bluuebunny/crossref_metadata_2025 huggingface dataset:
Luminescence and direct experimental observations of band-structure effects in nitrogen-doped GaxIn1−xP alloys
Authors: Mariette H. , Chevallier J.
Published: February 2003

Undoped and nitrogen-doped GaxIn1−xP layers (0.87<x<1) are grown by liquid-phase epitaxy. An increase of cathodoluminescence efficiency of nitrogen-doped GaxIn1−xP films is reported as a function of the NH3 partial pressure in the tube during the growth process. Photoluminescence spectra (4.2 °K) show a net change before and after the nitrogen doping. In undoped samples, a sharp high-energy C line due to excitons bound to neutral donors dominates the spectrum, while in nitrogen-doped samples additional lines appear with features depending on the composition. Particularly, we observe that, for x≳0.98, the nitrogen line is similar to the A line observed in GaP, whereas for x<0.98 nitrogen leads to a broader luminescence line Ao at lower energy than A. The origin of these recombinations is studied by time-resolved spectroscopy in undoped or nitrogen-doped materials. In undoped layers, the fast luminescence decay (20 ns) confirms the origin of the C line. For nitrogen-doped samples, we show that the measured luminescence decay time is the radiative lifetime τxR of the nitrogen-bound exciton. This lifetime decreases when the GaP content in the alloys decreases, i.e., when the X conduction band comes closer to the Γ conduction band. The experimental variation of τxR agrees with a simple theoretical model involving only the three minima Γ, X, and L and also with the more sophisticated model of Holonyak. Such a variation is a direct experimental observation of the band-structure effect.
Small-scale cw HF(DF) chemical laser
Authors: Spencer Donald J. , Beggs James A. , Mirels Harold
Published: February 2003

The construction and performance of a small-scale cw HF(DF) chemical laser is described. A multiline output of about 15 W was achieved. During single-line operation, 18 HF 2-1 and 1-0 transition lines, with powers from 0.1 to 2.4 W, and 24 DF 3-2, 2-1, and 1-0 transition lines, with powers from 0.01 to 0.30 W, were observed. Amplitude stability varied from ±1.5 to ±5%, and free-running short-term frequency stability was about ±10 MHz.
Laser fusion microballoon wall-thickness measurements: A comparative study
Authors: Halpern Gerald M. , Varon Joshua , Leiner Dennis C. , Moore Duncan T.
Published: February 2003

A comprehensive study of the measurement of the wall thickness of microballoons for laser-induced fusion has been completed. Four different techniques have been investigated: microradiography, scanning electron microscopy, and two interference methods. Measurements of wall thickness on 13 microballoons have been made by all techniques. The results obtained with the four methods were equal within the experimental error of each.
Second-breakdown characteristics of metal-oxide varistors
Authors: Lee J. J. , O’Brien J. K. , Cooper M. S.
Published: February 2003

Several new results on the electrical breakdown properties of ZnO-based ceramic varistors are presented. A second-breakdown phenomenon associated with thermal runaway and characterized by a negative differential conductivity was observed in dc tests. The curve of capacitance versus bias current exhibited hysteresis while the I-V characteristics became nonsymmetric and showed rectification after second breakdown.
Interfacial recombination velocity determination in In 0.5Ga0.05P/GaAs
Authors: Ettenberg M. , Nuese C. J. , Olsen G. H.
Published: February 2003

In this paper, we describe a one-wafer technique for detrermining the interfacial recombination velocity at III–V heterojunctions. The recombination velocity is determined from the relationship between the injected-carrier lifetime and the spacing between a p-n homojunction and a heterojunction interface in a single-heterojunction structure. The interfacial recombination velocity of an In0.5Ga0.5P/GaAS interface is found by this method to be 2×104 cm/sec, which is a factor of 3 larger than that of an Al0.5Ga0.5As/GaAs interface.
Finite-difference operators in inhomogeneous anisotropic media
Authors: Panizo M. , Castellanos A. , Rivas J.
Published: February 2003

Finite-difference equations in inhomogeneous anisotropic media, characterized by the position-independent principal axes for the relative permittivity tensor are obtained. Discrete inhomogeneities are discussed and results derived from the general equation. Finally, two examples are given to illustrate the application of the theory.
Steady-state self-focusing and filamentation of whistlers in a plasma
Authors: Sodha M. S. , Tripathi V. K.
Published: February 2003

Using the earlier expressions for the nonlinear dielectric tensor of a magnetoplasma, the authors have analyzed the steady-state self-focusing and filamentation of high-power whistlers. On the short time scale (t≪τε, τε being the energy relaxation time), the nonlinearity arises because of the ponderomotive force and is responsible for self-focusing up to very low frequencies. On the time scale of energy relaxation time, the dominant nonlinearity arises because of nonuniform heating and redistribution of electrons and causes self-focusing only when ω≳ωc/2 (ω and ωc being the wave and electron cyclotron frequencies, respectively). When the power of the whistler equals the critical power for self-focusing, it propagates without convergence or divergence and also guides a second weak whistler to propagate without convergence or divergence. These results are in quantitative agreement with the experiments of Stenzel. At very high powers, self-focusing of whistlers is not possible by any of the two mechanisms; in fact, the beam suffers divergence. A plane uniform whistler of high-power density is found to be unstable for small-scale intensity fluctuations and the growth rate of fluctuations is seen to be a saturating function of power density of the beam.
Self-scattering cross section of molecules in a beam
Authors: Lou Y. S.
Published: February 2003

