bluuebunny/crossref_metadata_2025 huggingface dataset:
Equivalence of donor and acceptor fits to temperature-dependent Hall data: General case
Authors: Look D. C.
Published: July 2002

Recently, it was shown that the usual statistical-mechanical formulation used to fit carrier concentration versus temperature data cannot distinguish between the donor or acceptor nature of one single-charge-state center. Here we generalize that result to include any number of donor and acceptor centers, of arbitrary charge multiplicity, and also show how that by fitting one particular case (e.g., every center assumed to be a donor), all of the other possible cases can be immediately solved by inspection.
Effect of interface structure on photoluminescence of InGaAs/GaAs pseudomorphic single quantum wells
Authors: Devine R. L. S. , Moore W. T.
Published: July 2002

Photoluminescence studies have been carried out on InGaAs pseudomorphic single quantum wells grown on GaAs by molecular beam epitaxy. Linewidths as narrow as 2.0 meV have been observed. The spectra typically consist of two peaks which on certain samples can be explained by intrawell thickness variations of one monolayer. On other samples the results are more consistent with exciton trapping at islands having a smaller lateral extent than the exciton Bohr radius.
Thermophotometric study of phase transformations in silver-zinc alloy thin films
Authors: Maeda Y. , Minemura T. , Andoh H.
Published: July 2002

The transformations between β1, ζ, and β phases in a sputter-deposited Ag-50 at. % Zn alloy thin film were examined by a developed thermophotometric apparatus. Good observations were made using the change in reflectivity of the thin film with temperature and time, and some characteristic transformation behaviors in the thin film were made clear. Kinetics of the β1→ζ transformation were analyzed using the Johnson–Mehl–Avrami equation. The activation energy obtained from the relaxation time measured at different temperatures was 220.6 kJ/mol. It was much larger than that in the bulk. The time exponent of the equation was 1.51. This shows that the ζ phase nucleates at the grain edge and/or the boundary of the β1 phase after site saturation under a zero nucleation rate. The activation entropy was a large positive value, and the transformation interface was expected to have a complicated structure.
Distribution of recombination coefficients of hole traps in phosphorus-doped hydrogenated amorphous silicon
Authors: Oheda Hidetoshi
Published: July 2002

Dispersiveness of the transient secondary photocurrent in phosphorus-doped hydrogenated amorphous silicon (a-Si:H) was discussed. Because the recombination kinetics in the system are bimolecular and, as shown previously, the excess electrons are in a quasithermal equilibrium between the conduction band and shallow traps within a very short period of time after pulsed excitation, it has been inferred that the dispersiveness of the transient secondary photocurrent can be attributed to a distribution of recombination coefficients of excess trapped holes. Following this result, the rate equations for representing relaxation processes of excess carriers, including the bimolecular recombination process, were analyzed and the procedure for evaluating the distribution of recombination coefficients of excess trapped holes was derived. The transient secondary photocurrents of phosphorus-doped a-S:H with different doping levels were analyzed according to the proposed method. Two components were noticed in the spectrum of the distribution of recombination coefficients; the main component was located in the range of 10−11–10−9 cm3 s−1 and the additional component was located in the range of 10−14–10−12 cm3 s−1. From the discussion about these results, combined with the results previously obtained, it was concluded that those distributed values of the recombination coefficients were those of the two hole traps in phosphorus-doped a-Si:H.
Origin of field-enhanced conductivity in amorphous hydrogenated silicon
Authors: Zhang D. H. , Haneman D.
Published: July 2002

It is shown that the phenomenon of field-enhanced conductivity in amorphous hydrogenated silicon films is due to alkali atom contamination from hot glass substrates. The various electrical phenomena can be explained by a reaction between alkali atoms and dangling bond sites in which alkali ions are formed and the dangling-bond-state distribution altered. The rate of the reverse reaction is reduced by applied fields, leaving an increase in conductivity that can be orders of magnitude in size.
High-forward-voltage junction capacitance including effects of excess carrier storage in electron-hole plasma
Authors: Liou J. J. , Lindholm F. A.
Published: July 2002

A previous quasistatic junction space-charge region capacitance model is improved by including the Fermi statistics and energy band-gap narrowing that occurs in electron-hole plasmas. The model is applicable for junctions under large forward voltages. A factor of 2–4 is predicted when the present capacitance model is compared with the previous capacitance model.
Electromagnetic wave generation utilizing plasma instabilities
Authors: Murukesapillai K.
Published: July 2002

A new device for the production of microwave radiation is proposed. The device exploits the electromagnetic instabilities of nonequilibrium plasmas. The plasma parameters are chosen in such a way as to avoid electrostatic instabilities. The main advantage of the proposed device over other microwave production devices is that in the former case one can achieve very high-power densities in the active medium and utilize large volume of the same. This opens the way to the generation of much larger amounts of microwave power than before. A linear stability analysis of a homogeneous magnetized plasma having anisotropic velocity distribution shows that a plasma of volume 104 cm3 immersed in a magnetic field of 1 T and having parallel and perpendicular temperatures of 1 and 2 keV, respectively, is capable of emitting about 0.4 kJ of energy in microwave form in a time span of about 10−10 s.
Matching beams from relativistic electron guns into solenoidal transport systems
Authors: Miller R. B. , Poukey J. W. , Shope S. L. , Mazarakis M. G.
Published: July 2002

