bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nanoindentation Behavior of Gold Single Crystals
Authors: McCann Martha M. , Corcoran Sean G. 
Published: April 2011

ABSTRACTNanoindentation is an increasingly used tool to investigate the mechanical properties of very small volumes of material. It is usually a very consistent measure of the elastic response of material and plastic response to point contact loading. Nanoindentation experiments on gold single crystals display tremendous variation in the residual deformation. The depth of penetration, which is vital in hardness determination, can differ by as much as 100%. This large variability of the load-depth data is usually explained by surface differences such as crystal orientation, oxide thic kness, presence of multiple solid phases, or contamination layers. None of these reasons apply to the variation observed in the gold system. The onset of plastic deformation is observed at a stress level on the order of the theoretical yield strength. The difference in depth of penetration is independent of this elastic -plastic transition. This paper reports on attempts to correlate the depth of penetration to surface feature size and surface preparation procedures.
Experimental Measurements of Surface Residual Stress Caused by Nano-scale Contact of Rough Surfaces
Authors: Wang J. , Shrotriya P. , Yu H. H. , Kim K.-S. 
Published: April 2011

ABSTRACTA previous dislocation model analysis predicts that nano-scale contacts of surface steps induce nucleation of dislocations leading to pro-load and anti-load dislocation segregation near the contact surface. Such dislocation segregation generates a sub-layer of tensile residual stress in a much thicker layer of compressive residual stress near the surface. The sub-layer thickness is expected to be about 50 to 100 times the step height. In order to verify the predictions of the model analysis, experiments are carried out on polycrystalline aluminum surface to determine the existence of the tensile sub-layer. The variation of the residual stress along the thickness direction is measured using a newly developed high sensitivity curvature-measurement interferometer. The interferometer measures the curvature change of the back surface of a plate specimen of about 1.9 mm thickness while the contact-loaded front surface is chemically etched. The residual stress distribution measured with sub-nanometer spatial resolution is compared with analytical predictions.
The fabrication of p-Ge/n-Si photodetectors, compatible with back-end Si CMOS processing, by low temperature (< 400 °C) molecular beam epitaxy and electron-beam evaporation
Authors: Bandaru Prabhakar , Sahni Subal , Yablonovitch Eli , Kim Hyung-Jun , Xie Ya-Hong 
Published: April 2011

ABSTRACTWe report on the low temperature growth, by molecular beam epitaxy (375 °C) and electron-beam evaporation (300 °C), of p-Ge films on n-Si substrates for fabricating p-n junction photodetectors, aimed at the integration of opto-electronic components with back-end Si CMOS processing. Various surface hydrogen and hydrocarbon removal treatments were attempted to improve device properties. We invoke Ge diffusion and growth modes as a function of deposition temperature and rate to correlate structural analysis with the device performance.
Strain Modulation of β-FeSi2 by Ge-Segregation in Solid-Phase Growth of [a-Si/a-FeSiGe]n Multi-Layer
Authors: Murakami Y. , Kenjo A. , Sadoh T. , Yoshitake T. , Itakura M. , Miyao M. 
Published: April 2011

ABSTRACTStrain modulation of β-FeSi2 by Ge doping was investigated. By solid-phase growth of [a-Si/a-Fe0.4Si0.5Ge0.1]n layered structures, the [a-SiGe/β-FeSi2-xGex]n multi-layered structures (n=1, 2, 4) were formed after annealing at 700 °C. From the analysis of the x-ray diffraction spectra, it was found that β-FeSi1.3Ge0.7 strained by 0.4–0.5 % was formed for the sample with n=1. This value corresponded to the band gap modulation of 30 meV based on the theoretical calculation. The strains decreased with increasing n, which was due to that segregation of Ge atoms from the a-Fe0.4Si0.5Ge0.1 layers to the a-Si layers became significant with increasing n. After annealing at 800 °C, agglomeration of β-FeSi2 occurred, and nanocrystals of relaxed β-FeSi2 and c-Si0.7Ge0.3 were formed. These new structures are useful for formation of opto-electrical devices.
Reduction of dark current in AlGaN/GaN Schottky barrier photodetectors with a low-temperature-grown GaN cap layer
Authors: Chi G. C. , Sheu J. K. , Lee M. L. , Kao C. J. , Su Y. K. , Chang S. J. , Lai W. C. 
Published: April 2011

