bluuebunny/crossref_metadata_2025_split huggingface dataset:
In-Situ Measurements of Islanding and Strain Relaxation of Ge/Si(111)
Authors: Deelman P. W. , Schowalter L. J. , Thundat T. 
Published: April 2011

AbstractWe have measured strain relaxation and islanding in Ge films grown by molecular beam epitaxy on Si(111) at substrate temperatures between 450°C and 700°C in real time with reflection high energy electron diffraction (RHEED). At 450°C, we observe an oscillation of the surface lattice parameter for the first three bilayers (BL), followed by a sharp 2D–3D growth mode transition, when transmission diffraction features appear in RHEED. The surface lattice parameter then begins to relax at an initial rate of about 0.5%/BL. The mechanisms of island growth and strain relaxation change with growth temperature. At 500°C the surface lattice parameter begins to relax after only 1BL; at 550°C relaxation begins immediately. However, 3D spots do not appear until after 3.5BL at either temperature. The initial rate of strain relaxation decreases with increasing temperature until, at 700°C (when 3D spots never appear), it is only 0.04%/BL. This behavior may be explained by a temperature-dependent roughness length scale, as well as by differences in dislocation nucleation at low and high temperatures. At low temperature, atomic force microscope images show the development of small (1000Å), faceted islands with aspect ratios (height/width) on the order of 0.07. The formation of well-defined facets is inhibited at higher temperatures. At 700°C, islands grow very large (lμm) from the outset, with aspect ratios less than 0.015. These islands cannot thicken much, because dislocations can glide in easily at their edges. The islands grow laterally quickly, and the strain in the “new” islands is not substantially less than that in the “old.” At 700°C, 28% of the Ge/Si misfit strain may be relieved by diffusion.
Stress of Platinum Thin Films Deposited by Dc Magnetron Sputtering Using Argon/Oxygen Gas Mixture
Authors: Kim Min Hong , Park Tae-Soon , Lee Dong-Su , Lee Yong Eui , Park Dong-Yeon , Woo Hyun-Jung , Chun Dong-Il , Yoon Euijoon , Ha Jowoong 
Published: April 2011

AbstractPt thin films were deposited by a DC magnetron sputtering with Ar/O2 gas mixtures. Due to the oxygen incorporation into the Pt films, deposition rate and resistivity of as-deposited Pt thin films increased with oxygen fraction in the sputtering gas. No peaks from crystalline Pt oxides were observed by x-ray diffraction (XRD) and excessive oxygen incorporation into Pt lead to an amorphous Pt oxide formation. More oxygen could be incorporated in the Pt thin films deposited at lower temperatures and at higher total pressures. Incorporated oxygen was completely removed after an annealing at 800 °C for an hour in air ambient, as the resistivity of the Pt thin films recovered their bulk resistivity values. Tensile stress of the Pt films decreased with oxygen incorporation, and approached a saturation level at high resistivity of the films, presumably due to the formation of amorphous Pt oxides.
3-D Atomistic Kinetic Monte Carlo Simulations of Point Defect Incorporation During CVD Diamond Film Growth
Authors: Battaile C. , Srolovitz D. J. , Butler J. E. 
Published: April 2011

AbstractThe incorporation of vacancies and H atoms into { 100}- and { 111 }-oriented diamond films during CVD growth in an atmosphere of H, H2, CH3, and C2H2is simulated atomistically. The growing films are represented in three dimensions by a diamond cubic lattice, and the temporal evolution of the surfaces is accomplished by a kinetic Monte Carlo method. The dimer bonding of diamond atoms on the { 100} surface is treated explicitly. Growth begins on { 100}(2xl):H and { 11 }:H surfaces containing 288 and 300 atoms, respectively, in the surface plane, and the growth of approximately sixty atomic layers (18,000 atoms) is accomplished at each of fifteen substrate temperatures between 800 and 1500 K. The growth rates depend on the combined contributions to growth from CH3and C2H2, whereas the point defect concentrations depend on the ratio of C2H2to CH3growth. The maximum { 100} growth rate is achieved at approximately 1200 K. Point defect concentrations are low at temperatures below 1300 K, but become high above 1300 K. Growth efficiency, defined as the ratio of growth rate to defect concentration, is maximum for both film orientations at substrate temperatures in the vicinity of 1100 to 1200 K.
Cluster Model Study to the As2-Adsorption on GaAs(001)-Surfaces
Authors: Marek T. , Strunk H. P. , Kunsági-Máté S. , Mareka N. 
Published: April 2011

