bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microstructure and Mechanical Properties Of Laser-Processed Ni-Al-Mo Base Alloys
Authors: Snow David B. 
Published: March 2011

ABSTRACTThe addition of molybdenum to nickel base superalloys which contain a γ′ volume fraction of ≦ 0.35 allows them to be consolidated from powder by laser processing at solidification rates of ∼1040C/s. The as-solidified microstructure of these alloys is dendritic, and consists of a fine dispersion ∼20nm cuboidal γ′ in a supersaturated FCC γ matrix. When annealed at 500–700°C, additional age hardening occurs via the precipitation of ≤l0nm, Dla-structure Ni4Mo, DO22- structure Ni3Mo and/or Pt2Mo-structure Ni2Mo. This combined strengthening by very fine γ′ and NixMo dispersions in laser-processed material makes alloys of this type attractive for potential turbine disk applications. However, the 6–15 at % molybdenum required to prevent cracking during laser consolidation renders many of these alloys prone to a previously unreported, embrittling cellular phase transformation, γ + γ′ + NixMo→ γ′ + orthorhombic Ni3Mo, at temperatures of ≦900°C.
Characterization and Properties of Laser Quenched Aluminum Bronzes
Authors: Draper C. W. , Vandenberg J. M. , Preece C. M. , Clayton C. R. 
Published: March 2011

ABSTRACTCommercial aluminum bronze (Cu-Al-Fe) alloys have been laser quenched with both continuous and pulsed CO2 laser sources. Metastable near surface regions of approximately 10 μm thickness have been produced. The quenched surfaces have been characterized by optical microscopy, SEM, EDX, AES and glancing angle XRD. The behavior of both laser quenched and “as received” conventional surfaces have been tested in both cavitation erosion and corrosion environments. In some cases significant differences are observed and can be rationalized from the microstructural changes accompanying the self quenching.
Property Enhancement in Rapidly Quenched Alloy Surfaces
Authors: Tuli M. , Strutt P. R. 
Published: March 2011

ABSTRACTElectron beam glazed surfaces on a circular bar are of sufficiently good quality either for direct use or after light mechanical grinding. The technique may be applied for reconstituting plasma deposited layers thereby eliminating porosity and obtaining a highly homogeneous refined microstructure. By this treatment it was found that the microhardness of a plasma deposited layer of chromium carbide in molybdenum binder increased from 525 V.H.N. to 750 V.H.N.
Rapidly Solidified Microstructure in Surface Layers of Laseralloyed Mo on Fe-C Substrates
Authors: Tucker T. R. , Clauer A. H. , Ream S. L. , Walters C. T. 
Published: March 2011

ABSTRACTShaped continuous-wave laser beams have been used to alloy molybdenum coatings into Fe-C substrates. The Mo overlay was first deposited by the plasma spray process in an inert gas environment. Slowly scanned laser radiation then melted a layer 2 to 5 times the thickness of the original Coating causing the two metallic species to mix. Melt proceeded from the coating/substrate interface, the Mo melt temperatures being significantly higher than that of the base material. Fusion zone microstructures for individual melt passes appeared to be homogeneous, and molybdenum composition was found to be relatively uniform. With overlapping melt passes, the microstructures became more complex with heat effects apparent in the overlap regions.
Morphological Stability of Electron Beam Melted Aluminum Alloys
Authors: Schaefer R. J. , Coriell S. R. , Mehrabian R. , Fenimore C. , Biancaniello F. S. 
Published: March 2011

ABSTRACTFor constant velocity solidification, morphological stability theory delineates the temperature gradients required for plane front solidification of a specific alloy. Using electron beams, surface heating of metals can be carried out with sufficiently well characterized thermal input to permit reliable use of computer models of melting and solidification. From numerical calculations, the growth velocity and temperature gradients as a function of position during resolidification can be obtained; combining these results with (constant velocity) morphological stability theory indicates the resolidification regimes for which the plane front is unstable. Presumably, completely planar solidification may be attained by selecting heating modes such that the region of instability is totally avoided, but the expected interface morphology is more difficult to predict if the interface passes briefly through an unstable region and then re-enters a region of stability. Aluminum-silver and aluminum-manganese alloys were melted under an electron beam with particular emphasis on attaining solidification sufficiently rapidly to satisfy the gradient-independent absolute stability condition. It was found that the velocities required to produce stability were considerably larger than expected.
MBE Growth of GaAs on Porous Silicon
Authors: Lin T. L. , Sadwick L. , Wang K. L. , Rhee S. S. , Kao Y. C , Hull R. , Nieh C.W. , Jamieson D. N. , Liu J. K. , Nicolet M-A. 
Published: March 2011