In this paper we develop a new approach for controlling the electron trajectories in a relativistic electron beam diode which is based on appropriately contouring an externally generated, axial magnetic field. The technique provides a convenient method of matching a beam produced by a shielded source injector into a uniform solenoidal transport system of a linear induction accelerator. To illustrate the method, we analyze a simple diode geometry and compare the analytical results with trajectory code calculations.
Pressure dependence of the nonradiative lifetime in GaAs/AlGaAs double-heterostructure lasers
Authors: Heasman K. C. , Blood P. , Adams A. R. , Fletcher E. D.
Published: July 2002

We have measured the linear losses in a GaAs/AlGaAs double-heterostructure laser as a function of applied hydrostatic pressure. The nonradiative lifetime increases by a factor 2.5 from zero to 7.6 kbar, and if this is due to recombination via a deep state, then the rate-limiting capture cross section decreases with pressure, suggesting capture by multiphonon emission. We find that it is necessary to postulate the existence of other nonlinear losses at threshold to account for the increase in threshold current with pressure measured on the same structure. Carrier transfer to higher conduction-band minima in the active or cladding regions are suggested as possible mechanisms.
Anisotropically etched deep gratings for InP/InGaAsP optical devices
Authors: Koch T. L. , Corvini P. J. , Tsang W. T.
Published: July 2002

We report a new grating fabrication technique for optical devices in the InP/InGaAsP system. Conventional, but very shallow, holographically defined wet etching is used to pattern ultrathin masking layers grown by chemical beam epitaxy. This is followed by selective and anisotropic wet etching, which is shown to yield exceptionally deep, narrow-pitch gratings with reproducible profiles and dimensions.
CO2 laser processing of diffusion induced lattice imperfections in silicon: Experiment and theory
Authors: James R. B. , Geist G. A. , Young R. T. , Christie W. H. , Greulich F. A.
Published: July 2002

The high-temperature diffusion of phosphorus into crystalline silicon causes the formation of electrically inactive phosphorus-rich precipitates near the surface. These precipitates decrease the carrier lifetime and mobility in the diffused layer, and thus lead to less than optimal diode characteristics of electrical junctions formed by diffusion of phosphorus into a p-type substrate. We show that the free-carrier absorption of a CO2 laser pulse can be used to completely dissolve the precipitates and remove dislocations in the diffused layer. Furthermore, we find that there are distinct advantages in depositing the pulse energy by way of free-carrier transitions, since the energy can be preferentially deposited in either confined doped layers or diffusion wells that are surrounded by lightly doped material. Our transmission electron microscopy results show that the annealing of the extended lattice defects is caused by melting of the near-surface region and subsequent liquid-phase epitaxial regrowth. Van der Pauw measurements are used to study the carrier concentration, mobility, and sheet resistivity of the samples before and after laser irradiation. The results of the electrical measurements show that there is a large increase in the carrier concentrations and a corresponding drop in the sheet resistivities of the laser irradiated samples. Using a Fourier transform

infrared spectrometer, we find that significant changes occur in the transmittance and reflectance spectra after CO2 laser annealing. Secondary ion mass spectrometry measurements are used to determine the redistribution of the phosphorus as a function of the pulse energy density. A time resolved pump-and-probe technique is utilized to measure the threshold for the onset of surface melting and the melt duration. We find that for energy densities greater than about 3 J/cm2, the reflectivity of the probe laser (at 633-nm wavelength) jumps rapidly to 70%, which is consistent with the reflectivity of liquid silicon. The interpretation of the laser induced changes in the electrical, optical, and structural properties is based on a thermal model, in which surface melting occurs for incident pulse energy densities exceeding a threshold value. Comparative calculations are reported for the melt depths and duration of surface melting, and good agreement is found. Other calculated results for the transient heating and cooling of the near-surface region are also reported.
Mode conversion in a cylindrical waveguide with periodic step changes in the radius
Authors: Schill Robert A. , Seshadri S. R.
Published: July 2002

For the transverse electric modes having azimuthal variation in a cylindrical waveguide with periodic step changes in the radius, the propagation of the modal voltages and currents is investigated. The transfer coefficients are deduced and their values are explicitly determined for small relative changes in the radius. The theory is applied to treat a mode converter in which there is a selective interaction between two forward traveling modes, and the theoretical results are compared with available experimental observations.
Fluid flow in a random porous medium: A network model and effective medium approximation
Authors: Blumenfeld Raphael , Bergman David J.
Published: July 2002

Fluid flow through a random porous medium is discussed in the context of a network model of a diluted array of planar cracks by an effective medium approximation. We find the threshold concentration of cracks pc above which flow occurs. It turns out to be much higher than the bond percolation threshold. The existing cracks are assumed to have a range of thicknesses. The flow permeability is found as a function of the concentration for a number of crack thickness distributions. Near the threshold, anomalous critical behavior, in the form of a nonuniversal critical exponent for the permeability, is found to occur even for a family of nonsingular thickness distributions.
Laser-induced melting of predeposited impurity doping technique used to fabricate shallow junctions
Authors: Sameshima T. , Usui S. , Sekiya M.
Published: July 2002