Molecular collision cross sections have always been measured by the beam scattering method, or by the measurements of thermal conductivity and/or viscosity coefficient, etc. The cross sections thus obtained have been found to be different quantitatively from that of the self-scattering of the molecules moving within a molecular beam. By perturbing the zeroth-order solution of the Boltzmann equation with a B-G-K kinetic model for the gas upstream to the orifice, and performing a particle scattering calculation for molecules within a beam downstream to the orifice, such self-scattering collision cross sections can be determined from the experimental data of velocity distribution functions of molecules in a beam.
Emission from an oxide cathode as a function of oxide thickness
Authors: Soukup R. J.
Published: February 2003

The stable electron emission current from oxide cathodes of varying thickness was measured. The emission current density was found to be a monotonically increasing function of oxide thickness over the range of thicknesses studied. This behavior is predicted by considering the cathode to be a porous array of small particles having a statistical distribution in size. This analysis may be oversimplified since it does predict a somewhat larger value of pore size than expected.
The melting temperature of magnesium under shock loading
Authors: Urtiew Paul A. , Grover Richard
Published: February 2003

Temperature data from optical intensity measurements through anvils at high shock pressures are reported for magnesium samples. When account is taken for imperfect gaps at the anvil interface, the temperature measurements are shown to determine the melting line of magnesium at pressures from 40 to 50 GPa (400 to 500 kbar). The resulting high-pressure melting line for magnesium is in good agreement with the Lindemann law, with reasonable high pressure values for the Grüneisen coefficient γG.
Volume, index-of-refraction, and stress changes in electron-irradiated vitreous silica
Authors: Dellin T. A. , Tichenor D. A. , Barsis E. H.
Published: February 2003

The volume, index-of-refraction, and stress changes induced in vitreous silica by irradiating with 18-keV electrons have been measured over the dose range from 2.5×1010 to 3×1012 rad. The volume and index measurements were performed using a new technique based on producing a spatial modulation of irradiated and unirradiated areas which is used as an optical phase grating. Comparison of the volume change and stress measurements shows there are two components to the compaction; one component, which dominates below doses of 2×1011 rad, is associated with stress generation, while the other component, which dominates at higher doses, proceeds without generating stress. In addition, the relationship between the index change and volume change observed for electron irradiation is different from that obtained by neutron irradiation and hydrostatic compression. The index-vs-volume change data can be interpreted using the Lorentz-Lorenz formalism and Neuman strain-optical constants, and provides further evidence of the two different compaction processes. The measured stress saturates at 1.5×108 N/m2 at approximately 6×1011 rad (0.24% volume change) and decreases with subsequent irradiation. In contrast the volume and index changes saturate at approximately 2×1012 rad (1.4% volume change).
Laser diffraction and reflection from crazes
Authors: Hsiao C. C.
Published: February 2003

Oblique laser diffraction and reflection from surface crazes of polystyrene have been observed. The diffraction and reflection patterns vary as the diameter of the laser field is reduced. Diffraction patterns of a portion of a single craze have also been recorded to show both symmetrical and antisymmetrical diffraction and reflection, respectively, from the center smooth boundaries and the curved tips of a craze.
High-performance GaAs photocathodes
Authors: Olsen G. H. , Szostak D. J. , Zamerowski T. J. , Ettenberg M.
Published: February 2003

Improved negative electron affinity (NEA) photoemission sensitivity has been obtained from GaAs reflection photocathodes grown from a stoichiometric (rather than arsenic-rich) vapor phase on {100} substrates. Sensitivities as high as 2150 μA/lm with electron diffusion lengths of ?5μm and escape probabilities of ?0.55 are reported.
Shock-induced polarization of a ferroelectric ceramic
Authors: Lysne P. C.
Published: February 2003

Electric fields existing in shock-wave-compressed specimens of poled ferroelectric ceramics are caused by both the piezoelectric effect and a randomization of the domains aligned in the poling process. The contribution of these effects to the electric field is governed by the dielectric equation of state of the material. In general, even the form of this equation of state is uncertain for the large electric field and stress values encountered in the shock-compression process. In this work a form is assumed for the equation giving the shock-induced polarization. It includes terms representing, respectively, a linear dielectric, a ferroelectric including the stress and field dependence of the remanent polarization, and a piezoelectric whose coefficients are proportional to the remanent polarization. An important prediction of this relation is that shock waves can increase the remanent polarization of a partially poled specimen. This effect has been observed, and the conditions under which it occurs are used to evaluate the equation of state of a representative material, PZT 65/35.
Fields and forces of a macroscopic sphere above a ground plane in a sinusoidally varying electric field
Authors: Dietz Peter W.
Published: February 2003

