Carlo calculations as functions of the electron concentration, of the ambient temperature, and of the alloy composition.
Interband Radiative Recombination Calculations In Ternary Nitride Solid Solutions
Authors: Dmitriev A. V. , Oruzheinikov A. L. 
Published: April 2011

AbstractWe calculated for the first time the interband radiative recombination rate R in the wide-gap semiconductors GaN, InN and AIN crystallizing in the hexagonal wurtzite structure, and in ternary InxGayAl1−x−yN alloys including also binary solid solutions GaxAl1−xN, InxAl1−xN and GaxIn1−xN. All our calculations were based on experimental data on energy band structures and optical absorption spectra of the nitride materials. The radiative recombination coefficient B defined according to the equation R = B np, n and p being the carrier densities, is higher in InN and lower in GaN, taking intermediate values in AlN. For example, B=(2.7, 0.4 and 0.15) × 10−10cm3/s for InN, AIN and GaN, correspondingly. The carrier lifetime in GaN equals 60ns at 300K and n=1 × 1017cm−3. The radiative recombination coefficient increases with the concentration of indium nitride in the ternary alloys.
Electron Irradiation Induced Trap In N-Type Gan
Authors: Fang Z-Q. , Hemsky J. W. , Look D. C. , Mack M. P. , Molnar R. J. , Via G. D. 
Published: April 2011

AbstractA 1-MeV-electron-irradiation (EI) induced trap at Ec-0.18 eV is found in n-type GaN by deep level transient spectroscopy (DLTS) measurements on Schottky barrier diodes, fabricated on both metal-organic-chemical-vapor-deposition and hydride-vapor-phase-epitaxy material grown on sapphire. The 300-K carrier concentrations of the two materials are 2.3 × 1016 cm−3 and 1.3 × 1017 cm−3, respectively. Up to an irradiation dose of 1 × 1015 cm−2, the electron concentrations and pre-existing traps in the GaN layers are not significantly affected, while the EI-induced trap is produced at a rate of at least 0.2 cm−1. The DLTS peaks in the two materials are shifted slightly, possibly due to electric-field effects. Comparison with theory suggests that the defect is most likely associated with the N vacancy or Ga interstitial.
Theoretical Study of Native Point Defects in Aln and InN
Authors: Stampfl C. , Walle Chris G. Van De 
Published: April 2011

AbstractWe have studied native point defects in AlN and InN using density-functional calculations employing both the local-density and generalized gradient approximations for the exchange-correlation functional. For both materials we find that the nitrogen vacancy acts as a compensating center in p-type material. For AIN in the zinc-blende structure, the aluminum interstitial has an equally low formation energy as the nitrogen vacancy. For n-type material the aluminum vacancy is the dominant compensating center in AlN. For n-type InN, all defect formation energies are high.
New Method of Computing Band Offsets and Its Application to AlGaN/GaN Heterostructures
Authors: Webster Richard T. , Anwar A. F. M. 
Published: April 2011

AbstractCalculated sheet carrier concentration as a function of Al mole fraction in the quantum well (QW) formed at the GaN/AlGaN heterointerface is calculated and compared to experimental data. Close agreement between experiment and theory is observed. The calculated sheet carrier concentration reflects the maximum carrier concentration possible in the GaN QW for a given Al mole fraction and can not be used to argue in favor of either interface charge or piezoelectric effect as giving rise to the carriers. Based on experimental data the charge density in the AlGaN layer is estimated to be 4 × 1012cm-2The calculations are based upon a simple technique to determine valence band alignments. Calculated values are compared to experimental data showing excellent agreement. A calculated valence band discontinuity of 0.42eV for AlN/GaN is well within the experimental bounds.
Investigation Of Nucleation And Initial Stage Of Gan Growth By Atomic Force Microscopy And X-Ray Diffraction
Authors: Yip P. W. , Wang S.-Q. , Drehman A. J. , Zhu L. D. , Norris P. E. 
Published: April 2011

