bluuebunny/crossref_metadata_2025 huggingface dataset:
The Electronic Structure pf Σ5 Grain Boundaries in CU
Authors: Sowa Erik C. , Gonis A. , Zhang X.-G.
Published: March 2011

We present first-principles calculations of the densities of states (DOS's) of unrelaxed and relaxed twist and tilt grain boundaries (GB's) in Cu. The relaxed configurations were obtained through the use of the Embedded Atom Method (EAM), while the DOS's were calculated using the real-space multiplescattering theory (RSMST) approach recently introduced in the literature. The DOS's of GB's are compared against those of bulk materials as well as against one another. Although the RSMST calculations are still not self-consistent, these comparisons allow us to verify certain expected trends in the DOS's, and to verify the usefulness and reliability of our method.
High-Resolution Electron Microscopy of Olivine-Magnetite Interfaces
Authors: Mckernan Stuart , Carter C. Barry , Ricoult Daniel , Cullis A. G.
Published: March 2011

The oxidation of iron-rich olivine to produce magnetite is a model system for the study of phase transitions involving mass transport. High-resolution lattice images of have been obtained from magnetite precipitates in naturally modified iron-rich olivines. The magnetite/olivine interface is shown to be extremely sharp. Steps and misfit dislocations are present at the interface.
Modeling of Nanophase Connectivity in Substance-Void Composite by Oblique Deposition
Authors: Motohiro T. , Noda S. , Isogai A. , Kamigaito O.
Published: March 2011

Obliquely vapor deposited thin film is characterized by its unique inclined columnar structure. Recently one of the authors developed thin film optical quarter-wave plate by oblique deposition. SEM observation revealed the inclined columns of ∼10 nm in diameter and ∼3 microns in length. Its birefringence indicates those columns are less closely spaced in the plane of vapor incidence (PVI) than normal to PVI, composing alternatively stacked substance layer (columns laterally connected with each other)-void layer(residual space) nanophase composite with 2–2 connectivity. The growth mechanism of the inclined columnar structure has been successfully explained by the self-shadowing effect in 2D-space computer simulation in PVI. However, the connectivity development perpendicular to PVI is not self-evident. In the present work, we performed simple 3D-space simulation of oblique depositipon and observed substantial feature of the connectivity development and related features on this nanophase structure.
Atomic Structure and Chemistry of Si/Ge Interfaces Determined by Z-Contrast Stem
Authors: Chisholm M. F. , Pennycook S. J. , Jesson D. E.
Published: March 2011

The technique of Z-contrast STEM provides a fundamentally new and powerful approach to determining the atomic scale structure and chemistry of interfaces. The images produced do not show contrast reversals with defocus or sample thickness, there are no Fresnel fringe effects at interfaces, and no contrast from within an amorphous phase. Such images are unambiguous and intuitively interpretable. In this paper, the technique has been used to directly image subnanometer interdiffusion in ultrathin (SimGen)p superlattices. The Z-contrast image of a (Si8Ge2)p superlattice grown by MBE at 400°C clearly shows significant broadening of the Gerich layer. Also, film formation and misfit accommodation in epitaxial Ge films on (001)Si produced by implantation and oxidation of Si wafers was studied. It was found that the Ge films, which are constrained to grow layer-by-layer, remain completely coherent with the Si substrate to a thickness of 5–6 nm. This is 3 to 6 times thicker than the observed critical thickness for Ge films grown on Si by MBE. It is observed that misfit accommodating dislocations nucleate at the film surface as Shockley partials. The Z-contrast images show these partials can combine to form perfect dislocations whose cores are found to lie entirely in the elastically softer Ge film.
Observation of Heteroepitaxially Grown Organic Ultrathin Layers on Inorganic Substrates by In Situ RHEED and by STM
Authors: Hara Masahiko , Sasabe Hiroyuki , Yamada Akira , Garito Anthony F.
Published: March 2011

An organic molecular beam epitaxy (OMBE) system has been designed and constructed with in situ reflection high-energy electron diffraction (RHEED) specifically for the deposition of organic molefelar layers under ultrahigh vacuum (UHV), the order of 10–10 torr. The system is equipped with a portable UHV chamber which allows easy transfer of the OMBE film samples to a separate UHV scanning tunneling microscopy (STM) system. A structural investigation of heteroepitaxially grown organic ultrathin layers of copper phthalocyanine (CuPc) on inorganic substrates was carried out by the combined UHV system from less than a monolayer of CuPc.
Critical Thickness of GaAs/InGaAs and AlGaAs/GaAsP Quantum Wells Grown by Atmospheric Pressure OMCVD
Authors: Bertolet Daniel C. , Hsu Jung-Kuei , May Lau Kei , Koteles Emil S.
Published: March 2011

A critical layer thickness study of strained GaAs/InGaAs and AlGaAs/GaAsP quantum wells (QWs) grown by atmospheric pressure organometallic chemical vapor deposition (OMCVD) is reported. Characterization by conventional photoluminescence (PL), photoluminescence excitation (PLE) spectroscopy, optical microscopy, and x-ray diffraction suggests that partial or regional relaxation begins to occur at critical thicknesses predicted by the force-balance model. To test the stability of strained quantum wells with well width near or exceeding the predicted critical thickness, annealing up to 850°C for ten minutes was carried out. No sign of degradation or complete relaxation of the QW layers was observed.
Electron Channeling Analysis of Elastic Strains in InGaAs Thin Films
Authors: Keller R. , Zielinski W. , Gerberich W.W. , Kozubowski J.A.
Published: March 2011

