bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction of reactively sputtered TaOx thin films with In-Sn-O thin films and properties of TaOx thin films
Authors: Oshio Shozo , Yamamoto Makoto , Kuwata Jun , Matsuoka Tomizo
Published: July 2002

The interaction of reactively sputtered TaOx films with In-Sn-O (ITO) films was investigated. Phenomena observed in the TaOx/ITO layer structure after a postannealing were studied. These phenomena were: a rise in electrical resistance of the ITO films and a change in color of the layer from transparent to yellowish. Monitoring the gases evolved from the TaOx films during the heating under vacuum showed that incorporation of water into the TaOx films takes place. Evolution of this water from the TaOx films started at around 350 °C, peaked at around 500 °C, and was largely complete at around 650 °C. It was found that the occurrence of the phenomena described above appeared at precisely the temperature at which water was evolved from the TaOx films. It was concluded that the water component incorporated into the TaOx films was the origin of both phenomena. Water present in the conditions under which discharge deposition takes place would be the cause of that incorporation.
Stoichiometry-dependent native acceptor and donor levels in Ga-rich-n-type gallium arsenide
Authors: Marrakchi G. , Kalboussi A. , Bremond G. , Guillot G. , Alaya S. , Maaref H. , Fornari R.
Published: July 2002

By combining photoluminescence and optical deep-level transient spectroscopy measurements, we have investigated the presence of a native acceptor level H01 situated at 0.32 eV above the valence band, in n-type Si-doped liquid-encapsulated Czochralski GaAs grown in stoichiometric and Ga-rich conditions. The concentration of H01 decreases when increasing the [Ga]/[As] ratio up to a critical threshold of 1.3. For [Ga]/[As] ratio greater than 1.3, H01 disappears and another acceptor level, H02 (Ev+0.23 eV), is detected. H02 is identified as the double-acceptor level of the gallium antisite GaAs. Photoluminescence results show the presence of a high-intensity 1-eV band which disappears for [Ga]/[As] ratios greater than 1.2. The annihilation of this band is accompanied by the appearance of two emission bands centered at 0.95 and 1.2 eV. The dependence of the free-carrier concentration on the presence of H01 is interpreted in terms of a complex defect formed by a gallium vacancy and silicon impurity which can be the possible origin of this defect. Finally, the evolution of native electron traps present in these samples, with [Ga]/[As] ratio, is also interpreted to give more information about the origin of the EL6 center in GaAs.
Feasibility of infrared imaging arrays using high-T
c superconducting bolometers
Authors: Verghese S. , Richards P. L. , Char K. , Fork D. K. , Geballe T. H.
Published: July 2002

The design of high-Tc superconducting bolometers for applications such as infrared imaging arrays is discussed. The dependence of bolometer sensitivity on excess voltage noise in the thermometer is a function of the detector area and thus of the wavelength to be detected. Measurements of the voltage noise in thin films of YBa2Cu3O7−δ on Si, Si3N4, and sapphire substrates are used to predict the performance of different bolometer architectures. Useful opportunities exist for bolometers made on both Si and Si3N4 membranes. A readout scheme for two-dimensional arrays of bolometers is also described in which real-time signal integration is performed on the chip.
Sample size dependence of the critical current density in polycrystalline YBa2Cu3O7−δ
Authors: Matthews D. N. , Müller K.-H.
Published: July 2002

The zero-field transport critical current density 〈Jc〉 of polycrystalline YBa2Cu3O7−δ has been measured at 77 K for slabs of different thickness d. It was found that 〈Jc〉 increases as the thickness decreases. The experimental data is in agreement with a field-dependent Jc(H) that decreases with increasing field. However, a clear distinction between a Kim, exponential, and power law model cannot be made.
Effects of thermal annealing on the magnetization dynamics of vitrovac amorphous ribbons
Authors: Valenzuela R. , Irvine J. T. S.
Published: July 2002

The effects of thermal annealing on the frequency behavior of the initial permeability, μ0, of Vitrovac(r) 6025 amorphous ribbons have been investigated. For annealing temperatures above the Curie point, Tc, μ0 shows a significant increase (from 13 760 to 39 600) as compared with the as-quenched sample; for annealing temperatures below Tc (‘‘aging’’), μ0 decreases (from 13 760 to 7700). The domain wall relaxation frequency exhibited the opposite behavior: a decrease with annealing at T≳Tc (from 69 to 18 kHz) and an increase with aging (from 69 to 127 kHz). The frequency behavior can be modeled by means of a simple, parallel RL circuit, where the inductance value is proportional to the initial permeability, and the equivalent resistance value, which is inversely related to the damping parameter, is the same for all the samples. These results can be interpreted on the basis of a variation of the extent of domain wall pinning, as manifested in changes in the spring constant α, decreasing with annealing and increasing with aging. The relaxation frequency is proportional to the extent of pinning, and initial permeability depends on the inverse.
Electronic properties of silicon δ-doped InSb
Authors: Yang M. J. , Moore W. J. , Wagner R. J. , Waterman J. R. , Yang C. H. , Thompson P. E. , Davis J. L.
Published: July 2002

We have investigated magneto-transport and cyclotron resonance (CR) of two-dimensional electron gas in silicon δ-doped p-InSb under a magnetic field of up to 12 T at 4.2 K. Because there are multiple subbands occupied, Shubnikov–de Haas oscillations show a beating behavior. The CR spectra also display several peaks originating from different subbands. Effective masses of electrons associated with the lowest three subbands can therefore be directly determined, and they are in excellent agreement with a self-consistent calculation, which takes into account the electrostatic Poisson equation, the Schrödinger equation, and realistic sample parameters. Furthermore, we observed an absorption peak, whose resonance position has anomalous angle dependence. It is attributed to impurity CR where donors are in the vicinity of the δ-doped sheet.
A model of diamond growth in low pressure premixed flames
Authors: Kim J. S. , Cappelli M. A.
Published: July 2002