Expressions are developed for the electric fields in and around a sphere of arbitrary conductivity and permittivity. The sphere is suspended in a fluid (also of arbitrary conductivity and permittivity) above a conducting grounded electrode with an applied field that varies sinusoidally in time. The force on the sphere is evaluated and typical results are presented. In the low- and high-frequency limits, the magnitude of the force is independent of frequency and can be represented on a single normalized graph. The results can be applied to two identical spheres in an axial electrical field (using symmetry) and to two permeable spheres in an axial magnetic field (by duality).
Bubble dielectrophoresis
Authors: Jones T. B. , Bliss G. W.
Published: February 2003

The force due to polarization exerted on dielectric particles, vapor or gas bubbles, and voids in insulating dielectric liquids is an example of dielectrophoresis. This force is directly proportional to the gradient of the electric field intensity. Bubbles and voids are attracted into regions of lower electric field intensity, while dielectric particles (with higher relative polarizability) are attracted into regions of higher electric field intensity. It is shown that local electric field intensity maxima cannot exist in space-charge-free electrostatic fields, while examples such as the three-dimensional quadrupole demonstrate the existence of local electric field intensity minima. Experimental investigation of the dielectrophoretic force on small gas bubbles (up to ∼1.0 mm in diameter) in insulating dielectric liquids shows that a simple model, which neglects bubble elongation effects, adequately describes the static and dynamic behavior. Experimental demonstration of a simple bubble trap which levitates and positions bubbles using dielectrophoresis is also provided. Applications of these bubble traps in laser target fabrication and zero-gravity space processing are envisioned.
The effect of metalloid composition on some magnetic and mechanical properties of Co75Si25−xBx glasses
Authors: van der Borst J. , den Broeder F. J. A. , Scheffers T.
Published: February 2003

It is found that the magnetic moment, Curie temperature, and microhardness of Co75Si25−xBx metallic glasses increase significantly upon substitution of boron for silicon. The increase in magnetic moment is accounted for by a smaller electron transfer from boron than from silicon to the cobalt 3d band. The present glasses differ remarkably from the phosphorus-containing glasses in that they do not embrittle as much on annealing just below the crystallization temperature.
Observation of surface recombination variations in GaAs surfaces
Authors: Jastrzebski L. , Gatos H. C. , Lagowski J.
Published: February 2003

The surface recombination velocity of GaAs p-n junction structures was determined from the dependence of the minority-carrier diffusion length on the depth from the surface, employing scanning electron microscopy. Pronounced variations in the recombination velocity (exceeding a factor of 3) were found along a given ’’real’’ surface; the high recombination regions can be of significance in accounting for the overall recombination characteristics of real GaAs surfaces.
Reply to ’’Comments on the evaluation of the irradiance of reflected light from rough surfaces’’
Authors: Holzer J. A. , Sung C. C.
Published: February 2003

Holzer and Sung criticized Leader and Fung’s calculations because of their use of the parameters kσfit∼1 and Qfit≫1. Leader and Fung contend that their work is justified because of the large kσexp and small Qexp inferred from actual surface measurements. Their calculation only magnifies the disagreement (Qfit/Qexp∼104) between the theory and the experimental data.
A note on the existing shock compression data of solid polycrystalline tungsten at 1223 K
Authors: Dandekar Dattatraya P.
Published: February 2003

In the present paper we show that the low estimates of the Grüneisen parameter (γ) of tungsten derived from the shock compression experiments of Rohde are a manifestation of two errors: (i) The Hugoniot of tungsten at 1223 K as determined by Rohde is invalid and (ii) the assumption concerning the elastic-plastic behavior of tungsten at least at room temperature is not true.
Zone-plate coded imaging of laser-produced plasmas
Authors: Ceglio N. M. , Attwood D. T. , George E. V.
Published: February 2003

The first successful demonstration of high-resolution tomographic imaging of a laboratory plasma using a coded imaging technique is reported. Zone-plate coded imaging has been used to image the x-ray emission from laser-compressed D-T-filled microballoon targets. The zone-plate camera exhibited a planar resolution ∼8 μm and had a tomographic resolution of ∼74 μm. This allowed three-dimensional viewing of the target emission from a single shot in planar slices.
Tunable-wavelength mode-locked Nd-glass laser with instant recording of temporal and spectral parameters
Authors: Lompre L. A. , Mainfray G. , Thebault J.
Published: February 2003

A tunable-wavelength mode-locked Nd-glass laser operating in a single transverse mode configuration has been developed. The intracavity bandwidth of the laser is narrowed by using eight highly dispersive Abbe prisms and a resonant reflector. A single bandwidth-limited pulse is isolated from the train, its duration being 30 psec and its linewidth being 0.8 Å. The wavelength can be tuned over a range of 80 Å between 10 580 and 10 660 Å. The pulse characteristics measurements are performed by using a streak camera and a spectrograph, both connected to a TV system giving immediate display of the shape, duration, spectral width, and wavelength of each laser shot.
X-ray optics and monochromators for synchrotron radiation
Authors: Hastings J. B.
Published: February 2003

Techniques of focusing and monochromating the x radiation from a synchrotron source will be discussed. Phase-space techniques, widely used in charged-particle beam transport, will be applied to describe the source and optical elements ni the focusing systems. The properties of focusing and nonfocusing x-ray optics will be presented with emphasis on the advantages of each.
Equilibrium temperatures in a CO2 TEA laser
Authors: Robinson A. M. , Hsieh Y.-K.
Published: February 2003

