bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural and magnetic properties of Tm2−xDyxFe14B and Tm2Fe14−xCoxB alloys systems
Authors: Pourarian F. , Jiang S. Y. , Zhang L. Y. , Boltich E. B. , Sankar S. G. , Wallace W. E.
Published: July 2002

Structural and intrinsic magnetic characteristics of Tm2−x Dyx Fe14 B (for the entire range of composition) and Tm2 Fe14−x Cox B (for x up to 4) were investigated in detail between 4.2 K and their Curie temperatures. Progressive replacement of Tm by Dy enhances the anisotropy field HA markedly. This was evidenced from the expansion of the uniaxial anisotropy temperature range determined by constructing the magnetic-phase diagram. These results are found to be in very good agreement with the crystal field theory, employing the second-order terms. Addition of Co in the lattice improves the magnetic ordering temperature, but reduces the saturation magnetization.
Resistivity and Hall effect in sputtered NiZr metallic glasses
Authors: Morel R. , Huai Yiming , Cochrane R. W.
Published: July 2002

Films of Ni1−xZrx metallic glasses have been prepared by sputter deposition over the composition range 0.1<x<0.86. In this paper we present data on the composition and temperature dependencies of the resistivity and the Hall coefficient from 77 to 300 K. Where applicable, both the resistivity and the Hall coefficient closely follow the values reported for melt-spun glasses of the same composition. The Hall coefficient changes sign from positive to negative with decreasing x; for x<0.4 it also becomes increasingly temperature dependent (dRH/dT>0). Both the change in sign and the temperature dependence can be understood within the framework of an important extraordinary contribution to the Hall coefficient for these paramagnetic alloys.
Domain mode ferromagnetic resonance studies in bismuth-substituted magnetic garnet films
Authors: Ramesh M. , Ren E. W. , Artman J. O. , Kryder M. H.
Published: July 2002

Bismuth-substituted magnetic garnet films, formulated so as to have a low magnetic quality factor Q, were grown from a bismuth-based melt using liquid-phase epitaxy. The lowest Q achieved was about 0.2. Such samples were observed to support parallel stripe domain structure and were theoretically predicted to have an ‘‘in-phase’’ domain mode ferromagnetic resonance response at frequencies as low as 250 MHz. Such ‘‘in-phase’’ resonances, along with the higher-frequency ‘‘out-of-phase’’ mode, were observed experimentally with a variable radio frequency/fixed dc field ferromagnetic resonance spectrometer. The data, which were taken as a function of dc in-plane field, were found to be in good agreement with the theory.
A critical discussion of emission mechanisms and reaction rates for the ion-assisted etching of GaAs(100)
Authors: O’Brien W. L. , Paulsen-Boaz C. M. , Rhodin T. N. , Rathbun L. C.
Published: July 2002

Emission mechanisms and reaction rates for the ion-assisted etching of GaAs(100) have been studied in detail using energetic argon ions and chlorine gas. Ion energies of 500 and 1000 eV were used with chlorine/argon ion surface-flux ratios of 1–120. The major molecular etchant products were found to be GaCl2 and AsCl3. Gas phase products were detected at different flight distances to investigate the nature of surface residence times. It is concluded, based on these measurements, that GaCl2 emission is best interpreted in terms of the collisional-cascade sputtering model for the specific range of ion energies and surface-flux ratios studied. Using a similar analysis, it is concluded that AsCl3 may be emitted by either the thermal desorption or the collisional-cascade mechanisms, with the former favored in the range of higher surface-flux ratios and lower ion energies. Furthermore, the thermal desorption of AsCl3 appears to follow a first-order surface process. Comparison of our data with those of others indicates general agreement. However, more extended analysis based on a broader and more intensive data base leads to some important distinctions among the final conclusions regarding the emission mechanisms.
Terracing in strained-layer superlattices
Authors: Neumann D. A. , Zabel H. , Morkoç H.
Published: July 2002

We report on an x-ray diffraction study of GaAs/GaAs1−xSbx superlattices grown by molecular-beam epitaxy on miscut GaAs (100) substrates. The fundamental reflections of the superlattice lie on a reciprocal lattice rod which is tilted with respect to the reciprocal lattice rod of the substrate. The satellite reflection, in turn, lies on lines making a constant angle with the reciprocal lattice rod containing the fundamental reflections. This result is attributed to a terraced superlattice which, in addition, is tilted with respect to the substrate. We describe a model which approximates the misfit strain imposed on the superlattice at the interfacial step, and which is capable of relating the average tilt angle to the misfit strain. The same model can also explain the transverse broadenings observed for the superlattice peaks.
Effect of surface electric field on the gate capacitance of metal-oxide-semiconductor structures of ternary semiconductors
Authors: Ghatak K. P. , Mondal M.
Published: July 2002

An attempt is made to derive a generalized expression for the gate capacitance of metal-oxide-semiconductor structures of ternary semiconductors without any approximations of weak or strong electric field limits. It is found, taking n-channel layers on p-type Hg1−xCdxTe as an example, that the same capacitance increases with increasing surface field and the approximated results overestimate the numerical values for both limits. The theoretical formulation is in good agreement with the experimental observation as reported elsewhere, and the corresponding well-known results for n-channel inversion layers on parabolic semiconductors are also obtained from the expressions derived.
Spin reorientation in melt-spun neodymium-iron-boron ribbons
Authors: Pinkerton F. E.
Published: July 2002