Recognizing the potential importance of diamond thin film growth from combustion environments, a computational investigation of diamond synthesis in low pressure premixed flames has been conducted. The model employed solves the two-dimensional continuity, momentum, global energy, and species conservation equations in stagnation point flow geometry, and accounts for gas phase and surface reaction kinetics. The heterogeneous mechanism employed to describe diamond growth assumes that the methyl radical is the primary growth precursor. The gas phase mechanism includes elementary reaction pathways which generate methyl radicals from acetylene and in addition, includes a mechanism for cyclization (the formation of benzene) via acetylene and ethylene precursors. In this way, the pathway towards soot formation, which is believed to be a consequence of the formation of fused polycyclic aromatics, is shown to be a possible explanation for an eventual decrease in diamond growth rates at increasing fuel to oxygen flow ratios. A competition between oxidative pyrolysis of post flame hydrocarbons and cyclization establishes a criterion for optimum growth conditions.
Analysis of terbium thermodynamic characteristics for magnetic heat pump applications
Authors: Chen G. L. , Mei V. C. , Chen F. C.
Published: July 2002

Based on molecular field theory, including the effect of the field-dependent nature of Néel temperature, the entropy, and the magnetocaloric effect in terbium (Tb) have been calculated with the external field between 0 and 7 T (Tesla). The calculated results are compared with the existing experimental measurements. The maximum magnetocaloric temperature change (ΔT) is approximately 14 K near the zero-field Néel temperature (230 K) for an external field at 7 T field. This relatively large magnetocaloric effect indicates that Tb could be an attractive candidate for magnetic heat pump application. The results are then used to study the performance of heat pumps for the Carnot cycle, the constant field cycle, and the ideal regenerative cycle. The performances of these three cycles are discussed and compared.
CoO-NiO superlattices: Interlayer interactions and exchange anisotropy with Ni81Fe19 (invited)
Authors: Carey M. J. , Berkowitz A. E.
Published: July 2002

A strong interlayer exchange interaction is observed in polycrystalline antiferromagnetic CoO-NiO thin-film superlattices. This was determined by measuring the exchange field He resulting from coupling these superlattices with Ni81Fe19. The temperature above which He is zero (the blocking temperature) is taken as a measure of the ordering temperature of the superlattice. In CoO-NiO superlattices with short repeat distances the CoO and NiO layers order at a single temperature that is between the ordering temperatures of bulk CoO and NiO. These ordering temperatures are the same as for CoxNi1−xO alloy films with the same overall composition. The temperature dependence of He in some of the superlattice exchange couples deviates from the linear behavior expected for cubic antiferromagnets. In addition, the exchange anisotropy induced by some CoO-NiO superlattices is greater than that induced by CoxNi1−xO. The higher He and nonlinear temperature dependence suggest that the interlayer coupling has a strong effect on the magnetocrystalline anisotropy of the layers within the superlattice. Thick-NiO/thin-CoO/Ni81Fe19 trilayers were produced to investigate the thickness dependence of the oxide-oxide interaction. When the CoO layers are sufficiently thin (≤20 Å), the CoO ordering temperature approximates the NiO value, indicating quite strong coupling throughout the CoO layer. The effect of the coupling is much weaker for thicker CoO layers (≥30 Å).
Hard magnetic properties of melt-spun Nd(Fe,M)12 nitrides and carbides
Authors: Tang Z. X. , Singleton E. W. , Hadjipanayis G. C.
Published: July 2002

The hard magnetic properties of melt-spun Nd(Fe,M)12 nitrides and carbides were studied. The highest coercivity was obtained in NdFe10Mo2Nx with values of 8.8 kOe at room temperature and 33.7 kOe at 10 K. Other Nd(Fe,M)12N(C)x compounds had similar intrinsic magnetic properties but a lower coercivity than NdFe10Mo2Nx. The low coercivities were attributed to the three soft sources; α-Fe, non-ThMn12 structure, and insufficient nitrogenation or carbonation.
High anisotropy Nd(Fe,T)12Nx, T=Ti, Mo, films and disordered RE(Fe,Ti) phases before and after nitriding
Authors: Navarathna A. , Hegde H. , Rani R. , Cadieu F. J.
Published: July 2002

Highly textured thin films, of ordered Nd(Fe,T)12, T=Ti, Mo, and disordered Nd(Fe,Ti)7 phases, were synthesized by rf sputter deposition. The 1–12 films were highly (002) textured with the c axes oriented perpendicular to the film plane. The disordered Nd-Fe-Ti films were fitted to the disordered TbCu7 phase and could be made highly (110) textured with the c axes randomly distributed in the film plane. Nitriding was carried out in N2 at P=400 Torr at ≊450 °C for 2 h. The room-temperature magnetocrystalline anisotropy fields of the NdFe11Ti and NdFe11Mo films, which were uniaxial, were 10 and 5 kOe, respectively. After nitriding the NdFe11TNx films remained uniaxial, but the anistropy fields increased to 108 and 130 kOe for Ti and Mo, respectively. The iHc perpendicular to the film plane of NdFe11T increased to 5.3 kOe, T=Ti, and to 7.2 kOe, T=Mo, after nitriding. At 293 K, the highest-energy product of 30.2 MGOe was obtained for a T=Mo nitrided sample. The hysteresis loops of disordered Nd(Fe,Ti)7 and Nd(Fe,Ti)7Nx films, measured in the film plane and perpendicular to the film plane, showed that the disordered 1–7 phase was a conical system and that the cone angle increased after nitriding. Thin films of the disordered 1–7 phase were also synthesized with Nd replaced by Sm and these directly crystallized disordered Sm(Fe,Ti)7 films were highly (200) textured with the c axes randomly distributed in the film plane. As observed for the disordered Nd(Fe,Ti)7 phase, hysteresis loops of disordered Sm(Fe,Ti)7 and Sm(Fe,Ti)7Nx showed a change in cone angle after nitriding and, in this case, the cone angle decreased.
Propagation coefficient in a superconducting asymmetrical parallel-plate transmission line with a buffer layer
Authors: Abbas Farhat , Davis L. E.
Published: July 2002