Equilibrium gas temperatures as high as 600±30 K have been observed in the center of a CO2 TEA laser discharge by measuring the absorption of a CO2 laser beam following the gain pulse. Uncertainties in the theoretical variation of absorption with temperature were avoided by measuring the absorption coefficient of the gas mix used in the laser in a temperature-controlled oven, up to a temperature of 610 K, so that the observed absorption in the laser discharge could then be directly related to the gas temperature. The temperature decreased from the center of the discharge towards the sides, and was initially constant along the direction of the transverse current. A temperature increase was observed with input energy, while a decrease was observed with pressure, distance between electrodes, and flatness of the electrode profile. A temperature of approximately 450 K was optimum for maximizing the small-signal gain in this system.
Low-temperature electrical studies on metal-oxide varistors—A clue to conduction mechanisms
Authors: Philipp H. R. , Levinson Lionel M.
Published: February 2003

Current-voltage data for metal-oxide varistors are presented in the temperature range 4.2–420 °K. These results and other general observations concerning varistor behavior are used to help decide which of the several mechanisms employed to explain varistor conduction are indeed applicable. We conclude that a tunneling process is the only viable mechanism so far proposed to qualitatively describe conduction at breakdown.
Photoluminescence excitation spectra of nitrogen-implanted AlxGa1−xAs
Authors: Makita Yunosuke , Gonda Shun-ichi
Published: February 2003

Photoluminescence excitation spectra have been measured for the nitrogen-implanted AlxGa1−xAs at 2 °K, because PLE spectroscopy has versatility for ion-implanted specimens. The results show that the absorption bands due to nitrogen isoelectronic impurities are formed below the Γ1 conduction-band minimum even in the indirect composition range, while the emission bands due to nitrogen impurities are situated below the X1 conduction-band minima.
Improved properties of melt-grown GaAs by short-time heat treatment
Authors: Kushiro Y. , Seimiya T. , Sinbori O. , Kobayasi T.
Published: February 2003

A large improvement of the properties of undoped melt-grown GaAs is obtained by short-time heat treatment with a SiO2 encapsulating layer. C-V and Hall measurements showed that deep acceptor traps lying at 0.23 eV below the conduction band were contained with the range of free-carrier concentration in the starting materials but they are completely removed by heat treatment above 800 °C. The photoluminescence efficiency for near-gap transition is improved considerably after heat treatment to approach that of solution-grown material. A highly doped thin surface layer was formed in most samples annealed above 850 °C. The introduction of a large concentration of shallow donors, however, never contributes to the intensity increase of the near-gap emission but induces low-energy broad-band emissions peaked at 1.30 and 1.15 eV. The behaviors of native defects responsible to the nonradiative centers are explained as follows: (i) in undoped material the defects, presumably Ga vacancies, are solely annealed out and (ii) if a large concentration of donors are presented, annealing accompanies the formation of more stable complex defects.
Admittance studies of neutron-irradiated silicon p+-n diodes
Authors: Tokuda Yutaka , Usami Akira
Published: February 2003

Defects introduced in n-type silicon by neutron irradiation were investigated by measuring the conductance (G) and the capacitance (C) of p+-n diodes. The method of the determination of the energy level, capture cross section, and concentration for each defect from the G-T and C-T curves for various frequencies was presented. Assuming that capture cross sections are independent of temperature, the energy levels of Ec−0.15 eV, Ec−0.22 eV, and Ec−0.39 eV were obtained. For these defects, the calculated values of the electron capture cross section were 2.6×10−14, 3.7×10−15, and 2.0×10−14 cm2, respectively. The introduction rate of defects for Ec−0.39 eV was twice that for Ec−0.22 eV which was twice that for Ec−0.15 eV. Comparing with other published data, the energy levels of Ec−0.15 eV and Ec−0.39 eV were found to be correlated with the A center and the divacancy, respectively.
Semileaky-type thin-film magneto-optic waveguide for modulator application
Authors: Yamamoto Sadahiko , Makimoto Toshio
Published: February 2003

This paper is concerned with a light-intensity modulator that utilizes codirectional magneto-optic coupling between orthogonally polarized guided and radiation modes a thin-film waveguide. The basic structure is the semileaky-type anisotropic waveguide that has been previously used as the polarization mode filter. Specific features of the modulator of this type are (1) phase matching is automatically achieved without introducing an acoustic wave, a gratinglike periodicity, or a precise control of film thickness and (2) direct intensity modulation is possible with no separate analyzer or mode splitter. As a practical example, a modulator configuration using LiNbO3/YIG/GGG layered structure operating in 1.15-μm wavelength region is considered. Radiation loss of 5–10 dB/cm may be obtainable in the film of thickness 6–7.5 μm for the lowest-order guided mode.
The anisotropy dependence of bubble dynamics in EuGaYIG films
Authors: DeLuca J. C. , Malozemoff A. P. , Su J. L. , Moore E. B.
Published: February 2003