AbstractWe study by using ab-initio methods the adsorption of As2-molecules on a Gaterminated GaAs(001) surface. We represent the GaAs crystal by a Ga5As2H8 cluster, which is large enough to resemble the crystal but sufficiently small to be tractable in a computer in a reasonable time. We calculate the reaction path along the symmetry axis C2 of this cluster and obtain the reaction path by minimizing the total energy of the system (cluster plus molecule). In the calculated positions above the cluster we account for the possibility of the As2-molecule to rotate around the C2 symmetry axis and for a change in the distance between the As-atoms. As a main result we obtain that for heights above the (001) surface less than about 3.5A we find a clear influence of the discrete atomic surface structure on the reaction path of the As2-molecule.
Morphology Studies of Oxide Films Deposited by Rf Plasma Technique
Authors: Hunt D. J. , Moss R. W. , Olson J. E. , Lee D. H. , Wang X. W. 
Published: April 2011

AbstractRecently, an energetic film growth technique was developed. In this process, an RF (radio frequency) plasma was ignited in an ambient atmospheric environment. An aqueous solution was excited into mist, which was then fed into the plasma reactor. After vaporization, films were formed on substrates outside the plasma. As a by-product, small amount of powders were collected in the plasma reactor. Films studied were indium-tin oxide (ITO), aluminum oxide (Al2O3), and lanthanum strontium manganite oxides (LaSrMnO). Films and powders were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX, EDS), and Ultraviolet-Visible (UV-Vis) transmission measurements. Morphology of a film surface was dependent on deposition conditions, such as chemical composition of the precursor materials, precursor feeding rate, and/or substrate temperature.
Nonlinear Optical Mapping of Cubic Silicon Carbide Micron Areas In Epitaxial Films of Hexagonal Polytypes
Authors: Lüpke G. , Meyer C. , Busch O. , Kamicuski E. Stein von , Göz A. , Kurz H. 
Published: April 2011

AbstractVarious silicon carbide polytypes, such as 4H-, 6H- and 3C-SiC are clearly distinguished by the magnitude and rotational anisotropy of their optical second-harmonic (SH) response. The large dynamic range of the SH response of more than two orders of magnitude between these polytypes allows a fast and non-invasive mapping of 3C-SiC micron areas in 4H - and 6H-SiC epilayers. 3C-Microcrystallites of different oricutations are identified from SH rotational anisotropy scans.
Multilayer Fresnel Zone Plate For 8KeV X-Ray by DC Magnetron Sputtering Deposition
Authors: Tamura S. , Mori K. , Maruhashi T. , Yoshida K. , Ohtani K. , Kamijyo N. , Suzuki Y. , Kihara H. 
Published: April 2011

AbstractHard X-ray microprobes from synchrotron radiation ( SR ) sources should be powerful tools for various fields of research. A Fresnel zone plate ( FZP ) is a promising focusing element for X-ray. In order to develop high performance multilayer FZP for use in hard X-ray region, Ag/C and Cu/Al concentric multilayers were prepared by some deposition parameters. A dependence of the zone boundary structures on the Ar gas pressure was observed: the multilayer prepared at lower Ar gas pressure had smoother zones. Substrate cooling did not improve the zone boundary structures. From the focusing test of the Cu/Al FZP by the SR, a microbeam of 1.3 μ m ø has been obtained for 8 KeV X-ray (λ =0.154nm).
Reliability Improvement of Aluminum Wirebonds in High‐Power Igbt Modules
Authors: Wu Yujing , Thome Gene , Scott Savage Timothy 
Published: April 2011

AbstractWirebonding is the weakest area of device packaging of power IGBT modules. Accelerated thermal fatigue testing causes cracks to form and propagate in the aluminum wirebond at the foot area. This study examined the relationship of the wirebond reliability and the aluminum wire grain structure, which can be affected by post‐wirebond heat treatment. A series of wirebonded IGBTs were annealed at a temperature range from 280°C to 400°C for up to 60 minutes. Wirebond shear strengths versus temperature cycles were examined. Cross‐sectional SEM was used to examine both aluminum grain size development by annealing and crack initiation and propagation in the wirebonds after temperature cycling. It was found that aluminum grain size was increased by post‐wirebond annealing. With temperature cycling, the wirebond shear strengths of the as‐wirebonded samples decrease rapidly, and lifted wirebonds were present after 1500 temperature cycles. The lifted wirebonds typically break within the aluminum wire near the wire/metallization interface. The shear strength of the wirebonds with post‐wirebond annealing showed no significant change even after 5000 temperature cycles, and there were no signs of significant deterioration of the wirebonds either. The wirebond crack initiation and growth rates were depressed substantially by larger aluminum grains. Annealing of the aluminum wire after wirebonding provided increased aluminum grain size resulting in improved reliability of the wirebonds of high power modules.
Application Of Electroless Copper Plating Technology For Thin Film Laminated Multilayer Wiring Board
Authors: Itabashi T. , Akahoshi H. , Takahashi A. , Suzuki M. , Maeda M. 
Published: April 2011

