bluuebunny/crossref_metadata_2025 huggingface dataset:
Leaky modes in metal-semiconductor junctions
Authors: Jestl M. , Beinstingl W. , Gornik E.
Published: July 2002

The reradiation of leaky surface plasmon polaritons into the semiconductor of a sinusoidally structured Schottky structure is investigated, to our knowledge for the first time. One of the two possible plasmon modes is bound at the metal-air interface, and is leaky at the interface between the metal film and the semiconductor. It is reradiated into the semiconductor either directly or by coupling with the grating. Therefore, emission of light from the back surface of the sample can be measured at two different angles of observation. The intensities of the two single emission beams and their ratios were measured at various thicknesses of the metal film and were found to be strongly dependent on this parameter.
Heteroepitaxial growth of HgTe on InSb at 200 °C by metalorganic chemical vapor deposition using ditertiarybutyltelluride
Authors: Oda Shunri , Tanaka Yuko , Sugiura Osamu , Matsumura Masakiyo
Published: July 2002

Low-temperature growth of heteroepitaxial HgTe on InSb is carried out by metalorganic chemical vapor deposition. Cracking of ditertiarybutyltelluride is found to be an effective method for reducing growth temperature. Epitaxial HgTe films are obtained at 200 °C with a deposition rate of 1 μm/h. The deposition rates and crystallographic properties of the films depend strongly upon the temperature of the reactor wall as well as upon the substrate temperature and the cracking temperature. Growth kinetics are also discussed.
1/f noise study in vacuum photodiodes
Authors: Fang P. , He L. , Peng Q. , Kang H. , van der Ziel A.
Published: July 2002

We report here measurements of 1/f noise in vacuum photodiodes. The theoretical expression for the Hooge parameter αH is formally equivalent to the one for secondary emission 1/f noise. There is also 1/fγ noise due to fluctuations in the cathode work function; here γ∼3/2 is expected. The spectrum SIa( f ) for the latter varies as I2aV0a and for the former it varies as IaV3/2a, where Va is the anode voltage, and Ia the anode current. Enhanced shot noise was observed at higher frequencies; at lower frequencies the noise spectrum was of the 1/f type. The latter could be separated into a V0a component and a V3/2a component by measuring SIa( f ) vs Va. The V3/2a component of the 1/f spectrum could also be deduced from the current dependence of SIa( f ); both measurements mutually agreed well. The measured V3/2a component also agreed well with Handel’s predictions; by proper choice of the anode-cathode distance dca (dca=0.6 cm) almost exact agreement could be obtained. In view of the fact that the overall accuracy of the data is not better than 25%–30%, any value of dca between 0.4 cm<dca<0.8 cm should be considered as giving good agreement; this is a very plausible range of values. We observed some poisoning effects in older devices. They are attributed to the decomposition of the dynode material under electron bombardment and give rise to long-term instability of the device noise.
Magnetic field dependencies of critical currents in InAs-coupled Josephson junctions
Authors: Inoue Koh , Kawakami Tsuyoshi
Published: July 2002

Magnetic field dependencies of critical currents in InAs-coupled proximity effect Josephson junctions with planar structures are studied from the viewpoint of the self-field effects, magnetic screening, and pair breaking in proximity superconducting InAs. A weak self-field gives a Fraunhofer pattern that shows the usual sinusoidal current-phase relation. The planar geometry must be taken into account when evaluating the Josephson penetration depth λJ. For ‘‘large’’ junctions (junction width W≫λJ), critical currents depend on how the external currents are injected. No magnetic screening was observed in InAs studied by measuring the period of the Fraunhofer pattern. Pair breaking was not observed at least below 20 G either.
Effect of stoichiometry and post-annealing conditions on magnetron sputtered films of YBa2Cu3O7 on cubic zirconia
Authors: Wiesmann H. , Chen De Huai , Sabatini R. L. , Hurst J. , Ochab J. , Ruckman M. W.
Published: July 2002

High-quality YBa2Cu3O7 films supported on yttrium stabilized cubic zirconia were made by simultaneous reactive magnetron sputtering using yttrium, barium, and copper metal targets. Superconductivity onsets of 92 K with transition widths of 1.5 K (10%–90%) have been achieved on yttrium stabilized cubic zirconia substrates. Various aspects of the deposition processes are described and the effect of deposition parameters and post-annealing on thin-film stoichiometry, structure, and superconducting properties is discussed.
Energy- and momentum-loss rates of one-dimensional hot electrons in semiconductor quantum-well wires
Authors: Kabasi A. , Chattopadhyay D. , Sarkar C. K.
Published: July 2002

Energy- and momentum-loss rates of degenerate hot electrons moving one-dimensionally in a quantum-well wire structure of square cross section of side length L are calculated theoretically considering polar coupling to longitudinal-optic (LO) phonons and deformation potential and piezoelectric couplings to acoustic phonons. Piezoelectric scattering contributes the least, while the effect of deformation potential scattering in energy loss is unimportant compared to that of LO phonon scattering for electron temperatures (Te) above about 50 K. In momentum-loss rate, however, acoustic scattering continues to be important at higher values of Te. The nonequilibrium distribution of LO phonons is found to reduce both the energy- and momentum-loss rates. The reduction factor of the total energy-loss rate is 4.4 for L=10 nm and 6.2 for L=6 nm at Te =100 K. The corresponding values for the net momentum-loss rate are 2.3 and 2.5, respectively.
Semiconductor heterostructure nonlinear Poisson equation
Authors: Krowne Clifford M.
Published: July 2002