ABSTRACTAlGaN/GaN-based ultraviolet (UV) Schottky barrier photodetectors (PDs) with and without the LT GaN cap layer were both fabricated. It was found that we could achieve a lower leakage current from sample A. With incident light wavelength of 320 nm and a –1 V reverse bias, the measured responsivity was around 0.03 A/W and 0.015 A/W for samples with and without the LT GaN cap layer, respectively. The response speed of the sample A was also found to be faster.
Evidence of strong indium segregation in MOCVD InxGa1-xN/GaN quantum layers
Authors: Maciejewski Grzegorz , Jurczak Grzegorz , Kret Sławomir , Dłużewski Paweł , Ruterana Pierre 
Published: April 2011

ABSTRACTAn investigation of 1–5 nm in diameter indium rich clusters in MOCVD InxGa1-xN/GaN quantum well is carried out. To this end, quantitative High Resolution Transmission Electron Microscopy (HRTEM) is coupled with the Finite Element Method (FEM) for the calculation of thin foil relaxation and for image simulation. The measurement of the tetragonal distortion from HRTEM images is a useful tool for the determination of chemical composition in heterostructures. However, for a correct interpretation of the measured lattice distortion on HRTEM images, one needs to take into account the strain averaging across TEM sample and inhomogeneous relaxation of the sample. As a first step, 3D FEM simulation of the relaxation process as a function of the position of indium rich cluster relative to the foil surface is performed. Next, the calculated 3D displacement field is used to simulate the HRTEM images. The results clearly show that the magnitude of the strain field depends on the cluster position. It is concluded that the HRTEM images of indium rich clusters can differ even for the same indium content due to different positions of the clusters.
Growth of non-polar a-plane and cubic InN on r-plane sapphire by molecular beam epitaxy
Authors: Lu Hai , Schaff William J. , Eastman Lester F. , Cimalla Volker , Pezoldt Joerg , Ambacher Oliver , Wu J. , Walukiewicz Wladek 
Published: April 2011

ABSTRACTGrowth of non-polar III-nitrides has been an important subject recently due to its potential improvement on the efficiency of III-nitride-based opto-electronic devices. Despite study of non-polar GaN and GaN-based heterostructures, there are few reports on epitaxial growth of non-polar InN, which is also an important component of the III-nitride system. In this study, we report heteroepitaxial growth of non-polar InN on r-plane sapphire substrates using plasma-assisted molecular beam epitaxy. It is found that when a GaN buffer is used, the following InN film appears to be non-polar (1120) a-plane which follows the a-plane GaN buffer. The room temperature Hall mobility of undoped a-plane InN is around 250 cm2/Vs with a carrier concentration around 6×1018 cm-3. Meanwhile, if InN film is directly deposited on r-plane sapphire without any buffer, the InN layer is found to consist of a predominant zincblende (cubic) structure along with a fraction of the wurtzite (hexagonal) phase with increasing content with proceeding growth.
Non-Equilibrium Acceptor Concentration in GaN:Mg Grown by Metalorganic Chemical Vapor Deposition
Authors: Gong Y. , Gu Y. , Kuskovsky Igor L. , Neumark G. F. , Li J. , Lin J. Y. , Jiang H. X. , Ferguson I. 
Published: April 2011

ABSTRACTIt is shown that the high p-type conductivity in GaN:Mg, grown by metal-organic chemical vapor deposition followed by post-growth annealing, is due to non-equilibrium acceptor concentrations. A series of samples cut from a single GaN:Mg wafer, which initially had undergone rapid thermal annealing (RTA) after growth, has been investigated. The samples were annealed at various temperatures in nitrogen ambient for over 12 hours, and temperature-dependent Hall effect measurements were performed. For samples annealed at temperatures higher than 850 °C, the hole concentrations decrease by at least an order of magnitude, compared with the original sample. This behavior is explained by an Mg acceptor concentration in excess of its equilibrium solubility limit in the original sample; thus, at high enough temperatures, in the absence of hydrogen, Mg acceptors diffuse either to form electrically inactive precipitates or are eliminated. It is worth noting that the acceptor activation energy remains the same for all samples.
Thermally stimulated current spectroscopy of carbon-doped GaN grown by molecular beam epitaxy
Authors: Fang Z-Q. , Look D. C. , Armitage R. , Yang Q. , Weber E. R. 
Published: April 2011