AbstractA thin film laminated high density multilayer wiring board was developed using electroless copper plating technology. The basic steps in the fabrication process are: laminating the high heat resistant polymer film, forming via holes by plasma etching and filling them by electroless copper metallization. The 25 μm diameter via holes can be completely filled with copper using the selective electroless plating method. This paper describes the fabrication process, focusing particularly on electroless copper plating.
High-Quality Photoconductive Ultraviolet GaN/6H-SiC Detector and Its Properties
Authors: Yang K. , Zhang R. , Zang L. , Shen B. , Chen Z.Z. , Zheng Y.D. , Bao X. M. , Huang Z.C. , Chen J.C. 
Published: April 2011

ABSTRACTThe properties of photoconductive ultraviolet detector based on GaN epilayer grown on 6H-SiC substrate by metalorganic chemical vapor deposition were investigated in this paper. We obtained the detectable energy span of the device up to ultraviolet by photocurrent measurement. The spectral responsivity remained nearly constant for wavelengths from 250 to 365 nm and dropped by three orders of magnitude within 10 nm of the band edge (by 380 nm). The detector was measured to have a responsivity of 133 A/W at a wavelength of 360 nm under a 5-V bias, and the voltage-dependent responsivity was performed. Furthermore, an easy method was developed to determine the response time, and the relationship between response time and bias was obtained.
Microstructures of AlN Buffer Layers for the Growth of GaN on (0001) Al2O3
Authors: Yeadon M. , Kim W. , Botchkarev A. E. , Mohammad S. N. , Morkoc H. , Gibson J. M. 
Published: April 2011

ABSTRACTIll-nitride semiconductors are emerging as highly promising candidates for the fabrication of wide band-gap electronic and opto-electronic devices. Sapphire ((α-A12O3) is currently one of the primary substrates of choice for the growth of GaN despite a large lattice mismatch. Significant improvements in the quality of III-nitride layers have been demonstrated by exposure of the substrate to reactive nitrogen species followed by deposition of a low temperature AIN or GaN buffer layer. In this paper we present a study of the evolution of the surface topography and defect microstructure of nitrided α-A12O3 substrates and AIN buffer layers deposited by reactive molecular beam epitaxy (RMBE). Their influence on the morphology and properties of GaN layers is also discussed. Both nitridation time and AIN deposit thickness were varied systematically, at different temperatures and buffer growth rates. The microstructures were characterized using the atomic force microscope (AFM) and transmission electron microscope (TEM). Initial growth studies are ideally suited to in-situ experiments, and further investigations are also in progress using a unique UHV TEM with the facility for in-situ RMBE.
Morphology and Dielectric Properties of Reactively Sputtered Aluminum Nitride Thin Films
Authors: Randolph A. G. , Kurinec S.K. 
Published: April 2011

ABSTRACTAluminum nitride thin films (∼ 100 mn) have been deposited on silicon substrate by reactive sputtering using Al target in 1:1 Ar:N2 environment. The atomic force microscopy examination revealed continuous microcrystalline film structure. The Auger electron spectroscopic analysis show the presence of oxygen in the films. The annealing at 850 C in nitrogen is found to cause recrystallization and further oxidation of the films. The films can be characterized as lossy dielectrics with relative permittivity ∼ 10, higher than the bulk value of 8.9. Annealing the films is found to reduce anion vacancies and improve the dielectric strength within a range of a few MV/cm in these thin films.
Growth of Hexagonal Gallium Nitride Films On The (111) Surfaces of Silicon with Zinc Oxide Buffer Layers
Authors: Kim Y. , Kim C. G. , Lee K-W. , Yu K-S. , Park J. T. , Kim Y. 
Published: April 2011

