bluuebunny/crossref_metadata_2025_split huggingface dataset:
Room Temperature Optical Studies of GaAs/AlGaAs Coupled Double Quantum Wells
Authors: Jagannath C. , Elman B. , Koteles Emil S. , Chen Y. J. , Brown S. , Armiento C. A. 
Published: March 2011

ABSTRACTRoom temperature photoreflectance (PR) spectroscopy has been utilized to study the effect of electric fields on the optical properties of GaAs/AlGaAs coupled double quantum wells (CDQWs). The behavior of optical transitions when subjected to electric fields ranging from 0 to 2×105V/cm, was found to be similar to that observed at low temperatures using photoluminescence excitation spectroscopy. Large shifts in the energies of spatially indirect transitions were observed when the CDQW was subjected to modest bias voltages.
Superlattice Optical Properties Measured by Variable Angle Spectroscopic Ellipsometry
Authors: Snyder P. G. , Merkel K. G. , De B. N. , Woollam J. A. , Langer D. W. , Stutz C. E. , Jones R. , Rai A. K. , Evans K. 
Published: March 2011

ABSTRACTVariable Angle of incidence Spectroscopic Ellipsometry (VASE) is a sensitive, nondestructive method of determining optical constants, layer thicknesses, alloy compositions and other parameters. We model the VASE data for a sample containing a 20 period Al0 5Ga0 5As-GaAs superlattice, to obtain the effective index of refraction (n) and e tinction coefficient (k) of the superlattice layer. The room temperature VASE spectra contain strong, sharp features at the e-hh(1), e-lh(1) and e-hh(2) excitonic tran-sition energies. In addition, VASE was used to characterize more compli-cated layered structures, which also contained superlattices.
Raman Scattering Characterization of GaAs-AlAs Superlattices Grown Along the [110] Direction
Authors: Kirillov D. , Pao Yi-Ching 
Published: March 2011

ABSTRACTRaman spectra of the GaAs-AlAs superlattice grown by molecular beam epi-taxy along the [110] direction were studied for the first time. The spectra were compared with spectra of the [100] superlattice and differences due to different crystallographic structure were analyzed. It was found that the energies of folded acoustical modes are higher in the [110] superlattice due to higher sound velocity in the [110] direction. Confined transverse optical phonons were a dominant feature of the spectrum of the [110] superlattice which allowed observation of the folding of transverse optical phonons. Stronger intensity of interface modes and lower intensity of folded acousti-cal modes in the [110] superlattice indicated that the quality of the layer interfaces was worse than in the [100] superlattice.
RHEED Intensity Oscillation Studies of the Kinetics of GaAs Deposition During Chemical Beam Epitaxy(CBE)
Authors: Robertson A. , Chiu T.H. , Tsang W.T. , Cunningham J.E. 
Published: March 2011

ABSTRACTRecently we have reported the measurement of RHEED intensity oscillations during Chemical Beam Epitaxy(CBE) of GaAs using triethylgallium(TEG) and As2 derived from an arsine cracker(Appl. Phys. Lett. 50(19), May 11,1987). The existence of RHEED intensity oscillations during CBE growth of GaAs indicates that over the range of conditions studied, growth proceeds via nucleation of islands which grow two-dimensionally as opposed to a vicinal step propagation mechanism. In the same study we observed a significant variation of the GaAs growth rate with substrate temperature at constant flux. In addition, the variation of growth rate with incident flux at constant temperature was found to be non-linear below approximately 500°C and linear above 500'C for incident fluxes yielding maximum growth rates between.2 and 1.8 monolayers/sec. Additional measurements of the dependence of the damping of RHEED intensity oscillations on V/11 ratio have indicated much less sensitivity of the growth front morphology to group V flux in CBE. This behavior is thought to reflect the role of highly mobile, partially saturated ethyl-gallium radicals in epitaxial growth by CBE. Measurements of As2 arrival rate limited intensity oscillations on gallium rich surfaces prepared by pyrolyzing TEG in the absence of As2 have shown that the pyrolysis of TEG is not self-limiting at 500°C and that excess gallium can be deposited on gallium rich surfaces. This paper also describes a simple model of the surface pyrolysis of TEG which is consistent with the above experimental observation.
Characterization and Physics of Threshold Voltage Dependence on Defect Related Properties of Channel-Buffer (Substrate) Interfaces in GaAs MESFET's Fabricated By Molecular Beam Epitaxy
Authors: Shenai K. 
Published: March 2011

