bluuebunny/crossref_metadata_2025 huggingface dataset:
Heavy doping of GaAs and AlGaAs with silicon by molecular beam epitaxy
Authors: Heiblum M. , Wang W. I. , Osterling L. E. , Deline V.
Published: February 2003

Heavy Si doping of GaAs and AlGaAs grown by molecular beam epitaxy has been studied. By using a slow growth rate of 1000 Å/h, the electron concentration obtained for GaAs was 1.1×1019 cm−3, which is higher than the previously reported limit of 5×1018 cm−3. The accumulation of excess Si near the surfaces of GaAs and AlGaAs has been identified by secondary ion mass spectroscopy. A Si-induced 3×2 surface structure has been observed, and the influence of arsenic to gallium flux ratio on the surface morphology is discussed. Photoluminescence spectra of the doped layers are presented.
Shock reverberations in tantalum
Authors: Mock Willis , Holt William H.
Published: February 2003

Shock reverberations near the Hugoniot elastic limit were produced in a tantalum disk by impacting it with an alpha titanium disk at a velocity of 0.111 km/s in a gas gun. The free-surface velocity of the impacted 3.73-mm-thick tantalum disk was measured with a capacitor gauge. An initial shock compressive stress slightly larger than the measured 2.1-GPa Hugoniot elastic limit was produced in the tantalum. The shape of the free-surface-velocity profile suggested that spall fracture did not occur in the specimen disk at this stress level. This result was verified by examining the recovered and sectioned disk.
Effects of overdriven shock states on the equation of state of 9404 explosive
Authors: van Thiel M. , Lee E. L. , Cochran S.
Published: February 2003

Shock wave data above the Chapman Jouguet state of 9404 have been corrected with an improved molybdenum standard equation of state that includes an explicit description of its strength. The results indicate that a large second derivative of pressure with respect to volume is needed to join the isentrope constructed from the Hugoniot data to the expansion isentrope of the Jones–Wilkins–Lee equation of state (EOS) in use now. Possible reasons for this abnormal behavior in the EOS are discussed.
Improvement of the performance of particulate phthalocyanine photovoltaic cells by the use of polar polymer binders
Authors: Minami Nobutsugu , Sasaki Kanji , Tsuda Keishiro
Published: February 2003

Effects of binder polymers on the performance of phthalocyanine photovoltaic cells have been investigated. The cells were fabricated by dispersing metal-free phthalocyanine fine particles in a binder polymer and sandwiching them between aluminum and In2O3 electrodes. Polymers such as poly (vinylidene fluoride), poly (vinyl fluoride), polyacrylonitrile, poly (4-vinylpyridine), poly (p-vinyl phenol), and poly (vinylidene chloride) were found to give a larger photocurrent and a higher conversion efficiency than did others. This is attributable to the enhancement of exciton dissociation due to a large electric field formed by the presence of polar groups in these polymers. An estimation based on a simple assumption showed that an electric field as high as 106 V/cm may be produced in the microenvironment of a photoactive site, strong enough to induce such an effect.
Observation of a two-dimensional electron gas in a GaAs1−yPy–GaAs (y=0.25) strained layer superlattice
Authors: Ludowise M. , Dietze W. T. , Lewis C. R. , Gavrilovic P. , Hsieh T. C. , Hess K.
Published: February 2003

The first observation of a high-mobility, two-dimensional electron gas in a modulation-doped, strained GaAs–GaAs1−xPx (x=0.25) superlattice is reported. Electron sheet concentrations of n=6.4×1011 cm−2 and mobilities (4 K) of μ=1.2×104 cm2 V−1 S−1 are measured.
A study of interface states in metal-GaAs 〈110〉 structures by Schottky capacitance spectroscopy
Authors: Chekir F. , Barret C. , Vapaille A.
Published: February 2003

A study of the capacitance of a forward biased Schottky diode as a function of bias, temperature, and frequency allows characterization of interface states at the metal-semiconductor junction. This method, called Schottky Capacitance Spectroscopy is applied to interfaces obtained by evaporating Au, Ag, or Al onto n-type cleaved GaAs 〈110〉 surfaces. We have explored the region of the semiconductor band gap about 1 eV below the conduction band minimum. There is evidence of three kinds of states. The energy levels of these states are quite reproducible while we have obtained a light dispersion of density of states and capture cross sections. Moreover, we have observed a correlation between the relative density of states C and the degradation of the I–V characteristic.
New model for the temperature coefficient of resistivity of polycrystalline films: Application to alkaline-earth metals
Authors: Renucci P. , Gaudart L. , Petrakian J. P. , Roux D.
Published: February 2003

The temperature coefficient of resistivity (tcr) is deduced for various temperatures from measurements of the resistivity of polycrystalline and continuous thin calcium films. It is shown that the single layer model derived from the Mayadas and Schatzkes (MS) theory is not sufficient to obtain the tcr of the bulk material from results on polycrystalline films. A new three-layer model based on nucleation processes and film growth is developed. It is assumed that an intermediate and inhomogeneous medium whose resistivity is a function of the ordinate in the film takes place between the island-like structure and the continuous one. The resistivity of the third and upper layer which has a really continuous and polycrystalline structure is deduced and used in the MS model to represent the resistivity of an infinite polycrystalline film. Then we calculated the tcr  β0 of bulk calcium for various temperatures and we found a very good agreement with previous values of Kayser and Soderquist studying the bulk material directly. Moreover this model is tested on sputtered aluminum films from the experimental results of Tellier and Tosser. With the same hypothesis as for calcium, it is shown that bulk electrical properties of Al can also be deduced from those of polycrystalline films using this three-layer model; in this case a good agreement between the three- and the two-layer model is observed.
Electrical properties of amorphous tantalum pentoxide thin films on silicon
Authors: Oehrlein G. S. , Reisman A.
Published: February 2003