A nonlinear Poisson partial differential equation descriptive of heterostructure physics is presented for two-dimensional device cross sections. The equation is solved using a hybrid nonlinear Jacobi–Newton iteration method. The approach has the characteristic of giving explicit numerical relationships which are amenable to the development of elegant proofs of numerical behavior based on local physical properties and boundary conditions. These proofs are provided in complete detail for nonequilibrium conditions.
A spectroscopic study using line ratios of lithiumlike ions in a laser-produced plasma
Authors: Moreno J. C. , Goldsmith S. , Griem H. R.
Published: July 2002

Spectra of highly ionized titanium and calcium in the extreme ultraviolet region were observed in laser-produced plasmas using the OMEGA 24 beam (351 nm) laser system at the University of Rochester. The plasmas were produced using glass microballoon targets coated with a layer of a medium Z element and a layer of parylene (CH). Time-integrated electron temperatures and densities were obtained by comparing measured line intensity ratios of lithiumlike charge states of Ti and Ca to numerical calculations from a collisional-radiative model. The variation of line intensity ratios with electron density and temperature using the collisional-radiative model is discussed.
Excitation of whistler modes in a sheath-helix loaded waveguide
Authors: Talukdar I. , Tripathi V. K.
Published: July 2002

The excitation of electromagnetic modes in a cylindrical plasma column by an electron beam is considerably improved by the introduction of a sheath helix inside the vacuum chamber. The helix slows down the whistler mode and relaxes the requirements on the beam energy for the generation of a given frequency.
Dynamical simulation of liquid- and solid-metal self-sputtering
Authors: Morgan W. Lowell
Published: July 2002

Molecular dynamics simulations of self-sputtering are performed using the recent picture [M. P. D’Evelyn and S. A. Rice. J. Chem. Phys. 78, 5081 (1983)] of a stratified liquid-metal surface as a model. These results are compared to those obtained from a liquid model having uniformly distributed atoms and a crystalline solid model. The stratified liquid-metal model shows an enhanced low-energy sputter yield, which falls below those of the other models for ion-impact energies above several hundred electron volts. These results are discussed in light of various published measurements of sputter yields of metals in their liquid and solid phases.
Photoelectrochemical studies of a Ga(As,P)/GaAs/Ga(As,P)/n+-GaAs multijunction electrode
Authors: Carlsson Per , Holmström Bertil
Published: July 2002

A multijunction structure, Ga(As,P)/GaAs/Ga(As,P)/n+-GaAs, and a conventional Ga(As,P)/n+-GaAs structure were compared using a variety of photoelectrochemical (PEC) techniques. The samples were grown, using metalorganic chemical vapor deposition, on n+-GaAs substrates with an initial graded region with gradually varying composition. The conventional sample had a terminating top layer with constant composition GaAs0.45 P0.55. In the multijunction sample, a GaAs region was introduced between the graded region and the top layer, resulting in an interface with an abrupt heterojunction. The multijunction electrode showed several unusual PEC features, including a very low dark current over a wide potential region, both cathodic and anodic photoeffects, and a pronounced decrease in photoactivity when going to shorter wavelengths. A plausible interpretation is presented, also providing insights into the effects of graded regions versus heterojunctions, and illustrating the value of PEC studies in probing the interior of complex semiconductor materials.
Film deposition temperature dependence of electron mobility for accumulation-mode InP metal-insulator-semiconductor field-effect transistors
Authors: Hirota Y. , Okamura M. , Yamaguchi E. , Hisaki T.
Published: July 2002

The effects of substrate temperature during film deposition on semi-insulating InP metal-insulator-semiconductor field-effect transistor characteristics are reported. The substrate temperature during film deposition, Ts, has a large influence on elastic and inelastic electron scattering times. With decreasing Ts, effective mobilities measured at room temperature and at 77 K increase, and the temperature dependence of effective mobility is more clearly observed. Electron scattering by neutral impurities is calculated in order to estimate the number of scattering centers near the InP surface, and to determine the activation energy (Ea=0.3±0.1 eV) of phosphorus migration (i.e., P hopping). Hikami–Larkin–Nagaoka’s theory [Prog. Theor. Phys. 63, 707 (1980)] is applied to negative-magnetoresistance data measured at low temperature and in the low induced electron density region to estimate the electron inelastic scattering times. The substrate temperature dependence of inelastic scattering time is discussed in terms of Anderson localization.
Electrochromic characteristics of high-density lithium incorporation into thin WO3 films
Authors: Ashrit P. V. , Bader G. , Girouard Fernand E. , Truong Vo-Van
Published: July 2002

Electrochromic coloration characteristics of thin WO3 films have been studied under Li+ ion insertion. It has been found that beyond certain charge densities of Li+ insertion there is an actual reduction in the optical density of the system, limiting the reversible electrochromic performance of thin WO3 films.
Observation of a deep level due to In doping in p-type GaAs
Authors: Smith S. R. , Evwaraye A. O. , Mitchel W. C.
Published: July 2002

