bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular Dynamic Structure Investigations of the Surface Stability and Adsorption of H, H2, CH3, C2H2: (100) Diamond
Authors: Frauenheim Th. , Blaudeck P. , Porezag D. 
Published: March 2011

ABSTRACTSurface properties - stability and reconstruction - of clean and hydrogenated diamond (100) have been studied by real temperature molecular dynarnic (MD) simulations using an approximate density functional (DF) theory expanding the total electronic wave function in a minimal basis of localized atomic valence electron orbitals (LCAO - ansatz). The clean surface is highly unstable against a spontaneous dimerization resulting in a 2×1 reconstruction. Atomic hydrogen in the gas phase above the top surface at all temperatures and H2 molecules approaching the center of the dimer bond at room temperature are reactive in breaking the dimer π-bonds forming a monohydrogenated surface which maintains a stable 2×1 structure but with elongated surface C-C dimer bonds remaining stable against continuing hydrogen supply. The dihydrogenated surface taking a 1×1 structure, because of steric overcrowding dynamically becomes unstable against forming a 1×1 (alternating) di-, monohydrogenated surface. As first elementary reaction processes which may be discussed in relation to diamond growth we studied the thermal adsorption of CH3 and C2H2 onto a clean 2×l reconstructed (100) diamond surface.
Temperature Programmed Desorption of Hydrogen and Deuterium from Cvd Diamond Samples
Authors: Schulberg Michelle T. , Kubiak Glenn D. , Stulen Richard H. 
Published: March 2011

ABSTRACTThe desorption kinetics of H2, HD, and D2 from a CVD-grown diamond sample have been measured using temperature programmed desorption. The sample was exposed to hydrogen and deuterium at ∼ 100 K. Molecular hydrogen does not react with the diamond surface but atomic hydrogen chemisorbs. The sample is then heated to 1500 K at a rate of 6 K/s. The hydrogen desorption spectrum from these polycrystalline specimens is surprisingly simple, consisting of a single peak near 1270 K for all coverages studied. The width of the desorption peak is ∼ 100 K. Neither the width nor the peak maximum shift with increasing hydrogen coverage. There is no isotope effect to the desorption. No other desorption products (water, small hydrocarbons) are detected. Kinetic parameters can be extracted from these spectra, and these can be compared to hydrogen desorption from natural diamond single crystal surfaces. These parameters can be used to model diamond growth processes.
Electrical Conductivity as a Function of Temperature of Diamond films Grown by Downstream Microwave Plasma Chemical Vapor Deposition
Authors: Stoner Brian R. , Windheim Jesko A. von , Glass Jeffrey T. 
Published: March 2011

ABSTRACTElectrical conductivity measurements were used to study the effects that sample distance from the plasma during growth has on the carrier transport properties of undoped CVD diamond. The films were grown by downstream microwave plasma chemical vapor deposition at distances from 0.5 to 2.0 cm from the edge of plasma glow. Electrical conductivity measurements were performed between room temperature and 1000 °C to gain a better understanding of the CVD growth process and the resulting electrical properties of the diamond film's. Room temperature electrical conductivity was found to vary by over 5 orders of magnitude with increasing growth distance from the plasma, and this is attributed to decreasing hydrogen incorporation efficiencies at further distances from the plasma.
Physical Property Characteristics of Pitch Materials
Authors: Anderson David P. , Wapner Philip G. , Curliss David B. 
Published: March 2011

ABSTRACTThe two most important material properties for foam process modeling are liquid viscosity and surface tension. Several different pitches were examined including Ashland petroleum pitches and a synthetic mesophase pitch (Mitsubishi AR). Viscosities of isotropic pitch were measured at various temperatures above their softening points using an oscillating disk rheometer and found to be independent of shear rate and closely match the manufacturer's data. Only a very weak dependence of surface tension on temperature was found from calculations made from pendent drop measurements. The density of these materials, which was needed for the surface tension calculations, was measured using an elevated temperature mercury dilatometer. Transitions indicated by the volumetric results were also investigated by DSC.
Influence of Growth Orientation and Uniaxial Stress on the Electronic Properties of GaAs / GaAlAs Quantum Wells
Authors: Saidi N. , Zitouni K. , Kadri A. 
Published: March 2011

ABSTRACTUsing the envelope function formalism and the effective mass thecry, we have studied the E(k) energy dispersion and the confinement energies of the lower lying conduction band and the higher lying valence bands states in GaAs /GaAlAs Single Qantum Well (SQW) structures grown on GaAs substrates with different orientations of the growth axis :(001),(111),and (113). Then, the valence subbands dispersions are calculated away from the zone center for a given well width and under uniaxial stress for the three different growth directions
Extended Pseudomorphic Limits Using Compliant Substrates
Authors: Lo Y. H. , Schaff W. J. , Teng D. 
Published: March 2011