The electrical characteristics of Al/Ta2O5/Si metal-insulator-semiconductor (MIS) capacitors were studied. Ta2O5 thin films on n- and p-type silicon had been prepared by thermal oxidation of sputter or electron-beam deposited Ta films. The direct current leakage was found to be about 3×l0−6 (Al positive) or 6×l0−5 A/cm2 (Al negative) at an applied field of 1 MV/cm. The breakdown strength is between 3 and 4 MV/cm (Al negative on p-type Si). The dielectric constant is 22–30 when measured at 1 MHz. The flat-band voltage is positive (+0.81±0.09 V) and exhibits an instability with respect to voltage-time stresses at room temperature. It can shift to more positive (maximum shift ∼−2 V) or more negative values (maximum shift ∼-2 V), depending on the conditions of the voltage-time stress. A post-metal (after the deposition of the Al electrodes) anneal of the MIS structure at 400 °C for 30 min in 90% Ar–l0% H2 yields a negative flat-band voltage (−0.08±0.11 V) and partly removes the instability.
Low temperature laser quenching studies of superconducting Mo–N and Mo–C alloys
Authors: Sekula S. T. , Thompson J. R. , Beardsley G. M. , Lowndes D. H.
Published: February 2003

Concentrated alloys of Mo1−x Nx and Mo1−x Cx were produced in near-surface layers by implantation of the respective ionic species into Mo foils or films at elevated temperatures. Subsequently the materials were rapidly heated and ‘‘laser quenched’’ while affixed to a substrate at 5 K. In situ measurements of the superconductive transition temperature after laser irradiation showed increases in Tc to ∼6.5 K for a range of compositions x>30 at. % for both N and C implanted foils. For x<30 at. % little change was observed. Finally, the Tc of a Mo–C film with x=43 at. % rose to 12.0 K following 0.5 J/cm2 of incident energy from the Q-switched ruby laser.
Surface pinning of superconducting Nb–Ta alloy
Authors: Matsushita T. , Honda T. , Hasegawa Y. , Monju Y.
Published: February 2003

Surface irreversibility of cold-rolled Nb–50 at. % Ta was investigated by using an ac measuring method. Deformation was varied from 0% to 95%. Both the surface and bulk critical current densities increased remarkably and were then saturated to almost the same value as the deformation was increased. A change in the surface critical current density over almost three decades due to dislocations nucleated by deformation cannot be explained by mechanisms other than surface flux pinning. Close correspondence of the deformation dependence of the two critical current densities also confirms this hypothesis.
Thermal activation from the fluxoid and the voltage states of dc SQUIDs
Authors: Ben-Jacob E. , Bergman D. J. , Imry Y. , Matkowsky B. J. , Schuss Z.
Published: February 2003

The probability density of thermal fluctuations about different types of nonequilibrium steady states of a dc SQUID are evaluated by generalizing a technique used before for the fluctuations of a single Josephson junction. Probability densities obtained for both ‘‘running’’ and ‘‘beating’’ modes are used to calculate thermal activation rates as well as the various branches of the I-V characteristic. The results are compared with the experiments of Voss et al. and good agreement is found.
Interface flux pinning in i
n s
i
t
u formed superconducting composites
Authors: Habbal F. , Bevk J.
Published: February 2003

Detailed flux flow studies of in situ formed wire and tape superconducting composites confirm our earlier findings that the filament-matrix interfaces are effective flux pinning centers. Angular dependence measurements on tape composites, where the ribbon-like filaments are parallel to the rolling plane, reveal a critical current anisotropy which depends on the magnetic field. The flux pinning force is also anisotropic; its complex field dependence, however, cannot be fully described using the existing flux pinning theories.
Low-field viscomagnetic behavior of annealed, quenched, and cold-worked polycrystalline nickel
Authors: Cho Seung-Am
Published: February 2003

Behavior of aftereffect in magnetization process of annealed, quenched, and cold-worked ferromagnetic polycrystalline nickel under constant applied fields is studied. The effect of relaxation of electronic circuit response of measurement system in the experiment is eliminated. The present results do not conform with the proposed early stage magnetization mechanisms such as interstitial atom diffusion, interstitial dumbbell rotation and dislocation interaction. The relaxations of all samples followed the Voigt–Kelvin-type viscoelastic behavior with a short unique time constant τ=1.50 sec for all samples.
Electron spin resonance study of oxygen donors in silicon crystals
Authors: Suezawa Masashi , Sumino Koji , Iwaizumi Masamoto
Published: February 2003

Measurements have been conducted on the electron spin resonance due to various types of oxygen donors (thermal, new, and deformation-induced donors) in Czochralski-grown silicon crystals of n type. g tensors determined for these donors all coincide well with that for phosphorus, the anisotropy being very small. Thus, the site symmetry of these oxygen donors is concluded to be very close to Td. From temperature dependence of the absorption, noninteracting paramagnetic spins are shown to reside on new and deformation-induced donors. Contrarily, spins interacting in an antiferromagnetic manner are found to reside on thermal donors.
Internal strain and photoelastic effects in Ga1−xAlxAs/GaAs and In1−xGaxAsyP1−y/InP crystals
Authors: Adachi Sadao , Oe Kunishige
Published: February 2003