We have observed a peak in deep-level transient spectroscopy DLTS spectra due to the presence of In in mph type='1' p-type GaAs samples. Both In-doped and nominally undoped samples of GaAs grown from a Ga-rich melt were examined. We observed an electron trap at Ev+0.095 eV in the In-doped material. Annealing experiments indicated that the trap level may be generated in In-doped material when not present in measurable quantities in as-grown crystals. However, annealing undoped samples under identical conditions failed to produce the level. We conclude that the electron trap is related to the presence of In in the p-type GaAs.
Effect of undoped GaAs spacers on the characteristics of GaAs-(Al,Ga)As-GaAs single barrier structures
Authors: Lacklison D. E. , Duggan G. , Battersby S. J. , Harris J. J. , Foxon C. T. , Hilton D. , Roberts C. , Hewett J. , Hellon C. M.
Published: July 2002

The effects of undoped spacer layers on the electrical properties of single barrier heterostructures (both alloy and superlattice) have been investigated by measuring incremental slope resistance over the bias range −400 to +400 mV and at convenient temperature intervals between 70 and 290 K. The zero bias slope resistance, Rs(0), and the effective barrier heights increase with spacer thickness. Also, the low-temperature slope resistances, Rs(V), decrease exponentially with the magnitude of the bias, V, while the effective barrier heights, deduced from high-temperature measurements, decrease approximately linearly. This suggests that the decrease in Rs(V) with bias is due simply to the voltage-induced decrease in effective barrier height. Rs(0) varies exponentially with zero bias effective barrier height for both alloy and superlattice barriers and this is consistent with the Γ electrons dominating the current transport through the barriers. All of our Rs(V) curves are asymmetric and, using Airy function calculations, we have modeled curves similar to the experimental ones by assuming different doping levels for the two doped GaAs layers on either side of the barriers. This is possibly due to Si migration into the ‘‘undoped’’ barrier or the spacer layer closest to the substrate.
Electron-beam-induced acoustic-wave enhancement of gaseous combustion
Authors: Bidwell S. W. , Bosch R. A. , Gilgenbach R. M.
Published: July 2002

The combustion rate of premixed gases in a closed vessel was increased by injecting a high-current electron beam into the gas mixture within about 20 ms of spark ignition. This effect was observed with the fuels ethylene, methane, ethane, propane, and n-butane. Experimental results provide strong evidence that e-beam excitation of the fundamental longitudinal-acoustic mode of the cylindrical chamber is the mechanism of combustion enhancement. An observable combustion enhancement required that the amplitude of the fluid velocity oscillation in this acoustic mode be greater than or approximately equal to the flame propagation speed and was associated with a wrinkled or cellular flame structure with dimensions on the order of 1/2 cm. These results are in good agreement with values for the threshold acoustic velocity amplitude and dimension of cellular structure predicted for a periodically accelerated flame.
Anisotropy control in CF4 microwave plasma etching
Authors: Pelletier J. , Cooke M. J.
Published: July 2002

A parametric study of the etching of silicon with CF4 has been performed in a multipolar microwave plasma with independent rf biasing. According to the plasma conditions, up to three transitions from anisotropic to nonanisotropic etching can be found. The mechanisms involved are discussed in terms of the coadsorption of reactive fluorine atoms and CFx radicals which are responsible for the wall passivation by polymer formation.
Substrate effect on the deposition of Zn3P2 thin films prepared by a hot-wall method
Authors: Fuke Shunro , Imai Tetsuji , Kawasaki Kazushige , Kuwahara Kazuhiro
Published: July 2002

Zn3P2 thin films have been deposited by a hot-wall method on Pyrex glass and (100)GaAs substrates. For GaAs crystalline substrates, higher deposition rates were obtained at the same source and substrate temperatures than those for glass substrates. Layers deposited on (100) GaAs substrates showed stronger preferential (004)orientation of the tetragonal structure, and hence an improved columnar structure is obtained as compared with those on glass substrates. The films having higher crystalline quality deposited on GaAs substrates have room-temperature resistivities as low as ∼10 Ω cm.
Evaporation of small water drops maintained at constant volume
Authors: Peiss Clarence N.
Published: July 2002

An apparatus was devised which permits measurement of the evaporative rate of small water drops maintained at constant volume. The surface temperature of the drop was measured with a small thermocouple. Evaporative rates were measured at drop radii ranging from 0.023 to 0.18 cm, with a total of 128 measurements. Mathematical analysis was performed using a multiple curve fitting program for 19 different curves. It was found that a plot of radius against evaporative rate (g/s/mm Hg) is best fit by a parabola with a correlation coefficient of 0.998.
Anodization of Al in microwave-discharged oxygen plasma
Authors: Matsumura Koki
Published: July 2002

This paper describes the plasma anodization of aluminum thin films in microwave-discharge oxygen plasma with electron-cyclotron-resonance conditions from the following two points of view. First, the change in the current efficiency with the anodizing conditions and the factors affecting the oxide growth are examined. The current efficiency depends on the microwave input power, the magnetic field, the distance between the specimen and the location where the plasma is generated, the pressure of oxygen gas, and the presence of ozone. Second, some considerations are given on the generation of the atomic oxygen that closely relates to the growth of the oxide film. The generation process was calculated with a simple model and an approximation. The result suggests that atomic oxygen is generated when electrons and positive ions are extinguished by dissociative recombination in the course of ambipolar diffusion in the plasma. In addition, on the supposition that only the rate of atomic oxygen supplied to the surface of the specimen limits the growth rate of the oxide film, the minimum density of atomic oxygen necessary for the oxide growth was estimated. It was found to be maximal under the appropriate conditions of oxygen gas pressure and position of the specimen. However, the atomic oxygen density is also a complicated function of other conditions such as the electron density, the molecular oxygen density, and the electron energy.
Defect states in 2.0-MeV electron-irradiated phosphorus-doped silicon
Authors: Awadelkarim O. O. , Monemar B.
Published: July 2002