Effects of the spin reorientation in Nd2Fe14B below Ts =135 K on the hard magnetic properties of melt-spun Nd-Fe-B ribbons are reported. As the ribbons are cooled from room temperature, the shape of the second quadrant demagnetization curve is maintained down to 150 K, with an intrinsic coercivity Hci which increases steadily from 14 to 24 kOe. As the magnetic structure of Nd2 Fe14 B changes from easy axis to easy cone below 135 K, however, demagnetization occurs in two steps, with a large decrease in magnetization at low reverse field followed by a second sharp drop at higher field. The size of the initial drop correlates well with the canting angle of the cone and is consistent with having little or no resistance to rotation of the magnetization along the cone. This effect artificially suppresses Hci , which decreases to 23 kOe at 5 K. Magnetization reversal from one easy cone to the opposite cone remains a hard process, and its effective coercivity is estimated to be 42 kOe at 5 K. The first quadrant magnetization is much closer to full saturation at low fields due to the improved net alignment of the moments. In thermomagnetic scans this appears as a large increase in magnetization as the sample cools through Ts at constant field. The observed behavior agrees with that predicted by the known easy cone structure of Nd2 Fe14 B below Ts .
High-power, diffraction-limited-beam operation from interferometric, phase-locked arrays of AlGaAs/GaAs diode lasers
Authors: Botez D. , Mawst L. J. , Hayashida P. , Roth T. J.
Published: July 2002

10/11-element interferometric phase-locked arrays with optimized facet coatings operate in array mode L=8, diffraction limited to 200 mW at 2.7 times threshold, and in beam patterns 1.4 times the diffraction limit to 290 mW at 4.3 times threshold. Unlike Y-junction-coupled arrays, the beam pattern quality is not sensitive to the facet(s) reflectivity value(s). Transformation to a single-lobe pattern requires a simple phase-corrector coating or plate. The device beam pattern as a function of the array geometry is discussed.
Surface photovoltage spectroscopy in hydrogenated amorphous silicon
Authors: Ukah C. I. , Perz J. M. , Zukotynski S.
Published: July 2002

Properties of the amorphous silicon Schottky barrier are investigated by surface photovoltage spectroscopy. A model of the recombination of carriers at the rectifying metal/amorphous silicon interface is presented, and tested by using it to calculate the surface photovoltage induced on a Schottky barrier by modulated light. A method is developed for the determination of the surface recombination velocity, surface recombination rate, built-in voltage of the barrier, and the junction ideality factor, using low frequencies of modulated light. Analysis of the data at intermediate frequencies yields the minority-carrier diffusion length. The junction capacitance and density of states near the Fermi level are deduced from high-frequency measurements.
On the thermoelectric power of the electrons in degenerate n-AII3BV2 compounds in the presence of a classically large magnetic field
Authors: Ghatak K. P. , Mondal M.
Published: July 2002

An expression is derived for the thermoelectric power of the electrons in degenerate n-AII3BV2 semiconductors in the presence of a classically large magnetic field by considering the anisotropies in the band parameters within the framework of k⋅p formalism. It is found, taking n-Cd3As2 as an example, that the thermoelectric power decreases with increasing electron concentration and the theoretical formulation is in agreement with the experimental observation as reported elsewhere. In addition, the well-known results for parabolic semiconductors are also obtained from the generalized expressions as special cases.
Optical modulation of light transmission in GaAs doping superlattices
Authors: Ruden P. P. , Lehman J. A. , Khan N. , Hibbs-Brenner M. K. , Kalweit E.
Published: July 2002

We report results of measurements of optically modulated optical transmittance of GaAs doping superlattices. The data extend over a spectral region of 1.39–1.58 eV. We find that the peak transmission modulation reaches 21% for a 2.6-μm-thick sample and an optical pump power density of <10 W/cm2 at room temperature. We interpret our data in the framework of a simple semiclassical model that includes the Franz–Keldysh effect both below and above the bulk GaAs band gap, as well as band filling and band shrinkage effects.
rf-sputtered tungsten-amorphous silicon Schottky barrier diodes
Authors: Khaidar M. , Essafti A. , Bennouna A. , Ameziane E. L. , Brunel M.
Published: July 2002

In this paper, we report on the results of a detailed study of the properties of a Mo/a-Si/a-Si:H/W Schottky barrier produced by rf diode reactive sputtering. This paper is divided into two sections. In the first part, the Mo/a-Si and W/a-Si:H interfaces are investigated using a grazing incidence x-ray diffraction method. The W/a-Si:H interface seems to be inert, while the Mo/a-Si one is highly reactive: the Mo3Si compound is identified without ambiguity. The second part deals with the electrical properties of a Mo/a-Si/a-Si:H/W Schottky barrier. The experimental I-V characteristics were analyzed using a numerical method. The most important diode parameters were deduced: the barrier height value was 0.69 eV, the density of states near the Fermi level was 1.2×1017 cm−3 eV−1, and the depletion region thickness was 0.2 μm.
An annealing study of relaxation and interface quality in Si-Si1−xGex strained-layer superlattices
Authors: Lockwood D. J. , Baribeau J.-M. , Timbrell P. Y.
Published: July 2002