A method for calculation of photoelastic coefficients in III-V compounds at energies below the direct band edge is presented. Spectral dependence of the photoelastic-coefficient data is analyzed on the basis of simplified model of the interband transitions. The theoretical prediction shows a quite good agreement with the experimental data of III-V binaries. This model is applied to Ga1−xAlxAs ternaries lattice-matched to GaAs and to In1−xGaxAsyP1−y quaternaries lattice-matched to InP. A method for analysis of the internal-strain induced effects in elastically-deformed heterostructure crystals is also discussed in detail.
Luminescence and impurity states in CuInSe2
Authors: Rincón C. , González J. , Sánchez Pérez G.
Published: February 2003

The photoluminescence spectrum of melt-grown n-CuInSe2 single crystal at 7 K, has been determined near the fundamental absorption edge. Three peaks, at approximately 0.980, 0.990, and 1.013 eV, have been observed. Considering the transition probabilities of recombination processes, donor-to-acceptor pair and the corresponding free-to-bound transitions have been identified. From the data, an absorption edge at (1.023±0.003) eV, a donor state at (10±2) meV, and an acceptor state at (33±2) meV have been determined.
An absolutely timed x-ray streak camera for laser fusion experiments
Authors: Letzring S. A. , Thorsos E. I. , Friedman W. D. , Seka W. , Rizzo J. E.
Published: February 2003

We report on the design and performance characteristics of an absolutely timed x-ray streak camera. The camera displays UV(4ω) laser fiducials along side multichannel x-ray streaks thus allowing absolute timing of the x-ray signals relative to the laser pulse. As illustration, the implosion times of spherically irradiated microballoons have been measured with this instrument and the results agree well with hydrocode predictions.
Time dependence and diffraction efficiency of optically-induced phase gratings in nematic liquid crystal films
Authors: Fuh Y. G. , Code R. F. , Xu G. X.
Published: February 2003

The time dependence and diffraction efficiency of optically-induced phase gratings in thin films of the nematic liquid crystals 5CB and 6CB are reported. The experimental results are in quantitative agreement with a three-dimensional model for the induced grating. This analysis provides an independent determination of the elastic constants K2 and K3 as well as a vicosity coefficient ν̄.
Radiation induced electron traps in silicon dioxide
Authors: Schmitz W. , Young D. R.
Published: February 2003

Trapping of electrons injected from an avalanche generated in the silicon substrate, into a thermally grown silicon dioxide film was used to investigate the effect of penetrating radiation (x rays; Cu target) on the electron transport properties of the oxide. Experiments with samples of different SiO2 thicknesses indicate that two sets of neutral centers are generated by the x rays which are still present after a 450 °C post metallization anneal in N2: one is uniformly distributed across the oxide with a cross section (σ) of 1.7×10−16 cm2; the second with σ=1.6×10−15 cm2 is concentrated near the silicon–silicon dioxide interface. This conclusion is supported by the results of photocurrent-voltage measurements. The photocurrent-voltage data also appear to indicate that x rays produce other traps near the gate electrode. Annealing the sample in N2 at 1000 °C before exposure was found to yield a distinct reduction in the density of the traps generated by subsequent irradiation of the samples by x rays. Optimal results were reached after ∼2 h. A discussion of a possible intrinsic mechanism and of a water related impurity model to explain the observed behavior is presented.
Variation of the midgap electron traps (EL2) in liquid encapsulated Czochralski GaAs
Authors: Taniguchi M. , Ikoma T.
Published: February 2003

We have characterized the midgap electron trap (so far believed to be EL2) in liquid encapsulated Czochralski GaAs by measuring deep level transient spectroscopy spectra, and found more than two midgap electron traps which can be classified into two groups. A trap belonging to the first group is rather stable in its properties and the other is unstable. The capture cross section of the levels in the latter group varies continuously in depth from the surface and also is changed by thermal annealing. We discuss these characteristics in connection with growth conditions.
Transport processes at grain boundaries in polycrystalline material under optical illumination
Authors: Mataré H. F.
Published: February 2003

Transport properties at grain boundaries in polycrystalline material, especially silicon, are reviewed. The type of grain boundary is defined which can give rise to the remarkable effects which characterize the so-called ‘‘electrically active’’ grain boundaries as they appear less frequently in silicon than in germanium and III-V compounds. The usual description of the recombination flow in grain boundaries (gb) is viewed from the point of view of anisotropy of conductance as it prevails in ‘‘active gb’s.’’ Experiments are discussed where such active gb’s have been used as vertical junction extensions with the result of increased solar cell efficiency, a possibility postulated earlier. For a pure tilt boundary, the case of nonsymmetrical photon injection is quantified. Effects of the barrier voltage change and attendant increase of interface charge density, minority carrier lifetime, and mobility at the gb core are discussed. Finally the lateral current through a bicrystal is expressed as a function of barrier height and lateral voltage, generated by photon injection.
Velocity diagnostics of mildly relativistic, high current electron beams
Authors: Shefer R. E. , Yin Y. Z. , Bekefi G.
Published: February 2003