ABSTRACTDeep traps in semi-insulating (SI) or high-resistivity C-doped GaN grown by metal-organic chemical-phase deposition or molecular-beam epitaxy have been studied by thermally stimulated current (TSC) spectroscopy. Incorporation of carbon in GaN introduces CNacceptors, resulting in compensation and formation of SI-GaN; however, as [C] increases in the GaN samples, both resistivity and activation energy of the dark current decrease. In the GaN samples with low [C], we find at least six TSC traps: B (0.61 eV), Bx(0.50 eV), C1(0.44 eV), C (0.32 eV), D (0.23 eV), and E (0.16 eV), all of which are very similar to electron traps typically found in n-type GaN by deep level transient spectroscopy (DLTS). However, in the GaN sample with the highest [C], both traps E and B are suppressed, and instead, trap Bxappears. Based on DLTS studies of electron-irradiated and plasma-etched GaN samples, we believe that traps E, D and C are related to VN, and that trap B is probably related to VGa, in the form of complexes such as VGa-ON. As [C] increases, CGadonors become more favorable, and the transition of trap B to trap Bxmay suggest that CGarelated complexes are forming. In comparison with lightly C-doped GaN, heavily C-doped GaN sample exhibits very strong PPC at 83 K. We show that the PPC in both cases can be simply explained by the thermal emission of carriers from shallower traps.
Time Resolved Photoluminescence of Si-doped High Al Mole Fraction AlGaN Epilayers Grown by Plasma-Enhanced Molecular Beam Epitaxy
Authors: Furis Madalina , Cartwright Alexander N. , Hwang Jeonghyun , Schaff William J. 
Published: April 2011

ABSTRACTWe report on detailed temperature dependent, time-resolved photoluminescence (TRPL) studies of Si-doped AlGaN epilayers. In these samples, the Al concentration varies from 25% to 66%. The samples were found to exhibit metallic-like temperature-independent conductivity. The deep level “yellow” emission, whose presence would indicate the existence of a large number of defects associated with growth, Si incorporation, and/or alloy formation, is absent. In addition to emission corresponding to the donor-bound exciton, the PL spectrum exhibits features associated with transitions involving localized carriers. This assignment of the emission mechanisms is based on the activation energies extracted from the temperature dependent photoluminescence (PL) quenching. Specifically, at room temperature the PL spectrum is dominated by transitions involving localized states. The localization energy varied from sample to sample and was observed to be between 115 meV to 200 meV. The PL intensity decay in the lower Al mole fraction epilayers exhibits a slow component associated with the presence of donor-bound excitons.
Anisotropic Dielectric Properties of GaN Epilayers on Sapphire
Authors: Rowell N. L. , Yu G. , Lockwood D. J. 
Published: April 2011

ABSTRACTPolarized infrared reflectance from 300 to 1200 cm-1 at different incidence angles was measured at room temperature for sapphire and GaN/sapphire samples. A film of GaN was grown approximately 1.5 μm thick on c-plane sapphire by MOCVD with a thin GaN buffer layer. Because of the hexagonal structure of sapphire and GaN, their uniaxial optical properties are anisotropic. In the p-polarized reflective spectrum, we observed the mixed effect between the distinct infrared-active modes with dipole-moment oscillation perpendicular (E-mode) and parallel (A-mode) to the c axis. The contribution of the A-mode increased with increasing incidence angle. Therefore, we were able to obtain simultaneously the infrared dielectric functions parallel and perpendicular to the c axis, by fitting simultaneously three polarized reflectance spectra at three different incident angles with a suitable model. In the procedure, we adopted a new fitting technique, i.e., fitting the first numerical derivative of the polarized reflectance spectra to improve the accuracy of the phonon parameters and to overcome the inconsistency between the model and measurement in the whole frequency range. Excellent agreement has been obtained between the measured and fitted first derivative reflectance spectra for both the sapphire and GaN/sapphire samples. The dielectric information thus obtained for sapphire and GaN is of greater accuracy than those reported previously.
Structural Defect-Related Photoluminescence in GaN
Authors: Chen L. , Skromme B. J. , Mikhov M. K. , Yamane H. , Aoki M. , DiSalvo F. J. , Wagner B. , Davis R. F. , Grudowski P. A. , Dupuis R. D. 
Published: April 2011

ABSTRACTBroad, low temperature photoluminescence (PL) peaks near 3.4–3.42 eV in GaN have previously been associated with basal-plane stacking faults. Recently, we observed unusually sharp and highly structured PL peaks in this region in high quality bulk GaN grown from a Na/Ga flux, some of which display characteristic shifts and narrowing as a function of excitation power. Here, we study these peaks as a function of excitation intensity and crystal polarity, and compare them to those observed in GaN grown on off-axis SiC or sapphire (0001) substrates by metalorganic chemical vapor deposition (MOCVD). In the off-axis material on either substrate, similar peaks are observed to those in the bulk samples. In addition, a low energy peak near 3.21 eV is observed, which does not occur in the bulk material.
Optical Study of Localized and Delocalized States in GaAsN/GaAs
Authors: Xu Z. Y. , Luo X. D. , Yang X. D. , Tan P. H. , Yang C. L. , Ge W. K. , Zhang Y. , Mascarenhas A. , Xin H. P. , Tu C. W. 
Published: April 2011