Inx Ga1-x As thin films were grown by MBE on (001) GaAs substrates. The associated 1% lattice mismatch resulted in the development of an elastic strain field in the systems. Electron channeling patterns (ECP) were then obtained from these samples in an SEM at different accelerating voltages, allowing data to be obtained over various information depths within the samples while keeping them intact. The ECPs showed sensitivity to the elastic strains both parallel and perpendicular to the film/substrate interface. Certain high order Laue zone (HOLZ) line positions showed good sensitivity to the Poisson strain in the films due to a rotation of atomic planes. These line positions varied with film thickness and distance from the interface. The technique shows promise as a tool for relatively easy elastic strain determination. Its limitations will also be discussed.
Microstructure of FCC/BCC Metal Multilayers
Authors: Jennett Nigel M. , Dingley D.J. , Ando Y.
Published: March 2011

Bilayers of Cu/Fe and Cu/V and multilayers of Ni/Fe have been grown under high vacuum and ultra high vacuum conditions respectively with [111] epitaxy. Multilayer layer thicknesses ranged from 3 monolayers to 15 monolayers per layer. Improved epitaxy of the UHV growth was, we believe, due to the better vacuum although perfect material could only be obtained for growth within a narrow and shifting substrate temperature ‘window’. Possible shortfall in the quality of the Cu backing layer epitaxy was averted by a 2hr anneal at 425°C.

In the Fe/Ni multilayers the Fe was observed to adopt the FCC lattice rather than the equilibrium BCC lattice for layer thicknesses less than 10 monolayers. This change of structure coincided with a reduction in sample magnetic moment per volume attributed to a collapse of the Fe moment to a value 7 times less than bulk.
An Investigation of the Dislocation Structure of the NI/AG Phase Boundary
Authors: Bamford T.A.
Published: March 2011

The Ni/Ag interphase boundary structure in the parallel cube-on-cube orientation was studied for the boundary planes (001) and (011). Coarsely spaced dislocations were found in all annealed interfaces; the origin of these was apparently differential thermal expansion of the bicrystal film. A detailed search for intrinsic periodic structure consistent with the O-lattice construction was made using X-ray diffraction, electron diffraction and transmission electron microscopy . No evidence for this could be found; such a relaxation, if present, is very weak. It is unlikely that such a small relaxation could account for the relative energy minimum associated with the parallel cube-on-cube orientation found by previous investigators.
Formation and Structure of Thin Mo Layers and Mo-Ni Multilayers on Ni(001) by Molecular Beam Epitaxy
Authors: Lee Y.H. , Burns R.P. , Posthill J.B. , Bachmann K.J.
Published: March 2011

The growth of Mo overtayers and Mo-Ni multilayers on single crystal Ni(001) substrates is described. The nucleation and growth processes of these thin films were analyzed by LEED, XPS, AES and SEM and High Resolution AES investigations without breaking vacuum. Growth of Mo-Ni multilayer heterostructures on Ni(001) with ≈20Å periodicity is possible at low temperature (≈200 °C). At high temperature (≈550 °C) the growth proceeds by the Volmer-Weber mechanism preventing the deposition of small period multilayers. Annealing experiments on ultra-thin (<20Å) Mo overiayers deposited at 200 °C show an onset of interdiffusion at ≈ 550°C coupled to the generation of a new surface periodicity.
Effect of Substrate Misorientation on Heteroepitaxy with Large Lattice Mismatch: Ag/Si(111)
Authors: McKenna D.C. , Park K.-H. , Wang G.-C. , Smith G.A.
Published: March 2011

Epitaxial films of Ag(111) were grown by Molecular Beam Epitaxy (MBE) on small angle misoriented Si(111) substrates. The surface normal was tilted 0 to 6° away from the Si(111) axis toward the [112] direction. The structure of the films was analyzed by x-ray diffraction and MeV He+ ion channeling. Despite a large lattice mismatch, good quality epitaxial films, 600–1200 Å thick, were grown on the misoriented Si substrates. Interestingly, the angle between the Si(111) axis of the substrate and the Ag(111) axis of the film (the misalignment angle) is not zero. In contrast to the perfect alignment on a flat substrate, the Ag(111) axis is tilted away from the Si(111) axis toward the surface normal. Axial MeV He+ ion channeling shows the misalignment angle (up to .6°) increases with substrate misorientation angle (~1/10 substrate misorientation angle).
Growth of Epitaxial CoSi2 and NiSi2 on (111), (100), and (110) Si at Room Temperature
Authors: Tung R. T. , Schrey F.
Published: March 2011

Growth of high quality type-B oriented NiSi2 and CoSi2 on Si(111) at room temperature was demonstrated recently. It is proposed that a few monolayers of metal reacts with Si(111) to form type B disilicide which then serves as a template for subsequent homoepitaxial growth during co-deposition. Thin, pre-annealed, silicide layers on Si (100) and (110) arc used as templates to demonstrate the homoepitaxial growth of NiSi2 and CoSi2 along these two directions at room temperature. The high temperatures usually required for the formation of NiSi2 and CoSi2 are related to the nucleation and mass transport processes.
Growth of Epitaxial IrSi3 Layers on Si(111)
Authors: Lin T. L. , Nieh C. W.
Published: March 2011