Shallow p+ junctions have been fabricated using a new technique in which doping is accomplished by depositing boron film on a silicon surface by radio-frequency glow discharge (rf-GD) and melting locally with a pulsed XeCl excimer laser. Sheet resistivity as low as 15 Ω/⧠ was obtained by irradiation of a single laser pulse. The junction depth was 0.07–0.3 μm, depending on the laser energy density. Electrical characteristics of p+-n junctions which were formed by the laser doping technique subsequently subjected to a 400 °C, 1-h furnace anneal show essentially ideal diode behavior with an ideality factor of 1.03.
Transport mean free path related to trajectory patterns: Comparison of nonrelativistic and highly relativistic electron penetration through matter
Authors: Liljequist D. , Ismail M.
Published: July 2002

This analysis is based on the similarity between multiple scattering and slowing down (random walk) processes described by the same transport mean-free-path function λtr(s) (s=path length). We discuss the connection between λtr(s) and the characteristic appearance and scale of the trajectory pattern. Straggling is considered by means by stochastically discontinuous λtr(s) functions. In the application to electron penetration, we show that while nonrelativistic electron penetration is modeled by λtr=(r−s)/α, where r is the range and α is a material-dependent dimensionless constant, highly relativistic electron penetration is modeled by λtr∝exp(−s/Λ), where Λ is a length characteristic for the penetrated material. The respective trajectory patterns are distinctly different. The effect of straggling on the trajectory pattern in the highly relativistic case is demonstrated by means of a simple model of the stochastic λtr(s) behavior.
Self-consistent Monte Carlo study of high-field carrier transport in graded heterostructures
Authors: Al-Omar A. , Krusius J. P.
Published: July 2002

Hot-electron transport over graded AlxGa1−xAs heterostructures is investigated using the self-consistent ensemble Monte Carlo method. A new formulation of the carrier transport based on a semiclassical limit of a position-dependent k⋅p two-valley Γ-L energy-band model and the phonon spectra has been developed. Quantum mechanical reflection, and ohmic contacts preserving the stochastic nature of carriers at device boundaries have been included. Using this formalism, nonequilibrium hot-carrier transport for the compositionally graded barrier diode and the heterojunction ballistic launchers is examined. Results show that transport across compositionally graded semiconductors structures cannot be described with thermionic drift diffusion. Heterostructure launchers are shown to generate a ballistic electron fraction as high as 15% and 40% of the total electron population for 300 and 77 K, respectively, but simultaneously reduce macroscopic average currents and carrier velocities. The decay length of the ballistic electron fraction is less than 200 nm for temperatures as low as 77 K. The width of the ballistic peak in the electron distribution is 60 meV and the contribution of the ballistic electrons to the total current as large as 78% at 77 K for an applied voltage of 1 V.
Characterization of biphase heterogeneous media using a numerical processing method
Authors: Delebarre C. , Rouvaen J. M. , Bruneel C. , Frohly J.
Published: July 2002

The ultrasonic nondestructive characterization of heterogeneous media is difficult due to the inherent inhomogeneity of the material. Previous studies have shown that the amplitude information is not fully correlated to the medium characteristics. Our main interest is to evaluate the mean spacing between heterogeneities randomly distributed in the medium. The mean spacing between heterogeneities is related to the autocorrelation function for the echoes. However, this function in the case of highly heterogeneous media does not reflect the medium characteristics: the impulse response of the whole measurement set (especially the transducer) biases the obtained signature. Our studies are based upon the introduction of an original method giving a nonbiased signature of highly heterogeneous media derived from the spectrum of the rf backscattered signal. This signature immediately gives the mean heterogeneities spacing parameter.
Coupled and energy-trapped thickness vibrations in piezoelectric crystal plates
Authors: Lee P. C. Y. , Guo X. , Tang M. S. H.
Published: July 2002

Simple form solutions are obtained for approximate two-dimensional equations of motion and dominant conditions for free edges of energy-trapped thickness vibrations of piezoelectric crystal plates. The resulting algebraic frequency equations are employed to calculate frequencies of fundamental and anharmonic overtones of thickness-shear vibrations in infinite quartz strips of SC cut with a pair of free edges and in rectangular AT-cut quartz plates with all four edges free. For circular quartz disks with free edge, frequencies of fundamental and harmonic overtones of thickness shear in AT cut, and frequencies of fundamental and anharmonic overtones of thickness shear in BT cut are computed. Presently predicted results are compared with either previously calculated results or existing experimental data. It is found that comparison is very close for all these cases.
Backscattering of a short ultrasonic pulse from thin cylindrical shells
Authors: Talmant M. , Quentin G.
Published: July 2002

We study the backscattered signal from thin cylindrical shells irradiated by short ultrasonic pulses. Various materials (duraluminum, stainless steel, copper) and various thicknesses of the shells are considered. The shells are filled with air and immersed in water except in one experiment where the surrounding medium is ethanol. From the experimental results, we deduce the variations of the group velocity of the waves circumnavigating the shell. Two such waves are observed experimentally and their dispersion curves are compared with those of the waves propagating in plates immersed in the same fluid.
Double-crystal x-ray investigations of semi-insulating (Ga,Fe) double-doped InP substrates
Authors: Haji L. , Caulet J. , Auvray P. , LeCorre A.
Published: July 2002