ABSTRACTTaking advantages of short pulse excitation and time-resolved photoluminescence (PL), we have studied the exciton localization effect in a number of GaAsN alloys and GaAsN/GaAs quantum wells (QWs). In the PL spectra, an extra transition located at the higher energy side of the commonly reported N-related emissions is observed. By measuring PL dependence on temperature and excitation power along with PL dynamics study, the new PL peak has been identified as a transition of the band edge-related recombination in dilute GaAsN alloy and delocalized transition in QWs. Using selective excitation PL we further attribute the localized emission in QWs to the excitons localized at the GaAsN/GaAs interfaces. This interface-related exciton localization could be greatly reduced by a rapid thermal annealing.
Reduction of Threading Dislocation Density in AlGaN by Indium Incorporation
Authors: Kang H. , Feng Z. C. , Ferguson I. , Guo S. P. , Pophristic M. 
Published: April 2011

ABSTRACTThe addition of indium, even to small concentrations, to AlGaN has resulted in improved optical and doping properties for these materials. This paper is the first report of improved structural properties for indium containing AlGaN layers. A systematic series of the AlGaN layers with nominal concentration of 20% aluminum were grown by metal-organic chemical vapor deposition with traces amounts of indium incorporated into the layers (up to 0.15% indium). X-ray diffraction analysis of the layers was completed using Williamson Hall plots and reciprocal space mapping to investigate any change in the columnar structure of the initial AlGaN layers. It was found that the threading dislocation densities and lateral coherence length showed a systematic variation with indium incorporation. The threading dislocation density is lowered as indium composition increased with a corresponding increase in lateral coherence length. This indicates that even the incorporation of trace amounts of indium improves the structural properties of these epilayers.
Experimental Analysis and a New Theoretical Model for Anomalously High Ideality Factors (n ≫ 2.0) in GaN-based p-n Junction Diodes
Authors: Shah Jay M. , Li Yunli , Gessmann Thomas , Fred Schubert E. 
Published: April 2011

ABSTRACTDiode ideality factors of 2.0–8.0 have been reported in GaN-based p-n junctions. These values are much higher than the expected values of 1.0–2.0 as per the Sah-Noyce-Shockley theory. We propose a fundamentally new model for the high ideality factors obtained in GaN-based diodes. This model is based on the effect of moderately doped unipolar heterojunctions as well as metal–semiconductor junctions in series with the p-n junction. A relation for the effective ideality factor of a system of junctions is developed. A detailed experimental study is performed on diodes fabricated from two different structures, a bulk GaN p-n junction structure and a p-n junction structure incorporating a p-type AlGaN/GaN superlattice. Bulk GaN p-n junction diode displays an ideality factor of 6.9, whereas the one with the superlattice structure displays an ideality factor of 4.0. In addition, device simulation results further strengthen the model by showing that moderately doped unipolar heterojunctions are rectifying and increase the effective ideality factor of a p-n junction structure.
Symposium Y: Gan and Related Alloys MOCVD AlGaN/GaN HFETs on Si: Challenges and Issues
Authors: Rajagopal Pradeep , Roberts John C. , Cook J. W. , Brown J. D. , Piner Edwin L. , Linthicum Kevin J. 
Published: April 2011

ABSTRACTAlGaN/GaN based high power, high frequency high electron mobility transistors (HEMTs) have been in development for over a decade. Although much progress has been made, AlGaN/GaN HEMT technology has yet to be commercialized. The choice of silicon as the substrate for the growth of GaN-based epi layers will enable commercialization of AlGaN/GaN based HEMTs, because of its maturity, scalability, reproducibility and economy. One of the epitaxial issues pertaining to the growth of AlGaN/GaN HEMTs on Si is the understanding of parasitic losses that can adversely impact the RF device performance. The effect of the III-N MOCVD process on the resistivity of the Si substrate, and correlations between the Si substrate resistivity and AlGaN/GaN HEMT RF characteristics are presented. Optimization of the MOCVD growth process led to a reduction in parasitic doping of the Si substrate. This resulted in the following improvements: (a) small signal gain increased from 17 to 21dB, (b) the cut-off frequency increased from 7 to 11GHz and (c) the maximum frequency of oscillation improved from 12 to 20GHz. This optimized process will enhance performance of AlGaN/GaN HEMTs at higher frequencies.
The Structure of Dislocations in GaN Grown by MBE as a Function of the Gallium to Nitrogen Ratio
Authors: Baines Marcus Q. , Cherns David , Novikov Sergei V. , Manfra Michael J. , Thomas Foxon C. 
Published: April 2011