Float-zoned n-type silicon samples with phosphorus concentrations in the range 1014–1017 P atoms cm−3 have been irradiated by 2-MeV electrons at room temperature with the aim of studying the role of phosphorus in the resulting damage. Using deep-level transient spectroscopy we were able to observe a number of previously unreported deep traps. A major post-irradiation bistable defect center detected in highly P-doped (∼1017 cm−3) material has an electron trap at Ec−0.42 eV, and a hole trap at Ev+0.15 eV (Ec and Ev are the conduction- and valence-band edges, respectively), each of which is associated with one of the two configurations of the center. The center, alternating between being acceptorlike to being donorlike as it undergoes configurational transformation, is suggested to be P related. Two metastable electron traps located at Ec−0.32 eV and Ec−0.42 eV are observed immediately after irradiation in moderately P-doped samples (∼1015–1016 cm−3). Interestingly, the configurational transformation rates of these states are observed to be dependent on the magnitude of the bias applied to the diode during cooldown to LN2 temperature. This is taken to indicate that configurational transformations, often thermally activated, can in some cases be influenced by the electric field strength within the depletion region. Upon thermal annealing at 200 °C of the latter two states, a couple of new states emerge; an electron trap at Ec−0.42 eV, stable up to temperatures above 300 °C, and a hole trap at Ev+0.25 eV which anneals out at 300 °C. An electron trap situated at Ec−0.24 eV with a quite small capture cross section for electrons is seen in lightly P-doped material (∼1014 cm−3) following annealing at 300 °C. Tentative propositions for the defect assignments of the observed traps are put forward.
Calculation and measurement of initial electron densities in x-ray preionized avalanche discharge lasers
Authors: Bonnie R. J. M. , Gerritsen J. W. , Zuidema R. J.
Published: July 2002

The initial electron density in x-ray preionized avalanche discharge lasers has been studied extensively. A computer model has been developed to calculate this initial electron density taking into account the characteristics of the x-ray source, x-ray physics, and geometric effects. Results of these calculations were verified for various experimental conditions using an ionization chamber. The experimental data are in excellent agreement with the calculations. Results from this work may be directly applied in the design of x-ray preionized gas lasers.
Measurement of barium ion density in the vicinity of fluorescent lamp electrodes
Authors: Bhattacharya A. K.
Published: July 2002

A laser-induced fluorescence technique for the detection and measurement of ionized barium atoms near the vicinity of an oxide-coated electrode in a low-pressure discharge lamp is presented. Ionized Ba atoms are produced by the ionization of neutral Ba atoms in the electrode fall region of the discharge. Radiation at 455.4 nm obtained from a pulsed dye laser was used to excite Ba ii from the ground state, 62S1/2, to the resonance level, 62P3/2, and the fluorescence radiation at 614.2 nm for the 62P3/2→52D5/2 transition was measured. The number density of Ba ii atoms as determined from the measured intensity of the fluorescence signal (614.2 nm) is dependent on the discharge current, and the polarity of the neighboring electrode. It is found to be larger when it is acting as an anode than when it is a cathode.
A cylindrical waveguide with periodic step changes in the radius: Interaction between transverse magnetic and transverse electric modes
Authors: Schill Robert A. , Seshadri S. R.
Published: July 2002

For modes having azimuthal variation in a cylindrical waveguide with periodic step changes in the radius, the coefficients of coupling between the transverse magnetic and transverse electric modes are determined for small relative changes in the radius. The theory is applied to treat the selective codirectional coupling between a transverse magnetic and transverse electric mode.
Josephson oscillations in a series array Josephson voltage standard
Authors: Meyer H. G. , Krech W. , Mikolajczak B.
Published: July 2002

Josephson oscillations in a large series array of Josephson junctions designed as a superconducting microwave transmission line are studied. For descriptions of the Josephson junctions both the Stewart–McCumber model and the Werthamer model are used. The attenuation of the Josephson oscillations in the considered array is composed of two terms rising from the stripline and from the Josephson junctions. The latter one is of increasing significance for lower than usually applied drive frequencies.
Structure of tungsten carbide-cobalt multilayers
Authors: Moustakas T. D. , Koo J. Y. , Ozekcin A. , Scanlon J.
Published: July 2002

Multilayers composed of ceramic and metallic materials, such as tungsten carbide and cobalt, have been synthesized for the first time. The structure of these multilayers was investigated by low-angle x-ray diffraction and transmission electron microscopy lattice imaging and microdiffraction. The data show that the low-temperature process of forming these two-dimensional composites leads to unique crystal structures and morphology in the nanometer scale.
Structural and magnetic studies of an artificial Eu/Mn superlattice
Authors: Maeda Atsushi , Satake Tohru , Fujimori Toshinari , Tajima Hiroyuki , Kobayashi Mototada , Kuroda Haruo
Published: July 2002