We report further x-ray double-crystal diffractometry experiments on the structural perfection of the semi-insulating (Ga, Fe) double-doped LEC-grown InP substrates. Series of x-ray reflection topographs were taken at different settings on the rocking curves using the double-crystal arrangement in parallel setting. Variations in lattice-plane spacings and lattice-plane orientations induced by Ga inhomogeneity were determined. (In, Ga)As layers grown by molecular-beam epitaxy on (001) oriented (Ga,Fe) double-doped InP substrates were also characterized.
Dynamics of a triangular loop containing three Josephson junctions with zero capacitance
Authors: Ichikawa Fusao , Aomine Takafumi , Hosogi Shinya
Published: July 2002

Dynamical properties of a triangular loop, each side of which consists of one Josephson junction with zero capacitance and inductance, are considered in this paper. For two kinds of applied currents, phase-time and current-voltage relations are calculated by integrating a set of derived nonlinear differential equations numerically. Time dependence of a fluxoid number in the loop is given by phase-time relations, and it is found that the calculated current-voltage relations exhibit uneven changes slightly above the threshold current for the voltage shifting from two to three junctions. The analytical result for the threshold currents under some conditions is in good agreement with the numerical one.
Different types of domain structures in 〈110〉 iron whiskers
Authors: Fuertes J. F. , Tejedor M.
Published: July 2002

Different types of magnetic-domain structures, depending on the dimensions, history, and perfection of the samples, are possible in the same external field in 〈110〉 iron whiskers. Estimations of the energies involved in the formation of every domain structure proposed, are made. Special attention is paid to the influence of the crystal dimensions in the domain formation. Some experimental results are reported and discussed.
Ordering and stability of Pb1−xEuxTe alloys
Authors: Salamanca-Young L. , Partin D. L. , Heremans J.
Published: July 2002

We have observed two kinds of ordering in Pb1−xEuxTe alloys using transmission electron microscopy. One kind of ordering corresponds to long wavelength periodicities of ∼18 Å that are observed for x∼0.4–0.51 along the 〈110〉 and 〈111〉 directions. This ordering is similar to that of spinodal decomposition observed in metallic alloys and is explained by a composition as well as interplanar spacing modulation. We have also obtained electron diffraction patterns from these alloys that show weak diffraction spots with reciprocal lattice vectors that are not allowed for the PbTe structure. The observation of these extra spots can be explained by assuming that the Pb1−xEuxTe alloy forms an ordered compound or superlattice with lattice constants that are multiples of the lattice constants of PbTe. We also present models for the structure of these superlattices.
Compensation ratios in high-purity InP using an improved Hall measurement technique
Authors: Whitney Peter S. , Uwai Kunihiko
Published: July 2002

Temperature-dependent Hall measurements were conducted on several high-purity n-type InP epitaxial layers grown by metalorganic chemical vapor deposition with the aim of clarifying the relationship between the 77-K Hall mobility, the free-carrier concentration, and the compensation ratio in high-purity InP. An improved method of Hall analysis for high-purity epitaxial layers was used which greatly reduces errors associated with depletion effects, as well as those associated with interfacial inhomogeneities in the growth direction. The method is essentially a modified version of the differential profiling method in which the difference between two successive Hall measurements, one before, and one after a controlled etch, is used to infer the properties of the portion of the epilayer removed during the etch. From curve fitting of the neutrality equation to the results of the temperature-dependent Hall measurements, the compensation ratios were estimated and compared to estimates obtained from previously reported calculations of the 77-K Hall mobility. The results are found to agree well with recently reported calculations for which the acoustic deformation potential and piezoelectric constant were assumed to be 6.5 eV and 0.01, respectively.
Properties of CO2 laser produced long-life plasmas observed by x-ray spectroscopic methods
Authors: Daido Hiroyuki , Nishihara Katsunobu , Mima Kunioki , Kitagawa Yoneyoshi , Nakai Sadao , Yamanaka Chiyoe , Hasegawa Akira
Published: July 2002

We present the properties of shell confinement long-life plasmas produced by a CO2 laser. The temperature measurement for parylene shell targets based on the x-ray spectroscopic method gives the electron temperature of more than 500 eV at the center of a 1-mm-diam target. An enchanced confinement time is obtained in a thick gold shell (100 μm thick) target coated internally with parylene. The duration of the x ray emitted from the hot core in a 3-mm-diam target of this type is 34 ns, while the laser pulse duration is 1 ns. The long duration of the x-ray manifests the hot core plasma lifetime; the observed duration presents a strong evidence of thermal insulation by the self-generated magnetic field.
Optimization of gas mixtures for electron-beam-controlled diffuse discharge opening switches
Authors: Korzekwa R. , Schaefer G. , Kristiansen M.
Published: July 2002

Electron-beam-controlled diffuse discharges are promising candidates for high-power opening switches in inductive energy storage circuits. An additive of an attaching gas must be used to obtain short opening times when the electron beam is turned off. A high switch efficiency requires low loss operation during conduction. This paper presents methods to optimize gas mixtures for such discharges. Gas mixtures utilizing one or two attaching gases are used and the effect of gas additives which influence the drift velocity is investigated. Experiments on the Jsw-E/N characteristics, the dc E/N breakdown limit, and the glow-to-arc transition E/N limit depending on the energy loading of the discharge are presented and the implications of these results to opening switches are discussed.
Laser-induced fluorescence study of Penning collision of Hei 23S atom with Xe in He+Xe gas discharge plasma
Authors: Shindo Haruo , Arinaga Kenji , Manabe Kazutaka , Uchiike Heiju , Fukushima Yoshifumi , Tamaru Takeshi
Published: July 2002