We have studied the dynamic properties of bubbles in a series of oxygen-annealed EuGaYIG films which have similar magnetic properties except for decreasing uniaxial anisotropy as a function of anneal time. The translational saturation velocity and skew angle of bubbles translated in a pulsed gradient field experiment increase as the anisotropy decreases. These results are in agreement with theoretical predictions of a Ku−1/2 dependence. We also observe that for a given anisotropy and bubble state (S=1), the skew angle decreases as the drive increases, in agreement with theory which predicts that if the velocity is saturated, drive and angle are inversely related.
An x-ray diffraction study of lattice imperfections in cold-worked fcc alloys: II. Copper-gallium (α phase)
Authors: Chatterjee S. K. , Halder S. K. , Sen Gupta S. P.
Published: February 2003

X-ray diffraction profiles from four compositions of α-phase Cu-Ga alloys with solute gallium at 3.40, 6.90, 10.85, and 15.00 at.% were recorded in a Geiger counter x-ray diffractometer for both cold-worked and annealed states of the samples. Detailed studies on the recorded profiles considering recent development in the analyses of line shift, line asymmetry, and Fourier line shape have been made in order to evaluate the microstructural parameters. Considerable influence of net stacking-fault density α (=α′−α″) over the lattice parameter change and long-range residual stresses in causing the changes in peak positions has been observed when the concentration of solute gallium is increased in the alloy system. An increased presence of intrinsic fault (density α′) over the extrinsic fault (density α″) has been found, while the twin fault (density β) is totally absent in the deformed structure analogous to the silver gallium (I) system. The logarithmic dependence of α with solute concentration X has been satisfactorily explained by the existing semiempirical relations. The values of the dislocation density ρ and also the parameter γ/μ (γ, stacking-fault energy; μ, shear modulus) have been evaluated and from the latter, the stacking-fault energy γ for pure copper has further been estimated.
Two-dimensional analysis of thermal induction plasmas in finite cylinders
Authors: Eckert Hans U.
Published: February 2003

The temperature field of a static thermal induction plasma, enclosed in a cylindrical container, is calculated from an approximate closed-form solution of the Elenbaas-Heller equation without radiation term. By the assumption that the induced electric field has only a radial dependence, the heat conduction potential can be separated into its radial and axial dependences. Integration of the latter yields a cosine function; solution of the former is obtained by Picard’s iteration method with a previously obtained Bessel-function solution for the infinite cylinder serving as zeroth approximation. The two integration constants are determined by the conditions of zero wall temperature and equality between dissipated rf power and heat conduction losses at the side and end walls. The method is applied to an argon plasma at atmospheric pressure. It is then shown how the results can be refined by including the quartz walls into the heat conduction system, so that the temperature variation along the plasma-wall interface is obtained.
On an inhomogeneous diffusion equation found in plasma physics
Authors: Lonngren K. E.
Published: February 2003

Analytical solutions using the method of self-similar solution of partial differential equations are obtained for the inhomogeneous diffusion equation (∂ρ/∂t)−(∂/∂x)[D0xm (∂ρ/∂x)]=0. Several diffusion problems found in plasma physics are characterized by this equation.
Production and properties of homogeneously nucleated germanium particles
Authors: Hecht J. , Eversole J. D. , Broida H. P.
Published: February 2003

Germanium particles were produced by homogeneous nucleation from the metal vapor in a flowing stream of nitrogen gas at pressures of 0.13–2.6 kPa. Light scattering and light absorption measurements showed particle sizes of 15–300-nm radii while in the stream. Electron microscopy indicated that these particles can coagulate into much larger sizes on electron microscope grids. Electron and x-ray diffraction measurements did not show any crystalline structure in these particles.
Thermodynamic properties of materials in the melt regime
Authors: Holsapple K. A.
Published: February 2003

Thermodynamic identities that relate the properties of a pure material just inside the two-phase solid-liquid melt regime to its properties in the solid region are derived. The ratios across the phase boundary of the Grüneisen parameter, specific heat, bulk modulus, and sound speed are all expressed in terms of two material parameters. A single graph giving these ratios is presented, this graph applies to any pure material. Specific numerical results are given for six common metals.
Elasticoviscous flow between a rotating and a stationary disk with uniform suction at the stationary disk
Authors: Mishra Shankar Prasad , Mohapatra Umakanta
Published: February 2003

The flow of an elasticoviscous fluid between a rotating and a stationary disk with uniform suction at the stationary disk is studied. The equations of motion are solved by a regular perturbation method for small suction Reynolds number and by the Runge-Kutta numerical integration method. The results from the two methods have been compared. The effects of the elasticity of the fluid and the suction parameter on the velocity components, torque on the disks, and the pressure coefficient have been studied.
Electric properties of GaN light-emitting diodes
Authors: Shintani Akira , Minagawa Shigekazu
Published: February 2003