Epitaxial IrSi3 films have been grown on Si (111) by molecular beam epitaxy (MBE) at temperatures ranging from 630 to 800 °C and by solid phase epitaxy (SPE) at 500 °C. Good surface morphology was observed for IrSi3 layers grown by MBE at temperatures below 680 °C, and an increasing tendency to form islands is noted in samples grown at higher temperatures. Transmission electron microscopy (TEM) analysis reveals that the IrSi3 layers grow epitaxially on Si(111) with three epitaxial modes depending on the growth conditions. For IrSi3 layers grown by MBE at 630 °C, two epitaxial modes were observed with ~ 50% area coverage for each mode. Single mode epitaxial growth was achieved at a higher MBE growth temperature, but with island formation in the IrSi3 layer. A template technique was used with MBE to improve the IrSi3 surface morphology at higher growth temperatures. Furthermore, single-crystal IrSi3 was grown on Si(111) at 500 °C by SPE, with annealing performed in-situ in a TEM chamber.
High Resolution X-Ray Scattering Studies of Strain in Epitaxial Thin Films of Yttrium Silicide Grown on Silicon(111)
Authors: Martinez-Miranda L. J. , Siegal M. P. , Heiney P. A. , Santiago-Aviles J. J. , Graham W. R.
Published: March 2011

We have used high resolution grazing incidence x-ray scattering (GIXS) to study the in-plane and out-of-plane structure of epitaxial YSi2-x films grown on Si (111), with thicknesses ranging from 85Å to 510Å. Our results indicate that the films are strained, and that film strain increases as a function of thickness, with lattice parameters varying from a = 3.846Å/c = 4.142Å for the 85Å film to a = 3.877Å/c = 4.121Å for the 510Å film. We correlate these results with an increase in pinhole areal coverage as a function of thickness. In addition, our measurements show no evidence for the existence of ordered silicon vacancies in the films.
Silicon Consumption During Self-Aligned Titanium Suicide Formation on Shallow Junctions
Authors: Smith P.L. , Osburn C.M. , Wen D.S. , McGuire G.
Published: March 2011

The self-aligned-silicide (SALICIDE) process was developed to overcome the conductivity and contact resistance limitations associated with very shallow junctions. However this process is fundamentally limited by the roughening and the consumption of the silicon substrate that occurs during its selective reaction with metal. As junctions scale to smaller dimensions, me silicon consumption must also be scaled so mat the suicide does not consume the junction. The use of argon gas atmospheres during titanium suicide formation leads to more silicon consumption (75%) than can be explained simply on the basis of suicide formation. Lateral loss of silicon into the metal surrounding patterns is believed to be the mechanism responsible for this excess silicon consumption. More surprisingly, nitrogen annealing, which suppresses lateral suicide formation, also leads to an anomalously large (50%) silicon consumption. Suicides formed on amorphous substrates during the concurrent formation of junctions and suicides result in even more silicon consumption.
Surface Morphologies and Interfaces of TiSi2 Formed from UHV Deposited Ti on Si
Authors: Jeon Hyeongtag , Nemanich R. J. , Honeycutt J.W. , Rozgonyi G. A.
Published: March 2011

The island formation of TiSi2 and the surface morphologies and interfaces of TiSi2 on Si have been examined and related to the surface and the interface energies. Ti (200Å and 400Å) films were deposited on clean, reconstructed Si(100) and Si(111) substrates at room temperature and also at high substrate temperatures (500°C~800°C). The TiSi2 formation process is monitored with in-situ LEED and AES and the surface morphologies and interfaces are examined with ex-situ SEM and TEM. For annealing to temperatures such that the C54 phase forms, the results indicate island formation with clean reconstructed substrate regions between the islands. The TiSi2 islands show different morphology on the (100) and (111) oriented substrates. The mechanism of TiSi2 island formation is described in terms of a liquid-liquid model, and the surface and interface energies for the TiSi2 island are determined from contact angle measurements.
Epitaxial Growth of Metallic Layers by Solid Phase Interdiffusion : Study of the Ni/GaAs and Ni/AlAs Systems
Authors: Guerin Roland , Deputier S. , Caulet J. , Minier M. , Poudoulec A. , Ballini Y. , Durel V. , Dupas G. , Guivarc’h A.
Published: March 2011

An ideal metal/III-V semiconductor contact should be made by stable and epitaxial metallic films. In principle, such a contact may be obtained by the solid state ΐnterdiffusion of a metal film with a III-V SC substrate. We studied the solid state interdiffusions in the Ni/GaAs and Ni/AlAs systems. Our starting point was the experimental determination of the Ni-Ga-As and Ni-Al-As ternary phase diagrams. The main steps of the interaction appear to be different in the two systems. During the Ni/GaAs one, three successive steps as a function of the annealing temperature are observed : first a mixture of a Ga-rich ternary phase (C phase) + NiAs, then C phase + NiAs + NiGa and at last the two binaries NiAs + NiGa where the reaction stops. In the case of the Ni/AlAs reactions, the three steps successively correspond to a mixture of NiAl + an As-rich ternary phase then NiAl + another As-rich ternary phase + NiAs and finally NiAl + NiAs. NiAs and NiAl are the key compounds in Ni/GaAs and Ni/AlAs reactions respectively and all the reaction compounds are either textured (pseudocubic NiAs and ternaries) or epitaxial (cubic binaries NiGa and NiAl).
Diffraction Studies of the Growth of Strained Epitaxial Layers
Authors: Whaley G.J. , Cohen P.I.
Published: March 2011

The molecular beam epitaxial growth of strained InGaAs films grown on GaAs(100) substrates has been studied using in situ reflection high-energy electron diffraction (RHEED). Both the intensity, shape and position of the diffracted beams were monitored during growth. Growth was found to be layer-by-layer up to a strain dependent thickness, at which point three-dimensional clusters were formed. These clusters exhibited (114) facets and were elongated in the [011] direction. The onset of 3D cluster formation was simultaneous with measurable lattice relaxation. The relaxation was determined using electromagnetic deflection of the RHEED pattern across two detectors. With this arrangement, the lattice constant could be measured to within 0.003Å. The onset could be delayed by lowering the growth temperature. For misfit strain greater than about 2%, the onset occurs at thicknesses less than the Matthews-Blakeslee critical thickness. For smaller strains, the onset occurs at larger thicknesses.
InAs and InGaAs Growth by Chloride Atomic Layer Epitaxy
Authors: Shimawaki H. , Kato Y. , Usui A.
Published: March 2011