We describe two diagnostic methods for measuring the velocity components of mildly relativistic, high current electron beams. The first involves a measurement of the radial electrostatic potential and of the beam current and yields the time resolved, spatially averaged axial beam velocity v∥. The second requires a measurement of the beam cyclotron wavelength in the guiding magnetic field and yields a spatially averaged product γv∥, where γ=(1−v2⊥/c2−v2⊥/c2)−1/2 and v⊥ is the transverse beam velocity. By combining the two techniques we obtain v∥ and v⊥ for a 0.4–1.2 MV electron beam carrying a current of 1–2 kA.
Studies of the effects of a long pulse electron beam on the autoaccelerator
Authors: Lockner T. R. , Friedman M. , Palmadesso P. , Kusse B. R.
Published: February 2003

The propagation of a long pulse (600–800 ns) electron beam in an evacuated drift tube and accelerator gap geometries has been studied. Particular attention has been focused on the drift tube and gap surfaces since formation of plasma here will effect the operation of accelerators such as the Autoaccelerator. Experimental evidence of energetic electron and ion flux to the wall have been obtained. These and other measurements have led to a model describing the space-charge neutralization of the beam and its effect on accelerator operation.
First-order model of the change with refractive index of the frequency of semiconductor lasers
Authors: Sommers H. S.
Published: February 2003

The derivative with refractive index of the frequency of a spectral line of a diode laser is deduced from a model of the internal structure as a rectangular dielectric waveguide. It is found that the derivative depends critically on the spreading of the optical field beyond the guide walls. If the field is strictly confined to the interior of the guide, the derivative depends on only the change of the index inside the guide, and it is negative. If the field extends appreciably outside the guide walls, the derivative depends on changes of the index outside as well as inside the guide, and it varies rapidly with guide design. For lasers operating in the fundamental spatial mode, its numerical value can be appreciably less than for a closely confined mode and its sign can be either negative or positive. Relating the results to frequency modulation of the fundamental mode laser suggests that its sign can change with dc bias, and also its magnitude.
Performance of an array of plasma pinches as a new optical pumping source for dye lasers
Authors: Rieger Harry , Kim Kyekyoon
Published: February 2003

A new optical pumping source consisting of an array of plasma pinches in the hypocycloidal-pinch geometry is employed to pump a variety of dye lasers. A dye cuvette is inserted along the symmetry axis of the plasma device such that it may be surrounded by the plasma pinch. The light from the plasma pinch is very intense and rich in ultraviolet, which makes it an attractive optical pumping source for dye lasers, particularly in the blue-green spectral region. Control of the plasma fluorescence is achieved by the choice of gas, its fill pressure, and the capacitor bank voltage and its stored energy. The rise time of this ‘‘plasma flashlamp’’ depends mainly on the gas species and the fill pressure. Output energy of ∼2 mJ per cm3 of lasing medium, or 2 kW/cm3 for a 1-μs laser pulse, is obtained from rhodamine 6G, coumarin 480, LD 490, and coumarin 504 dyes. That both the coumarin 480 and rhodamine 6G lasers have the comparable output power is a direct proof that the present optical pumping source is more efficient than the commercial xenon flashlamps in pumping lasers in the blue-green spectral region.
Strain-induced effects in GaAs directional coupler switches
Authors: Benson T. M.
Published: February 2003

Metal-gap directional coupler structures have been fabricated on n/n+ GaAs layers. Coupling lengths measured by a sequential cleaving technique are found to be dependent upon metal thickness. Strain-induced refractive index changes are shown to be the dominant cause of waveguiding.
Technique for estimating space-charge densities in systems containing air ions
Authors: Kaune William T. , Gillis Murlin F. , Weigel Richard J.
Published: February 2003

The exact analysis of electrified systems containing air ions is difficult because of the interdependence between the system electric-field and space-charge distributions. A technique is described in this paper for estimating space-charge densities in unipolar and bipolar systems of air ions. A formula is introduced for systems containing only one ionic species which relates the space-charge density at a point P to the space-charge density at the ionic source and the transit time required for an ion to move from this source to P. In systems where air flow determines ionic velocities, transit times can be directly estimated. For other systems, a lower bound for the ionic transit time is derived and used to set an upper bound on the ionic space-charge density. Two general results are derived for systems containing several species of ions during steady-state zero-wind conditions: the conversion of only a relatively few small ions into large ions, through collisions with condensation nucleii, results in dramatic reductions in small-ion space-charge densities; many bipolar systems may be broken into subsystems which can be analyzed using unipolar methods.
Analysis of air ions in biological exposure systems, near HV dc electric power transmission lines, in rooms containing ion generators, and near exposed humans and animals
Authors: Kaune William T. , Gillis Murlin F. , Weigel Richard J.
Published: February 2003