The mechanisms of electrical conduction processes in MIS GaN : Zn, yellow and green light-emitting diodes (LED’s), are analyzed by considering the I-V characteristics at room temperature and nitrogen temperatures and the temperature dependences of currents through the diodes with a constant forward bias. The diode current transport mechanisms are different between the two temperature regions, lower or higher than 150 K. The forward conduction current I is the sum of two contributions: I=I1+I2, where I1∝V1/2 exp(λV) and I2∝V exp(λ′V). At temperatures lower than 150 K, I1 dominates the current conduction controlled by tunnel-induced impact ionization. The electrons tunnel through a triangular potential barrier at the i-n junction. At temperatures higher than 150 K, I2 dominates as a result of electron thermal excitation, tunneling, and impact ionization. The electron thermal excitation occurs from the conduction band of the n layer to shallow donors of the i layer at the i-n junction. The thermal activation energy for the excitation depends on the Zn concentration in the i layer. The activation energies observed are 100 meV for the yellow LED and 14 meV for the green LED. From these activation energies and the donor binding energy, the Fermi levels of the i layers for the yellow and green diodes are estimated to locate 0.13–0.14 and 0.04–0.05 eV below the conduction band, respectively.
Shape of the p-n junction and crystalline structure of CuxS-CdS thin-film solar cells
Authors: Mukherjee M. K. , Pfisterer F. , Hewig G. H. , Schock H.-W. , Bloss W. H.
Published: February 2003

CuxS-CdS solar cells, prepared by the Clevite process, were bevelled at an angle of 40′ and suitably etched to expose grains of CdS, cracks, and the junction region. SEM pictures of this region reveal the average grain size and the distance between the cracks to be about 0.5 and 2 μm, respectively. Cathodoluminescence and SEM studies of the bevelled region of the cells show that the thickness of the CuxS layer perpendicular to the surface is highly nonuniform and thus forms vertical junctions. With the help of simple expressions it was shown that the reduction of the open-circuit voltage is a natural outcome, if the vertical parts of the junction are considered. It was also pointed out that there may be an optimum grain size of the CdS crystallites to obtain maximum power output from the cell.
Photo-induced currents in Ag-Al2O3-Al structures: Detection characteristics at 325 nm
Authors: Jain R. K. , Slayman C. W. , Farrier M. G. , Gustafson T. K.
Published: February 2003

We report the detection characteristics of planar Ag-Al2O3-Al structures at 325 nm as a function of angle, polarization, and bias. The experimental results are in excellent agreement with numerical computations based on a simple model in which the photoinduced currents are assumed to be proportional to the net absorptions in the Ag and Al films of the multilayered structure. Responsivities of the order of 1 V/W, and the simplicity of construction and operation of such metal-barrier structures indicate their usefulness as ultraviolet detectors.
Empirical electron backscatter model for thin resist films on a substrate
Authors: Heidenreich R. D.
Published: February 2003

An electron backscatter model applicable to the exposure of resists in electron lithography is developed. The model is empirical, being based on the direct observation of chemical change produced by backscatter electrons at different accelerating voltages on several substrates. The model is independent of scattering, trajectory, and energy dissipation calculations and is essentially a radial exponential decay of backscatter current density out to the backscatter radius determined by electron range. Predictions of the simple model are compared directly with published results of several authors. The model indicates, in agreement with Nosker, that substrate backscatter is not as deleterious to transverse resolution as predicted by other calculations. The actual numerical agreement among the scattering-model calculations themselves and this chemical-effect empirical model is not altogether satisfactory. The empirical model is in better agreement with Nosker at the higher backscatter angles and with Hawryluk et al. at small angles. The contribution of 50-eV secondary electrons to vinyl ferrocene crosslinking is concluded to be negligible and less than the experimental errors in this model. In the case of highly sensitive resists where the secondaries may be effective a substrate back dose coefficient ηSD must be employed which is about twice the backscatter coefficient η.
Variation of effective index of refraction in a double-heterojunction laser (In1−xGaxP1−zAsz)
Authors: Wright P. D. , Rezek E. A. , Ludowise M. J. , Holonyak N.
Published: February 2003

Data (197 °K) on InP-In1−xGaxP1−zAsz-InP DH diodes are presented showing that the effective index of refraction of a semiconductor laser, [n (λ)−λ dn/dλ], is not a single curve but, instead, is a family of curves that depends upon injection level.
Characterization of degraded hydrogen dissociator envelopes by AES
Authors: Ritz Victor H. , Bermudez Victor M. , Folen Vincent J.
Published: February 2003

The performance of hydrogen dissociators used in atomic clocks is known to degrade after prolonged operation, requiring large increases in rf power to maintain a constant output of atomic hydrogen. Auger electron spectroscopy (AES) has been used to characterize the inner surfaces of Pyrex dissociator envelopes. Prolonged operation of the dissociators leads to buildup of a dark film incorporating large quantities of carbon in its amorphous and carbide forms and smaller amounts of nitrogen. Possible mechanisms by which the film could interfere with the operation of the dissociator are given which involve its electrical conductivity and its role as a catalyst in the recombination of atomic hydrogen.
A note on the behavior of 〈111〉 single crystals of β-BaF2 under shock compression at room temperature
Authors: Dandekar Dattatraya P.
Published: February 2003

In the present paper a physical explanation for the ’’peculiar’’ stress profiles as observed in the direct-impact experiments on 〈111〉 single crystals of β-BaF2 on x-cut quartz gauges by Dandekar and Duvall is provided. The model implies that in some cases, such as in β-BaF2, surface properties of the material make a significant contribution to the nature of the shock-wave profile.
Vibrational modes of defects in ZnxCd1−xTe : P and MgxCd1−xTe : P
Authors: Dutt B. V. , Spitzer W. G.
Published: February 2003