AbstractThe nucleation and initial stage of GaN growth on sapphire was investigated by atomic force microscopy, X-ray diffraction and photoluminescence. A 15 to 30 nm thick GaN buffer layer deposited at proper conditions was extremely smooth and nearly amorphous. Proper post deposition annealing resulted in the buffer crystallized. The buffer layer deposition temperature, thickness and annealing time and temperature must be coordinated. Low deposition temperature and/or insufficient annealing of the buffer results in a GaN wafer which has fine spiking surface morphology with an RMS of 3.4 nm for 1.4 μm wafer, strong yellow luminescence and wide xray rocking curve FWHM. High deposition temperature, longer crystallization time, and a low growth rate results in a wafer which exhibits strong band edge luminescence without noticeable yellow luminescence, and a narrow (002) diffraction rocking curve. However, the surface morphology exhibits well developed hexagonal feature with RMS roughness of 14.3 nm for a 570 nm thick layer. X-ray rocking curve analysis revealed buffer crystallization, domain coalescence and alignment process. The FWHM of the ω–scan of GaN (101) diffraction was 1700–2000 arc seconds for 200–1400 nm wafers which indicates that the twist of the domains is not changing much with the growth.
Laser-Processing for Patterned and Free-Standing Nitride Films
Authors: Kelly M. K. , Ambacher O. , Dimitrov R. , Angerer H. , Handschuh R. , Stutzmann M. 
Published: April 2011

AbstractFilms of GaN and related materials can be processed by methods that invoke thermal decomposition, induced by intense illumination with a pulsed laser. At elevated temperatures, the nitride semiconductors undergo decomposition, with the effusion of nitrogen gas. We exploit this mechanism as an alternative to etching for the patterning of nitride films and for the opening of buried interfaces. Films of GaN have been etched to a depth of 1 μm in less than three seconds. This interface decomposition allows in particular the separation of nitride films from transparent growth substrates such as sapphire.
Recent Progress in Implantation and Annealing of Gan and Aigan
Authors: Zolper J. C. , Han J. , Deusen S. B. Van , Crawford M. H. , Biefeld R. M. , Jun J. , Suski T. , Baranowski J. M. , Pearton S. J. 
Published: April 2011

AbstractHeterostructure modulation doped transistors (MODFETs) based on AlGaN/GaN structures have demonstrated impressive DC and microwave performance often despite high transistor access resistance. One approach to reducing the access resistance is to use selective area Si-implantation. While several reports exist on Si-implantation in GaN, little work has been done on implantation in AlGaN. In addition, more information on the annealing of implantation damage in GaN is needed to optimize its use in FETs and thyristors.We report the electrical and structural properties of Si-implanted Al0.15Ga0.85N based on Hall measurements and Rutherford Backscattering (RBS) spectra, respectively. Al0.15Ga0.85N shows less damage accumulation than GaN for a room temperature Si-implant dose of 5×1015 cm-2 based on the minimum channeling yield (26% for AlGaN as compared to 34% for GaN), however, as with GaN, this damage is difficult to remove by thermal annealing at °C.
Formation Mechanism Of Negative Fixed Charge In Glass At Lead Glass/Silicon Interface
Authors: Murakami Susumu , Matsuzaki Hitoshi , Matsuzaki Mitsuyuki , Tsuruoka Masao , Kanno Minoru 
Published: April 2011

AbstractThe physical origins of negative fixed charges at the lead glass/silicon interface have been studied. It was found that a thin p-type region is present on the n-type substrate in the PbO-SiO2-Al2O3 glass/silicon system from the punch-through voltage, pinch-off voltage, and SIMS analysis. A new model of the negative fixed charge was proposed from the MIS structure with the surface pn junction.
Low-Temperature PECVD SiO2 On Si And SiC
Authors: Teng L. , Anderson W. A. 
Published: April 2011