The relaxation and interface quality of two representative molecular-beam-epitaxy-grown Si-Si1−xGex strained-layer superlattices have been investigated by Raman scattering spectroscopy, double-crystal x-ray diffraction, transmission electron microscopy, and charge collection microscopy in a scanning electron microscope. One of the superlattices appeared stable, and the other metastable, under thermal annealing at temperatures between 600 and 900 °C. The strain values perpendicular to the growth direction as a function of annealing temperature are obtained from a kinematical simulation of x-ray rocking curves. These results are compared with the frequency shifts of the longitudinal optical phonons in the Raman spectra. Deterioration of the crystal quality and progressive relaxation was observed in the metastable superlattice. The thermally induced relaxation occurred through formation of misfit dislocations at the first Si-Si1−xGex interface and these caused threading dislocations to form within the epilayer. The degradation of the interfaces for both superlattices on annealing is correlated with a sharp decrease in the acoustic mode Raman intensities.
Investigation of high-quality GaAs:In layers grown by molecular-beam epitaxy
Authors: Uddin A. , Andersson T. G.
Published: July 2002

Indium-doped GaAs layers are investigated by low-field Hall-effect, photoluminescence, deep-level transient spectroscopy, current-voltage, and capacitance-voltage measurements for the In value providing the best layer quality. The In doping concentrations were 20 ppm to 25%. The growth was made in the temperature range 530–575 °C. Layers grown at higher temperatures show increased carrier mobility, sharper photoluminescence peaks, as well as a lower concentration of deep levels. The investigation suggests that the In concentration should be between 100 and 5000 ppm and the growth temperature above 550 °C to provide the best quality of the layer.
Single-crystal YBa2Cu3O7−x and Bi2Ca1+xSr2−xCu2O8+y surfaces and Ag adatom-induced modification
Authors: Meyer III H. M. , Hill D. M. , Wagener T. J. , Weaver J. H. , Gallo C. F. , Goretta K. C.
Published: July 2002

Comparison of x-ray photoemission results for single crystal and polycrystalline YBa2Cu3O7−x allows us to identify oxygen vacancies in the Cu-O chains and determine their effects on the Cu, Ba, and Y core level line shapes. The deposition of adatoms of Ag onto single crystals of YBa2Cu3O7−x and Bi2Ca1+xSr2−xCu2O8+y leads to changes in the Cu 2p3/2 emission indicative of slight Cu2+ to Cu1+ surface reduction, with greater modification for the 1-2-3’s than the 2-1-2-2’s. O 1s core level results show Ag-induced broadening because of these surface effects. The Ba 3d and Y 3d structures showed minimal changes for the 1-2-3 surface. Ag deposition onto the 2-1-2-2 samples also leads to Bi dissociation and subsequent surface segregation.
Modeling of time-dependent laser-induced plasma spectra formed on a carbon surface
Authors: Shah P. , Armstrong R. L. , Radziemski L. J.
Published: July 2002

The blast wave theory coupled with ionization described by the Saha equations and the charge conservation equation, are used to calculate the time-dependent, spatial distribution of the number densities of the different species of a plasma formed on a carbon surface. The temporal behavior of the normalized intensity profiles of the C i (247.8 nm) and C ii (251.1 nm) lines and the Stark shifts of the C i (247.8 nm) line from 0.1 to 0.4 μs are obtained. Good agreement is found between theoretical and experimental time-dependent, normalized, line intensity profiles and Stark shift profiles.
On residual carbon acceptors in molecular-beam epitaxial GaAs
Authors: Kerr T. M. , Wood C. E. C. , Newstead S. M. , Wilcox J. D.
Published: July 2002

The unintentional background concentration in molecular-beam epitaxially grown GaAs has been found to vary between 1×1014 cm−3 n type and 2×1016 cm−3 p type when grown with solid arsenic from several different suppliers. This variation is largely due to carbon incorporation which in turn is directly traceable to the arsenic charge. Increases in arsenic flux and substrate temperature both give rise to increased carbon acceptor concentrations. We propose that this carbon arises form heavy organic molecules such as rotary pump oil incorporated during the vacuum sublimation process used by some commercial suppliers.
Temperature variation of energy gaps and deformation potentials in CuGa(SzSe1−z)2 semiconductor alloys
Authors: Quintero Miguel , Rincón Carlos , Grima Pedro
Published: July 2002

Measurements of wavelength modulated reflectance in the temperature range 10–300 K have been made on single crystals of the system CuGa(SzSe1−z)2. For each sample, values of EA,EB, and EC corresponding to the three valence to conduction bands transitions have been determined. These results are analyzed using an equation proposed by Manoogian and Woolley [Can. J. Phys. 62, 285 (1984)]. From the analysis of the variation of the EA energy gap, with temperature and pressure the valence and conduction band, deformation potentials have been estimated for the present compounds and alloys.
The macromolecular character of amber
Authors: Wert Charles A. , Weller Manfred , Schlee Dieter , Ledbetter Hassel
Published: July 2002

Measurements are reported of anelastic and dielectric loss of various ambers and copals. They show spectra typical of synthetic polymers. This similarity permits description of the macromolecular character of amber which was not possible from previous studies of chemical composition. Measurements on amber of several origins and geological ages show generally similar character, but also differences in detail. These may be caused by differences in chemistry of the original resin and the geological age and history of the amber, reflecting differences in degree of polymerization. Also reported are elastic constants measured at high frequency.
Selective silicon epitaxial growth at 800 °C by ultralow-pressure chemical vapor deposition using SiH4 and SiH4/H2
Authors: Yew Tri-Rung , Reif Rafael
Published: July 2002