A sinusoidal wave solution is found for a superconducting asymmetrical parallel-plate transmission line with a buffer layer, by using Maxwell’s and London’s equations, the two-fluid model, and the classical skin effect for the normal component of the current. Expressions for phase velocity and attenuation coefficient of the wave are derived. Values for the attenuation coefficient are computed for various combinations of material properties, and losses in the buffer layer are discussed.
Structures and properties of electron-beam-evaporated indium tin oxide films as studied by x-ray photoelectron spectroscopy and work-function measurements
Authors: Ishida T. , Kobayashi H. , Nakato Y.
Published: July 2002

Indium tin oxide (ITO) films deposited on single-crystal Si wafers by the electron-beam-(EB) evaporation method have been investigated by x-ray photoelectron spectroscopy (XPS) together with work-function and resistivity measurements. The XPS studies suggest that all the ITO films consist of crystalline and amorphous phases. The amount of the crystalline phase with respect to the amorphous phase for the ITO films, deposited with the incident angle of the ITO vapor to the Si substrate θi at 0°, is smaller than that for the ITO films deposited at θi=45°. The amount of the crystalline phase hardly depends on the conditions of postdeposition heat treatments, while that of the amorphous phase increases by raising the temperature of the heat treatments. Metal indium present in the films deposited at θi=0° is transformed into amorphous indium oxide by heating at 450 °C in air. Metal tin is also present near the ITO/Si interface for the ITO films deposited at θi=0°. The work function of the ITO films deposited at θi=0° is lower by 0.8 eV in maximum than that for the films deposited at θi=45°. It is concluded that the work function of the ITO films increases not only with a decrease in the amount of metal indium and metal tin in the films but also with an increase in the amount of the crystalline ITO phase with respect to that of the amorphous phase.
Carbon implanted into gallium arsenide
Authors: van Berlo W. H.
Published: July 2002

The annealing behavior of carbon implanted into GaAs at high doses has been studied. Implantations were done at room temperature and 200 °C. The implanted dopant atoms were activated by capless rapid thermal annealing. The effect of dual implantation with gallium atoms was also investigated. The activation efficiency of implanted carbon is typically low, but can be improved by implanting into a heated substrate or by coimplantation of gallium. The combination of dual implantation and implantation into a heated substrate does not lead to any improvement over the effect of a single, hot implant. It is also shown that the arsenic vacancy concentration determines the activation of the implanted carbon. The results lead to the conclusion that carbon is an amphoteric p-type dopant in GaAs.
Multilevel amplified spontaneous emission in I2
Authors: Glessner J. W. , Davis S. J.
Published: July 2002

We report the results of a study of amplified spontaneous emission (ASE) in the I2(B→X) system. For many (v′,v″) bands, several J′→J″ transitions contribute to the ASE in a cooperative manner. We present spectroscopic and kinetic data that contrast this cooperative stimulated emission to the emission in previously reported optically pumped lasers. Transitions that involve several cooperatively emitting levels produce efficient conversion of the pump laser to near-infrared output.
Secondary ion mass spectrometry generates swelling of GaSb: Depth resolution and secondary ion yields
Authors: Gauneau M. , Chaplain R. , Rupert A. , Toudic Y. , Callec R. , André E.
Published: July 2002

The III-V compound gallium antimonide (GaSb), which has a relatively narrow band gap, is of increasing importance for the fabrication of optoelectronic devices. However, GaSb was shown to swell during high energy ion implantation. The surface upheaval increased with the dose, energy, and mass of implanted ions, reaching heights of about 1 μm under the most harmful conditions. With the low energies used for secondary ion mass spectrometry (SIMS), i.e., between 1 and 20 keV, a similar behavior was observed under cesium bombardment, with elevations of 100 nm, giving rise to abnormal secondary ion yields and depth profile distortions. Here, the phenomenon has been investigated under cesium and oxygen bombardment, between 1.25 and 14.5 keV, with doses from 1015 cm−2 to above 1017 cm−2. The swelling of the material is confirmed whatever the nature of primary ions. The mechanism is related to the damage caused by the primary ion bombardment rather than to the presence of oxygen. The critical damage threshold of 1022 cm−3 atom displacements is largely exceeded, resulting in vacancy clusters, microtwins, and finally inducing polycrystallization of GaSb with an upheaval of the initial surface. In the case of SIMS, both swelling and sputtering occur simultaneously. Preferential sputtering reveals microcrystals whose dimensions depend on both the thicknesses of damaged layers, and hence, the penetration depths of primary ions and the beam impact angles. The phenomenon has two major consequences on SIMS measurements in (AlGa)Sb structures. First, it deteriorates the depth resolution, and second, it modifies the elemental secondary ion yields above a certain dose. Both these problems are addressed and a comparison with (AlGa)As is made.
Internal energy distributions of laser ablated species from YBa2Cu3O7−δ
Authors: Otis C. E. , Goodwin P. M.
Published: July 2002