ABSTRACTGaAs layers have been grown on porous silicon (PS) substrates by molecular beam epitaxyNo surface morphology deterioration was observed onGaAs-on-PS layers in spite of the roughness of PS. A 10% Rutherford backscattering spectroscopy (RBS) channeling minimum yield for GaAs-on-PS layers as compared to 16% for GaAs-on-Si layers grown under the same condition indicates a possible improvement of crystallinity when GaAs is grown on PS. Transmission electron microscopy (TEM) reveals that the dominant defects in the GaAs-on-PS layers are microtwins and stacking faults, which originate from the GaAs/PS interface. GaAs is found to penetrate into the PS layers.
Improved MOCVD Growth of GaAs on Si
Authors: Lum R.M. , Klingert J.K. , Davidson B.A. , Lamont M.G. 
Published: March 2011

ABSTRACTIn the direct growth of GaAs on Si by MOCVD the overall quality of the heteroepitaxial film is controlled to a large extent by the growth parameters of the initial GaAs buffer layer. We have investigated the structural properties of this layer using Rutherford Backscattering Spectrometry (RBS) and X-ray double crystal diffractometry. The crystallinity of the buffer layer was observed to improve with increasing layer thickness in the range 10–100nm, and then to rapidly degrade for thicker layers. High temperature (750°C) annealing of the buffer layers resulted in considerable reordering of all but the thicker (>200 nm) layers. Alteration of the usual GaAs/Si growth sequence to include an in-situ anneal of the buffer layer after growth interruption yielded GaAs films with improved structural, optical and electrical properties.
The Two-Step Growth Mechanism of MOCVD GaAs/Si
Authors: Ishida Koichi 
Published: March 2011

AbstractThe growth mechanism and lattice defects are studied for GaAs/Si grown by the two-step MOCVD growth procedure using transmission electron microscopy (TEM). The large misfit stress between GaAs and Si is relieved by misfit dislocations at the GaAs/Si interface, which are introduced during epitaxial regrowth of the thin (<200A) polycrystalline buffer layer grown at 400∼450°C. The regrown buffer layer is relaxed to a nearly stress free state, and therefore a thick GaAs layer can subsequently be grown at the higher growth temperature (∼750°C). The tensile stress in GaAs at room temperature is shown to be a direct consequence of the misfit stress relaxation at the higher growth temperature. TEM revealed high density (<106cm−2) of the threading dislocations in the GaAs layer, contrary to the results of molten KOH etching.
Materials Aspects of GaAs on Si
Authors: Fischer Russ 
Published: March 2011

SUMMARY ABSTRACTDespite the 4.2% lattice mismatch, several laboratories have demonstrated that the quality of GaAs grown on Si is high enough for practical device applications [1–5]. At the GaAs/Si interface, a dislocation density of roughly 1012cm−2 is required to accommodate the mismatch. Therefore various techniques of dislocation filtering are necessary to provide material with acceptable dislocation counts. Among these techniques are the use of tilted substrates, strained layer superlattices, and intermediate layers.
Raman Scattering Spectrum Along a Bevel Etched GaAs on Si, Tem Study and GaAs P-I-N Photodetector on Si
Authors: Lo Y.H. , Charasse M.-N. , Lee H. , Vakhshoori D. , Huang Y. , Yu Peter , Liliental-Weber Z. , Werner M. , Wang S. 
Published: March 2011

ABSTRACTRaman scattering is measured along a bevel etched GaAs epitaxial film grown on Si by molecular beam epitaxial (MBE). From the correlation length profile of Raman scatteringmost dislocation lines are confined in the 2000Å regions close to the interface. The strain profile calculated from the Raman peak shift shows that about 0.6% compressive strain exists near the interface because of lattice mismatch. However, as one moves away from the interface, the compressive strain is gradually counterbalanced by thermal expansion. Transmission electron microscope (TEM) studies of the local dislocation image and properties show that an ultra clean Si surface is essential for dislocation confinement. From high resolution TEM, we find that the distance between dislocations at the interface is nonuniform, varying from 50Å to 125Å with an average distance at 81Å. Finally, a GaAs p-i-n photodetector on Si substrate is fabricated. Even though a normal photoresponse curve is obtained, the high dark current (50nA) and relatively low responsivity (0.01A/W) show that the material quality needs to be further improved to make a minority carrier vertical transition device.
Epitaxial GaAs on Si: Progress and Potential Applications
Authors: Shaw Don W. 
Published: March 2011