InAs chloride ALE has been carried out in detail, resulting in successful InGaAs ALE on (111)B InP substrates. InAs growth of 0.9 ML/cycle is obtained for (111)B InAs substrates at temperatures below 375 °C, while growth rates for (100) and (111)A substrates steadily decrease with increases in growth temperature. The growth rates are independent of InCI pressure at 375 °C, suggesting a self-limiting growth factor in InAs chloride ALE. (GaAs)1(InAs)1 and (GaAs)2(InAs)2 superalloys can be prepared on (111)B InP substrates at 375 °C. Growth rates and crystal compositions for both layers agree well with the values expected for ideal superalloys. The presence of superlattice structures is indicated by X-ray diffraction measurement,
Trimethylgallium Decomposition on a Heated Si(100) Substrate
Authors: Gow T.R. , Lin R. , Masel R.I.
Published: March 2011

Trimethylgallium (TMGa) is an important source gas for metal-organic chemical vapor deposition (MOCVD) and metal-organic molecular beam epitaxy (MOMBE). In the last three years, workers in three different laboratories have examined the pyrolysis of trimethylgallium (TMGa) on heated substrates. However, the mechanism of the decomposition process is still not understood. In this paper we consider the mechanism of the TMGa decomposition on a hot Si(100) substrate in a molecular beam system. It is found that at TMGa doses of 1×1015 molecules/cm2 or less, the decomposition process in the beam system is the same as that reported by Lee et al., Surface Sci. 216, 173 (1989) in studies where TMGa was dosed at low temperature and then the substrate was heated. However, at higher TMGa doses, the mechanism in the molecular beam system is different than the ones reported previously. It is possible to transiently populate a weakly bound state which we assign to TMGa adsorption in the second monolayer. If me sample is below 400 K, the TMGa in the second monolayer desorbs. However, at higher temperatures, the TMGa in the second monolayer can react to form a CHx group (x=3 or 4) and dimethylgallium. The dimethylgallium desorbs. However, some of the CHx groups remain bound to the substrate leading to extra carbon incorporation. There also is evidence for formation of traces of monomethylgallium above 500 K and an indication of methyl radical desorption above 650 K. Thus it seems that at high doses, the decomposition of TMGa on a hot substrate is somewhat different than the decomposition of a monolayer of TMGa which has been adsorbed at low temperatures and then heated. These results explain some of the apparent discrepancies in the literature.
Effect of Stoichiometry on the Activation of Implanted Si in MBE-grown GaAs on Si
Authors: Kim T.S. , Kao Y.C.
Published: March 2011

In this work, activation of Si implanted into GaAs-on-Si layers grown by molecular beam epitaxy (MBE) is studied. We have found that activation efficiency of implanted Si is lower in GaAs on Si than in bulk GaAs and varies widely. By studying the activation of non-amphoteric dopants such as Be and S, we have found that no donor- or acceptor-like defects exist in high concentrations in GaAs on Si and that amphoteric behavior of Si is the major compensation mechanism in MBE-grown GaAs on Si. Increased Si-acceptor concentration and S activation in GaAs on Si are apparently due to a high density of As vacancies which result from a low V(As):III(Ga) flux ratio during growth. The effect of the threading dislocations does not appear to be significant compared to that of As vacancies as no correlation is found between the density of threading dislocations and implanted Si activation.
MBE Grown GaAs on Si(100) Studied by Infrared Spectroscopy
Authors: Eickhoff T. , Morley S. , Zahn D.R.T. , Richter W. , Woolf D.A. , Westwood D.I. , Williams R.H.
Published: March 2011

GaAs layers were deposited onto Si(100) substrates using molecular beam epitaxy (MBE). The substrates were prepared by various methods before the growth of 0.1µm thick GaAs buffer layers. Active GaAs layers were thereafter grown with thicknesses from 1 to 4µm. Infrared spectra were recorded in the spectral ranges from 12 to 65cm-4 and 50 to 500cm-1 of the thin buffer layers as well as the thick active layers. The infrared active phonon of GaAs already shows up in the spectra for the 0.1µm buffer layers. The phonon parameters were derived from a harmonic oscillator fit to the experimental data. The phonon damping constant is correlated with the bulk quality of the GaAs layers. These results are compared with those obtained from Raman and spectroscopic ellipsometry measurements.
A New Oxygen Plasma Source for In-Situ Thin Films Growth of DY1BA2CU3O7-x by Molecular Beam Epitaxy
Authors: Touzeau M. , Schuhl A. , Cabanel R. , Luzeau P. , Barski A. , Pagnon D. , Hirtz J.P. , Creuzet G.
Published: March 2011

We describe an atomic oxygen source based on a D.C. plasma discharge, compatible with cristal growth in a Molecular Beam Epitaxy(M.B.E.) system. The physical characteristics of the oxygen cell are presented. The efficiency of the cell has been proved by direct deposition of CuO at high temperature(500°C). Moreover, we used successfully this cell for direct epitaxial growth of high temperature superconductors, with an ambient pressure as low as 2 10-5 Torr.
Dependence of Mo/Si Multilayer Morphology on Deposition Angle
Authors: Cheng Yuanda , Beth Stearns Mary , Smith David J.
Published: March 2011