The first simultaneous measurements of the ground-state translational, rotational, and vibrational energy distributions of a laser ablated diatomic molecule (YO) liberated during a 351 nm excimer laser ablation of YBa2Cu3O7−δ, are reported. In addition, the translational energy distributions of Y, Y+, Ba, Ba+, and Cu are reported. Measurements made at low and high fluences on YO indicate that there are very large differences in the ‘‘temperatures’’ inferred between the translational and the vibrational/rotational energy channels, implying that energy is partitioned in a very nonequilibrium fashion in the expanding plume. A measurement of the rotational and vibrational temperatures shows that the internal degrees of freedom are equilibrated in the expansion plume (Boltzmann distributions) with a temperature of approximately 1000 K being observed at normal processing fluences. The translational energy distributions of YO are observed to fit a shifted Boltzmann distribution at high fluences. The atomic species monitored all display non-Boltzmann velocity distributions at high fluences. The peak of the observed velocity distributions corresponds to energies as high as 10 eV for the YO neutral diatomic and up to several hundred eV for Ba+ at ablation fluences of 5 J/cm2. Bimodal velocity distributions are observed for the Cu, Ba, and Y neutral atoms at high incident fluences, implying ion-electron recombination as a partial source of the high neutral velocities.
The metal-particle/insulating oil system: An ideal electrorheological fluid
Authors: Davis L. C.
Published: July 2002

The electrorheological (ER) properties of a model system consisting of oxidized metal particles in an insulating oil are analyzed. It is suggested that previous dc experiments on such systems have failed to reveal strong ER activity because of conductivity effects. Recent experiments by Inoue at 50 Hz excitation appear to have nearly obtained the ultimate strength of the metal-particle system studied.
Behavior of InP:Fe under high electric field
Authors: Turki K. , Picoli G. , Viallet J. E.
Published: July 2002

The behavior of semi-insulating InP:Fe under high electric field is investigated. The current-voltage (I-V) characteristics are studied on both long liquid-encapsulated Czochralski-grown samples and short epitaxial-grown layers. These characteristics show a linear regime at low voltages followed, for higher voltages, by a nonlinear behavior and a current breakdown. The critical electric field at which the nonlinearity begins is found to be independent of the sample thickness, the material compensation, and the nature of the contacts, and is equal to 10 kV/cm. This fact rules out the usual explanation in terms of Lampert’s injection theory. In the nonlinear regime, a slow transient response (≊1 s at room temperature) is observed only for long samples. The time constant of this effect exhibits a thermal activation energy (≊0.64 eV) close to that of the iron-related deep level. Field-dependent effects on the thermal emission rate and the capture cross section are discussed. Considering a field enhancement of the capture cross section, we propose a model to explain both the nonlinear characteristics and the slow dynamic behavior of long samples. The current breakdown observed at higher fields is attributed to an impact ionization of the deep levels and not to a trap-filled-limit voltage as previously reported.
Magnetic properties of the monoclinic FeRh2Se4
Authors: Kim Chul Sung , Shim In Bo , Ha Min Yong , Kim Chang Sik , Park Jae Yun
Published: July 2002

FeRh2Se4 has been studied by x-rays, Mössbauer spectroscopy, and superconducting quantum interference device (SQUID) magnetometry. Mössbauer spectra of FeRh2Se4 have been taken at various temperatures ranging from 4.2 to 550 K. Magnetic hyperfine and quadrupole interactions at 4.2 K have been fitted, yielding the following results: H=161.6 kOe, 1/2e2qQ(1+1/3η2)1/2=−0.93 mm/s, θ=61°, φ=0°, and η=0.1. The temperature dependence of the quadrupole splitting, calculated in terms of direct lattice-sum calculations using x-ray crystallographic data, is in good agreement with experimental values up to 550 K. The axial field parameter Δ1=2.0‖λ‖, the rhombic field parameter Δ2=3.3‖λ‖, and the covalency factor α2=0.65 were obtained. Magnetic susceptibility measurements by dc SQUID magnetometry show that superexchange interactions between Fe2+ ions are antiferromagnetic.
Measurement of trapped flux distribution in a high-T
c superconductor using a flux-gate magnetometer
Authors: Sasada I. , Oonaka Y. , Harada K.
Published: July 2002

The distribution of the trapped flux was measured using a miniaturized flux-gate magnetometer with resolution as high as 0.46 mG at 77 K for a BiSrCaCuO high-Tc superconductor cooled down to 77 K in the presence of ac magnetic field (0.5–50 Hz) of 0.6 G in peak-to-peak and in-plane thermal gradient. The amplitude of the trapped flux decreased with increasing the frequency of ac magnetic field. The amplitude was as small as 2 mG for a 50 Hz ac field, and 43 mG for a 0.5 Hz ac field. The amplitude also became small when the cooling rate was made slow. A symbiotic combination of the high-Tc superconducting magnetic shield and the ferromagnetic one with magnetic shaking is proposed, in which merits of both can be enhanced.
Thiophenol-capped ZnS quantum dots
Authors: Mahamuni Shailaja , Khosravi Ali Azam , Kundu Manisha , Kshirsagar Anjali , Bedekar Anjali , Avasare D. B. , Singh Prabhat , Kulkarni S. K.
Published: July 2002