This paper presents results of selective Si epitaxial growth at 800 °C on (100) silicon wafers with oxide patterns by ultralow-pressure chemical vapor deposition using pure SiH4 and SiH4/H2. Prior to deposition, the patterned wafers were in situ argon plasma sputtered at −100 V dc bias to remove native oxide. About 800 Å of Si epitaxial layer can be grown selectively on the exposed silicon windows using 3.5 mTorr of SiH4. By flowing H2 with SiH4 during deposition, selective epitaxial layers can be grown to a thickness of 1300 Å before polycrystalline silicon begins to nucleate on the SiO2 surfaces. The epitaxial films were examined by scanning electron microscopy and cross-sectional transmission electron microscopy and found to be of high structural quality. H2 was found to significantly improve the epi/substrate interface and the surface morphology of the epitaxial layers.
Study of the low-pressure chemical-vapor-deposited tungsten-silicon interface: Interfacial fluorine
Authors: Carlisle J. A. , Chopra D. R. , Dillingham T. R. , Gnade B. , Smith G.
Published: July 2002

Single-crystal silicon 〈100〉 substrates uniformly doped at ≳12 Ω cm with boron were deposited with ∼800 Å of low-pressure chemically vapor deposited W in a hot-quartz-walled (Anicon) system at a deposition temperature of 300 °C. The samples studied include an as-deposited sample and two others which were post-deposition annealed at 600 °C in Ar for 15 min each. X-ray photoelectron spectroscopy (XPS) coupled with an Ar+ ion sputter profiling technique was employed to investigate these structures as a function of depth. Particular emphasis was placed on the depth distribution, content, and chemical state of the fluorine present. Rutherford backscattering spectrometry and x-ray diffraction were used to corroborate the XPS data. Results show that, for the as-deposited and 600 °C annealed sample, the maximum concentration of fluorine (0.6–0.8 at. %) is observed, not at the W/Si interface, but rather at the W (H2 reduction)/W (Si displacement) interface. For the sample annealed at 850 °C, WSi2 is formed in the overlayer, and the peak in the F profile corresponds to the position of the WSi2/Si interface. The maximum concentration of fluorine is reduced by approximately 75% to 0.23 at. % in this sample. From the XPS spectra of the F 1s region, the chemical species of fluorine present in these samples have been identified as WF6, WF5, and WF4.
Simulations of short-channel and overlap effects in amorphous silicon thin-film transistors
Authors: Shaw John G. , Hack Mike
Published: July 2002

Through the use of two-dimensional computer simulations, we study short-channel and overlap effects in amorphous silicon thin-film transistors. As large-area fabrication techniques can lead to conductive source-drain overlaps being deposited on a portion of the upper passivation layer of inverted-gate thin-film transistors, it is important to understand how these overlaps affect performance. In saturation, charge accumulates under the drain overlap shortening the effective channel length. We contrast the performance of thin-film transistors with and without overlaps as a function of gate length.
Raman scattering study of the high-pressure oxidation of InP
Authors: Schwartz G. P. , Chakrabarti U. K. , Laudise R. A. , Caporaso A. J.
Published: July 2002

Air-grown oxide films formed on InP at temperatures below 500 °C are known to contain elemental phosphorus. Recent literature reports indicated that oxidation under high-pressure conditions converted the elemental phosphorus into P2O5. We have reexamined this finding for oxygen pressures up to 300 atm using Raman scattering. Red phosphorus is detected in both low- (1 atm)and high- (300 atm) pressure oxidized films independent of the substrate doping type.
Simultaneous measurement of in-material longitudinal and transverse particle velocity histories in a compression-shear experiment
Authors: Aidun John B. , Gupta Y. M.
Published: July 2002

An experimental procedure is described for making independent, in-material measurements of longitudinal and transverse particle velocity histories simultaneously in a combined compression-shear loading, plate-impact experiment. The experimental method is based on the suggestion of J. W. Swegle [J. Appl. Phys. 49, 4280 (1978)]. Representative data are shown from measurements in Carrara marble (polycrystalline calcium carbonate). The potential advantages of using this method for measuring complex material response are discussed.
A combined single-phonon Raman and photoluminescence study of direct and indirect band-gap AlxGa1−xAs alloys grown by molecular-beam epitaxy
Authors: Lao Pudong , Tang Wade C. , Madhukar A. , Chen P.
Published: July 2002

A combined Raman and photoluminescence study of one-phonon processes in direct and indirect band-gap AlxGa1−xAs alloys grown by molecular-beam epitaxy is presented. The appearance of the ‘‘forbidden’’ TO mode is attributed to twinning effects related to growth rather than the possible experimental deviation from the strict backscattering geometry or the presence of alloy disorder. LO phonons around X as well as Γ and L points are found to contribute to the phonon-assisted exciton recombination process though the dominant contribution is from phonons around the X point. A discrepancy between the results of existing methods of determining alloy concentration from Raman and photoluminescence data is found, indicating the need for reevaluation and further refinement of such methods.
Planar channeling in GaAs/InxGa1−xAs/GaAs strained-layer structures
Authors: Stevens J. L. E. , Robinson B. J. , Davies J. A. , Thompson D. A. , Jackman T. E.
Published: July 2002

Planar {110} channeling measurements with 1–2-MeV He+ ions have been used to investigate strained-layer structures of (100) GaAs/InxGa1−xAs/GaAs with x=0.07–0.17. Beam-steering effects in the surface GaAs layer are observed to have a major influence on {110} planar angular scans carried out in the InxGa1−xAs layers resulting generally in a double or more complex-shaped angular dip. A simple computer simulation has been developed which determines the main features of the experimental angular scan data. Comparison of simulation and experimental data allows a reasonable determination of the kink angle θK between the {110} planes for the surface GaAs and underlying strained layer. Only in limiting cases is it possible to unequivocally determine θK from the experimental data alone. They are as follows: (i) when θK=0; (ii) θK>2ψ pc (ψ pc is the critical angle for {110} planar channeling); and (iii) when the thickness t of the top layer is thin (t≪2d/ψ pc, where d is the {110} interplanar spacing).
Excimer laser photolysis study of NH3 and NO
Authors: Ikeda Tetsuya , Danno Minoru , Makihara Hiroshi
Published: July 2002