ABSTRACTThe growth of gallium nitride films on sapphire substrates has not been straightforward because of the large lattice mismatch between gallium nitride and sapphire. Zinc oxide is structurally the closest material to gallium nitride and therefore is finding use as the substrate for gallium nitride. Single crystal wafers of zinc oxide are hard to obtain and very expensive. However, a thin layer of zinc oxide on a suitable substrate might solve this problem. In this work, highly c-axis oriented zinc oxide buffer layers were grown on Si(lll) substrates at temperatures 410–540 °C by chemical vapor deposition of bis(2,2,6,6-tetramethyl–3,5-heptanedionato)zinc, Zn(tmhd)2, and the hexagonal GaN films were subsequently deposited on them at 500 °C using the single precursor tris(diethyl -μ-amido-gallium), [(C2H5)2 GaNH2]3. The compound Zn(tmhd)2 was found to require oxygen for the deposition of zinc oxide. In the case of gallium nitride, low pressure chemical vapor deposition of tris(diethyl-μ-amido-gallium) worked reasonably well with or without a carrier gas. The buffer layers and the GaN films were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and reflection high energy elctron diffraction (RHEED).
Observation of Midgap States in GaN with Optical-Isothermal Capacitance Transient Spectroscopy
Authors: Hacke P. , Miyoshi H. , Hiramatsu K. , Okumura H. , Yoshida S. , Okushi H. 
Published: April 2011

ABSTRACTOptical-isothermal capacitance transient spectroscopy (O-ICTS) was used to distinguish the deep levels which occur in unintentionally doped n-type GaN by means of their characteristic optical cross section. GaN grown by metalorganic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE) were compared. Correspondence between optical and thermal emission characteristics of previously discovered levels, E2 (∼Ec-0.55 eV) and E4 (∼EC-1.0 eV), were clearly determined by observing their sequential appearance in the ICTS spectra. Whether by thermal or optical stimulation, the emission from E4 was found to be broad in nature; it is consequently believed to involve a defect. The total measured concentration of deep levels, including a prominent level which photoionizes in the range 2.5 to 3.0 eV below the conduction band, is greater in the GaN grown by MOVPE than by HVPE that was tested.
Photoluminescence, Reflectance, and Magnetospectroscopy of Shallow Excitons in GaN
Authors: Skromme B. J. , Zhao H. , Goldenberg B. , Kong H. S. , Leonard M. T. , Bulman G. E. , Abernathy C. R. , Pearton S. J. 
Published: April 2011

ABSTRACTWe report several new aspects of the excitonic properties of heteroepitaxial GaN grown on sapphire or 6H-SiC. In particular, we observed the n = 2 free exciton associated with both A and B excitons (which are distinct from the n = 1 C exciton) using reflectance and 1.7 K photoluminescence. We also studied the behavior of the n = 2 A-exciton using magnetoluminescence in fields up to 12 T. The large diamagnetic shift and splitting positively confirm the identification, yielding an exciton binding energy of about 26.4 meV. Several previous identifications of the n = 2 free exciton yielding a smaller exciton binding energy are probably in error, based on our results. We have also detected the two-electron replica of the neutral donor-bound exciton for the first time in GaN and observed its splitting pattern in magnetic fields up to 12 T. This feature is 22 meV below the principal neutral donor-bound exciton peak, independently of strain shifts in the overall spectrum. It yields a precise donor binding energy of 29 meV for the shallow residual donor in material grown by metalorganic chemical vapor deposition and gas-source molecular beam epitaxy, considerably smaller than that of the residual donor reported earlier in hydride vapor phase epitaxial material (about 35.5 meV).
Variation of GaN Valence Bands with Biaxial Stress: Quantification of Residual Stress and Impact on Fundamental Band Parameters
Authors: Edwards N. V. , Yoo S. D. , Bremser M. D. , Horton M. N. , Perkins N. R. , Weeks T. W. , Liu H. , Stall R. A. , Kuech T. F. , Davis R. F. , Aspnes D. E. 
Published: April 2011

ABSTRACTWe provide the widest estimate thus far of the range of tensile and compressive stress (−3.8 to 3.5 kbar) that GaN epitaxial material can withstand before relaxation occurs, and an unambiguous determination of the spin-orbit splitting Δso = 17.0 ± 1 meV for the material. These are achieved by analyzing 10K reflectance data for the energy separation of transitions between the uppermost valence bands and the lowest conduction band of wurtzitic GaN as a function of biaxial stress for a series of GaN films grown on both Al2O3 and 6H-SiC substrates. Our data explicitly show the nonlinear behavior of the excitonic energy splittings B-A and C-A vs. the energy position of the A exciton, which stands in contrast to the linear approximations used by previous workers analyzing material grown only on Al2O3 substrates. Further, the lineshape ambiguities present in GaN reflectance spectra that hindered the accurate determination of such excitonic energies have also been resolved by analyzing these data in reciprocal space, where critical point energies are determined by phase effects to an accuracy of ±0.5 meV.
Shallow Impurity States in Wurtzite and Zinc Blende Structure GaN
Authors: Wang R. , Ruden P. P. , Kolnik J. , Oguzman I. , Brennan K. F. 
Published: April 2011