Free-standing, stable, single-sized, and highly pure ZnS nanosize particles or quantum dots are synthesized using a chemical route. The dimension of the quantum dots as estimated from x-ray diffraction was about 7 and 15 Å. The optical band gap for these particles was 5.2 and 4.8 eV, respectively, as compared with the bulk energy gap of 3.8 eV. These results are compared with the effective mass approximation. The observations indicate that only particular-sized stable particles can be synthesized which should have minimum energy configuration. X-ray photoelectron spectroscopy was utilized for examining stoichiometry and purity of the sample.
The mechanism of electromigration failure of narrow Al-2Cu-1Si thin-film interconnects
Authors: Kim Choongun , Morris J. W.
Published: July 2002

This work is principally concerned with the microstructure of electromigration failure in narrow Al-2Cu-1Si conducting lines on Si. Samples were patterned from 0.5-μm-thick vapor-deposited films with mean grain size of 2.4 μm, and had linewidths of 1.3 μm (W/G≊0.5), 2 μm (W/G≊0.8), and 6 μm (W/G≊2.5). The lines were tested to failure at T=226 °C and j=2.5×106 A/cm2. Other samples were tested over a range of substrate temperatures and current densities to test the effect of these variables, and 1.3 μm lines were tested after preaging at 226 °C for various times to change the Cu-precipitate distribution prior to testing. Three failure modes were observed: The 6 μm specimens failed by separation along grain boundaries with an apparent activation energy of 0.65 eV; the 1.3 μm specimens that were preaged for 24 h failed after very long times by gradual thinning to rupture; all other narrow lines failed by the transgranular-slit mechanism with an activation energy near 0.93 eV. Microstructural studies suggest that the transgranular-slit failure mechanism is due to the accumulation of a supersaturation of vacancies in the bamboo grains that terminate polygranular segments in the line. Failure occurs after Cu has been swept from the grain that fails. Failure happens first at the end of the longest polygranular segment of the line, at a time that decreases exponentially with the polygranular segment length. Preaging the line to create a more stable distribution of Cu lengthens the time required to sweep Cu from the longest polygranular segment, and significantly increases the time to failure. In the optimal case the transgranular-slit failure mechanism is suppressed, and the bamboo grain fails by diffuse thinning to rupture. Preaging is particularly effective in increasing the lifetimes of lines that contain very long polygranular segments, and has the consequence that the time to first failure in an array of lines is much longer than predicted by a log-normal fit to the distribution of failure times.
Spectroscopic ellipsometry characterization of strained and relaxed Si1−xGex epitaxial layers
Authors: Pickering C. , Carline R. T. , Robbins D. J. , Leong W. Y. , Barnett S. J. , Pitt A. D. , Cullis A. G.
Published: July 2002

Spectroscopic ellipsometry has been used to study thick, relaxed and thin, strained epilayers of Si1−xGex on Si in the range 0.1<x<0.25. Dielectric functions of relaxed Si0.87Ge0.13 and Si0.8Ge0.2 have been obtained and long-wavelength absorption coefficient values, required for interference fringe fitting, shown to be higher than measured previously. The dielectric function of strained Si0.78Ge0.22 has been measured for the first time and the effects of strain on the critical points shown to be consistent with deformation potential theory. An interpolation procedure has been developed for the fitting of layer composition and thickness, and excellent agreement with conventional techniques obtained for a series of uncapped single epilayers. The surface roughness of Si1−xGex epilayers has been studied as a function of time and deposition temperature and shown to play an important role in the modeling. The application of the technique to the characterization of buried strained layers is discussed.
The yttrium oxide chemiluminescence from the 308 nm excimer laser ablation of YBa2Cu3O7−X, Y2O3, and YCl3
Authors: Fried Daniel , Kushida Toshimoto , Reck Gene P. , Rothe Erhard W.
Published: July 2002

The yttrium oxide emission produced in the photoablation of Y2O3, YCl3, and YBa2Cu3O7−X in oxygen is investigated. Chemiluminescence from the B 2Σ-X2Σ and the A 2Π-X 2Σ YO electronic states, produced by the reaction Y+O2, is measured. The intensity of the A 2Π3/2 band is monitored as a function of pressure, distance from the target, and laser fluence. Hydrodynamic effects have a significant influence on the spatial and temporal evolution of the YO emission in the plume, which is governed by the dynamics of the shock wave generated in the excimer ablation. This shock wave compresses the ambient oxygen and leaves a trough of rarefied oxygen in its wake.
Photoluminescence of liquid-phase epitaxial Te-doped GaSb
Authors: Wu Meng-Chyi , Chen Chi-Ching
Published: July 2002

The photoluminescence (PL) spectra of Te-doped GaSb epitaxial layers grown from Ga-rich solutions by liquid-phase epitaxy have been studied in the electron concentrations from 8×1015 to 4×1018 cm−3. The electron concentration can be accurately controlled by varying the growth temperature and adding the polycrystalline Te-doped GaSb to replace half or all the undoped GaSb starting material in the growth solution. The dependence of line position, line intensity, spectral shape, and broadening on the doping level, power excitation, and temperature has been investigated in detail. At concentrations as low as 1×1016 cm−3, the GaSb sample has become degenerate because of the small effective mass of electrons and the broad band consisting of five partially resolved line dominates the low-temperature PL spectra. At concentrations above 1×1018 cm−3, the 19 K PL spectra is mainly dominated by the sub-band-gap, substrate-induced line A′ at 775.8 meV which is enhanced by the scattering of light off the back surface. This line A′ is direct evidence for the band-gap shrinkage at high doping level. This is the first report to present the detailed luminescence lines in the PL spectra of the Te-doped GaSb samples.
An analytical expression for phonon-limited electron mobility in silicon-inversion layers
Authors: Gámiz F. , Banqueri J. , Melchor I. , Carceller J. E. , Cartujo P. , López-Villanueva J. A.
Published: July 2002