A number of systems containing space charge are analyzed using the transit-time technique developed in an earlier paper. (1) An inequality is derived for a room containing an air-ion generator which relates the ion source current to the minimum space-charge density. (2) Published wind-tunnel data are treated, and the characteristics of space-charge plumes produced downstream from localized corona and radioactive sources are explained. (3) Space-charge data published by other researchers can be evaluated; three examples are given, and in two of them published space-charge densities substantially exceed calculated upper-bound values. (4) Formulae are derived for the extrapolation of ground-level space-charge-density, electric field, and ion-current-density data to points above ground level; these formulae are useful for characterizing the three-dimensional environments in systems where only ground-level measurements are available. (5) A simple upper bound is derived for ground-level space-charge densities produced by high-voltage direct-current (HV dc) transmission lines, and it is shown that actual lines do produce densities closely approaching this upper-bound value. (6) The perturbed space-charge density at the surface of the body of an animal or human exposed to air ions and electric fields is estimated, and it is shown that perturbed and unperturbed space-charge densities are approximately equal for exposure conditions simulating those at ground level near HV dc transmission lines.
Wavelength modification (Δℏω=10–40 meV) of room temperature continuous quantum-well heterostructure laser diodes by thermal annealing
Authors: Meehan K. , Holonyak N. , Burnham R. D. , Paoli T. L. , Streifer W.
Published: February 2003

Data are presented showing that wavelength modification, of at least 210 Å (from 8180 to 7970 Å), of broad area room temperature pulsed quantum well heterostructure (QWH) laser diodes is possible by thermal annealing. Thermal annealing at 900 °C for 8 h results in only a minor change in the threshold current density, 385–425 A/cm2, thus making possible similar wavelength modification (8180–8080 Å) of continuous (cw) 300 K stripe-geometry QWH laser diodes.
Circuit effects on Pierce instabilities
Authors: Raadu M. A. , Silevitch M. B.
Published: February 2003

The role of the Pierce instability in the formation of double layers is considered and compared with that of the Buneman instability. Pierce instabilities have been identified in a double-layer experiment, where they lead to ion trapping. Here the effects of external circuit elements are considered. In the case of immobile ions the onset criteria are unaffected, but in the unstable range the growth rate is reduced by the external impedance. Required experimental values of the circuit elements are estimated. The possible relevance to computer simulations is noted.
Self-developing UV photoresist using excimer laser exposure
Authors: Deutsch T. F. , Geis M. W.
Published: February 2003

Nitrocellulose functions as a self-developing photoresist which can be patterned using pulsed excimer laser radiation. The material exhibits a threshold fluence for ablation of 20 mJ/cm2 at a wavelength of 193 nm; this threshold results in higher contrast than can be obtained with most conventional photoresists. The effect of varying the laser wavelength has been examined. A simple model of ablative development has been used to predict the etch rate. The processing stability of the resist has been increased without changing the optical development rate by the addition of a dopant. The resolution of the resist is better than 0.3 μm.
Temperature dependence of the electrical characteristics in Au-n-type InP Schottky diodes
Authors: Hattori K. , Yamasaki T. , Uraoka Y. , Fujii T.
Published: February 2003

The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of Au-n-type InP Schottky diodes are measured over the temperature range 120–300 K. It is found that apparent barrier heights qφB obtained from I-V curves increase linearly with increasing temperature. The intercept voltage V0 of the 1/C2 vs V curve is observed to decrease with increasing temperature. The quantity q(V0+Vn+kT/q) shows a linear temperature variation, where qVn denotes the semiconductor Fermi level. Theoretical analysis is also developed, including the effects of an interfacial layer between the metal and semiconductor. Increase in qφB with temperature is due to the presence of the electron tunneling barrier in the interfacial layer. It is shown that the temperature variation of the barrier height qφB0 is closely related to that of q(V0+Vn+kT/q): for a sufficiently thin interfacial layer, we have dqφB0/dT ≊dq(V0+Vn +kT/q)/dT<0. As the interfacial layer is thick, ‖dqφB0/dT‖ becomes small, and we have dq(V0+Vn+kT/q) /dT<dqφB0/dT<0.
Ar ion bombardment effects of NbN/Pb Josephson junctions with plasma oxidized barriers
Authors: Hikita Makoto , Takei Koji , Igarashi Masaru
Published: February 2003

Details of the relation between Ar ion bombardment effects on NbN surface and I-V characteristics of NbN/Pb junctions with plasma oxidized barriers have been studied. NbN base electrodes, which behave as a strong coupling superconductor (Tc>15 K, 2Δ/kTc=4.2–4.3), were prepared onto substrates at 300 °C by reactive dc magnetron sputtering. In the NbN/Pb junction fabrication, cathode self-bias voltage VCSB during Ar sputter cleaning strongly influences the subgap leakage current value, which increases with VCSB . The VCSB also influences normalized normal tunnel resistance ARNN. It is found, in reflection electron diffraction and x-ray photoelectron spectroscopy studies, that the Ar ion bombardment at VCSB> 200 V on a NbN surface produces an amorphous structure in the surface layer. It is also found that the thickness of amorphous layer increases with Ar ion energy. Based on the experimental results, low subgap leakage current junctions, where Vm exceeds 100 mV at 4.2 K, were fabricated under low energy plasma oxidation conditions, where Vm is the product of Josephson critical current and subgap resistance. Sputter cleaning and plasma oxidation conditions for obtaining high quality junctions are also discussed.
Magnetic properties of sputtered Co-Pt thin films
Authors: Kitada Masahiro , Shimizu Noboru
Published: February 2003

Magnetic properties of sputtered Co-Pt thin films, and the relation between the properties and the film microstructures were studied. Thin films obtained by sputtering a Co-Pt alloy containing 5–35 at. % Pt exhibited high coercivity. A coercivity of 1800 Oe was obtained as the maximum value for a composition of Co-20 at. % Pt, while the remanence of the film was about 9500 G. Thin film coercivity was affected by ultimate vacuum pressure before the introduction of sputtering gas. Film coercivity also increased with an increase in the average grain diameter of the films.
Optical absorption of liquid phase epitaxial garnet films at 1.3-μm wavelength for magneto-optic application
Authors: Hibiya Taketoshi , Nakajima Junichiro
Published: February 2003