ABSTRACTWe propose a new approach, growth on compliant substrates, to achieve extended pseudomorphic limits. The compliant substrate can be approximately achieved with a corner supported membrane structure. Both thermal equilibrium model and dynamic model considering strain relaxation are used to analyze the relations between the extended critical thickness and the substrate thickness. Preliminary experimental results of InGaAs grown on GaAs membranes seem to support the theories.
Uniformity Control in Elemental Vapor Transport Epitaxy
Authors: Gurary A. I. , Tompa G. S. , Stall R. A. , Liang S. , Lu Y. , KUO H. C. 
Published: March 2011

ABSTRACTElemental Vapor Transport Epitaxy (EVTE) is a novel technique for semiconductor manufacturing, which combines the advantages of Molecular Beam Epitaxy (MBE) and Vapor Phase Epitaxy (VPE). EVTE provides a high level of elemental flux control, scaling to large deposition areas, and elimination of elemental Ga source related oval defects. EVTE has been successfully applied to the deposition of III-V and II-VI thin films and heterostructures. Design considerations and evaluations of the novel EVTE elements: elemental flux regulating valve operating at temperatures >1250°C with demonstrated response times less than 1 second and elemental flux distribution manifold are presented. The calculated operational parameters for EVTE are in good agreement with the observed experimental results.
GaAs / AlGaAs SQW Optical Switch on Si
Authors: Yuasa T. , Nagashima Y. , Egawa T. , Jimbo T. , Umeno M. 
Published: March 2011

ABSTRACTWe reported a waveguide-type optical switch fabricated on a Si substrate which utilized the Quantum Confined Stark Effect (QCSE). The prepared sample is an Al0.3Ga0.7As (cladding layer) / Al0.25Ga0.75As (guiding layer) double-heterostructure (DH) optical switch with a GaAs single quantum well (SQW) in the guiding layer by MOCVD. The absorption edge of the sample is measured by photocurrent method under reverse bias using a cw Ti: Sapphire laser for a light source. We measured about 10 nm shift of the absorption edge at -8 V from the sample with 8.3 nm SQW. This result demonstrates the Stark-shift effect of GaAs SQW on Si. A 2.5 μm-width ridge was formed by etching in the top cladding layer and the light traveling in the guiding layer was confined to a fundamental mode in vertical (parallel to growth direction) and horizontal direction. This switch showed 33.1 dB/mm modulation at 867 nm wavelength in -8 V bias.
Use of Low Temperature Si MBE Growth Techniques for High Performance SiGe/Si Electronics
Authors: Croke E. T. , Harrell M. J. , Mierzwinski M. E. , Plummer J. D. 
Published: March 2011

ABSTRACTThrough the use of low temperature Si molecular beam epitaxy (MBE), we have fabricated high performance Si1−x Gex/Si heterojunction bipolar transistors (HBTs) and bipolar inversion-channel field effect transistors (BICFETs). Our growth method employs a high temperature Si-assisted desorption followed by MBE growth at a temperature only slightly in excess of the critical temperature for two-dimensional layer-by-layer growth. [1] At this temperature, segregation of Sb has previously been shown to be kinetically limited. [2] In addition, significantly more strain can be frozen into such an epitaxial layer as compared with those grown at higher temperatures.[3] Secondary ion mass spectroscopy (SIMS) data verify the abruptness of the Sb doping profiles in our device structures. High resolution x-ray diffraction (HRXRD) data are consistent with planar, coherently strained Si1−x Gex layers in our HBTs. A gain of 2690 (3210) is observed in our BICFETs at 300 K (7 K).
Growth of Ge-on-Si Structures using Remote Plasma-Enhanced Chemical Vapor Deposition
Authors: Qian Rong Z. , Kinosky D. , Mahajan A. , Thomas S. , Fretwell J. , Munguia P. , Banerjee S. , Tasch A. 
Published: March 2011