This paper presents an experimental result on the population of the 23S of Hei in He+Xe gas discharge. The laser-induced fluorescence method was used to find the behavior of the 23S population, and a strong coupling of the 23S with 23P state enabled us to determine the 23S population from the measurement of Hei 5876 Å (23P–33D). The discharge condition considered ranged from 0.2 to 5 Torr in pressure and 20 to 260 mA in discharge current. The measured population of the 23S state in the Xe-mixed condition showed a significant reduction at the pressure of 3 and 5 Torr, but not when the pressure became as low as 0.2 Torr. It was demonstrated that the overall behavior of the observed population was quantitatively explainable with an inclusion of the Penning collision of the 23S with the Xe atom.
Annealing effect on the resistivity of polycrystalline silicon films passivated with plasma-deposited silicon-nitride films
Authors: Saito Yoji , Iio Nobuhiro , Kameshima Yuji , Takeda Ryo , Kuwano Hiroshi
Published: July 2002

The thermal annealing effect on resistivity is investigated for polycrystalline silicon films passivated with plasma-enhanced chemically vapor deposited silicon-nitride (p-SiN) films. The resistivity in the heavily doped polycrystalline silicon films has a minimum value at an annealing temperature of approximately 500 °C, and the resistivity in the lightly doped films monotonically increases with the increase of annealing temperature. The dependence of the resistivity on annealing temperature is explained in terms of the variations of the density and the energy level of the traps at the grain boundaries, which are caused by the adsorption or the decomposition of hydrogen atoms. These conclusions are obtained by comparing the dependence in the polycrystalline silicon films with  p-SiN films with that in the plasma-hydrogenated polycrystalline silicon films without  p-SiN films.
A comparison of the spectroscopic properties of Eu3+-doped fluoride and oxide glasses under high-power, picosecond-pulse excitation
Authors: Quarles Gregory J. , Suchocki Andrzej , Powell Richard C.
Published: July 2002

The frequency harmonic outputs of a Nd:YAG laser were used to excite Eu3+ ions in fluoride and oxide glasses with high-power, picosecond pulses. Time-resolved fluorescence spectra, fluorescence lifetimes, and rise times were measured on the fluoride glass to obtain information about the two-photon absorption transitions and the radiative and radiationless decay processes. The results show the importance of coherence in the intermediate state of the two-photon transition observed with 532.0-nm pumping. Multiphoton pumping with 345.7-nm excitation results in spectral shifts and lifetime changes which are attributed to local polarization effects. Similar experiments were performed on the oxide glass, and the results were found to be significantly different because of the more efficient radiationless decay processes in the oxide host compared to the fluoride host.
Theory of extrinsic oscillatory photoconductivity in polar semiconductors
Authors: Kartheuser E. , Schmit J. , Evrard R.
Published: July 2002

An analytical model for the oscillatory behavior of the photoconductivity excitation spectrum in the photoconductivity of polar semiconductors is presented. The model is a simple version of the theory by Stocker and Kaplan [Phys. Rev. 150, 619 (1966)], modified to include the effects of thermal longitudinal optical phonons. The theory is applied to the case of n-type CdTe. Comparison with the experimental results of Nicholas et al. [J. Phys. C 13, 5215 (1980)] suggests the existence of three trapping mechanisms: phonon-assisted trapping by donor levels lying, respectively, at Ee=3 meV and E0=12 meV below the conduction band edge, and a direct capture by very shallow states acting on the slow electrons at the bottom of the band. A value of τ=2.2×10−12 s is obtained for the average lifetime of the electrons in the conduction band.
Abrupt interface AlGaAs/GaAs heterojunction bipolar transistors: Carrier heating and junction characteristics
Authors: Ramberg Lennart P. , Ishibashi Tadao
Published: July 2002

We have fabricated and characterized a series of abrupt interface Npn AlGaAs/GaAs single heterojunction bipolar transistors in which the aluminum arsenide mole fraction in the emitter has been varied in the range 0% to 55%. Tunneling through the spike in the emitter conduction band is shown to be important. It affects the initial energy of carriers that are injected into the base, their effective mass distribution, and also the collector turn-on voltage. Hot electron injection heats the minority carriers in the base. In an Al0.35Ga0.65As emitter device held at room temperature we have optically measured a carrier temperature Tc=640 K. From diffusive transport theory it follows that the carrier heating reduces the base transit time by 70%. The elevated carrier temperature in this device is shown to be confirmed by the gain (hFE=3500). The gains of all the other devices are limited by imperfect injection efficiencies. Although electroluminescence (EL) spectra reveal that hole injection into the bulk of the emitter takes place in low aluminum composition structures, space-charge recombination is shown to be a more important mechanism. Appendices present Richardson’s constant for AlGaAs as a function of composition and the derivation from EL spectra of the ratio of electron-to-hole current across a heterojunction.
Controlled CO2 laser melting of silicon
Authors: Sheik-bahae M. , Kwok H. S.
Published: July 2002