ABSTRACTA fundamental understanding of the channel-buffer (substrate) interface is obtained from the experimental and theoretical investigation of long channel GaAs MESFET's fabricated by molecular beam epitaxy (MBE). The threshold voltage dependence on the semiconductor crystal lattice temperature indicates that the steady-state carrier trapping and accumulation of negative charge in donor-like states at the channel-buffer (substrate) interface play a detrimental role both in the linear and saturated regimes of device operation. The variations of the threshold voltage and gate capacitance with substrate bias are consistent with each other and suggest that significant reduction in the channel charge occurs with increased reverse bias on the substrate. The threshold voltage is found to decrease significantly as the sample temperature is increased both in the linear and saturated regimes of device operation.
Characterization of Mn-Doped in 1−x GaxAsyP1−y Grown By Lpee
Authors: Iyer Shanthi N. , Abul-Fadl Ali , Collis Ward J. , Khorrami Mohammad N. 
Published: March 2011

ABSTRACTMn-doped In1−x GaxAsyP1−y epilayers lattice matched to InP substrate have been grown by the liquid phase electroepitaxial (LPEE) technique. The variation of growth velocity of the epilayers with current density and the doping characteristics of Mn in the epilayer has been studied. The temperature dependence of the hole concentration and the mobility has been analysed to determine the donor and acceptor densities, thermal activation energy of the level associated with Mn and the dominant scattering mechanisms that limit the hole mobility. The photoluminescence spectra of the doped epilayers are examined at 10K as a function of the excitation level.
The Role of Covalent and Metallic Radii in Covalent Metallic Superlattices and Two-Dimensional Isoelectronic Alloys
Authors: Tsu Raphael 
Published: March 2011

ABSTRACTCovalent metallic superlattices and isoelectronic alloys consist of ordered layers of, for example, Si/AlP, Ge/GaAs, and Si/Sb,etc. Depending on design, wide range of electrical properties can result. The covalent, metallic and ionic radii play a crucial role in the stoichiometry of epitaxial systems.
A Tem Study of Rhodium on Gaas; Reactions and Morphology
Authors: Packer Stacy L , Gronsky Ronald 
Published: March 2011

ABSTRACTReaction between Rhodium films and n-type GaAs in the temperature range of 300° to 700°C has been examined using the TEM to look at the interface and phases present. The reaction between Rh and GaAs produces a layered structure of Rh/RhGa/RhAs2/GaAs based on RBS and TEM. Above 300°C, the RhGa phase has an orientation relationship of [011]RhGa // [100]GaAs. In cross-section, an interpenetrated layered structure was observed with equiaxed RhGa above columnar grains of RhAs2. Rhodium is the moving species as suggested by voids at the Rh/reacted layer interface. The interface between the reacted layer and GaAs was smooth at 450° and 20 minutes of annealing but showed 10 nm periodic penetrations when annealed at 400° for 90 minutes. Interface roughness may influence the low barrier height reported for the Rh Schottky diode annealed at 400°.
Characterization of Si MBE Layers Doped in Situ by As Ion Beams
Authors: Swanson Max L. , Parikh N.R. , Jackman T.E. , Houghton D.C. , Denhoff M.W. 
Published: March 2011

ABSTRACTTo achieve high concentrations and electrical activation of As in Si without subsequent annealing, 500-3000 eV As + ions were implanted during MBE growth of Si at 450-840°C. The epitaxial layers were characterized by Rutherford backscattering/channeling, transmission electron microscopy, secondary ion mald spectroscopy, and electrical measurements. Samples containing 1.2×1020 As cm-3 grown at 700°C showed little damage, high As substitutionality and high electrical activation. However, similarly doped layers grown at 460°C showed lower As activation and varying amounts of structural damage. In one case, a band of damage near the Si substrate was observed which persisted even after rapid thermal annealing at 1120°C (10 s); the damage was characterized by a dechanneling step, non-substitutional As atoms and dislocation loops. A sample grown at 460°C with a high implantation energy (3 keV) was highly defected.
Epitaxial Films of Germanium by MOCVD
Authors: Khan Altaf H. , Santiago Jorge J. 
Published: March 2011

ABSTRACTA simple and easily expandable atmospheric pressure MOCVD (metal organic chemical vapor deposition) reactor for the growth of germanium films is proposed and implemented. It employs a resistively heated horizontal quartz reaction chamber. The organometallic compound tetramethylgermanium (TMGe) is used as the germanium source, and hydrogen as the carrier gas. Using this reactor, epitaxial films of germanium on <111> germanium substrates were grown at 550-650°C. The growth rate was found to increase with temperature. The single crystallinity of these films was evaluated by x-ray rocking curves, and the interface strain between the film and substrate was found to be less than 1%. These Ge/Ge samples have the same morphology as the bare substrate and their sheet resistance is 30% higher than the bare substrate value.
Nickel Silicide Structures on Single-Crystal Silicon Membranes
Authors: Hren P. , Fernandez A. , Silcox J. 
Published: March 2011