Artificial superlattice materials composed of alternating layers of europium and manganese metals with a periodicity in the range of 19–227 Å were prepared by means of molecular-beam epitaxy. In situ reflection high-energy electron diffraction observations revealed that the Eu metal layer is amorphous up to a thickness of 23 Å, while a [110]-oriented single-crystal Eu layer grows over the amorphous Eu layer as the thickness exceeds 23 Å. On the other hand, the manganese layers were found to always be in an amorphous state independent of the thickness. The synthesized Eu/Mn systems exhibited a unique magnetic property associated with a magnetic interaction between the amorphous Eu layers.
Ion-bombardment-enhanced etching of LiNbO3 using damage profile tailoring
Authors: Ashby C. I. H. , Arnold G. W. , Brannon P. J.
Published: July 2002

The production of a tailored implant-damage profile by sequential implantation of ions at several different energies rather than at a single energy can increase the depth and improve the wall smoothness of features produced by ion-bombardment-enhanced etching of a solid. This has been demonstrated in the enhanced etching of LiNbO3 by HF following He+ implantation at several energies and fluences selected to produce a relatively flat damage depth profile. The use of lighter ions permits the etching of deeper features than is possible with heavier ions of the same energy. Buried microcracks are observed in heavily implanted Z-cut samples. Similar microcracks may play an important role in determining propagation losses in ion-implanted waveguides.
Charge-controlled phenomena in the surface-stabilized ferroelectric liquid-crystal structure
Authors: Hartmann W. J. A. M.
Published: July 2002

An important characteristic of the surface-stabilized ferroelectric liquid-crystal (SSFLC) effect is charge compensation. Investigations on SSFLC samples, which were electrically isolated after applying a voltage, showed that this voltage drops during the switching as a result of the compensation of the surface polarization caused by the rotation of the permanent dipoles. The final optical state depends exclusively on the initial conditions. Optically it can be observed that domains come into being, grow and stabilize, resulting into a certain distribution of black and white areas. Consequently, the bistable SSFLC effect can be used for a controllable continuous grayshading between black and white.
Very shallow donors in n-type GaAs
Authors: Benzaquen M. , Walsh D.
Published: July 2002

The presence of an unusually shallow donor, with 1.5–2 meV binding energy, in high-mobility GaAs grown by gas-source molecular-beam epitaxy, has recently been inferred from electrical transport and photoluminescence measurements by Cunningham and co-workers [Appl. Phys. Lett. 53, 1285 (1988)]. We show that the data provided in support of the existence of a donor with this binding energy is not sufficient to draw such a conclusion.
Piezoelectricity in electrically oriented films of poly-α-isobutyl-L-aspartate
Authors: Prieto A. , Perez R. , Subirana J. A.
Published: July 2002

Highly piezoelectric films of poly (α-isobutyl-L-aspartate) have been prepared from a solution in chloroform which was allowed to evaporate in a 2600-V/cm electric field, with the field direction parallel to the casting surface. The resulting oriented film has a macroscopic symmetry ∞2 (D∞), as revealed by x-ray diffraction, with a C∞ axis along the direction of the applied electric field. The shear piezoelectric constant d14 has a value of 11.2 pC/N measured at a frequency of 4 Hz.
Epitaxial NiSi layers on 〈111〉-oriented Si obtained by pulsed laser irradiation
Authors: Baeri P. , Grimaldi M. G. , Priolo F. , Cullis A. G. , Chew N. G.
Published: July 2002

Thermally grown NiSi layers on (111) Si substrates have been irradiated by 35-ns Nd laser pulses in the energy density range of 0.3–2.0 J/cm2. The duration of the laser-induced melt was monitored in situ by transient reflectivity measurements. Samples have been subsequently analyzed by Rutherford backscattering in combination with channeling and by transmission electron microscopy. It is shown that laser irradiation in a narrow energy density range results in the formation of a novel epitaxial NiSi phase on (111) Si. Electron microscopy studies show that this silicide phase could have a cubic symmetry with a lattice constant very similar to that of Si. This phase is, however, metastable and it transforms into the orthorhombic one upon thermal annealing at about 300 °C.
Mössbauer study of the thermally induced transformation of the Fe0.91B0.09 rapidly quenched crystalline alloy
Authors: Fernández van Raap M. B. , Sánchez F. H.
Published: July 2002

The transformation of the Fe0.91B0.09 rapidly quenched crystalline alloy from its original metastable state to its equilibrium state has been studied by Mössbauer effect spectroscopy. It was found that the alloy transforms in a single step from a fine dispersion of orthorhombic-Fe3B-like complexes embedded in metallic bcc iron to a system consisting of Fe2B precipitates in the α-Fe matrix. The kinetics and temperature dependence of the process have been measured. It was determined that the relative fraction of Fe2B increases as Ω=1−exp(−kt3/2) with k=k0 exp(−Ea/kBT), indicating a diffusion-controlled, Arrhenius-type transformation, where k0=(1.92±0.26)×1014 s3/2 and Ea=(3.56±0.07) eV/atoms. Magnetization versus temperature scans have been simulated and compared to previously measured scans. A simple picture of the transformation process is given.
Effects of methylarsine homologs (CH3)nAsH3−n on the metalorganic vapor-phase epitaxy of GaAs
Authors: Lum R. M. , Klingert J. K. , Kisker D. W.
Published: July 2002