Photolysis in the NH3-NO system was studied by using an ArF-excimer laser. It was found that the concentration of NO decreases during laser irradiation for a mixture of gaseous of NH3 and NO. From a quadrupole-mass spectroscopic analysis of the gases, the decomposition of NO molecules yields selectively H2O and N2 molecules. The dependence of quantum yield of NO decomposition on the concentration of NH3 shows a maximum at the same concentration as that of NO.
Tantalum silicide Schottky contacts to GaAs
Authors: Lee C. P. , Liu T. H. , Lei T. F. , Wu S. C.
Published: July 2002

Tantalum silicide (TaSix ) films with different Si to Ta ratios (x) as Schottky contacts to GaAs have been studied. The films were prepared by coevaporation. The metallurgical properties of the film and the stability of the silicide-GaAs interface were studied by x-ray diffraction, Auger electron spectroscopy, and Rutherford backscattering spectroscopy. The films were annealed at various temperatures (up to 850 °C) for thermal stability evaluation and the Schottky diodes were characterized by I-V and C-V measurements. It was found that the Si to Ta ratio (x) plays an important role in the thermal stability of the Schottky diode. For small x values, there are interactions between Ta and GaAs, probably a compound formation, after high-temperature annealing. For large x values, the degradation mechanism for the Schottky diodes after high-temperature annealing appears to be the out-diffusion of Ga and As from the substrate. The best composition for a thermally stable Schottky barrier is Ta5 Si3, which shows stable Schottky characteristics after annealing with temperatures up to 800 °C.
Modeling the microwave properties of the YBa2Cu3O7−x superconductors
Authors: Gittleman J. I. , Matey J. R.
Published: July 2002

We have used the two-fluid model and the Bruggeman effective-medium approximation to compute the microwave surface resistance Rs of superconductor-nonsuperconductor composites. The results are relevant to the new high-Tc superconductors: because of extreme anisotropy, unfavorably oriented crystallites may be considered nonsuperconducting; because of chemical reactions with the atmosphere, the surface can be a superconductor-nonsuperconductor composite. The model predicts very low values of Rs and very large unloaded Q’s. In most applications reduction of the operating temperature from 77 to 4 K will not result in technologically important improvements. The conditions on which these conclusions are based are discussed, as well as the dependence of microwave surface resistance on superconducting fraction, conductivity of the nonsuperconducting component, temperature, frequency, normal electron-scattering time, and grain size.
Effect of substrate temperature on the growth rate and surface morphology of heteroepitaxial indium antimonide layers grown on (100) GaAs by metalorganic magnetron sputtering
Authors: Rao T. Sudersena , Halpin C. , Webb J. B. , Noad J. P. , McCaffrey J.
Published: July 2002

The effect of substrate temperature and III/V ratio on the growth rate and surface morphology of heteroepitaxial InSb films grown on GaAs(100) using metalorganic magnetron sputtering has been studied. The surface morphology showed a strong dependence on growth temperature and III/V ratio. Films with ‘‘mirrorlike’’ surfaces could be routinely obtained for deposition temperatures near 400 °C. For films grown above 300 °C, the growth rate increased with increasing trimethylindium flow, at constant antimony sputter power, and exhibited a peak near 400 °C. In this region the growth rate was thermally activated with an observed activation energy of 0.24 eV. Above 400 °C the growth rate decreased with increasing temperature. The surface morphology of these higher-temperature layers indicated a selective etching process as the mechanism for growth rate reduction. Cross-sectional transmission electron microscopy studies indicated a defect density in excess of 1011 cm−2 at the InSb/GaAs interface which decreased to 4.0×109 cm−2 at a distance of 0.3 μm from the interface.
A quantitative study of oxygen behavior during CrSi2 and TiSi2 formation
Authors: Jiang H. , Whitlow H. J. , Östling M. , Niemi E. , d’Heurle F. M. , Petersson C. S.
Published: July 2002

Oxygen behavior during the formation of CrSi2 and TiSi2 was studied using 16O(α,α)16O resonant scattering and mass dispersive recoil detection analysis. The Ti and Cr films were deposited by e-beam evaporation in a cryopumped system. The oxygen content in the films was varied by evaporating at different pressures. The silicide films were formed by solid-solid reaction of the metal layers with the silicon substrate, and the annealing conditions were such that both partly and fully reacted silicides were obtained. The extent of the silicide formation was monitored by backscattering spectrometry. In the case of CrSi2, oxygen was found to be uniformly distributed throughout the silicide layer after annealing. For the Ti/TiSi2 system, however, oxygen seems to have preferentially remained in the Ti layer during the silicide growth, and its final distribution was confined in a region in the silicide close to the surface. It was also observed in the latter case that silicon diffused to the surface at the initial stage of annealing. A model based on the Nernst–Einstein equation is proposed to provide a general explanation for the oxygen behavior in metal/silicon systems. In addition, it was shown that oxygen which was initially in the form of metal oxides and in solid solution had been transformed into SiO2 after the silicide formation. Oxygen loss is observed for all samples, and increases with the extent of annealing.
Third-harmonic generation in an AlGaAs/AlAs superlattice
Authors: Kobayashi Hideki , Iwamura Hidetoshi , Kubodera Ken’ichi
Published: July 2002

