bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Continuum Approach to Two-Component Thin Film Growth
Authors: Yu Yi-Kug , Wille Luc T. 
Published: April 2011

AbstractTheoretical effort so far in understanding epitaxial growth has focused mainly on the one-component growth, i.e. growth that can be fully characterized by a surface (or height) profile. The predictions are also quite limited to the height-height correlation functions as a function of substrate size and the amount of deposition. In this paper, we consider the case of a two-component growth which is quite common in metallic thin films. Instead of using large-scale simulation, we first write down the appropriate two-component growth equations in continuum form. These equations are carefully designed such that in the limit of one-component growth the corresponding equation is recovered. Analytical and numerical analysis of the proposed equations allow us to study the long-range physics associated with these growth processes. Comparison with computer growth experiments is also mentioned.
Bending of an Optical Glass Fiber “Pigtail” in a Splice Box Structure
Authors: Suhir E. 
Published: April 2011

AbstractWe examine a glass fiber “pigtail” in a gain equalization filter (GEF) splice box (SB) design. The fiber experiences bending on the surface of the SB cylinder. The objective of the analysis is to evaluate the “natural” configuration of the fiber, and to suggest, its optimized configuration for minimum curvatures and lower bending stresses. We show that the effect of such an optimization is the largest (about 20%) for cylindrical surfaces of large radii. The obtained solutions can be helpful in the analysis of optical glass fibers experiencing bending on cylindrical surfaces.
RBS Lattice Site Location and Damage Recovery Studies In GaN
Authors: Alves E. , DaSilva M.F. , Soares J.C. , Bartels J. , Vianden R. , Abernathy C.R. , Pearton S.J. 
Published: April 2011

AbstractErbium was implanted with 160 keV at doses between 5x1014 and 5x1015 at/cm2 into (0001) epitaxial GaN on sapphire and annealed at various temperatures between 6000° and 10000° C. The RBS/Channeling technique was used to analyze the damage recovery during different annealing steps and to determine the lattice location of the implanted Er. For a sample implanted with 5x1014 and annealed for 30 min at 600° C a complete overlap of the Er and Ga angular scans across the <0001> axis was observed, indicating that 100% of Er occupies substitutional sites. Measurements along the <101> channel show that Er is located on Ga sites. The damage recovery was slightly better for the samples co-implanted with the same dose of Oxygen in an overlapping profile (E=25 keV). However, a complete recovery of the damage caused by the implantation was not achieved. Samples implanted with higher Er and 0 doses (5x 1015 at/cm2) and at the same energies as above were annealed at 600° for 30 min and at 900°, 1000° C for 120 s using a proximity cap. The higher dose caused an almost complete amorphisation of the surface layer. After annealing indications of epitaxial regrowth were observed, however, the substitutional fraction remains substantially lower and the damage recovery is less complete.
Optical and Structural Properties of AlGaN/GaN Quantum Wells Grown by Molecular Beam Epitaxy
Authors: Grandjean Nicolas , Massies Jean , Leroux Mathieu , Latigt Marguerite , Lefebvre Pierre , Gil Bernard , Allègre Jacques , Bigenwald Pierre 
Published: April 2011

AbstractAIGaN/GaN quantum well (QWs) were grown on (0001) sapphire substrates by molecular beam epitaxy (MBE) using ammonia as nitrogen precursor. The Al composition in the barriers was varied between 8 and 27 % and the well thickness from 4 to 17 monolayers (MLs, 1ML = 2.59Å). X-ray diffraction (XRD) experiments are used to investigate the strain state of both the well and the barriers. The QW transition energy are measured by low temperature photoluminescence (PL). A large quantum confined Stark effect is observed leading to QW luminescence much lower than the emission line of the GaN buffer layer for well width above a certain critical thickness. The built-in electric field responsible for such a phenomenon is deduced from fit of the PL data. Its magnitude is of several hundred kV/cm and increases linearly with the Al composition.
Defect Luminescence in Heavily Mg Doped GaN
Authors: Reshchikov M. A. , Yi G.-C. , Wessels B. W. 
Published: April 2011

AbstractBehavior of the photoluminescence band at about 2.8 eV in heavily Mg doped GaN has been studied at different temperatures and excitation intensities. The 2.8 eV band is attributed to donor-acceptor transitions involving a Mg acceptor. The large blue shift of the band with increasing excitation intensity is explained by variation in the contribution of close and distant pairs to the luminescence. The red shift of the band with increasing temperature under high excitation intensity conditions results from thermal release of carriers from close pairs. The thermal activation energy of the deep donor, about 0.4 eV, is determined from the quenching of the 2.8 eV luminescence band at high temperatures.
Mechanisms of Optical Gain in Cubic GaN and Ingan
Authors: Holst J. , Hoffmann A. , Broser I. , Frey T. , Schöttker B. , As D.J. , Schikora D. , Lischka K. 
Published: April 2011