ABSTRACTNickel structures have been deposited on large (300 μm diameter), thin (1400 to 3000Å) single crystal (111) silicon membranes. On annealing, the nickel-silicon reaction generates strain which can be partially accommodated through buckling of the membrane, a mode of strain relief not available on bulk wafers. Examples of such buckling are presented in this paper. Features of the silicide structures observed include thin epitaxial Ni2 Si that grows on clean surfaces during deposition, vertical and lateral growth of NiSi2 into the membrane from nickel dots, and the absence of interfacial dislocations between NiSi2 and silicon, probably due to the stress relief.
Electron Beam Source Molecular Beam Epitaxy of AlxGa1−Xas Graded Band Gap Device Structures
Authors: Malik R. J. , Levi A. F. J. , Levine B. F. , Miller R. C. , Lang D. V. , Hopkins L. C. , Ryan R. W. 
Published: March 2011

ABSTRACTA new method has been developed for the growth of graded band-gap AlxGal-xAs alloys by molecular beam epitaxy which is based upon electron beam evaporation of the Group III elements. The metal evaporation rates are measured real-time and feedback controlled using beam flux sensors. The system is computer controlled which allows precise programming of the Ga and Al evaporation rates. The large dynamic response of the metal sources enables for the first time the synthesis of variable band-gap AlxGal-.xAs with arbitrary composition profiles. This new technique has been demonstrated in the growth of unipolar hot electron transistors, graded base bipolar transistors, and Mshaped barrier superlattices.
OMVPE Growth of GalnAs/InP Quantum Well Structures
Authors: Stringfellow G. B. 
Published: March 2011

ABSTRACTInP/GalnAs/InP quantum well structures have been grown using atmospheric pressure organometallic vapor phase epitaxy (AP-OMVPE). The optimum conditions for growth of extremely abrupt interfaces were studied. The optimum orientation was exactly (100). The growth had to be interrupted for 40 seconds at the first interface and 2 minutes at the 2nd interface to obtain the most abrupt interfaces. The narrowest photoluminescence half widths were obtained at the lowest values (31) of V/III ratio in the input vapor phase. These growth conditions allow the growth of wells as thin as <10Å with photoluminescence (PL) spectra consisting of doublets or triplets. The extremely narrow peaks correspond to regions of the quantum well differing in thickness by a single monolayer. The energy separations of the neighboring peaks are found to increase with decreasing well width until, at a thickness of approximately 12 Å, the separation begins to decrease rapidly with decreasing well width. The exciton binding energies in the quantum wells have also been measured using thermally modulated PL. The binding energy is found to increase with decreasing well width until a maximum value of approximately 17 meV is measured for a nominal well width of approximately 13 Å. For thinner wells the exciton binding energy is found to decrease with decreasing well width.
Dislocation Detection by MeV Ion Channelling
Authors: Wielunski Leszek S. 
Published: March 2011

ABSTRACTMeV H+ and He+ ion channelling has been used to characterise the post annealing, residual ion implantation damage in silicon. The observed energy dependence of direct scattering peaks agrees with theoretical predictions for direct scattering on dislocations. Similar peaks are observed in the channelling spectrum from the hetero-epitaxial structure In0.3Ga0.7 As on GaAs and are also interpreted as direct scattering on interfacial dislocations. The sensitivity for dislocation detection by this technique is about 1×105 cm−1 therefore, when high dislocation densities are expected, it is suggested that direct scattering on dislocations should be included in the analysis of channelling data.
Energy Loss Rates for Light Holes in Ingaas/GaAs Strained-Layer Single Quantum Wells
Authors: Smith M. C. , Jones E. D. , Fritz I. J. , Drummond T. J. , Zipperian T. E. , Schirber J. E. 
Published: March 2011

ABSTRACTEnergy relaxation rates for light holes in InGaAs/GaAs strained layer quantum wells are measured. Two techniques were used to measure light hole temperatures as a function of power dissipated in the hole gas. For Th < 20K, Shubnikov-de Haas oscillations were used and for Th> 20K, a photoluminescence technique was employed.
Photoluminescence Characterization of Heteroepitaxial ZnSe/GaAs and ZnSe/AlAs Grown By MBE
Authors: Skromme B. J. , Tamargo M. C. , De Miguel J. L. , Nahory R. E. 
Published: March 2011