ABSTRACTRemote Plasma-enhanced Chemical Vapor Deposition (RPCVD) has been successfully used to grow GexSi1−x/Si (x = 0.1 – 1.0) heteroepitaxial structures at low temperatures (∼450°C). This technique utilizes a noble gas (Ar or He) r-f plasma to decompose reactant gases (SiH4 and GeH4) and drive the chemical deposition reactions in the gas phase as well as on the substrate surface. Growth of pure Ge on Si is of great interest because it provides a promising technique for making suitable low-cost substrates for thin-film Ge photodetectors as well as GaAs devices on Si substrates. The realization of these applications depends on the ability to grow high-quality epitaxial Ge layers on Si substrates. Since GaAs is lattice matched to Ge, growth of Ge layers on Si substrates with good crystalline perfection would permit the integration of GaAs and Si devices. Islanding was observed after the growth of pure Ge films directly on Si(100) for a wide range of plasma powers (7W ∼ 16W) in RPCVD. Cross-sectional TEM analysis showed that the islands have complicated facet structures, including {311} planes. Graded Gex Si1−x buffer layers with different Ge profiles have been used prior to the growth of Ge. It was found that uniform Ge films can be obtained using a buffer with an abrupt Ge profile, and the dislocation density in the Ge film decreases with increasing distance from the substrate.
Transport in High-Mobility Si1−xGex Heterostructures Grown by Molecular-Beam Epitaxy
Authors: Monroe Don , Xie Y.-H. , Fitzgerald E. A. , Silverman P. J. 
Published: March 2011

ABSTRACTWe report Hall mobilities (at T = 4.2K) as high as 180,000cm2V−1 s−1 in modulation-doped Si layers in Si1−x Gex heterostructures grown by Molecular-Beam Epitaxy. These mobilities reflect dramatic improvements in the quality of relaxed Si1−xGex buffer layers (with x'30%) grown by gradual grading of composition at high temperature. The resulting moderate threading dislocation densities (< 106 cm−2 ) appear to cause no mobility degradation. The strong damping of Shubnikov de Haas oscillations, as well as the increase of mobility with carrier density, indicate predominantly small-angle scattering. This suggests that residual Coulomb scattering from background impurities limit the mobility, rather than interface-roughness scattering as for the Si/SiO2 interface. The reduced interfacial scattering, as well as the strain-induced splitting of the valley degeneracy to select the two low-effective-mass valleys, significantly enhance room-temperature transport as well, with μHall ' 2,100cm2 V−1 s−1. We also observe a small splitting of the remaining twofold valley degeneracy using the integral quantized Hall effect. As a further indication of the high sample quality, measurements to 17T at 0.3K show indications of the v = 2/3 fractional quantum Hall effect.
The Influence of Strain-Mediated Morphological Changes on the Structural and Optical Properties of MBE-Grown GeSi/Si
Authors: Perovic D. D. , Whitehurst J. , Noel J. P. , Rowell N. L. , Houghton D. C. 
Published: March 2011

ABSTRACTRecent studies on strained layer heteroepitaxy in high misfit systems (eg. Ge on Si) have clearly indicated the importance of elastic strain on a number of surface-mediated growth effects. In this work we consider the transition from ideal, 2-D layer-by-layer growth to the initial stages of a 3-D growth morphology as a precursor to misfit dislocation injection in GexSi1−x/Si heterostructures with x as low as 0.15. Experimentally, we have studied a wide range of MBE-and CVD-grown single and multilayer GexSi1−x/Si (x<0.5) structures using transmission electron microscopy and photoluminescence spectroscopy. Firstly, we describe a new mechanism for the heterogeneous nucleation of misfit dislocations in strained epitaxial layers, the ‘double half-loop’ source, which originates from atomic-scale (<1.5 nm) interfacial perturbations. Secondly, the atomic-scale dilatational perturbations, which can exist in areal densities up to ∼109 cm−2, have been identified as the origin of intense, broad-band PL from MBE-grown GexSi1−x/Si strained layers. The change in PL behaviour with increasing strained layer thickness has been used to study the effects of elastic strain-induced surface roughening at low misfits.
Single Crystalline / Porous Amorphous Superlattice Formation by the Etching of MBE Grown Si/Si1−x Gex Layers on Si Substrates
Authors: George T. , Pike W. T. , Fathauer R. W. , Jones E. W. , Ksendzov A. 
Published: March 2011

ABSTRACTNovel porous amorphous/crystalline superlattices were produced by the etching of mesas containing superlattices of alternating layers of Si and Si1−xGex. These layers were grown by molecular beam epitaxy on (100) Si substrates and etched in an aqueous HF:HNO3 solution. Preferential attack and amorphization of the Si1−x Gex layers was observed, leading to the formation of alternating layers of single crystal Si and porous amorphous Si1−xGex. The etchant is highly selective and it was possible to etch extremely thin (5nm) Si0.7Ge0.3 layers between 30nm Si layers. Complete conversion of the Si0.7Ge0.3 layers to the porous amorphous state was seen in lμm wide mesas. The role of composition and thickness of the Si1−xGex layers was studied. The variation in the lateral etch depths of the Si1−xGex layers in the superlattices demonstrates that lattice strain in these layers is an important factor in the selectivity of the etch process. As the thickness of the Si1−xGex layers is decreased, transport of the etchant to and the etch products from the reaction front is reduced, limiting the penetration of the etching process. The porosities of these etched Si1−xGex layers were determined to be comparable to measured values for thick etched alloy layers.
Transmission Electron Microscopy of Nitrogen Doped ZnSe/GaAs
Authors: Kuo L. H. , Salamanca-Riba L. , Depuydt J. M. , Cheng H. , Qiu J. 
Published: March 2011