AbstractThe epitaxial growth of zinc-blende (cubic) GaN and InGaN on GaAs with a common cleavage plane and readily high-quality, low-cost wafers may be considered as an alternative approach for the future realization of cleaved laser cavities. To obtain detailed information about the potential of cubic GaN and InGaN for device applications we performed optical gain spectroscopy accompanied by time-integrated and time-dependent photoluminescence measurements at 2 K and 300 K. From intensity-dependent gain measurements, the identification of the gain processes was possible. For moderate excitation levels, the biexciton decay is likely to be responsible for a gain structure at 3.265 eV in cubic GaN [10]. For the highest pump intensities, the electron- hole-plasma is the dominant gain process, providing gain values up to 200 cm-1. Furthermore cubic GaN samples with different cavity lengths from 250 to 600 mim were cleaved to investigate the influence of the sample geometry on the gain mechanisms. In these samples increased gain values up to 150 cm-1 as well as lower threshold excitation densities were observed, indicating the potential of cubic GaN for device applications. The results of GaN will be compared with intensity-dependent gain measurements on InGaN samples, grown on GaAs with varying In-content. The observed gain mechanisms in cubic InGaN will be discussed in detail.
Spectroscopic Studies in InGaN Quantum Wells
Authors: Chichibu S. E , Sota T. , Wada K. , DenBaars S. P , Nakamura S. 
Published: April 2011

AbstractFundamental electronic modulations in strained wurtzite If-nitride, in particular InxGa1-xN, quantum wells (QWs) were treated to explore the reason why practical InGaN devices emit bright luminescences in spite of the large threading dislocation (TD) density. The emission mechanisms were shown to vary depending on the well thickness L and InN molar fraction x. The electric field across the QW plane, F, which is a sum of the fields due to spontaneous and piezoelectric polarization and the pn junction field, causes the redshift of the ground state resonance energy through the quantum confined Stark effect (QCSE). The absorption spectrum is modulated by QCSE, quantum-confined Franz-Keldysh effect (QCFK), and Franz-Keldysh (FK) effect from the barrires when, for the first approximation, potential drop across the well (F/L) exceeds the valence band discontinuity, δEv. Under large F/L, holes are confined in the triangular potential well formed at one side of the well. This produces apparent Stokes-like shift in addition to the in-plane net Stokes shift on the absorption spectrum. The QCFK and FK further modulate the electronic structure of the wells with L greater than the three dimensional (3D) free exciton (FE) Bohr radius, aB. When F/L exceeds ΔEc, both electron (e) and hole (h) confined levels drop into the triangular potential wells at opposite sides of the wells, which reduces the wavefunction overlap. Doping of Si in the barriers partially screens the F resulting in a smaller Stokes-like shift, shorter recombination decay time, and higher emission efficiency. Finally, the use of InGaN was found to overcome the field-induced oscillator strength lowering due to the spontaneous and piezoelectric polarization. Effective in-plane localization of the QW excitons (confined excitons, or quantized excitons) in quantum disk (Q-disk) size potential minima, which are produced by nonrandom alloy potential fluctuation enhanced by the large bowing parameter and F, produces confined e-h pairs whose wavefunctions are still overlapped when L<aB. Their Coulomb interaction is more pronounced for F L<ΔEv.
Ranges of Deposition Temperatures Applicable for Metalorganic Vapor Phase Epitaxy of GaN Films Via the Technique of Pendeo-Epitaxy
Authors: Thomson D. B. , Gehrke T. , Linthicum K. J. , Rajagopal P. , Davis R. F. 
Published: April 2011

AbstractPendeo-epitaxy is a type of selective growth of thin films from the sidewalls of etched forms. The resulting films are suspended from the sidewalls and do not interface with the substrate. This process route has advantages over conventional lateral epitaxial overgrowth (LEO) techniques. In this research, pendeo-epitaxial growth of GaN films has been achieved on elongated GaN seed columns. The seed columns were etched from GaN grown on 6H-SiC (0001) substrates via metalorganic vapor phase epitaxy (MOVPE). Silicon nitride mask layers atop the GaN seed columns forced growth from the sidewalls. Pendeo-epitaxial growth of GaN was investigated using several growth temperatures. Higher growth temperatures resulted in improved coalescence due to greater lateral to vertical growth ratios.
High Quality Hydrothermal ZnO Crystals
Authors: Suscavage M. , Harris M. , Bliss D. , Yip P. , Wang S.-Q. , Schwall D. , Bouthillette L. , Bailey J. , Callahan M. , Look D. C. , Reynolds D. C. , Jones R. L. , Litton C. W. 
Published: April 2011