Studies have been made of the dependence of the structure on the deposition angle and the substrate temperature of a series of Mo/Si multilyers fabricated in a UHV system by e-beam evaporation. The detailed morphology was determined by cross-sectional high resolution electron microscopy. Columnar growth in the crystalline Mo layers was found to follow the tangent rule. The overall quality of the multilayers was found to depend strongly on the growth conditions.
Reduction of Defect Density in Heteroepitaxial GexSi1-x Grown on Patterned Si Substrates
Authors: Fitzgerald E.A. , Xie Y.-H. , Michel J. , Freeland P.E. , Weir B.E.
Published: March 2011

We have investigated the molecular beam epitaxial growth of GexSi1-x on small growth areas patterned in Si substrates. Electron beam induced current, etch-pit density measurements, transmission electron microscopy, and photoluminescence were used to compare dislocation densities in GexSi1-x on patterned and unpattemed substrates. We find a dramatic reduction in both misfit and threading dislocation densities for the patterned substrate growth. Our results also show that dislocation introduction is dominated by heterogeneous nucleation.
An Introduction to Wavefunction Engineering
Authors: Pearsall T.P.
Published: March 2011

Experimental and theoretical studies demonstrate that it is possible to redefine the basic character of band-edge electronic wavefunctions in superlattices, the period of which is comparable to the lattice parameter of the constituent materials. In using superlattice periodicity to redefine electronic wavefunctions, strain and crystalline orientation can be used to select which wavefunctions will form the band edge states. These principles can be used to form a direct bandgap semiconductor superlattice from Si and Ge, two indirect bandgap materials.
Photoluminescence from Si/Ge Superlattices
Authors: van de Walle G.F.A. , Montie E.A. , Gravesteijn D.J. , Fredriksz C.W.
Published: March 2011

The luminescence of short period Si/Ge superlattices was systematically studied as a function of composition, strain and superlattice period. With Rutherford backscattering spectrometry the composition was determined, while X-ray diffraction was used to determine the strain and superlattice period. Two luminescence bands around 1,6 µm were observed. Etching experiments showed that the signal originated from the superlattice. Changes in wavelength and intensity were found to be related to the composition and the strain, while no clear influence of the superlattice period was observed.
Characterization of Undoped Pseudomorphic InGaAs/GaAs Quantum Wells by Electron Beam Electroreflectance (EBER) and Photoluminescence (PL)
Authors: Herman M. H. , Dodabalafur A. , Ward I. D. , Streetman B. G.
Published: March 2011

We have investigated the interband optical transitions within undoped pseudomorphic InyGa1-yAs/GaAs quantum wells of a range of thickness from 50Å to 150Å, and y values 0.1 to 0.2. From photoluminescence (PL), we identify the lowest interband transitions. Electron beam electroreflectance (EBER) modulation spectroscopy is utilized to detect the lowest and the higher energy interband transitions within the quantum wells. We compare the measured interband energies to those calculated theoretically.

We have observed exciton-like transitions attributable to the heavy hole and light hole levels and most importantly, confined states of the split-off valence band, not reported to date. The multiplicity of observed quantum transitions allows rectangular barrier model parametrization of these wells, using hypothetical strain splitting of the various subbands. For five such quantum wells, we find the estimated indium contents and well widths to be nearly nominal, with consistent values between independent 300K and 100K data. With respect to the heavy hole subband, the conduction band offset Qc is estimated to be 0.586 ±0.024. With suitable values, all of the transitions, including those of the splitoff band, are predicted accurately.
Magneto-Optical Studies of 2-D Electrons in GaAs-AlGaAs Single Heterojunctions
Authors: Lee K-S. , Perry C.H. , Worlock J.M.
Published: March 2011

We report low temperature magneto-photoluminescence(PL) investigations of ex-citon spectra of n-doped (AlGa)As-GaAs single heterojunctions. At zero field, the PL spectrum is dominated by the free excitons and excitons bound to the impurities in the bulk GaAs, which overlap a weak emission band associated with the radiative transition between the two dimensional electron gas(2DEG) and the photoexcited holes. In the presence of a magnetic field applied parallel to the growth axis the transitions from the 2DEG, now quantized into Landau levels, become well pronounced. Additionally, intensity oscillations are observed when the 2DEG line crosses the exciton lines, which we believe is due to the effect of a resonant tunneling of the 2DEG from the quantum well region to the bulk GaAs.
Raman Scattering from an Interfacial Thin Layer of GaAs Heteroepitaxially Grown on Silicon (100) Substrate
Authors: Akagi Yoshiro , Ishino Mariko , Nakajima Yoshiharu
Published: March 2011

In an epi-layer of GaAs less than 300nm to 100nm thick grown on silicon substrate by two-step MOCVD lethod, broad Raman scattering centered at 700cm-1(L+) and TO-like phonon at 268cm-1(L-1) were observed as well as LO phonon spectrum (292cm -1) in a back-scattering optical geometry. Emission peak of photoluminescence spectra in these epilayer of GaAs were found to shift by 33meV at 300K towards high energy side. In a thin buffer layer of GaAs less than 20nm thick, however, Raman spectra showed only LO phonon peak. These experimental facts shows n-carrier generation of 1018cm-3 only within interfacial epi-layer of GaAs less than 300nm thick, except for the very thin buffer layer of GaAs, because of incorporation of silicon atoms during growth of epilayer at 700°C. In addition, in both layers of GaAs less than 300nm, compressive stress of 109dyn·cm-2 was observed, which were found to relax abruptly with thickness.
Raman Characterization of InSb/GaAs Grown by Metalorganic Magnetron Sputtering
Authors: Feng Z. C. , Perkowitz S. , Rao T. S. , Webb J. B.
Published: March 2011