ABSTRACTTransmission election microscopy studies show that nitrogen doping changes the misfit dislocation structure in ZnSe films and decreases the density of threading dislocations. There appears to be a critical N doping concentration of ∼ 1.5 × 1018/cm3 above which the density of threading dislocations increases again. Samples with high N doping concentrations (> 1019/cm3 ) also show compensation or decrease in the carrier density of the films. Our TEM observations show that N doping can produce low energy nucleation sites for the 60° misfit dislocations at or close to the ZnSe/GaAs interface.
Fabrication of Short Period ZnSe-GaAs Superlattices by MOVPE
Authors: Funato Mitsuru , Fujita Shizuo , Fujita Shigeo 
Published: March 2011

ABSTRACTThe growth condition and the structural properties of short period ZnSe-GaAs superlattices grown by metalorganic vapor phase epitaxy (MOVPE) are described. First, the growth condition was investigated. Superlattices (SLs) grown at 450°C have better structural property than those grown at 500°C. The thickness fluctuation of each constituent layer was investigated by means of the X-ray diffraction analysis, and it was indicated that the fluctuation in the fabricated structure was within 1 and 2 monomolecular layers for GaAs and ZnSe, respectively. Further optimization for growing thinner layers successfully brought SL with 25Å well and 140Å barrier layers. X-ray diffraction analysis and transmission electron microscopy (TEM) observation showed its good structural properties; high crystalline quality, high degree of lateral uniformity, well defined interfaces and strong periodicity. Another SL with 100 periods of ZnSe (33Å) / GaAs (25Å), which have smaller layer thickness and much larger number of periods compared with the SL mentioned above, could be also fabricated and the crystalline quality was found to be excellent by X-ray diffraction measurement.
Trapping and Luminescence Mechanism Studies in SrS:Eu2+, Sm3+ Thin Films at Various Temperatures
Authors: Hua Susan Z. , Salamanca-Riba L. , Wuttig M. , Soltani P. K. 
Published: March 2011

ABSTRACTThe temperature dependence of photoluminescence in SrS singly and doubly doped with Eu2+, Sm3+ was studied with different excitation energies. Different energy transfer mechanisms, namely, phonon-assisted energy transfer and electron transfer through energy bands, depending on the excitation energy, are proposed to take place in SrS:Eu2+, Sm3+ thin films. We estimate that under UV light excitation 10% of Eu2+ emission originates from electronic transitions between Eu2+ and Sm3+ through the conduction and valance bands. In contrast, direct inter-ionic transitions take place for 2.84 eV excitation energy via a phonon assistance mechanism.
Exciton Magnetoluminescence Studies in Ordered and Disordered In0.48Ga0.52P Semiconductor Alloys
Authors: Jones E. D. , Follstaedt D. M. , Lyo S. K. , Schneider R. P. 
Published: March 2011

ABSTRACTWe report the observation of magnetic-field dependent excitonic photoluminescence energies and linewidths in ordered and disordered In0.48Ga0.52P alloys (lattice matched to GaAs). The photoluminescence measurements were made at 1.4 K and the applied magnetic field ranged between 0 and 13.6 tesla. With increasing magnetic fields, we observe increasing photoluminescence linewidths for disordered alloys and decreasing photoluminescence linewidths for the ordered alloys. The magnetic field dependence of the photoluminescence peak-energy shifts for all samples (ordered and disordered) is in good agreement with theoretical considerations. The presence of CuPt-type ordering was confirmed by transmission electron microscopy.
Optical Properties and Band Offset of PbTe/Pb1−xEuxTe Diluted Magnetic Semiconductor Multiquantum Wells Studied by Transmission and Photoconductivity Measurements
Authors: Yuan Shu , Krenn H. , Springholz G. , Bauer G. , Kriechbaum M. 
Published: March 2011