Optical absorption of liquid phase epitaxial magneto-optic Gd0.2Y2.8Fe5O12 films was measured at 1.3-μm wavelength using a waveguide technique. An optical absorption coefficient of α=0.2 cm−1 at 1.3 μm was obtained. This is the smallest value which has ever been reported for a garnet film and corresponds to 230 deg/dB in the figure of merit for Gd:YIG with the Faraday rotation coefficient of 200 deg/cm. α≤0.6 cm−1 is obtained, when garnet films are grown under the supercooling temperature of less than 10 °C. The supercooling temperature dependence of the α value is more insensitive for films grown from melts poor in B2O3 than for films from B2O3 rich melts. A mechanism of increase in optical absorption is discussed from the viewpoint of lead ion condensation at the solid/liquid interface and of incorporation into garnet films.
Optical evaluation of indium gallium arsenide phosphide double-heterostructure material for injection lasers
Authors: Degani J. , Besomi P. , Wilt D. P. , Nelson R. J. , Wilson R. B.
Published: February 2003

Optical methods used for evaluation of InGaAsP double-heterostructure (DH) material are described. The photoluminescence (PL) efficiency of the active layer in DH wafers and its spatial variation are shown to be correlated with the threshold current density of the broad area lasers processed from the corresponding wafers. The simultaneous measurement of the PL signal and the transmitted intensity of the excitation source through the active layer is a useful technique for monitoring imperfection in the active layer. The sheet conductivity of the epitaxial p layers and p-n junction misplacement can be determined from the variation of the PL signal as a function of the power of the optical pump source. In addition, conventional spectrally and spatially resolved PL indicates the compositional homogeneity and the doping concentration of the active layer. In general, we find the 1.06-μm yttrium aluminum garnet (YAG) laser to be a most convenient tool for evaluation of InGaAsP DH material.
Properties of Hg0.71Cd0.29Te and some native oxides by spectroscopic ellipsometry
Authors: Arwin H. , Aspnes D. E. , Rhiger D. R.
Published: February 2003

We have used spectroscopic ellipsometry to determine the complex dielectric function from 1.5 to 6.0 eV for Hg0.71Cd0.29Te and some of its native oxides. The electrochemically grown anodic oxide was found to have an absorption threshold near 3 eV and its dielectric function shows some of the features of TeO2. We found no evidence for a Te-rich layer between the native oxide and the semiconductor. However, after stripping the oxide with HCl, a residual layer with Te-like optical and chemical properties did appear. Thin native oxides formed by exposure to ozone-containing oxygen had dielectric functions similar to that of the anodic oxide but with a broader absorption edge. These oxides could be stripped partly by water and totally by HCl. This confirms that they are a mixture of several oxides as also concluded in other investigations. We found no evidence for any disorder or defects induced in HgCdTe by anodization or etching.
Multiplexing of twisted nematic cells under nonrigid boundary conditions
Authors: Yang K. H.
Published: February 2003

The possibility of increasing the degree of multiplexing of twisted nematic cells has been investigated by taking the following factors into consideration: unequal elastic constants and arbitrary dielectric anisotropy for the liquid crystal medium, and a general anisotropic interfacial potential. It can be shown that the achievable degree of multiplexing of twisted nematic cells under the nonrigid boundary condition can be improved by a factor of 10 to 50 over the case of the rigid boundary condition, in contradiction to a factor of two predicted by Nehring, Kmetz, and Scheffer [J. Appl. Phys. 47, 850 (1976)]. The effect on the degree of multiplexing by different forms of the anisotropic interfacial potential is also discussed.
Dislocation relaxation peaks involving hydrogen drag in deformed Ni-H alloys
Authors: Tanaka K. , Inukai T. , Uchida K. , Yamada M.
Published: February 2003

The internal friction and modulus changes in pure and hydrogenated nickel are measured after plastic deformation at frequencies of 2 Hz and 30 kHz. The hydrogen dissolution strongly diminishes a Bordoni-type peak (B peak) but develops a Snoek–Köster-type peak (SK peak) at a temperature well above the B peak. The SK peak increases in height and shifts toward higher temperature with increasing hydrogen concentration up to 1600 at. ppm. It has an effective activation enthalpy of 0.50±0.05 eV. An analysis of the concentration dependence of the peak shift suggests that this peak is caused by dislocations dragging pairs of hydrogen atoms, rather than isolated ones, segregated in the vicinity of the dislocations. A simple model is proposed which involves both dislocation pinning and impurity drag with changes in temperature. It explains well the observed correlation between the B peak and the SK peak as well as the conservation of their total relaxation strength with changes in the hydrogen concentration.
Interaction of a dislocation with a crack
Authors: Eringen A. Cemal
Published: February 2003