Third-harmonic generation in an AlGaAs/AlAs superlattice is observed for the first time at a pump-light wavelength of around 2 μm. The value of third-order optical susceptibility χ(3), for the polarization parallel to the superlattice layer in a nonresonant region, is close to that reported for bulk GaAs. Enhancement of χ(3), giving more than three times the nonresonant value, is observed near a three-photon resonance region. A characteristic third-harmonic signal is observed when the pump-light polarization has a component perpendicular to the superlattice layer. This is considered to be another χ(3) enhancement which is caused by nonparabolicity in the superlattice.
Piezobirefringence effect in GaAs disks subjected to diametrical compression
Authors: Dutta Aloke K. , Ajmera Pratul K. , Huner Burke
Published: July 2002

In this communication, the simulated piezobirefringent images for a diametrically compressed GaAs disk are compared with those obtained experimentally. The values of the piezo-optic coefficients used in these simulations are derived from the elasto-optic coefficients and the stiffness constants for GaAs. The behavior of the stress-optic coefficient C for GaAs is also investigated. For (100)-oriented GaAs, the calculated value of C is found to vary with position for a given load and also found to depend on the orientation of the loading axis with respect to the principal crystal direction chosen to be 〈010〉 in this work. The calculated values of C for this case range from 0.8 to 2.6×10−12 cm2 /dyn. However, for (111)-oriented GaAs, no such dependence is observed and C is a constant with a calculated value of 1.94×10−12 cm2 /dyn.
Electrical characteristics of Au/p-AlSb metal-insulator-semiconductor Schottky diodes
Authors: Sadiq Shatha , Joullié André
Published: July 2002

Metal-insulator-semiconductor Schottky barrier diodes have been prepared on p-type bulk AlSb by evaporating gold on a chemically etched (100) AlSb surface. The existence of an oxide-rich interfacial layer between gold and AlSb of ∼70 Å thickness was shown by means of secondary ion mass spectrometry analysis. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics were measured. The barrier height qφBp(0) obtained from the Richardson plot log(Is/T2) vs (1/nT) is 0.71 eV. The 1/C2-vs-V plot was not a straight line. From the ideality factor at room temperature (n=1.4) and the intercept voltage V0 of the 1/C2-vs-V curve (V0=1.2 V), a density Ds of interface states was evaluated around 5×1011 cm−2 eV−1.
Effect of thermal history on oxygen precipitates in Czochralski silicon annealed at 1050 °C
Authors: Kung Chung Yuan
Published: July 2002

The precipitation of oxygen in bulk Czochralski silicon wafers subjected to single-step isothermal, two-step (low-high), two-step (high-high), and three-step (high-low-high) annealing is studied by means of infrared spectroscopy and by preferential etching. Comparisons are made with transmission electron micrographs obtained on similar wafers. With the same amount of precipitated oxygen, the IR spectra near 1230 cm−1 and the precipitate morphology are different for samples that undergo different thermal cycles. For the single-step and three-step annealed samples, platelet precipitates are the dominant defect type and a peak is observed at 1230-cm−1. For the two-step annealed samples, the majority defects are polyhedral precipitates and stacking faults, no platelet precipitates are found and the 1230-cm−1 peak is absent. It is believed that the stacking faults generated during two-step annealing have a strong effect in converting the oxygen precipitate morphology from platelets to polyhedra. A model is proposed to explain this phenomenon according to the coarsening concept.
Physical properties of diphenyldiacetylenic liquid crystals
Authors: Wu Shin-Tson , Finkenzeller Ulrich , Reiffenrath Volker
Published: July 2002

Optical and electro-optic properties of two highly conjugated diphenyldiacetylenic liquid crystals (LCs) [1.4-bis-(4-propylphenyl)-butadiyne, abbreviated as PTTP-mm] and their eutectic mixture were characterized in the nematic range. These LCs are found to exhibit extraordinarily high birefringence and very low viscoelastic coefficient. Their figure of merit is significantly higher than that of the widely used commercial LC mixture BDH-E7. Potential application of PTTP-mm in modulating infrared radiation is addressed.
Some properties of organometallic vapor-phase epitaxial grown GaAs layers on In-doped GaAs substrates
Authors: Imai Tetsuji , Fuke Shunro , Mori Katsumi , Kuwahara Kazuhiro
Published: July 2002

Undoped GaAs epilayers are grown on heavily In-doped dislocation-free GaAs substrates by the organometallic vapor-phase epitaxial method. Some phenomena related to the misfit dislocation generation caused by the lattice mismatch between epilayer and substrate are investigated as a function of epilayer thickness. As the epilayer thickness increases, the surface morphology changes from mirrorlike to a streaky or cross-hatched pattern, and also the perpendicular lattice constant increases gradually from the lattice constant of coherently grown epilayers to that inherent in pure GaAs. These phenomena are related to the relaxation process from the coherently grown crystalline lattice to that inherent in GaAs by generation of misfit dislocations. This relaxation process is also ascertained by both the increase of the exciton peak energy implying the recovery of the biaxial tensile strain and the increase of etch pit density, revealing the generation of the misfit dislocations at the epilayer/substrate interface.
Investigation of current redistribution in superstabilized superconducting winding when switching to the normal resistive state
Authors: Devred A.
Published: July 2002