AbstractZinc Oxide crystals have historically been grown in hydrothermal autoclaves with a basic mineralizer; however, doubts have been raised about the quality of such crystals because they have often exhibited large x-ray rocking curve widths and low photoluminescence (PL) yield with large linewidths. Several ZnO crystals were grown hydrothermally and sliced parallel to the c-plane. This resulted in opposite surfaces (the C+ and C-) exhibiting pronounced chemical and mechanical differences. Different surface treatments were investigated and compared by PL both at room temperature and liquid helium temperatures, and by double axis X-ray rocking curve measurements. The high quality of hydrothermally-grown ZnO is substantiated by the narrow rocking curve widths and sharp PL peaks obtained. A critical factor in obtaining these results was found to be surface preparation.
Si Delta Doped GaN Grown by Low-Pressure Metalorganic Chemical Vapor Deposition
Authors: Kim Jong-Hee , Yang Gye Mo , Choi Sung Chul , Choi Ji Youn , Cho Hyun Kyung , Lim Kee Young , Lee Hyung Jae 
Published: April 2011

AbstractSi delta-doping in the GaN layer has been successfully demonstrated by low-pressure metalorganic chemical vapor deposition at a growth temperature of 1040°C. Si delta-doping concentration increases and then decreases with an increase in delta-doping time. This indicates that delta-doping concentration is limited by the desorption process owing to much higher thermal decomposition efficiency of silane at high growth temperatures of GaN. In addition, it was observed that the use of a post-purge step in the ammonia ambient reduces Si delta-doping concentration. From capacitance-voltage measurement, a sharp carrier concentration profile with a full-width at half maximum of 4.1 nm has been achieved with a high peak concentration of 9.8 x 1018 cm-3
Influence of Doping on the Lattice Dynamics of Gallium Nitride
Authors: Kaschner A. , Siegle H. , Hoffmann A. , Thomsen C. , Birkle U. , Einfeldt S. , Hommel D. 
Published: April 2011

AbstractWe present results of Raman-scattering experiments on GaN doped with Si, C, and Mg, respectively, grown by molecular beam epitaxy (MBE). The influence of the different dopants on strain and free-carrier concentration was investigated. Furthermore, we report on several local vibrational modes (LVM) around 2200 cm-1 in Raman spectra of highly Mg-doped GaN. A possible explanation of these high-energy modes in terms of hydrogen-related vibrations is given. We also found a variety of new structures in the range of the GaN host lattice phonons. Secondary ion mass spectroscopy (SIMS) was applied to determine the concentration of magnesium and unintentionally incorporated hydrogen.
Photoluminescence Excitation Spectroscopy of Carbon-Doped Gallium Nitride
Authors: Reuter E. E. , Zhang R. , Kuech T. F. , Bishop S. G. 
Published: April 2011

AbstractWe have done a comparative study of carbon-doped GaN and undoped GaN utilizing photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies in order to investigate deep levels involved in yellow luminescence (YL) and red luminescence (RL). When the GaN was excited by above-bandgap light, red luminescence (RL) centered at 1.82 eV was the dominant below-gap PL from undoped GaN, but carbon-doped GaN below-gap PL was dominated by yellow luminescence (YL) centered at 2.2 eV. When exciting PL below the band-gap with 2.4 eV light, undoped GaN had a RL peak centered at 1.5 eV and carbon-doped GaN had a RL peak centered at 1.65 eV. PLE spectra of carbon-doped GaN, detecting at 1.56 eV, exhibited a strong, broad excitation band extending from about 2.1 to 2.8 eV with an unusual shape that may be due to two or more overlapping excitation bands. This RL PLE band was not observed in undoped GaN. We also demonstrate that PL spectra excited by below gap light in GaN films on sapphire substrates are readily contaminated by 1.6-1.8 eV and 2.1-2.5 eV chromium-related emission from the substrate. A complete characterization of the Cr emission and excitation bands for sapphire substrates enables the determination of the excitation and detection wavelengths required to obtain GaN PL and PLE spectra that are free of contributions from substrate emission.
Selective Area Growth (SAG) and Epitaxial Lateral Overgrowth (Elo) of GaN Using Tungsten Mask
Authors: Kawaguchi Yasutoshi , Nambu Shingo , Sone Hiroki , Yamaguchi Masahito , Miyake Hideto , Hiramatsu Kazumasa , Sawaki Nobuhiko , Iyechika Yasushi , Maeda Takayoshi 
Published: April 2011