Infrared absorption measurements of phosphorus defects in ZnxCd1−xTe : P and MgxCd1−xTe : P are reported. The localized vibrational modes of Zn-P and Mg-P pairs suggest a difference in pairing behavior of Zn and Mg with two P centers previously noticed in CdTe : P. Magnesium primarily pairs with a neutral phosphorous complex, while zinc pairs with a phosphorus substitutional on a Te sublattice, a shallow acceptor.
Free-carrier absorption of n-type ZnSe : Al
Authors: Dutt B. V. , Kim O. K. , Spitzer W. G.
Published: February 2003

Free-carrier-absorption measurements of ZnSe : Al annealed under Zn-rich conditions are reported. The absorption is nearly temperature independent, linear in carrier density, and shows a ν−3 behavior. The experimental results are compared with calculations based on polar optical-mode scattering. The agreement is reasonable except for the small temperature dependence observed in the experimental absorption. The conclusions are very similar to those reached previously for CdTe : Al.
Mechanical properties and microstructure of sintered PVC powder. II. Permeability and porous structure
Authors: Behrens E. W. , Butto A. M.
Published: February 2003

Static and dynamic air-flow impedance measurements were conducted with thin specimens of a variously sintered PVC powder. The results were interpreted by a statistical theory that expresses the parameters of a quasihomogeneous acoustic absorber in terms of porosity averages of channel radius and orientation. The low-frequency behavior of the air-flow impedance is determined by the porosity, a structure factor, and three different average channel radii that are related by inequalities. The latter could be established from general statistical considerations and were confirmed in most cases by experiment. Photomicrographs of sections through sintered powder layers were analyzed by stereological techniques in terms of specific surfaces. The channel radii derived from such measurements compared favorably with the average acoustic channel radii.
uv dye lasers optically pumped by a CO2-laser-produced plasma
Authors: Wood II O. R. , Szeto L. H. , Silfvast W. T.
Published: February 2003

Radiation from a CO2-laser-produced plasma has been used to pump a number of short-wavelength organic dyes. The results suggest that with a sufficiently fast-rise-time source, stimulated emission can be produced in dyes with low quantum efficiencies as long as they possess large A coefficients.
Observation of the upper branch (N′Γ) of the nitrogen isoelectronic trap in GaAs1−yPy
Authors: Holonyak N. , Nelson R. J. , Coleman J. J. , Wright P. D. , Finn D. , Groves W. O. , Keune D. L.
Published: February 2003

Luminescence data are presented on nitrogen-doped GaAs1−yPy in the composition region 0.38≲x≲0.47, near the direct-indirect crossover (yc?0.45, 77 °K), which permit the identification of the upper branch, N′Γ, of the N trap. The existence of such a state has been predicted by a recent theory of the N trap that includes both the long-range (Vl) and short-range (Vs) character of the isoelectronic impurity potential in III–V alloys. The N′Γ state is observed to lie in the band gap for 0.40≲y≲0.47 and is a resonant state in the Γ continuum for y<0.40. The identification here of laser operation on both the N′Γ and NΓ states (the latter becoming the short-range state N for y≳0.42), along with previous work demonstrating laser operation on the low-energy NX state, shows that all three N-trap states have sufficient oscillator strength for laser operation if the Γ-N separation is small enough for band-structure enhancement to be efffective.
Broadening of the longitudinal modes due to transient heating in optically pumped semiconductor lasers
Authors: Figueroa Luis , Botez Dan , Wang Shyh
Published: February 2003

We have found that the output spectra of cleaved GaAs lasers are broadened when they are optically pumped with a high-energy pulsed laser. We believe the effect is due to transient heating. A one-dimensional heat-flow equation is solved and the results predict the observed broadening. Ways of improving the mode spectra by reducing the broadening are discussed.
Structural and electrical characteristics of platinum-silicide-silicon contacts as influenced by sputter etching and annealing ambient
Authors: Severi M. , Gabilli E. , Guerri S. , Celotti G.
Published: February 2003

The influence of the surface-cleaning procedure, and the most common annealing ambients on the structure of the platinum-silicide and on the electrical properties of the resulting Schottky barrier have been investigated. With regard to the silicide formation, it has been found that the annealing ambient is the dominant factor; a simple chemical cleaning is sufficient for a complete Pt/Si reaction, provided the annealing is performed in vacuum. However, reproducible and nearly ideal electrical characteristics can be obtained only in sputter-etched samples, regardless of the annealing ambient. Sputter etching has also been found to play an important role in determining the breakdown voltage.
Negative bias stress of MOS devices at high electric fields and degradation of MNOS devices
Authors: Jeppson Kjell O. , Svensson Christer M.
Published: February 2003