ABSTRACTHeteroepitaxial ZnSe grown by molecular beam epitaxy (MBE) has been characterized using low temperature photoluminescence (PL) and reflectance. Excitonic PL linewidths of thick (relaxed) ZnSe layers are>1.4 meV, and depend little on the type of substrate or buffer layer used (e.g. GaAs or AlAs). In contrast, thin (pseudomorphic) ZnSe layers on AlAs buffer layers of moderate thickness are found to exhibit by far the sharpest (FWHM=0.22-0.37 meV) excitonic features ever observed for heteroepitaxial ZnSe grown by any technique. A tentative explanation for this result is that step-grading the lattice constant (by the AlAs buffer layer) has eliminated the crystal defects which produce localized strain fields that inhomogeneously broaden the peaks in ZnSe/GaAs. Acceptor-related PL peaks are discussed, and the first discrete donor-acceptor pair line spectrum in heteroepitaxial ZnSe is reported.
Study of Diffusion Length and Alloy Segregation in MOCVD AlGaAs
Authors: Bradshaw J. L. , Choyke W. J. , Feng Z. C. , Meier D. L. , Messham R. L. 
Published: March 2011

ABSTRACTVarious thicknesses of AlGaAs are grown on GaAs substrates by MOCVD. Low temperature photoluminescence of the substrate is observed even for layers of AlGaAs 24μm thick. Direct excitation by the 488.0 nm pumping radiation and excitation by reradiation from the AlGaAs are eliminated as causes. From photoluminescence and EBIC studies, evidence is given to show that the substrate luminescence is caused by a much larger than expected electron diffusion length. A small trace of GaAs luminescence may be due to alloy segregation in the AlGaAs films themselves.
High Quality n-Cd0.2 Hg0.8 Te Grown by Liquid Phase Epitaxy
Authors: Yasumura K. , Kimura H. , Komine Y. , Sato K. 
Published: March 2011

ABSTRACTInfluential factors to the detectivity of n-CMT grown by liquid phase epitaxy on CdTe(111)B substrate are investigated. The factors are such as qualities of the substratesdopants and electrical parameters by which photoconductivity in CMT is governed.We show that the doping with small amounts of In is an appropriate mean not only to raise the mobility but also to make reproductivity better. The In- doped epitagia�r after annealed has the highest mobility among tested in 3×10 cm5 /Vsec, and the photoconductive lifetime in 0.54 μsec at 77K.The resultant detectivity of an infrared device is 3×1010 cmHz1/2 w−1.
The Mechanisms of Relaxation in Strained Layer GeSi/Si Superlattices: Diffusion Vs. Dislocation Formation
Authors: LeGoues F. K. , Iyer S. S. , Tu K. N. , Delage S. L. 
Published: March 2011

ABSTRACTSixGe1−x strained layer superlattices are known to be metastable in that they can be grown fully commensurate with layer thickness higher than the equilibrium, calculated Tc at which dislocation formation becomes energetically favorable. In this paper, we describe the mechanism of relaxation in such multilayers. Both plane-view and cross-sectional transmission electron microscopy (TEM) were used to examine the formation of dislocation at the different interfaces. RBS was used to follow interdiffusion. We found two competing mechanisms for relaxation: The preferred mode for relaxation is the creation of dislocation networks at each of the interfaces. This process can be stopped or considerably inhibited by the difficulty of forming new dislocations in samples which are perfectly commensurate after growth; Some dislocations appear necessary in order to generate more dislocations during annealing. When this is not the case, the only possible way to attain relaxation is through diffusion. In such a case, stress-enhanced diffusion is observed, with a diffusion coefficient 200 times higher than expected.
Relaxation of Metastable Semiconductor Strained-Layer Structures by Plastic Flow
Authors: Dodson Brian W. , Tsao Jeffrey Y. 
Published: March 2011

ABSTRACTThe relaxation of misfit strain in metastable structures by plastic flow is described using a continuum model based on Haasen's picture of plastic flow in bulk diamond-phase semiconductors and the concept of excess stress. This model provides a unified explanation of the equilibrium critical thickness, the relaxation behavior of metastable strained-layer structures, and the “metastable” critical thicknesses reported in many semiconductor strained-layer geometries.
Crystallization and Melting in Multilayered Structures
Authors: Sevenhans W. , Vanderstraeten H. , Locquet J. P. , Bruynseraede Y. , Homma H. , Scihuller Ivan K. 
Published: March 2011