The new technique of metalorganic magnetron sputtering (MOMS) produces high-quality (100) epitaxial InSb films on (100) GaAs substrates, despite the large 14.6% lattice mismatch between InSb and GaAs. We have used Raman scattering to examine MOMS-grown InSb films of thicknesses 0.17 - 2.67 µm, and commercial bulk InSb. We observe the longitudinal optical (LO) phonon peak, and the second order 2LO peak, which is enhanced by outgoing resonance with the E1 + Δ1, gap of InSb. The half-widths and intensities of these bands are related to sample quality as a function of film thickness and to the role of biaxial stress in the InSb film.
High Pressure Optical Studies of GaSb-AlSb Multiple Quantum Wells
Authors: Rockwell Benjamin , Chandrasekhar H.R. , Chandrasekhar Meera , Pollak Fred H. , Shen H. , Chang L.L. , Wang W.I. , Esaki L.
Published: March 2011

The pressure coefficients (α) of the excitonic transitions arising from the conduction (CB) to the heavy (HH) and light (LH) hole sub-bands of a GaSb-AlSb multiple quantum well structure (MQW) grown on a GaAs substrate are determined. Photoreflectance (PR) and Photoluminescence (PL) studies are employed at cryogenic temperatures. The α for the ground sub-band transition is ~10% smaller than that for bulk GaSb. This effect is explained by in-plane deformation of the MQW arising from the substrate under external pressure. On the other hand, the α get progressively smaller for the higher sub-band transitions due to quantum confinement The PL intensity drops dramatically as the direct Γ CB crosses the L CB at ~10kBars but the PR intensity persists until the X CB crosses each sub-band energy.
Field Effect Transistor Structure Based on Strain Induced Polarization Charges
Authors: Smith D.L. , Collins R.T. , Kuech T.F. , Mailhiot C.
Published: March 2011

We suggest a new field effect transistor based on strain-induced polarization charges. The structure utilizes the pseudomorphic growth of a strained barrier layer on a substrate oriented in a polar direction such as [111] or [211]. Polarization charges in the barrier layer are generated by the piezoelectric effect. A two-dimensional (2-D) electron gas, whose density can be modulated by an external bias, forms at the hetero-interface and it screens the polarization charge. Zero bias densities of several 1011 e/cm2 and threshold voltages of 0.5 V can be achieved. Both normally-on and normally-off structures are possible.
Morphology of Diamond Films Grown by DC Plasma Jet CVD
Authors: Kurihara Kazuaki , Sasaki Ken-Ichi , Kawarada Motonobu , Koshino Nagaaki
Published: March 2011

It is well known that diamond films synthesized from the gas phase have well defined crystal habits which are affected strongly by synthesis conditions. Though there have been many studies of the morphologies of diamond films synthesized by microwave plasma CVD [1,2,3], there have been relatively few reports on the morphologies of these films grown using new high growth rate techniques such as DC plasma jet CVD [4]. Morphology control is very important to keep flat surface, when producing thick diamond films by high growth rate techniques. In this paper we report our investigation of the morphology and growth of diamond films synthesized by DC plasma jet CVD.
Deposition and Characterization of Carbon Films Produced by Nitrogen/Argon Mixture RF Sputtering
Authors: Tomg C. J. , Yeh T. , Sivertsen J. M. , Judy J. H.
Published: March 2011

Thin carbon films were prepared by RF diode sputtering of a graphite target in a mixed nitrogen/argon plasma. A series of carbon films were deposited as a function of nitrogen partial pressure. We have observed a systematic variation of the properties of the carbon films with an increase of the nitrogen partial pressure. AES, XPS and energy gap studies showed that nitrogen will enhance the diamond sp3 bonding. Consistent with this the optical energy gap of our C:N films shows an increase from 1.1 eV to 1.4 eV using, respectively, 25 to 100 % nitrogen plasma. The mechanical properties also are shown to be enhanced for certain applications.
Predicted Infrared Spectrum and X-Ray Diffraction Patterns for Diamond Polyiypes
Authors: Phelps Andrew W. , Howard William , White William B. , Spear Karl E. , Huang D.
Published: March 2011

The concept of diamond polytypism was examined and extended beyond the previous work to gain more analytical tools with which to understand and characterize these materials. This paper reports the band positions predicted for the expected infrared active modes of several diamond polytypes and the calculated diffraction patterns for the 21R and 15R polytypes. The infrared active modes were predicted on the basis of a generalized Brlllouin zone similar to that developed for silicon carbide polytypes. The diffraction patterns for the 21R and 15R polytypes were calculated in a manner similar to that used previously for the hexagonal polytypes. These results complete the suite of basic diffraction patterns for diamond polytypes.
A Study of the Electronic Structure Near Individual Dislocations in Diamond by Energy-Loss Spectroscopy
Authors: Bruley J. , Batson P. E.
Published: March 2011

Spatially resolved electron energy-loss spectra recorded from very small volumes of diamond containing individual dislocations show extra intensity within the band-gap just below the 1s to bulk conduction band threshold energy, when compared to spectra recorded from neighboring defect free regions. This is interpreted as direct evidence for the presence of vacant defect states associated with the dislocation structure. The contribution of the π* states from the surface layers to this region of the spectra is completely removed by calculating the difference between the spectra recorded on and off the defect. A comparison is drawn between the measured near edge structure and calculations of local density of states reported in the literature.
Intra- and Intergranular Fracture of Diamond Thin Films
Authors: Hoff H. A. , Morrish A. A. , Carrington W. A. , Butler J. E. , Rath B. B.
Published: March 2011