AbstractThe deposition of SiO2 films by plasma-enhanced-chemical-vapor-deposition (PECVD) using tetraethylorthosilicate (TEOS) was studied. MOS capacitors were fabricated on both Si and SiC for this study. Several different sets of experiments were conducted for PECVD deposition according to different growth parameters and the results compared. For Si samples with SiO2 deposited at a substrate temperature 300°C, the C∼V curve gave a flat-band voltage of 1V and a transition slope of 112 pF/V. The dielectric constant of the deposited SiO2 film was 4.2 and the Si/SiO2 interface trap density was calculated to be 1.8×1010 cm−2. The I-V curve showed a leakage current density of l.2×10−9 A/cm2 and dielectric breakdown field strength of 9.2 MV/cm. For SiC samples, the PECVD deposition gave a uniform SiO2 film with a controllable deposition rate of 0.3nm/sec. The refractive index and dielectric constant of the as-deposited SiO2 film were 1.46 and 3.84 respectively. The I∼V curve showed a leakage current density of 2×10−9 A/cm2 and a breakdown field of 4.7 MV/cm.
Etching And Hydrogen Incorporation In ScAlMgO4
Authors: Brandlel C. D. , Ren F. , Wilson R. G. , Lee J. W. , Pearton S. J. , Zavada J. M. 
Published: April 2011

AbstractScAlMgO4 is a potential substrate for GaN epitaxy. We have compared three different plasma chemistries for dry patterning of ScAlMgO4, namely Cl2−, F2− or CH4/H2-based. Significant etch rates (>1000Å.min−1) were obtained only with Cl2 (and BCl3), and the rates were directly proportional to both ion energy and ion density in the plasma. Since the etching is ionassisted under all conditions, extremely anisotropic sidewalls are produced on patterned features. Of the wet chemistries investigated at 300K, only HF wet chemical solutions were found to etch ScAlMgO4, although HNO3 can be used at ≤150°C for removal of substrate polishing damage. Hydrogen as 2H has been incorporated into ScAlMgO4 by both ion implantation and by exposure to a plasma at 250°C. In the implanted material diffusion begins at ˜500°C and most of the hydrogen is lost by ≤ 750°C. This thermal stability for hydrogen retention is considerably lower than for other substrate materials for GaN epilayer growth, such as Al2O3 and SiC. There is minimal permeation of 2H from a plasma at 250°C (DH ˜5×10−16 cm2·s−1) in ScAlMgO4, and thus unintentional hydrogen incorporation into GaN overlayers should be minimal at typical growth temperatures.
Optical Characterization Of Silicon Oxycarbide Thin Films
Authors: Wolfe D. M. , Wang F. , Hinds B. J. , Lucovsky G. 
Published: April 2011

AbstractThe local bonding environments in silicon oxycarbide thin films with different amounts of carbon were analyzed using the complementary optical techniques of Fourier transform infrared (FTIR) and Raman spectroscopies. Film formation was accomplished by low-temperature (250°C), plasma-enhanced CVD using SiH4, CH4 and O2 as the source gases. Control samples were also deposited using only SiH4 and CH4, and SiH4 and O2 source gases. The films were then subjected to rapid thermal annealing at 800, 900 and 1100 °C for 90 seconds. Results showed that carbon incorporation into the oxide hinders stoichiometric SiO2 formation upon annealing at 800 and 900 °C. Annealing at 1100 °C produced films which showed stoichiometric SiO2 formation. Phase separation into nano-crystalline silicon (<5 nm) and a mixture of amorphous silicon carbide and silicon oxide was also observed upon annealing, with crystallite size decreasing as the carbon content of the films was increased.
Influence Of Open-Tube Ga Diffusion On The Characteristics For Thyristor
Authors: Ruimei Wen , Suhua Pei 
Published: April 2011

AbstractOpen-tube Ga diffusion into a SiO2/Si structure was used for fabrication of the high speed thyristor. The advantages of open-tube Ga diffusion are as follows; it is easier to operate and easier to control the profile of the Ga concentration during processing, a clean surface, which is free from alloy spots can be obtained, this technique ensures to improve the on-state characteristics and dynamic characteristics.
Microraman Characterization Of Microdefects In Bulk Sic
Authors: Martín E. , Chafai M. , Jiménez J. 
Published: April 2011