A complete Monte Carlo study of phonon-limited electron mobility in (100) silicon-inversion layers has been carried out. It has been determined advantageous to consider more than three energy subbands for electron motion. First-order intervalley scattering has also been shown to play an important role in ohmic transport. The results of the Monte Carlo simulation can be fitted by a simple analytical expression that coincides with the phonon-limited mobility for the bulk in the zero transverse-electric-field limit.
Effective conductivity of composites containing spheroidal inclusions: Comparison of simulations with theory
Authors: Kim In Chan , Torquato S.
Published: July 2002

We determine, by first-passage-time simulations, the effective conductivity tensor σe of anisotropic suspensions of aligned spheroidal inclusions with aspect ratio b/a. This is a versatile model of composite media, containing the special limiting cases of aligned disks (b/a=0), spheres (b/a=1), and aligned needles (b/a=∞), and may be employed to model aligned, long- and short-fiber composites, anisotropic sandstones, certain laminates, and cracked media. Data for σe are obtained for prolate cases (b/a=2, 5, and 10) and oblate cases (b/a=0.1, 0.2, and 0.5) over a wide range of inclusion volume fractions and selected phase conductivities (including superconducting inclusions and perfectly insulating ‘‘voids’’). The data always lie within second-order rigorous bounds on σe due to Willis [J. Mech. Phys. Solids 25, 185 (1977)] for this model. We compare our data for prolate and oblate spheroids to our previously obtained data for spheres [J. Appl. Phys. 69, 2280 (1991)].
Control of GaAs Schottky barrier height using a thin nonstoichiometric GaAs interface layer grown by low-temperature molecular beam epitaxy
Authors: Fujieda Shinji
Published: July 2002

This article proposes a novel Schottky junction structure on (100) GaAs, which has a thin nonstoichiometric GaAs interface layer. A 10- to 20-Å-thick As-rich or Ga-rich interface layer was grown by low-temperature molecular beam epitaxy at 200 °C, and placed at the metal-GaAs junction interface. Independent of metal work functions, the interlayer insertion causes a wide variation in barrier heights in the range of 0.5–1.0 eV on n-GaAs, and 0.4–0.9 eV on p-GaAs. The barrier height variation is attributed to a strong Fermi-level pinning controlled by stoichiometric defect levels in the interlayer. The levels were characterized by isothermal capacitance transient spectroscopy of a metal-insulator-semiconductor structure having a nonstoichiometric interlayer between an aluminum nitride insulating film and GaAs. High concentrations of defect levels were confirmed around 0.4 eV below the conduction band edge in the As-rich interlayer and around 0.3 eV above the valence band edge in the Ga-rich interlayer. An anomalous transient response, exhibiting what appears to be low activation energy and a small capture cross section, was found in addition to the normal response. This anomaly can be explained by variable range hopping conduction via defect sites along the interlayer. In diodes with dense interfacial defects, this relaxation process for trapped carriers is considered to proceed faster than the usual emission to the conduction or valence band, at low temperatures.
Energy density distribution of interface states in Au Schottky contacts to epitaxial In0.21Ga0.79As:Zn layers grown on GaAs by metalorganic vapor phase epitaxy
Authors: Singh A. , Cova P. , Masut R. A.
Published: July 2002

Au/p-In0.21Ga0.79As Schottky barrier diodes were fabricated by evaporation of Au on chemically etched surfaces of Zn doped In0.21Ga0.79As epitaxial layers grown on highly p-doped GaAs substrates by metalorganic vapor phase epitaxy (MOVPE). Room temperature current-voltage measurements show that Au forms high quality rectifying contacts to p-In0.21Ga0.79As:Zn with an ideality factor of 1.2. High frequency capacitance-voltage (C-V) and capacitance-frequency (C-f ) measurements over a wide frequency range (1 kHz<f<1 MHz) were carried out at room temperature on Au Schottky diodes made on four p-In0.21Ga0.79As:Zn samples with varying acceptor doping concentrations (NA) in a range between 5.8×1014 and 4.3×1017 cm−3. Under forward bias, the capacitance showed large frequency dispersion, possibly caused by interface states in thermal equilibrium with the semiconductor. The C-f data was analyzed in terms of Lehovec’s model of an interface state continuum with a single time constant. The density and relaxation time of interface states were obtained in an energy range between 0.40 and 0.65 eV from the top of the valence band. The density of interface states varied between 1×1011 and 3.5×1012 eV−1 cm−2, and the relaxation times were in the range of 7×10−6–6×10−5 s. For samples with NA between 1.5×1017 and 4.3×1017 cm−3, the interface state density increased exponentially with interface energy in the range of 0.65 and 0.40 eV, from midgap towards the top of the valence band. The density of interface states in the highly doped samples (NA=4.3×1017 cm−3) was one order of magnitude higher than that in the lightly doped samples (NA=5.8×1014 cm−3).
Time-dependent model of an optically triggered GaAs switch
Authors: Capps C. D. , Falk R. A. , Adams J. C.
Published: July 2002