Diamond thin films have been synthesized at low pressures by chemical vapor deposition (CVD) and, recently, at ambient atmosphere with an oxygen-acetylene welding torch. By the application of appropriate thermal or mechanical stresses to the substrate, the diamond films can be delaminated. The delaminated films which are only a few microns thick have been fractured by manual bending. Scanning electron microscopy (SEM) examination of fractured CVD diamond films shows the presence of primarily intragranular fracture attesting to the inherent strength of the films. Using transmission electron microscopy (TEM), twinning and stacking faults are seen within the crystallites of the films along the fracture surfaces. By combining SEM and TEM examination, the relative degree of intragranular fracture found in films synthesized by both CVD and oxygen-acetylene torch has been investigated. Possible mechanisms for the intragranular fracture and the relative strength of such films are discussed.
Metallization of Semiconducting Diamond: Mo, Mo/Au and Mo/Ni/Au
Authors: Moazed K. L. , Zeidler J. R. , Taylor M. J.
Published: March 2011

A processing technology has been developed to make ohmic contacts to naturally doped semiconducting diamond. The approach follows, as far as possible, conventional photolithographic techniques for metallization of semiconductors currently in use in the microelectronics industry.
Carbon - silicon heterojunction diodes formed by CH4/ Ar rf plasma thin film deposition on Si substrates
Authors: Amaratunga G. A. J. , Milne W. I. , Putnis A. , Chan K. K. , Clay K. J. , Welland M. E.
Published: March 2011

Thin C films deposited from a CH4/Ar plasma on Si substrates kept at 20C are shown to be semiconducting. The semiconducting properties are associated with the poly-crystalline diamond grains present within the films. Diode type I-V characteristics observed from AVC/Si verticle structures are explained by the action of a C-Si heterojunction. A band gap of 2eV, a resistivity of 106Ω.cm and an electrical breakdown strength of 5.106 V/cm are estimated for the C.
Liquid Phase Homoepitaxial Growth of 4H-SiC Crystals and Fabrication Techniques of Bluish-Purple Light-Emitting Diodes
Authors: Ueda Y. , Nakata T. , Koga K. , Matsushita Y. , Fujikawa Y. , Uetani T. , Yamaguchi T. , Niina T.
Published: March 2011

4H-SiC single crystals have been fabricated on the seeds of 6H-type crystals by the vacuum-sublimation (modified Lely) method at a temperature of 2400 °C and under a pressure of 2–60 mbar in an argon atmosphere. Liquid phase epitaxy was attempted by using a dipping method with a 4H-SiC off-orientation substrate whose {0001} C-face varied toward the <1120> direction by 5 degrees. The polytype of the grown crystals was found to be the 4H-type through measurements of Raman scattering and photoluminescence. P-n junction diodes were epitaxially obtained on 4H-SiC substrates. Aluminum and nitrogen were doped as acceptors and donors, respectively. The LED emitted bluish-purple light with a high brightness of 2.2 mcd at a forward current of 20 mA. Other characteristics were as follows : 420–425 nm peak wavelength, 90 % color purity, and a light output of 4 μW.
Status of β-SiC, Diamond and C-BN Semiconductors; Comparison of a Si Power Fet to a Hypothetical Diamond Fet
Authors: Koba Richard , Russell William
Published: March 2011

Monocrystalline β-SiC, diamond and cubic boron nitride (c-BN) are the three ultimate semiconductors. These materials show great promise as active semiconductors for power electronics because of their wide bandgap, the existence of substitutional dopants, their high dielectric strength, their low dielectric constant, and their high thermal conductivity. To illustrate their superiority, a conventional Si.power FET is compared to a theoretical diamond FET. By assuming the diamond FET can operate hotter and at a higher voltage, it is calculated that the diamond FET should deliver up to 35 times more power-to-load than the Si FET.
Infrared Study of Amorphous Crystalline Phase Transition in an Annealed Amorphous Hydrogenated Silicon Carbon Alloy Film
Authors: Basa D. K. , Smith F. W.
Published: March 2011

An amorphous hydrogenated silicon carbon alloy film (a Si1 x Cx :H with x = 0.29) was prepared by glow discharge decomposition of a silane and ethylene gas mixture. A careful and detailed investigation of the infrared absorption was undertaken in the range 400 to 4000 cm1 for both the as deposited (T =250°C) and annealed (up to 1200°C) film. This study demonstrates clearly that there is a structural change from amorphous to microcrystalline at T =8000C and then to crystalline phase at T a=1200° C.
Native Defects, Diffusion, Self-Compensation, and Boron Doping in Cubic Silicon Carbide
Authors: Wang C. , Bemholc J. , Davis R. F.
Published: March 2011

We report the results of a comprehensive theoretical investigation of the effects of stoichiometry and boron doping on the properties of cubic SiC. Supercell calculations using ab initio pseudopotentials show that the lowest energy defect in Si-rich n-type and intrinsic SiC is the electrically inactive Sic antisite, while VC++ is the lowest energy defect in p-type SiC. The electrons released by the carbon vacancies compensate acceptor dopants and lead to strong self-compensation effects when doping occurs during the growth of crystal. In C-rich SiC the dominant defect for all Fermi level positions is the electrically inactive CSi antisite. In stoichiometric and Si-rich cubic SiC, the BC site is energetically preferred, while BC and BSi have similar incorporation energies in C-rich material. In heavily doped p-type SiC the diffusion of BC proceeds by the dissociative (Frank-Turnbull) mechanism.
Deep-Level Dominated Electrical Characteristics of Au Contacts on β-SiC
Authors: Das K. , Kong H. S. , Petit J. B. , Bumgarner J. W. , Matus L. G. , Davis R. F.
Published: March 2011