AbstractMicroRaman spectroscopy is used for characterizing defects in large SiC crystals with micrometer spatial resolution. The ability to identify microscopic inclusions of polytypes different than the crystal matrix is demonstrated; silicon and carbon inclusions and disorder effects are found in micropipes. A study of the Longitudinal Optic Phonon Plasmon Coupled (LOPC) Raman modes allowed to obtain local fluctuations of the net donor concentration, ND-NA, and the electron mobility around defects, which allowed impurity gettering effects to be observed.
A Novel Bi-Layer Photoresist T-Gate Technique To Reduce Gate Resistance.
Authors: Lothian J. R. , Ren F. 
Published: April 2011

AbstractAs the gate dimensions of FET's continue to shrink, the gate resistance increases. This increased gate resistance is undesirable for power applications. In order to reduce this problem short gate length features are covered with a larger length feature to reduce the gate resistance (T-gate)1. Generally this is done using bi-layer PMMA and E-beam writing for the upper and lower features, but this technique is very expensive and time consuming2,3. It is desirable to find a technique using conventional photoresist that would replace e-beam to produce T-gates.We demonstrate a novel technique that utilizes conventional photoresist and optical stepper to create T-gate features4. The bottom feature is exposed and developed creating the lower part of the T. A short exposure of the photoresist pattern to an argon plasma hardens the resist just enough to allow a second layer to be put on without mixing of the two layers. This second layer is then exposed and developed forming the T. Plasma exposure allows us to create the second resist layer pattern without distorting or changing the bottom layer pattern. This technique is very robust, fast and much cheaper than e-beam technology.
Breakdown Degradation Associated With Elementary Screw Dislocations In 4H-SiC P+N Junction Rectifiers
Authors: Neudeck P. G. , Huang W. , Dudley M. 
Published: April 2011

AbstractIt is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vector > 2c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector = Ic with no hollow core) in densities on the order of thousands per cm2, nearly 100-fold micropipe densities. This paper describes an initial study into the impact of elementary screw dislocations on the reverse-bias current-voltage (I-V) characteristics of 4H-SiC p+n diodes. First, Synchrotron White Beam X-ray Topography (SWBXT) was employed to map the exact locations of elementary screw dislocations within small-area 4H-SiC p+n mesa diodes. Then the high-field reverse leakage and breakdown properties of these diodes were subsequently characterized on a probing station outfitted with a dark box and video camera. Most devices without screw dislocations exhibited excellent characteristics, with no detectable leakage current prior to breakdown, a sharp breakdown I-V knee, and no visible concentration of breakdown current. In contrast devices that contained at least one elementary screw dislocation exhibited a 5% to 35% reduction in breakdown voltage, a softer breakdown I-V knee, and visible microplasmas in which highly localized breakdown current was concentrated. The locations of observed breakdown microplasmas corresponded exactly to the locations of elementary screw dislocations identified by SWBXT mapping. While not as detrimental to SiC device performance as micropipes, the undesirable breakdown characteristics of elementary screw dislocations could nevertheless adversely affect the performance and reliability of 4H-SiC power devices.
Introduction Of Ions Into Wide Band Gap Semiconductors
Authors: Maruska H. Paul , Lioubtchenko Mike , Tetreault Thomas G. , Osinskif Marek , Pearton Stephen J. , Schurmant Matthew , Vaudo Robert , Sakap Shiro , Chen Qisheng , Shult Randy J. 
Published: April 2011

AbstractWith great attention now being given to the wide band gap materials for electronic and optoelectronic device applications, there is interest in using ion implantation to introduce dopants into selected regions of devices. Work on ion implantation into SiC and the III-V nitrides is reviewed, new device concepts are given, and recent results are presented. These include SiC implantations at elevated temperatures, a GaN sample implanted with Si having an electron mobility after annealing of 106 cm2/V-s, and a novel GaN np junction diode created by implantation.
Material Requirements For High Voltage, High Power Igbt Devices
Authors: Zehringer R. , Stuck A. , Lang T. 
Published: April 2011

AbstractThe two basic package types of current IGBT modules, which evolved from opposing requirements of traction and power transmission applications, are presented. It is shown that reliability and lifetime aspects given by traction puts most stringent limitations on the choice of materials at given cost targets. The materials used today for high power packaging and the future developments of high power IGBT-packages are discussed.