A solution is given of the field equations of nonlocal elasticity for a line crack interacting with a screw dislocation in an elastic plane under antiplane shear loading. Displacement and stress fields are determined throughout the core region and beyond. In the case when the dislocation is absent, the circumferential stress is shown to vanish at the crack tip, increasing to a maximum along the crack line afterwards decreasing to its classical value at large distances from the crack tip. This is in contradiction with the classical elasticity solutions which predicts stress singularity at the crack tip and it is in accordance with the physical condition that the crack tip surface must be free of surface tractions. The presence of the dislocation alters the stress distribution considerably when it is close to the crack tip. The stress distributions in the core region are displayed. A fracture criterion based on the maximum stress is established and used to determine the theoretical strengths of pure crystals that contain a line crack. Results are in good agreement with those based on the atomic theories and experiments.
Determination of N2(B3πg) and N2(C3πu) vibrational temperatures in e-beam pumped Ar-N2 and He-Ar-N2 mixtures
Authors: Polak-Dingels P. , Djeu N.
Published: February 2003

We report the results of a study to determine the vibrational temperatures of N2(B3πg) and N2(C3πu) in e-beam pumped N2 rare-gas mixtures. They are analyzed in terms of the kinetics of the e-beam pumped gas mixtures, and a number of qualitative conclusions are reached.
Measurements with an optimized regenerator for a liquid-working-substance heat engine
Authors: Swift G. W. , Migliori A. , Wheatley John
Published: February 2003

A regenerator for use with a liquid in a Stirling cycle heat engine is described. Because of the thermophysical characteristics of liquids, such a regenerator can be nearly ideally effective and has thermal properties that can be calculated directly without resort to empirical information. The regenerator described here is designed to minimize loss arising from three sources: thermal conductivity along the regenerator, viscous heating in the working fluid, and imperfect thermal contact between the working fluid and the second thermodynamic medium in the regenerator. Measurements using liquid propylene as a test fluid in the regenerator confirm the design calculations.
Growth and defect chemistry of amorphous hydrogenated silicon
Authors: Scott Bruce A. , Reimer Jeffrey A. , Longeway Paul A.
Published: February 2003

Magnetic resonance (NMR,EPR) and infrared studies are presented of amorphous hydrogenated silicon (a-Si:H) films prepared by homogeneous chemical vapor deposition (HOMOCVD) and rf plasma decomposition using silane and disilane. Hydrogen incorporation occurs with a small activation energy (∼0.06 eV) for all films, while the barrier for changes in spin defect density is almost an order of magnitude larger and comparable to that measured in defect annealing studies. Films deposited by rf(Si2H6) plasma exhibit the greatest hydrogen contents, followed by HOMOCVD and rf(SiH4) plasma material. NMR measurements suggest that HOMOCVD films are less disordered than plasma-deposited a-Si:H. Previous work and recent kinetic studies of plasma and thermal environments are extensively analyzed, along with thermodynamic and kinetic data, to determine a a-Si:H growth mechanisms most consistent with the experimental results. The model presented to explain compositional and defect changes with substrate temperature emphasizes plasma deposition by monoradical precursors and HOMOCVD growth by diradicals, resulting initially in a similar surface-bound intermediate in all cases. Plasma growth from Si2H6 involves the surface attachment of longer radical chains, compared to SiH4, while oligomeric diradicals could be present in HOMOCVD. The possibility that reactions at the hot reactor wall, as well as in the gas, create monoradicals in HOMOCVD is also explored in detail. Finally, film dehydrogenation and crosslinking reactions are examined, and experiments proposed to determine the channels most relevant for each deposition environment.
Electron microscope studies of an alloyed Au/Ni/Au-Ge ohmic contact to GaAs
Authors: Kuan T. S. , Batson P. E. , Jackson T. N. , Rupprecht H. , Wilkie E. L.
Published: February 2003

The interface structures resulting from the alloying reactions between a Au/Ni/Au-Ge composite film and a (100) GaAs substrate were studied by transmission electron microscopy and scanning transmission electron microscopy. Electron microscope examinations of the cross-sectional samples prepared in this study offered excellent lateral and depth resolution of local structures which are not available by other analytical techniques used previously in similar studies. The distributions and chemical compositions of various phases formed, and the morphologies of the interfaces between these phases were monitored and compared with the measured contact resistances at three different stages of alloying. A correlation between the interface structure and the contact resistance was found.
An analytic model for barrier height enhancement of the Schottky barrier diode using low-energy ion implantation
Authors: Wu Ching-Yuan
Published: February 2003

This paper describes an analytic model for the barrier height enhancement of the Schottky barrier diode where the metal-np semiconductor (or metal-pn semiconductor) has been derived by considering the implanted profile of the Gaussian type in the surface-doped layer and the surface properties of the metal-semiconductor system. Experiments have also been carried out by fabricating the Al-p silicon Schottky barrier diodes with low-energy (25 keV) arsenic implantation. It is shown that the barrier height enhancement of the fabricated Schottky barrier diodes as a function of ion dose is in good agreement with the developed model.
Compositional depth profiles of chemiplated Cu2S/(Zn,Cd)S heterojunction solar cells
Authors: Uppal P. N. , Burton L. C. , Rivaud L. , Greene J. E.
Published: February 2003