A numerical model for optically triggered switching in bulk GaAs is presented. First, a one-dimensional model is described and calculated behavior compared to experimental observations. Results from the one-dimensional model are not consistent with observed switching behavior. The model is then modified to include filament formation. Results from the modified model agree qualitatively and quantitatively with experimental data. Details of the dynamic behavior of the device are shown and a unified picture of the switching phenomenon presented. On the basis of the agreement of the numerical model and experimental observation it is concluded that switching is a result of localized impact ionization creating a conductive filament channel through the bulk material.
Raman investigations of elastic strain relief in Si1−xGex layers on patterned silicon substrate
Authors: Dietrich B. , Bugiel E. , Osten H. J. , Zaumseil P.
Published: July 2002

The appearance of an elastic strain relief in narrow mesalike patterned Si1−xGex heteroepitaxial layers is shown. A Si1−xGex layer was deposited on a mesalike patterned Si(001) substrate by molecular-beam epitaxy. The germanium concentration was x=14%, the layer thickness h=96 μm was several times larger than the critical thickness hc. The layers on top of the mesas were investigated by Raman microscopy. The Raman line shifts of the wider mesas and their dislocation densities agree with the predicted strain reduction by generation of misfit dislocations. On the narrow mesas an additional shift of the Raman lines toward the unstrained alloylike Raman frequency was measured. It is caused by an elastic strain relief on top of the narrow mesas. An estimation of the expected Raman line shifts is given assuming an uniaxially strained SiGe layer. The calculated line shifts agree sufficiently with the measured values. The elastic strain relief reduces the free energy of the layer-substrate system, reduces the stress in the pseudomorphic layer, and stabilizes the structure. The effect arises if the mesas are narrower than 2 μm. It is therefore of interest in all submicrometer technologies.
Soft magnetic properties of nanocrystalline Fe-Hf-C-N films
Authors: Choi J. O. , Lee J. J. , Han S. H. , Kim H. J. , Kang I. K.
Published: July 2002

Fe-Hf-C-N films with excellent soft magnetic properties were fabricated by Ar+N2 reactive sputtering for the first time. The newly developed films were found to have better soft magnetic properties than those of Fe-Hf-C or Fe-Hf-N films. The best magnetic properties achieved in this work are  Hc of 0.15 Oe, μeff of 8200, and 4πMs of 17 kG. The thermal stability of the Fe-Hf-C-N films was also found to be excellent, e.g., Hc was less than 0.3 Oe and μeff was about 4000 for the films annealed up to 700 °C. It was observed by transmission electron microscopy that the films consisted of two phases: a fine crystalline α-Fe phase whose grain size is about 6 nm, and Hf(C,N) precipitates with a size of less than 2 nm. The fine grained α-Fe structures, together with finely dispersed Hf(C,N) precipitates, is considered to be one of the main factors for the excellent magnetic properties and thermal stability.
Magnetization reversal processes in epitaxial Fe/GaAs(001) films
Authors: Daboo C. , Hicken R. J. , Eley D. E. P. , Gester M. , Gray S. J. , Ives A. J. R. , Bland J. A. C.
Published: July 2002

In this article we present the results of a detailed study of the switching behavior observed in epitaxial single Fe films of thickness between 30 and 450 Å, and a wedge shaped Fe film with a thickness range of 10–60 Å grown on GaAs (001). These films have cubic and uniaxial anisotropies which change with film thickness. For the fixed thickness films the values of the anisotropy constants were accurately determined by Brillouin light scattering (BLS) measurements together with polar magneto-optic Kerr effect (MOKE) measurements that gave the value of the magnetization. The switching behavior of these samples was observed with in-plane MOKE magnetometry as a function of the angle between the applied field and the in-plane crystallographic axes. Measurements of the component of magnetization perpendicular to the applied field allow a precise determination of the relative orientation of the hard and easy in-plane anisotropy axes. This can be used to accurately determine the ratio of uniaxial to cubic anisotropy constants, when this ratio is less than one. The ratios obtained from MOKE agree well with those obtained from BLS. Minimum energy calculations predict that the reversal process should proceed by a continuous rotation of the magnetization vector with either one or two irreversible jumps, depending on the applied field orientation and the nature of the anisotropy of the film. The calculations provide a good qualitative description of the observed reversal process, although the magnetic microstructure influences the exact values of the switching fields.
Heat capacity and magnetic properties of CoCl2⋅H2O
Authors: Lukin J. A. , Friedberg S. A. , Chardarlapaty S. , Brubaker W. W. , Cinquina C. C. , DeFotis G. C.
Published: July 2002

Recent magnetic studies of polycrystalline CoCl2⋅H2O showed an antiferromagnetic ordering transition at TN∼14 K and an apparent spin glass transition at ∼7 K. We now have extended the magnetic susceptibility measurements up to 300 K. The results above TN can be well described if the lowest electronic states of Co2+ in this salt are two Kramers doublets separated by ΔE/k=230 K, and if a predominantly ferromagnetic mean field interaction is introduced. The heat capacity of CoCl2⋅H2O over the range 0.6–80 K has also been measured. Below ∼10 K, Cp≊aT−2+bT3. The first term is the hyperfine contribution of the 59Co2+ nuclei. The second is the sum of lattice vibrational and electronic spin parts. Cp exhibits a λ-type peak at TN1=15.0±0.05 K, and a second λ anomaly of comparable size at TN2=13.9±0.05 K, which appears to be associated with a spin reorientation transition. Correcting the observed Cp data for the nuclear spin contribution, one may calculate the sum of lattice vibration and electron spin entropies, and thus obtain at TN1 an upper limit to the critical magnetic entropy. This amounts to 0.38 R ln 2, suggesting that a substantial part of the spin ordering in this system is of short-range and lower dimensionality. Cp also exhibits an inflection point near 4.5 K, where an unusual feature in the temperature dependence of the spin glass thermoremanent magnetization was found.
Study of ion heating and cooling in a nitrogen plasma by laser-induced fluorescence
Authors: Fukuchi T. , Wuerker R. F. , Wong A. Y.
Published: July 2002