The application of a CO2 laser to the controlled melting of doped silicon surfaces was studied theoretically and corroborated with previous experimental results. Because of the lack of interband transition at 10.6 μm, energy deposition was dominated by free-carrier absorption, which could be affected by the doping concentration and the dopant spatial distribution. It was shown that for undoped samples, avalanche ionization played an important role in the initiation of the melting process. In most cases, melting could be induced on the surface without concomitant laser breakdown. The resolidified surface remained smooth under scanning electron microscopy examination. The effect of pulse duration on the controlled melting of silicon was also studied in detail. It was found that ultrashort CO2 laser pulses could melt silicon without breakdown damage over a wide range of intensities and sample impurities. For nanosecond duration pulses, similar intensity ranges were not available, except for highly doped samples.
Wavelength dependence of short-circuit current decay in solar cells
Authors: Ray U. C. , Agarwal S. K.
Published: July 2002

The short-circuit current decay technique has been used in the literature to determine the minority-carrier lifetime in the base of solar cells. The dependence of the short-circuit current decay on the wavelength of the excitation light is reported in detail. Both the theoretical expressions and experimental results are presented. The experimental results agree reasonably well with the theory.
Quasistatic capacitance of p/n junction space-charge layers by the Leibnitz rule
Authors: Lindholm F. A. , Liou J. J.
Published: July 2002

The Leibnitz rule of integral calculus yields a useful expression for the quasistatic capacitance versus voltage characteristic of a p/n junction space-charge layer that holds for all doping profiles and for forward as well as for reverse applied voltages. This capacitance is the sum of two components. One accounts for the incremental mobile charge within the volume of the layer. The other accounts for the incremental mobile charge at its edges.This expression enables novel analytical characterizations and interpretations of numerical solutions.
Thermal conductivity of single-crystal barium fluoride
Authors: Morelli D. T. , Heremans J.
Published: July 2002

We have measured the thermal conductivity κ of a single crystal of barium fluoride from room temperature down to 20 K. This material is used as a substrate for growth of PbTe and other semiconductor materials with applications as electronic devices. The room temperature value of κ is 0.07 W cm−1 K−1, and the thermal conductivity increases as temperature is lowered. At 20 K, the onset of a peak is observed, with a maximum value of approximately 13 W cm−1 K−1. The results are compared with existing data in the literature, and a fit to the data assuming Umklapp scattering of phonons is performed.
Cross-sectional transmission electron microscope study of intrinsic solid-phase epitaxial growth in self-ion-implanted (001) Si
Authors: Nieh C. W. , Chen L. J.
Published: July 2002

A cross-sectional transmisson electron microscope (XTEM) study of intrinsic solid-phase epitaxial (SPE) growth in self-ion-implanted (001) Si has been carried out. The activation energy of the self-ion-implanted silicon was measured to be 2.6±0.2 eV. The value is remarkably close to those obtained in the two most recent studies by other techniques. The pre-exponential factor is lower than that reported by Lietoila et al. [J. Appl. Phys. 53, 4399 (1982)] annealed under similar conditions. The variation in proximity to the surface and difference in the distribution of the microstructural defects in the two studies are suggested to be possible causes for the discrepancy. The advantages of utilizing the XTEM technique to study epitaxial growth of self-ion-implanted amorphous thin films are demonstrated. The accuracy in the XTEM measurement of the SPE regrowth rate in Si+-implanted (001) Si is discussed.
Characterization of phosphorus liquid-metal ion source as a dopant source in focused ion beam systems
Authors: Higuchi-Rusli R. H. , Corelli J. C.
Published: July 2002

Characteristics of a phosphorus liquid-metal ion source (LMIS) for use in focused ion beam systems was investigated because of its potential as an n-type dopant for integrated circuit device fabrication. A continuous lifetime of more than 33 h was recorded as a part of the source stability measurement. Short-term stability measurements indicated a very stable beam emission during its operation. Three different emitter tip radii of 2.5, 5.0, and 10 μm were selected to examine phosphorus beam emission characteristics. Mass spectrum measurements were used to examine phosphorus ion content and beam stability by repeat scanning. Steep current-voltage characteristics were observed for 5.0- and 10-μm emitter tip radii. The beam purity was characterized with Auger electron spectroscopy and a scanning electron microprobe by analysis of the deposited beam on a flat silicon substrate. Microstructure analysis by optical metallography indicated no liquid-metal corrosion on the emitter tip. A thorough analysis was carried out on beam purity and metallurgical aspects of LMIS in order to develop a more reliable phosphorus liquid-metal ion source.
Spin-density wave in spin glasses (C
uMn) and other dilute alloys (YGd) (invited) (abstract)
Authors: Mydosh J. A.
Published: July 2002