We have investigated the methyl derivatives of arsine, (CH3)nAsH3−n (n=1–3), in metalorganic vapor-phase epitaxy of GaAs to determine the effects of the degree of hydrogen atom substitution on film properties. Direct comparisons were obtained in the same reactor under identical conditions of the thermal decomposition and growth characteristics of the methylarsine reactants and arsine. The relative thermal stability of the As precursors, AsH3>MenAsH3−n>Et3As>t-BuAsH2, did not correlate with differences observed in their film growth rates. The quality of GaAs films grown with the methylarsines was limited by both the incorporation of carbon from the precursor reactant itself, and by extrinsic donor and acceptor contaminants present in the source material. Film electrical properties appeared to be dominated at low temperatures (<650 °C) by the thermochemistry of the methylarsine species, and at higher temperatures by the doping characteristics of the extrinsic impurities.
On the nature of photoreflectance line shape in GaAs
Authors: Gal M. , Shi R. , Tann J.
Published: July 2002

The photoreflectance (PR) spectra of epitaxial GaAs layers were studied, with emphasis on the sharp ‘‘spike’’ that has been previously observed in the PR spectra of some GaAs samples. By chemically etching the surface of our samples, we were able to separate the ‘‘spike’’ from the rest of the line shape. We conclude that this ‘‘spike’’ is associated with doping inhomogeneities in the samples.
The formation of thin-film tungsten silicide annealed in ultrahigh vacuum
Authors: Siegal M. P. , Graham W. R. , Santiago J. J.
Published: July 2002

Thin films of tungsten silicide have been formed by sputter depositing 710 Å of W metal onto (100)-oriented, 3–7 Ω cm, p-type silicon wafers. The samples were annealed in an ultrahigh vacuum ambient (pressure≤1.0×10−9 Torr) at temperatures ranging from 845 to 1100 °C for 30 s. The lack of oxygen contamination in the ambient allows the W-Si interaction to proceed, first producing both the W-rich W5 Si3 phase and the tetragonal WSi2 phase near 900 °C, followed by only the tetragonal, low-resistivity (30–40 μΩ cm) WSi2 phase above 1000 °C. This result is in contrast to previous work where films formed by rapid thermal processing in vacuum showed no significant W-Si interaction for temperatures below 1100 °C due to the formation of an interfacial oxide diffusion barrier gettered into the films from the 10−6 Torr ambient.
Temperature formation of the inversion layer in metal-oxide-semiconductor structures: Theoretical model and application to the determination of minority-capture cross sections of the gold acceptor level in silicon
Authors: Vuillaume D. , Lannoo M. , Bourgoin J. C. , Rosencher E.
Published: July 2002

We study the formation of the inversion layer in metal-oxide-semiconductor (MOS) capacitors under reverse dc bias as the temperature is scanned from low (100-K) to high (400-K) values. It gives rise to a capacitance step on the capacitance-temperature (C-T) characteristics and to an artifact peak in the deep-level transient spectroscopy (DLTS) spectra. A theoretical simulation of the C-T characteristics, taking into account the generation of minority carriers via deep states in the bulk substrate and via interface states, is in good agreement with the experimental results. We describe accurately the evolution of the inversion charge from an exact determination of the depth limits in the space-charge region between which a single energy level behaves as a generation center. Moreover, we propose a method using C-T measurements, DLTS, and C-T simulations by our model to determine the minority-carrier capture cross section of bulk defects in the semiconductor substrate of the MOS capacitors. We successfully apply this method to determine the hole-capture cross section of the gold acceptor level in n-type silicon.
Radio-frequency probe for plasma conductivity measurements. II. Application to an electron beam created plasma in oxygen
Authors: Zeller P. , Pointu A. M.
Published: July 2002

Calculations establishing the principles of a radio-frequency coil to measure the electron characteristics of a plasma column have been discussed in the previous article. They are illustrated by an application to a low-pressure oxygen plasma created by an electron beam of some keV. Original experimental apparatus and methodology are described. Electron densities of the order of 1011 cm−3 and electron temperatures around 0.15 eV are readily measured.
Photoluminescence decay time studies of type-II GaAs/AlAs quantum well structures
Authors: Sturge M. D. , Mackay Janet L. , Maloney Colette , Pribram J.K.
Published: July 2002

This is a comment on a paper with the same title by Dawson et al. [J.Appl. Phys. 65, 3606 (1989)], which argues that the nonexponential decay of X-point excitons in type-II GaAs/AlAs superlattices previously reported by one of us [E. Finkman, M. D. Sturge, and M. C. Tamargo, Appl. Phys. Lett. 49, 1299 (1986)] is due to spectral diffusion within the inhomogeneous line, and that where diffusion is absent, the decay is exponential. We report time decay measurements as a function of excitation intensity on the samples used by Dawson et al., and on similar ones from a different source. We find that at very low intensities the results agree with those of Finkman et al., while at high intensities they agree with Dawson et al. We argue that spatial fluctuations in the transition matrix element due to irregularities in the interfaces are responsible for the nonexponential behavior, and that the change at high intensity is due to delocalization of excitons and consequent spatial averaging of the transition matrix element.
Quantum interference effects in transient electronic transport
Authors: Poole D. R. , Bandyopadhyay S.
Published: July 2002