Current-voltage characteristics of Au contacts formed on β-SiC films grown heteroepitaxially on both nominally (100) oriented and off-axis (100) silicon substrates have been investigated. Logarithmic plots of the I-V characteristics in the forward direction indicate space charge limited current conduction through the active volume of the diodes. The β-SiC films grown on nominally (100) oriented substrates show the presence of two deep levels located approximately between 0.26 eV and 0.38 eV below the conduction band edge. In some films on nominal (100) substrates, the I-V characteristics are also influenced by additional traps which are exponentially distributed in energy with a maximum occurring at the conduction band edge. In contrast, the films deposited on off-axis substrates have only one deep level located at approximately 0.49 eV for the 2° off (100) substrates and 0.57 eV for the 4° off (100) substrates. Previous microstructural analysis revealed that the nature and density of defects in the β-SiC heteroepitaxial films on both nominal and off-axis (100) silicon are similar except that the films on nominal (100) substrates have a high density of antiphase domain boundaries. Therefore, the presence of the shallower deep-level states observed in the β-SiC films grown on nominal (100) substrates is speculated to be due to the electrical activity of antiphase domain boundaries.
A New Deep Acceptor in Epitaxial Cubic SiC
Authors: Freitas J. A. , Bishop S. G.
Published: March 2011

The temperature and excitation intensity dependence of photoluminescence (PL) spectra have been studied in thin films of SiC grown by chemical vapor deposition on Si (100) substrates. The low power PL spectra from all samples exhibited a donor-acceptor pair PL band which involves a previously undetected deep acceptor whose binding energy is approximately 470 meV. This deep acceptor is found in every sample studied independent of growth reactor, suggesting the possibility that this background acceptor is at least partially responsible for the high compensation observed in Hall effect studies of undoped films of cubic SiC.
Electronic Structure of Wide Bandgap Semiconductor Interfaces: Cubic SiC/AIN, SiC/BP, C/BN
Authors: Lambrecht W. R. L. , Segall B.
Published: March 2011

The linear muffin-tin orbital supercell band-structure method is used to calculate the interface energy of formation, band offsets and local densities of states at the latticematched (110) heterojunctions between (cubic SiC)/(cubic AIN), (cubic SiC)/(cubic BP) and (diamond C)/(cubic BN). The lowest energy bonding configuration for SiC/AIN is found to be Si to N and C to Al bonding while for SiC/BP, Si is found to bind to B and C to P. The causes for these preferred bonding configurations are explained in terms of electrostatic effects. The band offsets are found to be of type II for SiC/BP and SiC/BN and of type I for SiC/AIN.
Growth and Physical Properties of rf-Magnetron Sputtered InN Semiconducting Films
Authors: Bryden W. A. , Morgan J. S. , Kistenmacher T. J. , Dayan D. , Fainchtein R. , Poehler T. O.
Published: March 2011

Indium nitride thin films have been deposited using reactive rf-magnetron sputtering and characterized by their electrical, structural and morphological properties. Films have been prepared on fused quartz and (0001) sapphire. Films deposited on sapphire at temperatures from 50–300°C are typified by a slowly increasing mobility and a transition from mixtures of epitaxial and textured grains to complete epitaxy. Comparisons of films deposited on quartz and sapphire (with two different surface preparations) indicates that electrical mobility is enhanced by the epitaxial nature of the material deposited on sapphire and that a higher quality surface finish results in superior films. Somewhat above 300°C the morphology of the epitaxial films changes from continuous to granular, with a concomitant loss in electrical connectivity. This manifests itself as a sharp rise in the resistivity of the film and hence a sharp decline in the mobility. The carrier concentration shows a general decline as the substrate temperature is increased, indicating that the mechanism of mobility degradation is probably not due to thermally induced nitrogen vacancy formation but more likely to unintentional oxygen doping. This is in accord with the surface oxidation observed in the films using Auger electron spectroscopy.
Substrate and Temperature Dependent Morphology of rf-Sputtered Indium Nitride Films
Authors: Kistenmacher T. J. , Dayan D. , Fainchtein R. , Bryden W. A. , Morgan J. S. , Poehler T. O.
Published: March 2011

The morphology of rf-sputtered films of the wide bandgap semiconductor InN on a variety of substrates over a range of temperatures have been studied by X-ray diffraction (XRD) and scanning tunneling microscopy (STM). For films deposited on fused quartz and the (111) face of silicon, there is a transition from an off-normal inclination to a fully textured (0001) film with increasing substrate temperature. In contrast, films deposited on the (0001) face of sapphire are textured or heteroepitaxial depending on the substrate temperature. For the heteroepitaxial domains, the rotation of the reciprocal lattice of InN by 30° to that of the sapphire substrate was established by X-ray precession photography. Finally, STM has proven to be a practicable method for non-destructively determining the substrate and temperature dependence of the grain size and surface roughness of these textured and heteroepitaxial films.
Electron Microscopy of InN Films
Authors: Morgan J. S. , Kistenmacher T. J. , Bryden W. A. , Poehler T. O.
Published: March 2011

This paper describes growth morphology and structure of rfmagnetron sputtered thin films of InN, studied by plan-view transmission electron microscopy (TEM) and by scanning electron microscopy (SEM). Films deposited on TEM grids, (0001) sapphire, (111) silicon and amorphous quartz were prepared for TEM by mechanical abrasion of the substrate followed by sputter etching. At low deposition temperatures (<400°C), films consisted of small, basal-oriented, columnar grains. Above 500°C, growth consisted of larger, faceted, basal-oriented, mesa-island grains. Observations of growth morphology and defect structure are correlated with structural, compositional and electrical properties.