AbstractSelective area growth (SAG) and epitaxial lateral overgrowth (ELO) of GaN using tungsten (W) mask by metalorganic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE) have been studied. The selectivity of the GaN growth on the W mask as well as the SiO2 mask is excellent for both MOVPE and HVPE. The ELO-GaN layers are successfully obtained by HVPE on the stripe patterns along the <1100> crystal axis with the W mask as well as the SiO2 mask. There are no voids between the SiO2 mask and the overgrown GaN layer, while there are triangular voids between the W mask and the overgrown layer. The surface of the ELO-GaN layer is quite uniform for both mask materials. In the case of MOVPE, the structures of ELO layers on the W mask are the same as those on the SiO2 mask for the <1120> and <1100> stripe patterns. No voids are observed between the W or SiO2 mask and the overgrown GaN layer by using MOVPE.
Epitaxial Lateral Overgrowth of GaN on SiC and Sapphire Substrates
Authors: Yu Zhonghai , Johnson M.A.L. , Brown J.D. , El-Masry N.A. , Muth J. F. , Cook J.W. , Schetzina J.F. , Haberern K.W. , Kong H.S. , Edmond J.A. 
Published: April 2011

AbstractThe epitaxial lateral overgrowth (ELO) process for GaN has been studied using SiC and sapphire substrates. Both MBE and MOVPE growth processes were employed in the study. The use of SiO2 versus SiNx insulator stripes was investigated using window/stripe widths ranging from 2 μm/4 μm to 3 μm/15 μm. GaN film depositions were completed at temperatures ranging from 800°C to 1120°C. Characterization experiments included RHEED, TEM, SEM and cathodolumenescence studies. The MBE growth experiments produced polycrystalline GaN over the insulator stripes even at deposition temperatures as high as 990°C. In contrast, MOVPE growth produced single-crystal GaN stripes with no observable threading dislocations.
Photoluminescence of Fs-GaN Treated in Alcoholic Sulfide Solutions
Authors: Zhilyaev Y.V. , Kompan M.E. , Konenkova E.V. , Raevskii S.D. 
Published: April 2011

AbstractResults are presented on the photoluminescence of n-GaN (T=300 K) after surface treatment with sulfide (Na2S and (NH4)2S) solutions in water or isopropyl alcohol.It has been shown that the intensity of the n-GaN photoluminescence band is enhanced as a result of the surface treatment with alcoholic sulfide solutions, this enhancement being greater for a strongly basic Na2S solution than for a weakly basic (NH4)2S solution.
Xps Study of Oxygen Adsorption on (3X3) Reconstructed MBE Grown GaN Surfaces
Authors: Beach R. A. , Piquette E. C. , McGill T. C. , Watson T. J. 
Published: April 2011

AbstractThe incorporation of oxygen onto the (3x3) reconstructed surface of GaN(0001) has been studied using X-ray Photoelectron Spectroscopy (XPS). It was found that the (3x3) reconstruction corresponds to a fractional Ga adlayer atop a Ga terminated GaN surface. Our measurements indicate a surface coverage of 1.15 ± 0.2 monolayers of relaxed Ga on the surface. The binding energy separation between the relaxed surface Ga3d core level and bulk Ga3d level was measured to be 1.1 ± 0.1 eV. A metallic component extending from the bulk GaN valence band maximum out to 0 eV was also present in the XPS spectrum. The separation between the bulk valence band maximum and the Fermi level of the metallic component was found to be 2.1 ± 0. 1 eV. The relaxation of the surface Ga was found to decrease with oxygen exposure indicating Ga-O bonding, with oxygen adsorption terminating at 1.3 ± 0.2 monolayers. The Ols core level was found to have a FWHM of 2.0 ± 0.1 eV.
Extrinsic Performance Limitations of AlGaN/GaN Heterostructure Field Effect Transistors
Authors: Ruden P.P. , Albrecht J.D. , Sutandi A. , Binaril S.C. , Ikossi-Anastasiou K. , Ancona M.G. , Henry R.L. , Kolesket D.D. , Wickendent A.E. 
Published: April 2011

AbstractExtrinsic effects on the DC output characteristics of AlGaN/GaN HFETs with lllm gate lengths are examined. The devices investigated were fabricated on MOCVD-grown AlGaN/GaN heterostructures on sapphire substrates. An analytical model that takes into account parasitic resistances and thermal effects is constructed, and its results are compared with experimental data. With parameters determined from characterization experiments on the same wafer and from independent theoretical results, the agreement between the data and the model predictions is found to be very good. The model is then applied to performance predictions for devices with improved series resistances and heat sinking.
Temperature Dependence of Bound Exciton Emissions in GaN
Authors: Chtchekine D. G. , Gilliland G. D. , Feng Z. C. , Chua S. J. , Wolford D. J. , Ralph S. E. , Schurman M. J. , Ferguson I. 
Published: April 2011