Spin glasses have been of particular interest in magnetism for the past 15 years. Their present theoretical description, based upon a simple physical model, requires a fundamentally new type of statistical mechanics for its solution. Most experimental interpretations have attempted to follow this approach, although its physical meaning and direct comparison are partially obscured and somewhat strained. Almost 30 years ago Overhauser proposed a spin-density-wave (SDW) model which endeavored to explain the ‘‘antiferromagnetic’’ behavior in dilute alloys such as CuMn. In the intervening period the spin-glass phenomenon has mainly evolved unconnected with the SDW approach. However, in recent times a series of neutron-scattering experiments has renewed the connection and introduced the distinction between a ‘‘long-range’’ SDW as found in YGd and the ‘‘short-range’’ SDW of the spin glasses, e.g., CuMn. It is the purpose of this paper to review the available evidence for a SDW mechanism in these dilute alloys relying not only on neutron-scattering data, but also on macroscopic measurements such as specific heat, magnetization, and susceptibility. Here clear-cut differences arise between the long-range and short-range SDW’s which are related to the glassy dynamics of the latter systems.
High-pressure operation of a beam diode for relativistic electron beams
Authors: Matsuzawa Hidenori , Akitsu Tetsuya
Published: July 2002

A beam diode was operated successfully at a pressure as high as 10−1–10−2 Torr of gases (He, H2, Ne, N2, CO2, and SF6). Each gas had its optimum pressure pm at which electron beam currents were higher in peak values than those for conventional in-vacuum operation by a factor of 1.5 or more. A relationship pm×σ1.18H =const. was obtained where σH is the total ionization cross section in gases at some hundred keV. A model was proposed for such operations, and those high-pressure operations are preferable to the conventional if one needs higher currents.
Period competition in a stripe domain structure subjected to a periodic field
Authors: Molho P. , Porteseil J. L. , Souche Y.
Published: July 2002

The behavior of a parallel array of stripe domains subjected to a periodic field was studied. Experiments were performed on a layer of single-crystal ferrimagnetic garnet (bubble material) featuring in zero field a periodic pattern of parallel stripe domains. The layer was applied to a magnetic tape on which a sinusoidal waveform was recorded. The garnet-tape distance, and hence the interaction strength, could be varied. The resulting domain patterns were observed in polarized light. We present results obtained for a recorded wavelength (66 μm) equal to six times the natural domain period (11 μm). The domain structure adapted itself by reducing the number of stripes, in particular by means of dislocation glide in the stripe array. This resulted in various modulated stripe patterns. The transitions between structures with different stripe numbers could be observed. These were achieved by local distortions of the parallel array around dislocations. The total energy of the garnet layer was calculated as the sum of magnetostatic, wall, and interaction energies for various interaction strengths. The equilibrium domain configuration could be deduced by minimizing the energy with respect to wall positions. The calculated modulated domain structures are in agreement with the observed one.
Rb2Cu1−xCoxF4, a two-dimensional Ising spin glass
Authors: Dekker C. , Arts A. F. M. , de Wijn H. W.
Published: July 2002

We report on the dc susceptibility of the insulating spin glass Rb2Cu1−xCoxF4, with x=0.22. This model compound is a realization of the two-dimensional short-range Edwards–Anderson model, which has competing nearest-neighbor Ising interactions. Below a frequency-dependent freezing temperature spin-glass behavior is observed for longitudinal spin components only. The nonlinear part of the susceptibility is found to excellently obey static Tc=0 scaling with β=0.0±0.1 and Δ=3.2±0.2, in conformity with the Monte Carlo results for the two-dimensional Edwards–Anderson model, Tc=0, β=0, and Δ=3.5±0.5. These findings thus provide experimental evidence for the lower critical dimensionality for Ising spin glasses to exceed 2.
Effect of magnetic field cooling and magnetization anomaly in magnetic fluids near melting point
Authors: Miyajima H. , Inaba N. , Taketomi S. , Sakurai M. , Chikazumi S.
Published: July 2002

The magnetization process of ferrofluids with carrier fluids of water, paraffin, and alkylnaphtalene was investigated in a temperature range from 77 to 300 K as functions of the freezing rate and the intensity of cooling magnetic fields. A uniaxial magnetic anisotropy is induced by field cooling in frozen ferrofluids. This induced anisotropy which is caused by the formation of clustering of magnetic particles disappears on heating near the melting point. The magnetization of the frozen fluids exhibits an anomalous increase below the melting point of the carrier fluids. In a frozen state, no relative motion of particles, such as Brownian motion, occurs. With increasing temperature, the inhibited motion will be released gradually by the recovery of viscosity. The anomaly may be related to glassy transition and premelting. These magnetic properties are discussed in terms of mesoscopic phase transition between liquid and solid.
Electrical transport properties of thin epitaxially grown iron films on GaAs
Authors: Rachford F. J. , Rubinstein M. , Prinz G. A.
Published: July 2002

We have determined the components of the magnetoresistance tensor through fifth order in the magnetic direction cosines for four epitaxially grown iron films with thicknesses between 200 and 60 Å at 300, 77, and 4.2 K. We have also determined their magnetic anisotropy parameters from ferromagnetic resonance at 300 K. These phenomenological parameters provide an excellent description of the magnetic field dependence of the planar magnetoresistivity for electric current directed along the [001], [11̄0], and [11̄(2)1/2 ] directions and the applied fields necessary to produce spin flops.
Magnetothermal conductivity of ErAl2 for cryogenic applications
Authors: Zimm C. B. , Campenni C. K. , Barclay J. A.
Published: July 2002