ABSTRACTFrom transmission experiments in the mid infrared region the optical interband transitions between electric subbands in the valence and conduction band of the PbTe wells embedded in Pb1−xEuxTe barriers (x = 2.6% to 3.0%) were determined and compared with calculations based on the envelope function approximation. The frequency dependence of the absorption constant α was calculated, taking the in-plane dispersion of the multiquantum well band structure into account. The frequency dependence of the refractive index n(ω) was derived from α(ω) using a Kramers-Kronig transformation and it exhibits several extrema which coincide with the onset of the various interband transitions. Experimentally the onset of these transitions was also observed in photoconductivity experiments. The changes in n(ω) are as large as 15 % and therefore important for the optical confinement in quantum well lasers grown with these materials.
Growth of Single Crystal Si/NiSi2/Si(100) and Si/CoSi2/Si(100) Structures by Molecular Beam Epitaxy and Furnace Annealing
Authors: Tung R. T. , Eaglesham D. J. , Schrey F. , Sullivan J. P. 
Published: March 2011

ABSTRACTUniform, single crystal Si/NiSi2/Si(100) and Si/CoSi2/Si(100) structures were fabricated by molecular beam epitaxy and furnace annealing. A Si template technique and a post-growth anneal at ∼960°C led to high quality buried NiSi2 layers with thickness ∼1000Å. The conditions for fabricating high quality buried CoSi2 layers by the recently proposed allotaxy process were studied and discussed. The endotaxial growth of buried CoSi2 layers in Si(100) was also studied.
Electrical and Structural Properties of Cobalt Annealed on Silicon-Germanium Epilayers
Authors: Sarcona G. , Lin F. , Hatalis M. K. , Cserhati A. F. , Austin Eva , Greve D. W. 
Published: March 2011

ABSTRACTThe structural and electrical properties of cobalt annealed on heteroepitaxial, strained-layer silicon-germanium were studied by transmission electron microscopy, four-point-probe and four-terminal resistor resistivity measurements, and junction diodes. The I50nm thick epitaxial p-Si0.87Ge0.13 was grown by UHV-CVD at 590°C. Cobalt was deposited by DC magnetron sputtering. The cobalt was rapid-thermally annealed at various temperatures in forming gas.The cobalt film and the SiGe layer reacted, as illustrated by changes in their film thicknesses, and increased interfacial roughness. The roughness and reacted-film thickness increased with increasing temperature. The sheet resistances of the samples were dependant on the anneal temperature and time. Films formed by annealing at 700°C, 3 min, were 80nm thick, and had 2.8ω/sq sheet resistivity, corresponding to 20μω-cm resistivity. The contact was ohmic, with contact resistivity of l.6×10−4ω-cm2. SiGe/ Si heterojunction diodes contacted by the reacted film, containing Co, Si, and Ge, were compared to diodes contacted by aluminum.
Electrical and Structural Properties of Ti Contacts on an Atomically Clean N-Type GaAs Surface
Authors: Lin X. W. , Liliental-Weber Z. , Swider W. , McCants T. , Newman N. , Spicer W. E. , Washburn J. , Weber E. R. 
Published: March 2011

ABSTRACTUsing current-voltage measurements and high-resolution electron microscopy (HREM), we have studied the electrical and structural properties of Ti contacts on an atomically clean n-type GaAs (110) surface. The Ti/n-GaAs diodes are formed at room temperature in ultrahigh vacuum and in situ isochronally (10 min) annealed at temperatures ranging from 200 to 450°C. We find that the Schottky barrier height of the diodes increases by ≈0.10 eV upon annealing at 200°C and remains basically stable for higher-temperature anneals. HREM investigation reveals that Ti reacts with GaAs in its as-deposited state to form an amorphous interlayer ≈1.5 nm thick. After anneals to 450°C, extensive reactions occur at the interface, resulting in the formation of a layered structure Ti/Ga3Ti2/TiAs/GaAs, with TiAs protruding into the GaAs substrate.
Structure of Chalcogen-Stabilized GaAs Interface
Authors: Takatani Shinichiro , Nakano Asao , Ogata Kiyoshi , Kikawa Takeshi , Nakazawa Masatoshi 
Published: March 2011

ABSTRACTA photo chemical vapor deposited silicon dioxide - gallium arsenide interface treated by a selenium(Se)-molecular beam is investigated using extended X-ray absorption fine structure (EXAFS) analysis. The Se K-edge EXAFS shows the presence of Ga2Se3-related compound at the SiO2/GaAs interface, indicating that the Ga2Se3 layer formed by the Se-treatment is preserved after the deposition of the SiO2film. The effective coordination number of the Se atoms is found to depend on the direction of the polarizing vector with respect to the crystal orientation. An attempt is made to interpret this dependence using a simple atomic layer model.