AbstractThe dissociation channels of two prominent bound exciton complexes in wurtzite GaN thin films are determined via an extensive temperature dependent photoluminescence study. The shallow donor bound exciton dissociation at low temperatures (T ≤ 50 K) is found to be dominated by the release of a free exciton with thermal activation energy consistent with the exciton localization energy. At higher temperatures a second dissociation channel with activation energy EA = 28 ± 2 meV is observed. The dissociation of a bound exciton complex with exciton localization energy Exloc = 11.7 meV is also dominated by the release of a free exciton. In contrast to previous studies evidence is presented against the hypothesis of this emission being due to the exciton bound to an ionized donor. We find that it originates most likely from an exciton bound to a neutral acceptor.
Physics-Based Intrinsic Model for AlGaN/GaN HEMTs
Authors: Wu Shangli , Webster Richard T. , Anwar A. F. M. 
Published: April 2011

AbstractDC and intrinsic small signal parameters are reported for AlGaN/GaN high electron mobility transistors. The calculations are based upon a self-consistent solution of Schrödinger and Poisson's equation to model the quantum well formed in GaN. Transport parameters are obtained from an ensemble Monte Carlo simulation.
Theoretical Studies of ZnO and Related MgxZn1-xO Alloy Band Structures
Authors: Lambrecht Walter R. L. , Limpijumnong Sukit , Segall B. 
Published: April 2011

AbstractFirst principles calculations are carried out for ZnO, MgO and ZnMgO2 in various crystal structures. The nature of the valence band ordering in ZnO is shown to depend strongly on the Zn3d band position. MgO in the wurtzitic form is found to gave an unusual 5-fold coordiated structure. The band gap dependence in the alloy system is found to be in fair agreement with experimental data and the band-offset is predicted to be type I.
Uniformity and Performance Characterization of GaN P-I-N Photodetectors Fabricated From 3-Inch Epitaxy
Authors: Hickman R. , Klaassen J. J. , Hove J. M. Van , Wowchak A. M. , Polley C. , Rosamond M. F. , Chow P. P. 
Published: April 2011

AbstractGallium nitride wafer epitaxy on large diameter substrates is critical for the future fabrication of large area UV linear or 2D imaging arrays, as well as for the economical production of other GaN-based devices. Typical group III-nitride deposition is now performed on 2-inch diameter or smaller sapphire substrates. Reported here are visible blind, UV GaN p-in photodetectors which have been fabricated on 3-inch diameter (0001) sapphire substrates by RF atomic nitrogen plasma MBE. The uniformity across the wafer of spectral responsivity and shunt resistance (R0) for the p-i-n photodetectors has been characterized. Spectral responsivity and 1/f noise as a function of temperature exceeding 250°C will be presented for the GaN p-i-n photodetectors. Spectral response with >0.17 A/W at peak wavelength and having 4-6 orders of magnitude visible rejection has been achieved. 1/f noise typically less than 10-14 A/Hz1/2 at room temperature also has been achieved with GaN p-i-n photodiodes. The results have been correlated with proposed models for dark current and 1/f noise in GaN diodes.
Analysis of Compression Behavior of a [011] TA Single Crystal with Orientation Imaging Microscopy and Crystal Plasticity
Authors: Schwartz A.J. , Stölken J.S. , King W.E. , Campbell G.H. , Lassila D.H. , Shu J.Y. , Sun S. , Adams B.L. 
Published: April 2011

AbstractHigh-purity tantalum single crystal cylinders oriented with [011] parallel to the cylinder axis were deformed 10, 20, and 30 percent in compression. The engineering stress-strain curve exhibited an up-turn at strains greater than ∼20% while the samples took on an ellipsoidal shape during testing, elongated along the [100] direction with almost no dimensional change along [011]. Two orthogonal planes were selected for characterization using Orientation Imaging Microscopy (OIM): one plane containing [100] and [011] (longitudinal) and the other in the plane containing [011] and [011] (transverse). OIM revealed patterns of alternating crystal rotations that develop as a function of strain and exhibit evolving length scales. The spacing and magnitude of these alternating misorientations increases in number density and decreases in spacing with increasing strain. Classical crystal plasticity calculations were performed to simulate the effects of compression deformation with and without the presence of friction. The calculated stressstrain response, local lattice reorientations, and specimen shape are compared with experiment.