The thermal conductivity K of rare-earth intermetallic compounds with magnetic ordering temperatures T0 below 100 K is a key parameter affecting their use in magnetic refrigerators and regenerators. We have measured the thermal conductivity of ErAl2, T0=12 K, between 5 and 170 K in 0- and 7-T applied magnetic fields. The zero-field results show a strong, 20-K-wide minimum in the thermal conductivity near the ordering temperature. The results at 7 T indicate that the magnetic field eliminates the minimum and produces a monotonic temperature dependence. We attribute these effects to magnetic scattering of electrons.
Pairing and magnetic instabilities in high T
c systems with finite U (abstract)
Authors: Fedro A. J. , Sinha S. K.
Published: July 2002

We consider the Anderson lattice for finite U using a novel equation of motion technique. The method employs a truncation scheme based on a projection operator which projects out of any operator its exact thermal average in the space of correlated single-particlelike excitations, i.e., excitations both in the presence and absence of the opposite spin state. Thus, this method is good for all U. This is important in these superconducting transition metal oxide systems since experimental evidence has shown that the bandwidth/U is not small. For the single-particle spectrum we naturally generate the anomalous correction induced pairing and resulting gap equation for finite U, in contrast to previous treatments based on the large-U limit, where on-site double occupancy is excluded. The magnetic and pairing susceptibilities are calculated in a similar manner, again for finite U, and the competition between these instabilities will be discussed.
Some novel melt-spun superconducting materials (abstract)
Authors: Inoue Akihisa , Matsuzaki Kunio , Masumoto T. , Rao K. V. , He Han Zeng , Chen D-X.
Published: July 2002

A new class of Fe-, Co-, Ni-, Cu-, and Ge-based ductile ribbons in which an amorphous matrix containing less than 12 vol. % of a fine dispersion of 0.1–3-μm size particles of immiscible elements M=Pb, Bi, Sn, or In have been produced by a modified melt-quenching technique. The Fe- and Co-based alloys containing Bi and Pb are found to be ferromagnetic above room temperature and also superconducting at temperatures in a range 7–9 K depending on the alloy. The saturation magnetization in these usual alloys range from 92 emu/gm for Co-Si-B-Pb-Bi to 15 emu/g for Fe-P-Pb-Bi at 77 K. At the superconducting transition the resistivity typically is found to drop by 2–3 orders of magnitude with a transition width ∼0.5 K before the ‘‘zero’’ resistance value is reached. In all the alloys studied the T dependence of the resistivity shows a typical metallic behavior despite its high magnitude (a few thousand μΩ cm in some cases). Extremely high values are found for the upper critical fields (1.6–1.72 T at 4.2 K) with critical current densities typically around 1.3×107 A m−2 at 4.2 K. For Ge-Pb-Bi-Sn Hc2 values of 5 T are obtained at 3 K. Along with detailed studies of magnetic and superconducting properties, extensive TEM, and x-ray characterization data will also be presented. Attempts to explain the above described behavior in terms of proximity, percolation, and surface properties at the dispersed Pb, Bi particles are found to be unsatisfactory. As far as we know there exists no theory that can explain the co-existence of ferromagnetism and superconductivity of the type described above. Time permitting, we will also discuss our recent work on high Tc oxide materials produced by melt-quenching techniques. Thus amorphous composite materials exhibiting unique and useful characteristics which cannot be achieved for homogeneous amorphous alloys can be produced by melt quenching. These materials are of importance both for scientific and engineering points of view.
Superconducting and magnetic properties of RBa2Cu3O7−x compounds
Authors: Shaheen S. A. , Jisrawi N. , Lee Y. H. , Croft M. , McLean W. L. , Zhen H. , Rebelsky L. , Horn S.
Published: July 2002

Superconducting properties of RBa2Cu3O7−x compounds (R=Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Yb) have been studied by dc electrical resistivity and ac magnetic susceptibility techniques. Except for R=La, which is superconducting below 50 K, RBa2Cu3O7−x compounds exhibit sharp resistive and inductive transitions in the 90-K range. The nearly constant value of Tc for magnetic R ions indicates a very weak interaction between R ions, as anticipated from the known crystal structure of these materials. The effects of annealing in oxygen and argon, and air quenching, on the superconducting properties are also discussed.
Iron-vacancy-oxygen complex in silicon
Authors: You Zhi-pu , Gong Min , Chen Ji-yong , Corbett J. W.
Published: July 2002

The interaction between iron and defects produced by electron irradiation in iron-doped silicon has been observed by using deep-level transient spectroscopy. A new electron trap level due to the iron-vacancy-oxygen complex [Fe+(V⋅O)] was detected at Ec−0.36 eV. The role of the A center (V⋅O) in the formation of the complex was confirmed by the observation that during low-temperature annealing (<150 °C) the increases in the concentration of the [Fe+(V⋅O)] complex was accompanied by an equal and opposite change in the concentration of the A center. Besides the interaction with the A center, iron was found to influence the annealing behavior of the divacancy and E center.
Observation of gas-phase Si atoms in the chemical vapor deposition of silicon from dichlorosilane
Authors: Ho Pauline , Breiland William G.
Published: July 2002

Gas-phase silicon atoms have been observed during the chemical vapor deposition (CVD) of silicon from SiH2Cl2 in helium at 625 Torr total pressure. The silicon atoms are products of gas-phase reactions as evidenced by a maximum in the relative density profile. Under identical deposition conditions, SiH2Cl2 CVD yields Si atom densities that are one to two orders of magnitude smaller than those observed during SiH4 CVD.