ABSTRACTTransmission electron microscopy (TEM) and atomic force microscopy (AFM) have been used to analyse the core structure of dislocations in GaN grown by molecular beam epitaxy (MBE) as a function of the gallium to nitrogen ratio. Ga-rich samples had a much smoother morphology; TEM observations showed that amorphous deposits decorated some dislocations and occasional surface pits, but weak beam and end-on imaging suggested that, away from the growth surface, dislocations of all types had closed core structures, in contrast to previous observations (Hsu et al, Appl. Phys. Lett. 78, 3980 (2001), Baines et al, Mat. Res. Soc. Symp. Proc. 743, L2.5 (2003)). Ga-poor samples were found to have much rougher surfaces; dislocations were often at the centers of deep surface pits but were observed to be undecorated and to have closed core structures. It is concluded that in growth under Ga-rich conditions, decoration of dislocation cores depends on the accumulation of Ga at surface pits, rather than being a fundamental property of dislocation formation.
Growth of Rhombohedral B12P2 Thin Films on 6H-SiC(0001) By Chemical Vapor Deposition
Authors: Lu Peng , Edgar J. H. , Pomeroy J. , Kuball M. , Meyer H. M. , Aselage T. 
Published: April 2011

ABSTRACTThe parameters necessary to deposit oriented rhombohedral boron phosphide (B12P2) thin films on on-axis Si-face 6H-SiC(0001) substrates by chemical vapor deposition are reported. Ultra high purity BBr3 and PBr3 were used as reactants, with hydrogen as the carrier gas. The BBr3 to PBr3 flow rate ratio was adjusted to obtain good surface morphology of the B12P2 films. BBr3 to PBr3 ratios in the range of 1 to 1.5 produced smooth surfaces and moderate growth rates of 10μm/hr. Higher growth rates were obtained by increasing the BBr3 flow rate, but the surfaces became very rough. The c-axis of the B12P2 film was aligned with the c -axis of the substrate at temperatures between 1650°C-1700°C. The surface morphologies were investigated by SEM and the crystalline properties of the films were characterized by XRD and Raman spectroscopy.
Submicrometer scale growth morphology control for the making of photonic crystal structures
Authors: Gil-Lafon E. , Trassoudaine A. , Castelluci D. , Pimpinelli A. , Saoudi R. , Parriaux O. , Muravaud A. , Darraud C. 
Published: April 2011

ABSTRACTThe feasibility of micrometer scale dielectric periodic structures by using a single selective hydride vapour phase epitaxy (HVPE) step was assessed. HVPE is a near-equilibrium growth process which offers perfect selectivity whatever the pattern design, thus giving rise to a great flexibility. The HVPE growth is also mainly governed by the intrinsic anisotropy of the surface kinetics of the crystal. We demonstrate here that micrometer scale dielectric periodic structures, constituted of perfectly defined 1μm wide GaAs beams alternately stacked with air, can be grown by selective HVPE by controlling the hierarchy of the growth rates of the low index faces of the III-V crystal via the growth temperature and the composition of the vapour phase. Potential of the HVPE growth technic for the making of submicrometer scale structures is finally discussed.
Growth and Properties of AlGaInP Resonant Cavity Light Emitting Diodes (RCLEDs)on Ge/SiGe/Si Substrates
Authors: Kwon O. , Boeckl J. , Lee M. L. , Pitera A. J. , Fitzgerald E. A. , Ringel S. A. 
Published: April 2011

ABSTRACTAlGaInP visible resonant cavity light emitting diodes (RCLEDs) were grown and fabricated on low-dislocation density, SiGe/Si metamorphic substrates by molecular beam epitaxy. A comparison with devices grown on GaAs and Ge substrates showed that not only did the RCLED device structure successfully transfer to the SiGe substrate, but also a higher optical output power was obtained. This is a result of a high thermal conductivity and an enhanced lateral current spreading. In addition, the growth of an AlGaAs current spreading layer and a modified top metal contact were incorporated to the SiGe RCLED to improve the device performance. With these improvements, a 410μm × 410μm device was fabricated with an optical power of 166μW at 665nm peak wavelength under 500mA current injection and an extremely narrow full width half maximum (FWHM) value of 3.63nm for electroluminescent emission under 50mA injection current.