A simple quantum-mechanical model is presented for simulating transient electronic transport in disordered mesoscopic structures in the absence of phase-randomizing inelastic collisions. We have applied this model to study the time-dependent decay of an electron’s momentum in ultrasmall GaAs structures with various impurity concentrations. As expected, we find that the momentum decay rate (and hence effectively the mobility) depends sensitively on the exact locations of the impurities within the structure because of long-range phase coherence. We also find that the momentum relaxation rate, calculated quantum mechanically, is larger than the ‘‘semiclassical’’ rate calculated from Fermi’s Golden Rule possibly because of coherent backscattering that gives rise to the Anderson localization effect.
The steady-state model for coupled defect-impurity diffusion in silicon
Authors: Morehead F. F. , Lever R. F.
Published: July 2002

We extend and generalize our earlier model which was proposed to explain tails in the diffusion profiles of high-concentration boron and phosphorus in silicon. Our quasi-steady-state approach is generalized here to include both vacancies (V) and interstitials (I) at equivalent levels. I-V recombination is regarded as near local equilibrium, occurring through reactions of the defects with defect-impurity pairs. This approach leads to important details such as the well-known plateau, kink, and tail in high-surface-concentration P diffusions in Si, and to the less well-recognized tails in B as well, with no additional ad hoc assumptions. Our extended model, in its simplest form, allows a more complete and less restrictive treatment than the usual models of Au in-diffusion in Si. An important advantage is the direct inclusion of these defect-impurity interactions and the resulting gradients in the defect concentrations, which are ignored in even the latest versions of popular process simulation programs, such as suprem iv.
Quantum well emission transistor with tunneling output current
Authors: Grinberg A. A. , Kastalsky A. , Shantharama L. G.
Published: July 2002

We propose a novel tunneling quantum well emission transistor (TQWET), in which the gate-induced modulation of the Fermi level in the quantum well leads to a strong variation of the tunneling current to the collector through the specially designed collector barrier. The device is calculated to possess a high transconductance and a large current drive. Low-temperature utilization of the transistor implies a high electron mobility in the quantum well (QW) and, therefore, low lateral resistance along the QW, a major current and speed limitation of the device. With this limitation taken into account, the TQWET shows the delay times ∼1.4 and 1.5 ps for temperatures 10 and 77 K, respectively.
Shubnikov–de Haas measurements on n- and p-type HgTe-CdTe superlattices
Authors: Seiler D. G. , Ward G. B. , Justice R. J. , Koestner R. J. , Goodwin M. W. , Kinch M. A. , Meyer J. R.
Published: July 2002

Oscillatory magnetoresistance (Shubnikov–de Haas) measurements have been used to determine free-carrier effective masses in HgTe-CdTe superlattices. Measurements on an n-type superlattice yield an electron mass that is in excellent agreement with theoretical results from a tight-binding band-structure calculation. The p-type data are more complex, showing evidence for a light-hole mass at low magnetic fields and a much heavier mass at fields above 2.0 T. This finding is also in agreement with the predictions of band-structure theory.
Nonlinear effects and transient response of interband and subgap photoconductivity in polycrystalline silicon
Authors: Bock W. , Prettl W.
Published: July 2002

The steady-state photoconductance and the transient photoresponse of boron-doped polycrystalline silicon films have been measured as a function of intensity at photon energies above and below the band gap applying several semiconductor lasers. The intensity dependence of the dc photosignal and the transient behavior are distinctly different for interband and subgap excitation. A kinetic model taking into account grain boundary as well as bulk carrier generation and recombination has been developed describing the observed nonlinear and transient effects consistently. The experimental results yield the density of occupied and unoccupied trap states, absolute values for the optical absorption cross section and thermal capture cross sections and relaxation time constants.
Proposed new resonant tunneling structures with impurity planes of deep levels in barriers
Authors: Arsenault C. J. , Meunier M.
Published: July 2002

Theoretical calculations of the transmission coefficient and the current density using a transfer matrix method are presented for several resonant tunneling structures in which impurity planes of deep levels (IPDL) are incorporated. Increases of several orders of magnitude in the width of the resonant peak, as well as in the peak current density, are obtained as compared to conventional double barrier resonant tunneling structures. Furthermore, an optimal position of the IPDLs is obtained in order to maximize the width of the resonant peak. Our results suggest that the incorporation of impurity planes of deep levels can considerably improve the characteristics of resonant tunneling devices.
Kinetic study by viscosity measurements on direct synthesis of gallium antimonide
Authors: Kakimoto Koichi , Hibiya Taketoshi
Published: July 2002

Reaction kinetics for the direct synthesis process of compound GaSb from Ga and Sb metals was studied by observing viscosity changes of the melt during the reaction process. The mole fraction of Ga (cGa) was obtained during synthesis using the equation; log η=cGa(log ηGa +log ηSb)+(1−2cGa)log ηGaSb, where η is the viscosity of the total system, and ηGa,ηSb, and ηGaSb are the viscosities of molten Ga metal, molten Sb metal, and molten GaSb, respectively. The reaction rate was obtained from the variation of the mole fraction of reactant cGa. Assuming a second-order reaction, the activation energy was estimated to be 15.5 kcal/mol.
Oscillator strengths, quantum efficiencies, and laser cross sections of Yb3+ and Er3+ in III-V compounds
Authors: Auzel F. , Jean-Louis A. M. , Toudic Y.
Published: July 2002