ABSTRACTThe stability of Pb/Ge and Pb/C multilayers has been studied over a broad temperature range by x-ray diffraction experiments. In the Pb/Ge system an amorphous to microcrystalline phase transformation of the Ge-layers was already observed at ≃ 100 °C. This transition destroys the modulation structure and improves the Pb(111) texture. In the Pb/C multilayers, the layered structure was still present at temperatures higher than the melting temperature of Pb. Contrary to recent publications, no depression of the melting temperature of the two-dimensional Pb layers could be observed.
Superconducting Superlattice Structures
Authors: Makous John L. , Leavitt John A. , Mcintyre Laurence C. , Maritato Luigi , Vaglio Ruggero , Cucolo Annamaria , Falco Charles M. 
Published: March 2011

ABSTRACTSuperlattice superconductors exhibit behavior different from other “homogeneous” superconductors because of their layered structures. Sputtering has proved to be an excellent technique for producing such multilayered systems. Also, systems naturally having layered structures, such as the new high-Tc materials, can be fabricated by sputtering. Here we describe the preparation of superconducting superlattices by dc triode sputtering and techniques useful for characterizing them. In particular, we discuss Mo/Ta superconducting superlattices and high Tc thin films of YBa2Cu3O7-x.
The Sputter Deposition of Metal Multilayers
Authors: Somekh R. E. , Highmore R. J. , Page K. , Home R. J. , Barber Z. H. 
Published: March 2011

ABSTRACTWe describe the strategy that we are using to make precision metal multilayers. Differential scanning calorimetry has been used with the Ni/Zr system to study the abruptness of the interface as a function of the sputtering pressure. For 10nm period multilayers there is a monotonic increase in the width of the interface with increasing sputtering pressure. W/Si multilayers have been studied as a function of both the sputtering pressure and the relative thicknesses of tungsten and silicon. At reasonably low sputtering pressures a well textured (110) tungsten X-ray peak is seen which is compatible with the expected thickness of the tungsten layers.Finally, we report some preliminary work on sputtering from tungsten and silicon targets which are at different distances from the substrate so that the degrees of bombardment on the growing layers of the film can be independently varied.
Critical Field Measurements on Superconducting Graphite-KHG Multilayers
Authors: Chaiken A. , Tedrow P. M. , Dresselhaus G. 
Published: March 2011

ABSTRACTUpper critical fields of graphite-KHg multilayers with 10Å periodicity were measured as a function of angle and temperature. The Hc2 (θ, T) data were compared to the anisotropic Ginzburg-Landau model and were found to be in qualitative agreement, except at the lowest reduced temperatures, where significant deviations are found. The primary deviations from the anisotropic GL model are first, that the values of the critical field at the lowest temperatures are found to be higher than that predicted by the model, and secondly, the critical field anistropy ratio is found to be temperaturedependent. These deviations are discussed in light of more detailed models of anisotropic superconductivity.
Thin Film Growth
Authors: Vook R. W. 
Published: March 2011

ABSTRACTA review of the experimental and theoretical results describing thin film growth modes is presented. Thermodynamic criteria for determining which growth mode might be expected to occur in a particular case along with some kinetic considerations are given. The characteristics of each of the three principal growth modes, namely Frank and van der Merwe (layer), Stranski-Krastanov (layer plus island), and Volmer-Weber (island), are discussed. Lastly, the requirements favoring the growth of epitaxial multilayers are briefly considered.
Elastic Properties of Artificially Layered Thin Films
Authors: Cammarata Robert C. 
Published: March 2011

ABSTRACTEnhancements in the elastic moduli by factors of two or more in compositionally modulated metallic thin films have been observed for a certain range of composition modulation wavelengths. The experimental and theoretical understanding of this phenomenon, known as the supermodulus effect, is reviewed. Also, the mechanical properties of other artificially layered and composite materials are discussed and compared with the behavior of metallic superlattice thin films.
Growth and Structure of Tungsten Carbide-Transition Metal Superlattices
Authors: Moustakas T. D. , Koo J. Y. , Ozekcin A. 
Published: March 2011

ABSTRACTSuperlattices between ceramic materials, such as tungsten carbide, and transition metals have been synthesized for the first time. The growth and structure of these superlattices were investigated by low angle X-ray diffraction and TEM lattice imaging and microdiffraction. The data show that the low temperature process of forming these two dimensional composites leads to unique crystal structures and morphology in the nanoscale range.