Laser-induced fluorescence from a low-pressure, magnetized, radio-frequency-generated plasma was observed for the first negative (1N) system of N+2 (B2Σ+u−X2Σ+g). A tunable dye laser was used to excite the 1N system in the (0-0) and (0-1) transitions; individual rotational lines in the R branch were seen up to N=30, with the spin-slit doublets resolved for N≳16. Rotational ion temperature derived from the distribution of lines in the R branch is compared against translational temperature found from the linewidth. The heating of the plasma ions during the discharge and their cooling in the afterglow is observed by both rotational and translational temperatures. Results show that, for the present apparatus, the translational temperature is higher than the rotational temperature by a factor of approximately 10.
ac complex conductivity in NaCl: No new universality
Authors: Macdonald J. Ross
Published: July 2002

A new universality has been recently proposed by Lee, Liu, and Nowick [Phys. Rev. Lett. 67, 1559 (1991)] for dispersion in high-resistivity crystalline and disordered solids which posits that the real part of the conductivity σ′ exhibits ωγ frequency response, with γ=1 over an appreciable temperature range. To investigate this surprising conclusion in further detail, several powerful analysis methods were applied to Lee and co-worker’s ac relaxation data for single-crystal NaCl doped with Zn2+. In the past, no significant information has been obtained from the σ″ data. Complex nonlinear least-squares fitting was used to analyze simultaneously both parts of the admittance data, Y(ω)=Y′(ω)+iY″(ω), with several conductive-system response models. The dispersive part of the response is here generally very small compared to the low-frequency-limiting conductance, G0 and capacitance. New forms of the Barton, Nakajima, and Namikawa relation were derived and shown to be applicable for the data and the most appropriate model. Contrary to previous work, analysis and interpretation in terms of conductive-system dispersion, rather than dielectric dispersion, led to new results which vitiate the new universality assumption. Arrhenius plotting of G0(T) yielded a curved line, but a split of R0≡G−10≡R∞+ΔR, into the undispersed high-frequency-limiting part R∞ and the strength of the dispersed part ΔR, showed that while both quantities were separately thermally activated, R∞ exhibited a large, abrupt entropy transition near 363 K. From these results the vacancy migration activation energy was estimated to be 0.695 eV, and the R∞ vacancy-association activation energy changed from about 0.66 eV below the transition to about 0.56 above it, suggesting a transition from nearest-neighbor association to next-nearest-neighbor association.
Thermally annealed GaN nucleation layers and the device-quality metal organic chemical vapor deposition growth of Si-doped GaN films on (00.1) sapphire
Authors: Wickenden D. K. , Miragliotta J. A. , Bryden W. A. , Kistenmacher T. J.
Published: July 2002

The effect of epitaxial growth temperature (985–1050 °C) on the properties of Si-doped GaN layers on self-nucleated (00.1) sapphire has been investigated. Several device-related properties monotonically improve with increasing growth temperature, including (a) carrier density and (b) volume fraction of heteroepitaxial domains. However, a number of equally important device-related properties show a local maximum and include (a) optical second-harmonic generation intensity, (b) structural coherence, and particularly (c) surface morphology. The antecedents of the first class lie in increases in surface and bulk diffusion and reductions in film defect incorporation and stress at the GaN/GaN (nucleation layer)/α-Al2O3 heterointerface. The second class arises from the quite limited range over which the thermally annealed GaN nucleation layer stimulates pseudo-two-dimensional growth of the GaN overlayer.
X-ray diffraction from laterally structured surfaces: Crystal truncation rods
Authors: Tolan M. , Press W. , Brinkop F. , Kotthaus J. P.
Published: July 2002

X-ray-diffraction measurements from single-crystalline GaAs(001) surface gratings are presented. The experiments were performed using a three-crystal diffractometer. The vicinity of the (004) Bragg reflection for five samples was investigated in detail. Model calculations based on the kinematical crystal truncation rod theory are able to explain all measurements quantitatively. Mesoscopic grating parameters as well as microscopic surface roughnesses of the samples were obtained from fits of the data. For three samples scanning electron microscope pictures were taken. The analysis of these pictures leads to the same mesoscopic parameters as obtained from x-ray Bragg diffraction.
Compositional dependence of the structural and magnetic properties of PtMnSb films
Authors: Carey R. , Jenniches H. , Newman D. M. , Thomas B. W. J.
Published: July 2002

Nonstoichiometric, Pt deficient, PtMnSb films have been investigated for evidence of the increase in coercivity suggested by the work of Marinero [Appl. Surf. Sci. 43, 117 (1989)]. Structural, magnetic, and magneto-optic properties of thin PtMnSb films of different compositions annealed in under 30 s using a rapid thermal processing (RTP) system [Carey et al., IEEE Meeting on Current Topics in Applied Magnetism, Keele University, 4 November 1992 (unpublished), Paper 15; J. Magn. Soc. Jpn. 17, 290 (1993)], have been determined. It is shown that the crystalline texture of the films can be controlled by adjustments in composition and RTP time and that Pt deficiency produces increases in coercivity. The production of coercivity does not correlate with the marked changes in texture but appears to be associated with the development of MnSb phases within the PtMnSb microstructure.