Atomic absorption spectroscopy combined with controlled chemical etching and Auger electron spectroscopy profiling with ion beam etching have been used to obtain composition versus depth analyses of Cu2S/(Zn,Cd)S heterojunction solar cells formed by an aqueous cation exchange, or chemiplating, process. The Cu2S films, ranging from 0.5 to 6 μm in thickness, were polycrystalline and exhibited a (001) preferred orientation on either textured polycrystalline or cleaved single crystal (Zn,Cd)S substrates. The profiling results showed that the interfacial regions were compositionally graded over very large distances ranging from tens to hundreds of nonometers depending on the Cu2S film thickness. This is much wider than observed for comparable Cu2S/CdS cells. Moreover, excess Zn in the form of both elemental Zn and ZnS was always found in the interfacial region and may be responsible for the short circuit current being lower than expected for these cells.
Perturbation calculation of magnetic field dependence of fluxon dynamics in long inline and overlap Josephson junctions
Authors: Levring O. A. , Pedersen N. F. , Samuelsen M. R.
Published: February 2003

The motion of a single fluxon in long Josephson-junctions of overlap and inline geometries is investigated in the presence of an applied external magnetic field. The form of the first zero-field step for various parameters is given in closed analytic forms in both cases, and the differences and similarities between the two geometries are emphasized.
Photodoping sensitivity of Ag into amorphous As2S3 films
Authors: Yaji Tamaki , Kurita Shoichi
Published: February 2003

The photodoping of Ag into as-evaporated, annealed, and pre-exposed As2S3 films has been studied by measuring the resistance and the optical density of Ag films and the depth of Ag doping estimated by the refractive index change. The photodoping consists of a dissolution process and a diffusion process. In the dissolution process, the spectral sensitivity reflects the absorption spectra of As2S3 films and the sensitivity limit is at about 650 nm. The dissolution rate of Ag into As2S3 is largest in the pre-exposed films and is smallest in the as-evaporated films. In the diffusion process, the spectral sensitivity limit is at about 700 nm and the diffusion rate varies only slightly over the three sets of As2S3 film conditions.
Thermal stability of Pb-alloy Josephson junction electrode materials. VII. Concentration range of single ε-phase Pb-Bi films used in counterelectrodes
Authors: Murakami Masanori , Huang H.-C. W. , Angilello J. , Gilbert B. L.
Published: February 2003

From the viewpoint of mechanical stability upon repeated thermal cycling between 298 and 4.2 K, Pb-Bi films with single ε-phase have been found to be desirable as the counterelectrode material of Pb-alloy Josephson junction devices. The Bi concentration range of the ε-phase was studied by using x-ray diffraction and electron microprobe techniques for Pb-Bi films with various Bi contents prepared by evaporation from an alloy source. The film composition was determined by controlled-potential coulometry. From the lattice constants and phase identification experiments, the Bi content range of the single ε-phase was determined to be 27.5∼31.8 wt. % (±0.3 wt. %) at room temperature. The lower limit of the Bi content of the ε-phase agrees reasonably well with those reported previously, but the upper limit of the Bi content is ∼1 wt. % higher than that of Preece and King, and ∼2 wt. % lower than that of Predel and Schwermann. Although Predel and Schwermann indicated that there would be a eutectoid at 27.5 wt. % Bi and 227 K, no evidence of phase separation of the ε-phase was obtained upon cooling as low as 4.2 K, or upon heating to 350 K. It was found by electron microprobe analysis that Bi-rich regions (β-phase) as large as 100 μm in size segregated in the Pb-Bi film surface when the Bi concentration is within the ε+β phase region.
Compression behavior of CdS and BP up to 68 GPa
Authors: Suzuki Toshihiro , Yagi Takehiko , Akimoto Syun-iti , Kawamura Tetsuya , Toyoda Shuhei , Endo Shoichi
Published: February 2003

High-pressure in situ x-ray diffraction study on CdS and BP was performed using a diamond anvil cell up to 68 GPa at room temperature. The rocksalt structure type CdS was found to transform to a new high-pressure polymorph at about 56 GPa. X-ray diffraction pattern of the new high-pressure polymorph was successfully indexed by the lowest temperature KCN structure type with the distorted rocksalt structure. Volume change accompanied with the transformation was calculated to be about 0.8%. This small volume change may be responsible to the undetectable change in refractive index of CdS at the transformation. No phase transformation was observed on BP: the zincblende structure is stable up to 68 GPa.
Third-order elastic constants and Grüneisen parameters of silicon and germanium between 3 and 300 °K
Authors: Philip Jacob , Breazeale M. A.
Published: February 2003

We present a method to determine all six independent third-order elastic (TOE) constants of diamond-like solids as a function of temperature from measured values of the ultrasonic nonlinearity parameters. Ultrasonic harmonic generation experiments along the three principal directions of a cubic crystal lead to the determination of the nonlinearity parameters, which contain three linear combinations of TOE constants. These data are sufficient to determine the three anharmonic first and second neighbor force constants in the Keating model for diamond-like solids. Ultrasonic velocity data are used to determine the two harmonic force constants in this model. Since our experiments have given data on silicon and germanium between liquid helium temperature and room temperature, we are able to evaluate and plot the Keating model force constants and hence all the six third-order elastic constants between 3 and 300 °K. Most of the TOE constants of silicon and germanium are smoothly varying functions of temperature; however, C123 and C144 go through zero and assume positive values at low temperatures. To determine whether the behavior of the calculated TOE constants is reasonable, we have used them to calculate the generalized Grüneisen parameters γ in the quasiharmonic approximation and have plotted γ as a function of temperature. These curves are in better agreement with curves obtained from thermal expansion experiments than the curves plotted by earlier workers using room temperature values of third-order elastic constants. For completeness we also have calculated the pressure dependence of the SOE constants and the Anderson Grüneisen parameters over the same temperature range.