ABSTRACTRecent successes, such as the demonstration of a 1K SRAM, have established epitaxial GaAs on Si substrates as a promising technology rather than a device designer's dream. For the first time we can seriously consider combining the individual electronic and optical properties of GaAs and Si within a single epitaxial structure. Applications for GaAs on Si range from those that simply utilize the Si as a low-cost, large-areapassive substrate with superior strength and thermal conductivity to the long-sought multifunction integrated circuits where Si and III–V components are integrated within a single monolithic chip. This paper will attempt to provide a realistic appraisal of the potential applications of epitaxial GaAs on Si with emphasis on the special demands imposed by each application and barriers that must be circumvented.
Structural Characterization of Thin, Low Temperature Films of GaAs on Si Substrates
Authors: Rosner S. J. , Koch S. M. , Harris J. S. 
Published: March 2011

ABSTRACTThe technology of heteroepitaxially growing compound semiconductors, particularly GaAs, on Si has attracted an increasing volume of attention in the past 3–5 years. In the past two years there have been few major advances in the growth recipes, which all include a high temperature Si preheat, a two-step growth temperature profile, and the use of misoriented substrates. The need for mechanistic understanding of the effect of these parameters is crucial to advancing the state of the art beyond this current practice. This work focusses on the effect of the misorientation in inducing asymmetry in early stages of the molecular beam epitaxy of GaAs on Si substrates. The strain in the films is found to have greatly different rates of relaxation in the plane of the film when measured in the two orthogonal <220> directions. This asymmetry persists to greater than 30 nm film thickness at 400°C. The nucleation morphology was also examined as a function of substrate misorientation. At low substrate tilts, nucleation density was sparse and there was not substantial ordering of the nuclei. As the tilt was increased, a distinct habit emerged where collections of nuclei were quite coherent along the steps for several 100 nm, with dimensions of the order of 10's of nm perpendicular to the steps. The density of steps with nuclei was also substantially less than that predicted by the widely accepted “array of double-height steps” used to explain the curious lack of anti-phase disorder in these films.
MBE Growth of GaAs on Si (100)
Authors: Ahearn J. S. , Uppal P. 
Published: March 2011

ABSTRACTMolecular beam epitaxy (MBE) growth of GaAs on Si was investigated for three Si substrate orientations: exact (100), 4° off (100) towards (011), and 4° off towards (010). Cross-sectional transmission electron microscopy (X-TEM) analysis indicated a high dislocation density at the GaAs-Si interface that decreased away from the interface. Changing the orientation significantly affected the dislocation arrangement in the films.In the exact (100) case, dislocations from different glide systems formed pyramids, and dislocation annihilation resulted in linear defects propagating to the bottom of pits on the GaAs surface. On Si substrates oriented 4° off of (100), dislocation pyramids were not observed which we attribute to the different stresses acting on different glide systems. Planar TEM sections indicated that the dislocation densities at th surfaces of the 2-μm-thick films were 8 × 108 /cm2 for exact (100), 3.4 × 108/cm2 for 4° off (100) towards (010), and 1.6 × 108/cm2 for 4° off towards (011) orientations. When etching was used to evaluate anti-phase domain (APD) density, the exact (100) and off (100) orientations toward (010) showed APD's in some areas; off (100) toward (011) orientations were apparently APD-free. Results of photoluminescence (PL) spectroscopy of each of the wafers showed marked differences in peak intensities for the different orientations. Secondary ion mass spectrometry (SIMS) showed that roughly 1/4 of a monolayer of Si was incorporated in the GaAs, mostly concentrated in the first 250 nm near the GaAs-Si interface.
Characterization of APBs in GaAs Grown on Si and Ge
Authors: Carter C.B. , Cho N.-H. , Mckernan S. , Wagner D.K. 
Published: March 2011

ABSTRACTAntiphase boundaries are observed in epilayers of GaAs grown by organometallic vapor phase epitaxy on Ge substrates and are then invariably found to show a tendency to facet. Stacking-fault-like fringes caused by the translation of adjacent grains give the information on the relative displacement of the two grains at these interfaces and show that this translation does not have a fixed magnitude for a particular interface but varies with the orientation of the interface. Preferred orientations of the antiphase boundaries and the rigid-body translations have been studied using transmission electron microscopy. Interactions between antiphase boundaries and interfaces have been examined here in heterolayer structures consisting of alternating layers of GaAs and AlxGal−xAs grown on an (001) Ge substrate. The possibility of using atomic-resolution imaging to investigate the atomic structure of APBs is illustrated and the images are compared with those predicted by image simulation.
{224} Plane X-Ray Diffraction Study of GaAs on Si Wafers Using a Conventional Double Crystal Diffractometer
Authors: Lee J.W. , Bowen D.K. , Salerno J.P. 
Published: March 2011