We have investigated the electromagnetic behavior of a layer of superstabilized superconductive composite conductors when switching instantaneously and uniformly to the normal resistive state. The Laplace transform was used to solve the current diffusion equation in the superstabilizing material. The value of power dissipated per unit volume, averaged over the layer thickness, was then computed using the ‘‘pseudo’’-convolution theorem in the complex plane. Last, we present a simple interpretation of the phenomenon with the help of two time constants.
Transmission electron microscopy studies of YBa2(Cu1−x,Mx)3O7−δ with M=Fe, Ni
Authors: Sastry G. V. S. , Wördenweber R. , Freyhardt H. C.
Published: July 2002

Substitution of 3d elements Fe and Ni in the YBa2Cu3O7−δ superconductor was studied with the aim of understanding the role of substitution on the twin structure of the superconductor and the resultant microstructure on the pinning properties and Tc variation. The results of transmission electron microscopy (TEM), electron diffraction, and high-resolution electron microscopic studies (HREM) on the substituted samples of YBa2(Cu1−x,Mx)3O7−δ with M=Fe,Ni are reported here. TEM studies showed that the twin width decreases as x increases up to 0.015 for Fe substitution and is replaced by a 5-nm-size twin domain structure in the regime 0.015≤x≤0.05. This domain structure vanishes by x=0.12. HREM studies showed that these domains retain the orthorhombic structure of the unsubstituted sample contrary to the x-ray diffraction reports. In the case of Ni-substituted samples for x=0.05 the orthorhombic structure and the twin lamellas of the unsubstituted sample remain unaltered. The cooperative Jahn–Teller effect, limited in extent by the presence of Fe on the Cu(1) site, is proposed to be responsible for the formation of twin domains.
A quantitative study of the creation of EL2 defects in GaAs by plastic deformation
Authors: Vignaud D. , Farvacque J. L.
Published: July 2002

Optical absorption quenching measurements have been carried out on a lot of plastically deformed n+ samples (either Si or Se doped), which were EL2 free before deformation. It is shown that the density of EL2 defects created during the deformation increases linearly first with the dislocation density and then saturates for higher strains. The introduction rate of EL2 is also higher in the Se- than in the Si-doped material. Photoluminescence characterization of these same samples shows the appearance of the 0.93-eV band only after deformation; this band being associated with the divacancy. A possible model of EL2 creation during deformation is finally proposed.
Cathode ions from microsecond aluminum vacuum arcs
Authors: Miller H. Craig
Published: July 2002

A triggered vacuum gap with a 1.25-mm-diam aluminum cathode, a nickel mesh anode, and a separate two-terminal gold trigger, were used to generate vacuum arcs of 60–90 A, 6–40 μs in duration. A retarding potential analyzer was used to investigate the cathode ion flux. A typical ion signal showed an initial peak about 10–20 μs after arc initiation, followed by a rapid decay, then the signal leveled off at about 30–35 μs to a fairly constant signal (plateau), which persisted until a few microseconds after the arc current was cut off; finally the ion signal decayed to zero. The initial peak was primarily composed of ions produced during the initial stage of the vacuum arc. The plateau represented ions produced after the arc settled down to a reasonably steady state. Conclusions were as follows: (1) The cathode ions produced during the initiation stage of such vacuum arcs are more energetic than those produced after the arc has settled down to a steady state, and (2) after this steady state has been reached, the cathode ion flux still appears somewhat more energetic than the cathode ion flux from dc vacuum arcs, although this may be because of the higher arc voltage caused by the relatively small ratio of electrode diameter to gap length in these experiments.
A generalized plasma etching model with an oblique magnetic field
Authors: Zawaideh Emad , Kim N. S.
Published: July 2002

A generalized plasma etching model with an oblique magnetic field has been developed. The new model is a continuation of our previous models presented in recent papers [E. Zawaideh and N. S. Kim, J. Appl. Phys. 62, 2498 (1987); 64, 4199 (1988)]. New generalized plasma transport equations that are valid in the limit of large drifts (e.g., E×B drift, where E and B are the electric and magnetic field vectors, respectively) are introduced. These new generalized plasma transport equations are also valid for collisional [λ/L≪1] to weakly collisional plasmas [λ/L∼0(1)], where λ is the ion mean free path and L is the smallest of the scale lengths of the electric field or the gradient in the macroscopic plasma parameters. The new plasma transport equations coupled with both Poisson’s equation and our previous generalized etching equations are used to model the magnetron plasma etching processes. As an example, silicon (Si) plasma etching with a mixture of helium (He) and chlorine (Cl2) gases is applicable to illustrate this new generalized model. The model has shown a definite trend toward agreement with the experimental etch rates of Si for various plasma and reactor parameters (e.g., neutral gas pressure and rf power).
Transition from thermal- to electron-impact decomposition of diborane in plasma-enhanced chemical vapor deposition of boron films from B2H6+He
Authors: Komatsu Shojiro , Moriyoshi Yusuke
Published: July 2002