An absolute oscillator strength is obtained for the first time for a rare earth in a III-V compound semiconductor. The value for Yb3+ in InP is f=(3±1)×10−6. It is of same order as for insulating ionic hosts, confirming what available theory can predict. From observed emission spectra, laser cross sections of 10−21 cm2 for Yb3+ at 1.0 μm and <1.4×10−20 cm2 for Er3+ at 1.54 μm are obtained. Yb3+, entering III-V compounds more covalently, presents a quantum efficiency for direct photon excitation two orders of magnitude smaller than Er3+. Predicted laser gains are in the range of 10−2 to a few 10−1 cm−1, showing that gains will be marginal in semiconductor devices of usual dimensions.
Interfacial roughness in InAs/GaAs heterostructures determined by soft x-ray reflectivity
Authors: Woronick S. C. , Yang B. X. , Król A. , Kao Y. H. , Munekata H. , Chang L. L.
Published: July 2002

X-ray reflectivity has been used to determine interfacial roughness of as-grown 250-Å-thick InAs overlayers deposited on GaAs substrates by molecular-beam epitaxy under differing growth and substrate conditions. Results indicate that in each case the top surface was smooth, but that the buried interface separating these highly lattice-mismatched materials exhibits root-mean-square roughness parameters in the range of 10–19 Å. As-stabilized growth produced the roughest InAs-GaAs (buried) interface, while In-stabilized growth on a slightly misoriented substrate produced the smoothest InAs-GaAs interface.
Phase-locking of a triangular loop with three Josephson junctions having zero capacitance
Authors: Ichikawa Fusao , Aomine Takafumi
Published: July 2002

A voltage-locking of a triangular loop containing three Josephson junctions with zero capacitance has been studied by calculating phase-space trajectories. Attractors show that there are both phase-locking and quasiperiodicity in the region of the uneven changes. It is found from the figure of applied current versus winding number that phase-locking occurs in some intervals of an applied current.
Ytterbium as a probe of the local lattice environment in GaxIn(1−x)P crystals
Authors: Kozanecki A. , Kaliński Z. , Raczyńska J. , Langer J. M.
Published: July 2002

Environmental effects in the intraimpurity emission of Yb3+(2F5/2-2F7/2 intracenter transition) in GaxIn1−xP (0<x<0.3) bulk crystals are reported. Cationic disorder manifests itself in the appearance of line splittings and substantial broadening of all the emission lines with increasing Ga contents. Spectra of the crystals with small Ga contents are dominated by emission from two types of centers. One, typical of InP:Yb, corresponds to Td symmetry, while the second is most likely due to a Yb center perturbed by the presence of a single Ga atom in the next-nearest-neighbor position (Yb-P4-In11-Ga).
The negative glow in a magnetic field in a helium discharge
Authors: Cohen C. , Kagan Yu. M. , Avivi P.
Published: July 2002

The negative-glow plasma in a magnetic field of an inverse-brush cathode discharge has been studied by absolute emission spectroscopy. The absolute density of the levels was measured as a function of the distance from the cathode for different currents, pressures, and magnetic fields. A comparison of line emission from the positive column and the negative glow in helium has been made both with and without a magnetic field. A simple theoretical model is presented in order to explain the experimental results.
Modeling the diffusion of hydrogen in GaAs
Authors: Morrow Richard A.
Published: July 2002

Concentration depth profiles of carriers (or of electrically active defects) and/or deuterium in GaAs following exposure to a hydrogen plasma (or, in one case, to molecular hydrogen) are fit using a simple diffusion model with second-order reactions. We find that (1) the activation energy for hydrogen diffusion and the dissociation energies of hydrogen-defect complexes are dependent on the concentration of hydrogen, (2) there is no molecular hydrogen formation and no fast-diffusing species of hydrogen away from the near-surface region, and (3) atomic hydrogen can in-diffuse and passivate EL2 defects when semi-insulating GaAs is annealed at a high temperature in a molecular hydrogen ambient.
Theory of intensity-dependent optical activity in dilute composites
Authors: Stroud D.
Published: July 2002

We propose a new method to create a medium with an intensity-dependent optical activity. The medium consists of a dilute suspension of nonlinear, but optically inactive particles, such as crystallites of CdSxSe1−x, in a linear but optically active host. We derive formulas for calculating the intensity dependence of the optical rotatory power in the dilute limit, and apply these formulas to calculate the optical rotation of a model dilute composite.
Characterization of AlGaAs/GaAs heterojunction bipolar transistors and circuits by localized filtered low-temperature cathodoluminescence
Authors: Dubon-Chevallier C. , Papadopoulo A. C. , Bresse J. F. , Duchenois A. M.
Published: July 2002

Cathodoluminescence (CL) performed at low temperature has been used for the characterization of the fabrication technology of circuits implemented with heterojunction bipolar transistors. The cathodoluminescence signal from each GaAs layer has been identified. Different ion implantation masks, which protect the structure and the integrated resistors during the ion-implantation step used for device insulation, have been investigated. Thin bilayers have to be used for the fabrication of the integrated resistors to obtain uniformity adequate for integrated circuits operation. Thicker bilayers are necessary in order to achieve an effective protection of the bottom and top layers of the mesa. CL results have been compared with electrical measurements showing a very good correlation. Its ability to obtain different penetration depths and to perform CL images as well as secondary- or backscattered-electron images makes of the CL technique a powerful microcharacterization method.