ABSTRACTIn an effort to evaluate the near surface crystal quality of GaAs on Si wafers, {224} plane diffraction were investigated using a conventional double crystal x-ray diffractometer without any high intensity radiation source. The x-ray incident angle to wafer surface varied from 3.6 to 9.6 degrees for different {224} planes due to the substrate tilt angle of 3 degrees. The GaAs to Si rocking curve intensity ratio increased significantly as the incident angle decreased. For the diffraction with 3.6 degree incident angle, only the GaAs peak was detected from the 3.5 um thick GaAs on Si wafer and the GaAs peak became narrower. These indicates that this conventional x-ray diffraction technique is applicable for the near surface quality evaluation of GaAs on Si wafers.
Prospects for GaAs-on-Si LSI Circuits
Authors: Shichijo H. , Tran L.T. , Matyi R.J. , Lee J.W. 
Published: March 2011

ABSTRACTThis paper will review some of the recent progress in GaAs-on-Si devices and circuits, and discuss the issues involved in realizing large scale ICs in GaAs-on-Si wafers. With a recent success in fabricating 1 Kbit static RAMs in GaAs-on-Si wafers, it has become apparent that this material is indeed acceptable for LSI complexity circuits. GaAs MESFETs fabricated using a standard process show an excellent threshold voltage uniformity which is comparable to that for bulk GaAs devices. GaAs bipolar devices on GaAs-on-Si have realized a gain of 25 which is the highest reported for bipolar devices in GaAs-on-Si material. Bipolar ring oscillators and 256-bit ROMs consisting of more than 100 gates have also been realized. In spite of these successes, however, there are numerous issues that need to be solved before this material becomes practical.
Deep Electron Traps In Mbe Gaas On Si
Authors: Nauka K. , Reid G.A. , Rosner S.J. , Koch S.M. , Harris J.S. 
Published: March 2011

ABSTRACTDeep electron traps were investigated in MBE GaAs grown directly on Si substrates with orientations a few degrees off the <100> axis. Capacitance Deep Level Transient Spectroscopy (CDLTS) revealed the presence of eleven electron traps in the GaAs epilayer. Their activation energies ranged from 0.21 eV to 0.83 eV below the conduction band. Most of these traps were previously observed in homoepitaxial GaAs films grown under As-rich conditions (VPE, MBE), or in electron irradiated bulk GaAs. Trap concentrations tracked Si dopant density and MBE growth conditions. Observed deep levels are not introduced by metals or other contaminants present at the GaAs-Si interfaces. Rather, they are caused by defect complexes. These complexes involve native point defects, whose formation is favoured by As-rich environments, by lattice mismatch, and by different thermal expansion coefficients. Si dopant atoms may also participate in the formation of these defects. A similar deep level generation mechanism is proposed for the electron traps in homoepitaxial MBE GaAs layers.
Low-Temperature Photoluminescence of Mocvd GaAs Grown Directly on Si
Authors: Wilson B.A. , Bonner Carl E. , Harris T. D. , Lamont M. G. , Miller R. C. , Sputz S. K. , Vernon S. M. , Haven V. E. , Lum R. M. , Klingert J. K. 
Published: March 2011

ABSTRACTWe present a systematic study of the low-temperature photoluminescence from undoped GaAs layers grown directly on Si substrates by MOCVD. GaAs layers from 100Å to 4 μm in thickness were deposited on Si substrates prepared with a variety of doping levels and orientations. The emission from thicker samples is dominated by pairs of lines in the band-edge region. Photoluminescence excitation measurements show that this multiplicity results from two regions in the material with different levels of strain. The stress-induced splitting of the valence band is also studied using excitation spectroscopy. In thinner samples we observe strong emission in the midgap range due to stoichiometric defects. The nature of the defects near the interface depends strongly on the character of the substrate.
Optoelectronic Properties of Pseudomorphic SixGel1−x,/Ge Heterostructures on (001) Ge
Authors: People R. 
Published: March 2011