The apparent reaction orders for the growth of boron films in plasma-enhanced chemical vapor deposition from B2 H6 + He were measured as a function of the plasma power, which ranged from 0.4 to 1.6 kW. The conditions were as follows: substrate temperature, 890 °C; pressure, 200 Pa; and total flowrate of gases, 200 sccm. It was found that the reaction order (n) makes a transition from 1/2 to 1 at 900 W with an increase of the plasma power, and which accompanied a corresponding morphological transition. On the basis of a simple kinetic model, the observed reaction-order transition is related with a transition from thermal- to electron-impact decomposition of diborane occurring at 900 W: the n of 1/2 observed at the power range below 900 W is attributed to a pyrolysis-dominant growth mechanism in which the association of two BH3 into B2 H6 cannot be neglected, whereas the n of 1 observed at the power range above 900 W is related to a growth mechanism in which the electron-impact dissociation of diborane is dominant.
Window size effect on lateral growth of nickel silicide
Authors: Singh Awatar , Khokle W. S. , Prudenziati M. , Majni G. , Morten B.
Published: July 2002

Window size effect on lateral growth of nickel silicide in contact windows cut into oxide grown on Si (100) is studied. The growth rate is found to be independent of window size and follows the diffusion-limited process with activation energy of 1.5 eV. The Si erosions are observed to grow due to predominant Si diffusion for vacuum anneal above 600 °C. This phenomenon becomes greatly pronounced with fine windows of 2 μm in diameter. We attribute this to (i) an enhanced stress level in fine windows causing reduction in the growth temperature of epitaxial NiSi2 in the windows and (ii) difference in surface energies of epitaxial NiSi2 formed and the Si substrate resulting in the shrinkage of the epitaxial NiSi2 dimension in the window. No such behavior is observed under identical conditions when Si (111) is used. We believe this is due to the fact that the lateral growth of nickel silicide in this case is about a quarter of that for Ni-Si (100) lateral samples. Finally the technological importance of this study is pointed out.
Supermode control and phase front measurements of phase-locked offset-coupled laser arrays with a large optical waveguide structure
Authors: Shinozaki K. , Furukawa R. , Fukunaga T. , Watanabe N.
Published: July 2002

Phase-locked array lasers with large optical waveguide structures are demonstrated. The refractive index guides of each laser are evanescently coupled with and without offset-coupling structure. An evanescently coupled three-element laser array without offset coupling regions emits up to 200 mW and an offset-coupled laser array with a 4/5 element emits up to 150 mW under pulsed operation. Both laser arrays emit with all elements in-phase locked and produce a single narrow far-field lobe. The full widths at half maximum of the three-element and 4/5-element laser arrays are 5° and 2.5°, respectively. In phase measurements of the lobe of the 4/5-element laser array, we find that the root-mean-square aberration is less than 0.11λ under pulsed operation. This phase aberration is constant with varying power from 75 to 150 mW.
Optical properties of Hg1−xCdxTe sawtooth superlattices
Authors: Chang Yia-Chung , Cheung J. , Chiou A. , Khoshnevisan M.
Published: July 2002

Theoretical studies of the band structures, photoabsorption, electro-optic coefficient, and second-order susceptibility (χ(2)) of Hg1−xCdxTe sawtooth superlattices are reported.
Formation of the Ni-SiC(001) interface studied by high-resolution ion backscattering
Authors: Slijkerman W. F. J. , Fischer A. E. M. J. , van der Veen J. F. , Ohdomari I. , Yoshida S. , Misawa S.
Published: July 2002

Ion backscattering in conjunction with channeling and blocking has been used to study the Ni-SiC(001) system after Ni deposition at room temperature and after annealing up to a temperature of 870 K. Detailed analysis of the energy spectra of backscattered ions reveals morphology and composition on an atomic scale. The results show that up to the Ni coverage studied (14.1×1015 Ni atoms/cm2) no mixing occurs between Ni and Si or Ni and C at room temperature. At a temperature of 570 K, Ni starts to react with Si and forms a disordered film with a composition close to that of Ni2Si. Prolonged annealing at temperatures up to 870 K does not result in reaction to Si-richer silicide phases. Upon annealing, C segregates to the surface of the Ni2Si film to form a layer of graphite.
Monte Carlo studies of electronic transport in compensated InP
Authors: Costa Julio , Peczalski Andrzej , Shur Michael
Published: July 2002

The steady-state velocity-field characteristics for n-type InP are obtained via a Monte Carlo calculation for temperatures between 77 and 400 K, as well as for impurity compensation ratios between 0.0 and 0.9. Electron drift mobilities, peak velocities, and peak electric fields are extracted by a curve fitting procedure. A comparison with reported GaAs values suggests that InP has some superior transport characteristics and is well suited for high-frequency/gain electronic device applications. This improvement was seen to be due mainly to high L-Γ and X-Γ energy valley separations in InP. An empirical relationship between drift velocity and applied electric field, with the low-field drift mobility as an input parameter is presented for use in computer modeling of InP devices.
Formation, crystallization, and magnetic properties of Nd-Fe-B glasses
Authors: Liao L. X. , Altounian Z.
Published: July 2002

The glass formation, crystallization, and magnetic properties of (Fe1−xNdx)100−yBy (0.025≤x≤0.25, 5≤y≤20) have been investigated. Glass formation by melt spinning was found possible for Nd-Fe-B alloys with iron content less than 87.5 at. %. The thermal stability of ternary amorphous Nd-Fe-B alloys is proportional to boron concentrations, but is strongly dependent on Nd:Fe ratio as well. The strong increase of the crystallization temperature with additions of small amounts of neodymium to Fe-B can be attributed to the suppression of α-Fe formation upon crystallization. With increasing Nd:Fe ratio, the increase in Curie temperature with boron content is gradually diminished, and for Nd:Fe≥0.176 even a decrease of Curie temperature with increasing boron content is observed. Three metastable ternary structures were produced during the crystallization process.