ABSTRACTCalculations of shallow donor states for wurtzite and zincblende structure GaN, and acceptor states for zincblende GaN in an effective mass approximation are presented. Band parameters were taken from experiment or determined from band structure calculations. The effect of wavevector dependent screening is examined, based on dielectric functions calculated from empirical pseudopotential band structures. For donor states, the effects of electron-phonon coupling and free carrier screening in the Thomas-Fermi and Debye approximations are discussed briefly.
Blue Luminescence from SiOx Films Containing Ge Nanocrystals
Authors: Zacharias M. , Weigand R. , Bläsing J. , Christen J. 
Published: April 2011

AbstractWe present a systematic analysis of SiOx alloys films containing Ge nanocrystals prepared by dc magnetron sputtering. Increasing the sputtering power (50–175W) reduces the average Ge nanocrystal size exponentially down to ∼2nm. Broad band photoluminescence spectra are observed in the visible at room temperature centered at ∼3eV or/and ∼2eV. Neither the 3eV nor the 2eV luminescence can be correlated to the change in the size. Excluding the quantum-confined origin, the presence of a luminescence center located in the inhomogeneous strain field of the Ge nanocrystal surface is discussed.
Soft X-Ray Emission Studies of the Electronic Structure in Silicon Nanoclusters
Authors: Van Buuren T. , Dinh L. N. , Chase L. L. , Siekhaus W. J. , Jimenez I. , Terminello L. J. , Grush M. , Callcott T. A. , Carlisle J. A. 
Published: April 2011

AbstractDensity of states changes in the valence and conduction band of silicon nanoclusters were monitored using soft x-ray emission and absorption spectroscopy as a function of cluster size. A progressive increase in the valence band edge toward lower energy is found for clusters with decreasing diameters. A similar but smaller shift is observed in the near-edge x-ray absorption data of the silicon nanoclusters.
Raman Scattering Investigation of Superconductivity in Si46 Clathrates
Authors: Fang S. L. , Grigorian L. , Rao A. M. , Eklund P. C. , Dresselhaus G. , Dresselhaus M. S. , Kawaji H. , Yamanaka S. 
Published: April 2011

AbstractRoom temperature Raman scattering spectra are reported for the type II superconductors MxBaySi46 (M-Na, K) which were recently shown to exhibit Tc's ∼ 3.5 K. The spectra are compared to those of other Si46-clathrates which exhibit normal metallic behavior down to 2K. Thirteen of the twenty first-order Raman frequencies predicted by group theory have been detected, and the frequencies are found to be sensitive to the particular dopants. The Raman linewidths observed for the MxBaySi46 system are comparable to those observed for Na8Si46 and K7Si46. The data, taken collectively, suggest that the line broadening in the metallic Si-clathrates is due to important contributions from both the electron-phonon interaction as well as to a random filling of the Si cages.
Synthesis of Mn2+ Doped CdS Nanocrystals Embedded in a Sol-Gel Silica Matrix: Characterization of the Luminescence Activator
Authors: Counio G. , Esnouf S. , Gacoin T. , Barboux P. , Hofstaetter A. , Boilot J.-P. 
Published: April 2011

AbstractMn2+-doped CdS nanocrystals (1.2 to 2.4 nm in diameter) embedded in organic-inorganic silica xerogels have been synthesized. Extensive studies (EXAFS, ESR and ENDOR) allow us to localize the ions responsible for the bright luminescence observed in such materials (quantum yield of 7%). The average number of Mn2+ per nanocrystal is in the 0.2–0.8 range, and the emission arises from an energy transfer from surface trapped carriers to Mn2+ ions.
Depth Gradients in Porous Silicon: How to Measure Them and How to Avoid Them
Authors: Thönissen M. , Berger M. G. , Theiβ W. , Hilbrich S. , Krüger M. , Arens-Fischer R. , Billat S. , Lerondel G. , Lüth H. 
Published: April 2011

AbstractFor the formation of single layers and layer systems the depth homogeneity of porous silicon (PS) plays a key role. We have measured qualitatively and quantitatively structural gradients in p-PS layers with increasing layer thicknesses by fitting reflectance spectra in the infrared and by measuring thickness oscillations in the reflectance during the formation of PS layers. These results allow us to give recipes for the formation of PS layers with a homogenous optical thickness in depth.