ABSTRACTThe optical and electronic properties of pseudomorphic SixGel1−x/Ge heterostructures are reviewed in brief. Potential applications of conduction and valence band alignments for modulation doped field effect transistors are outlined. Optical transition energies are calculated for ultra-thin, alternating four monolayer, Si/Ge heterostructures on (001) Ge.
Atomic-Scale Simulation of Silicon Atomic Beam Deposition
Authors: Dodson Brian W. 
Published: March 2011

ABSTRACTThe mechanisms which control low energy (10–100 eV) beam deposition of silicon onto a relaxed (111) silicon substrate have been studied using a molecular dynamics technique. A many-body empirical potential was used to describe the covalent Si-Si bonding. 10 eV silicon beams with near-perpendicular incidence were simulated to study capture mechanisms and the local lattice excitation resulting from impact. Grazing angles of incidence (3°–30°) were studied for beam energies of 20–100 eV. For incidence angles less than an energy- and orientation-dependent critical value, the phenomenon of ‘surface channeling’ is predicted, in which the incoming particle is steered parallel to, and roughly 2 Å above, the surface of the substrate through inelastic substrate interactions. The phenomena seen in low-energy beam deposition offer new avenues of control over growth of modulated semiconductor structures.
Fabrication of Si-Gate CMOS Devices In A Heteroepitaxial Si/Caf2/Si Structure
Authors: Onoda Hiroshi , Sasaki Masayoshi , Katoh Teruo , Hirashita Norio 
Published: March 2011

ABSTRACTThe results of recent developments on device fabrication in a heteroepitaxial Si/CaF2/Si structure have been presented and discussed. A high quality heteroepitaxial Si/CaF2/Si structure has been obtained by successive molecular beam epitaxy of CaF2 and Si. The epitaxial Si film on CaF2/Si structure has an ion channeling minimum yield of 7 %. It was found, however, that Ca and F segregated at the surface of epitaxial Si films. A possibility of reducing the segregation effect by the use of solid phase epitaxy of Si has been proposed.Si-gate CMOS devices have been successfully fabricated in a Si/CaF2/Si structure with alt improved CMOS proress. The maximum effective mobiliiies are about 570 cm2/V.sec and 240 cm2/V.sec for n-channel and p-channel transistors, respectively. Propagation delays below 360 ps have been obtained for CMOS inverter chains with Leff = 2 μm. These results indicate that the Si/CaF2/Si structure has potential for the fabrication of high-speed silicon-on-insulator devices.
Lattice-Matched Gaas/Ca0.45Sr0.55F2/Ge(100) Heterostrucuures Grown By Molecular Beam Epitaxy
Authors: Tu C. W. , Beggy J. C. , Baiocchi F. A. , Abys S. M. , Pearton S. J. , Hsieh S. J. , Kopf R. F. , Caruso R. , Jordan A. S. 
Published: March 2011

ABSTRACTEpitaxial, lattice-matched GaAs/Ca0.45Sr0.55/F2 heterostructures were grown on Ge(100) substrates by molecular beam epitaxy. The films were analyzed by Rutherford backscattering and secondary ion mass spectroscopy to determine crystallinity and Ge outdiffusion. The Xmin (channeling over random yield) of a 1.5 μm-thick GaAs film grown on the fluoride is 0.075, indicating reasonably good epitaxy. After rapid thermal annealing, the crystallinity of higher-Xmin films improves, and Ge diffuses only 200 A into the fluoride, indicating that a thin fluoride layer is an effective barrier to Ge outdiffusion.
Liquid Phase Epitaxy of Si1−xGex(O<×≲1) On Partially Masked Si-Substrates
Authors: Trah H.-P. , Alonso M.I. , Konuma M. , Bauser E. , Cerva H. , Strunk H.P. 
Published: March 2011

ABSTRACTSingle-crystal Si1−x Gex(O<×≲1) layers are grown by seeded growth on partially SiO2-masked Si-substrates, using a one-step liquid phase epitaxy (LPE) process. The seed regions are stripe- and hole-shaped windows in the oxide, having linear dimensions between 1.5 and 100 μm. The windows extend in different orientation on (111) and (100) orientated substrates. Lateral overgrowth over the oxide-masked areas is achieved up to 70 μm in <110>-directions. X-ray diffraction and Raman scattering show that the epitaxial islands are homogeneous and of excellent crystal quality. In the regions of lateral overgrowth the dislocation density is reduced considerably as shown by defect-etching and cross section transmission electron microscopy.