One of the most important degradation effects observed in MNOS memory transistors is a negative shift of the threshold window. This negative shift is caused by a strong increase of the density of Si-SiO2 surface traps. This effect has been proposed to be caused by the same effect that is observed in MOS devices subjected to negative-bias stress (NBS). In this paper, a detailed study of the increase of the number of surface traps in MOS structures after NBS at temperatures (25–125 °C) and fields (400–700 MV/m) comparable to those used in MNOS devices is presented. Two different behaviors are observed. At low fields the surface-trap density increases as t1/4 and at high fields it increases linearly with the stress time t. The low-field behavior is temperature and field dependent and the zero-field activation energy is determined to be 0.3 eV. The high-field behavior is strongly field dependent but independent of temperature. A physical model is proposed to explain the surface-trap growth as being diffusion controlled at low fields and tunneling limited at high fields. A comparison with MNOS degradation is made and it was found to be related to the t1/4 behavior mentioned above.
Longitudinal field losses in multifilament superconductors over a range of frequencies
Authors: Carr W. J.
Published: February 2003

The power loss in a twisted multifilament superconductor due to a time-dependent longitudinal magnetic field is calculated as a function of frequency. The longitudinal field is assumed to have a sinusoidal dependence on both space and time, alternately changing direction along the conductor over a length l. The eddy current loss, as a function of frequency, initially is approximately proportional to l2 and rises as the square of the frequency, until it reaches a plateau which tends to be frequency independent and inversely proportional to l2. After a further increase with frequency, the skin effect region is reached with frequency to the one-half power dependence. The current-density distribution in the conductor is calculated, and it is shown that for large l the entire cross section of the conductor can become current saturated if the amplitude of the ac field is greater than Lλjc where L is the twist length, jc is the critical current density, and λ is the fraction of superconductor.
Thermal effects in superconducting proximity-effect bridges
Authors: Decker S. K. , Palmer D. W.
Published: February 2003

Thermal properties of superconducting proximity-effect bridges, fabricated from Nb, Ta, and Ti films, were measured by two experimental methods: (1) measurement of the low-frequency (20–2000 Hz) noise-fluctuation power spectrum in the bridge and (2) measurement of the Joule heating needed to elevate the bridge region to an easily identified fixed temperature above that of the helium bath. A comparison was made between the measurements and calculations based on a simple thermal boundary model in which the bridge volume alone is treated as elevated in temperature. Thermal effects were shown responsible for critical current hysteresis, high-frequency Josephson step limitations, the low-frequency 1/f2 noise power spectrum, and an unstable resistance regime of current bias. Methods for alleviating these limitations by correct bridge geometry were found. Thermal effects were found not to be responsible for the excess current which appears on the current-voltage trace of the proximity-effect bridge.
Heat pulse formation of superconducting phases
Authors: Testardi L. R. , Wakiyama T. , Royer W. A.
Published: February 2003

Current pulses of several amperes applied for ∼1 sec at T≲20 K to quasiamorphous nonsuperconducting (at 4.2 K) films of V3Si, V3Al, Nb3Sn, Nb3Ga, Nb3Al, and Nb3Si cause structural transformations to superconducting phases. The method attempts to utilize kinetics as a new variable in producing metastable superconducting phases. The suggestion is supported by the results for V3Al where Tc onsets ∼12 K or higher are achieved more readily than by other ’’equilibrium’’ growth methods. For Nb3Si several films with Tc onsets ∼12 K show the method can produce Tc’s which are higher than those obtained by hot-substrate deposition. Though much less tested, films irradiated by laser pulses at 300 K showed qualitatively similar behavior.
Ion acceleration in the evacuated drift-tube geometry
Authors: Hoeberling R. F. , Payton III Daniel N.
Published: February 2003

The effect of varying the space-charge-limited current on the ion acceleration in the evacuated drift-tube geometry with no external magnetic field has been experimentally tested. The time-resolved current injected into the drift tube, the ion energy spectrum, and the region of ion acceleration have been measured. Different anode and cathode materials have been used. The results of these measurements indicate that ions are collectively accelerated inside the drift tube and that ion acceleration occurs in the drift tube only when the injected beam current exceeds the limiting current, set by the drift-tube radius.
Accurate determination of liquid-crystal tilt bias angles
Authors: Scheffer T. J. , Nehring J.
Published: February 2003

A detailed analysis is given for three techniques used to determine the tilt bias angle of a nematic liquid crystal in contact with a boundary surface. Two of these methods, the crystal rotation and capacitive methods, have severe disadvantages, such as a restricted range of application, an insufficient accuracy, and sometimes require knowledge of nematic material constants which have to be determined by separate experiments. A third and more useful method, a magnetic null method, makes it possible to determine the tilt bias angle directly with only one measurement to an accuracy of 0.1°, regardless of the size of the angle or the nature of the nematic liquid crystal. Using the magnetic null method we have investigated the tilt bias angles of nematics in contact with glass substrates onto which a coating of SiO had been obliquely evaporated. We find that the tilt bias angle decreases with increasing evaporation angle (both angles measured from sample plane) until a critical evaporation angle of ?14° is reached, whereupon the director reorients out of the plane of incidence of the evaporation beam and assumes a direction normal to this plane with a 0° tilt bias. We also find that the tilt bias angle varies from compound to compound for the same evaporation parameters and is influenced by temperature and trace impurities.
Charge injection between concentric cylindrical electrodes
Authors: Zahn Markus , Chatelon Helene
Published: February 2003

The transient electric field and space-charge distributions and terminal voltage-current characteristics are solved for drift-dominated unipolar ion conduction between concentric cylindrical electrodes. Special attention is directed to comparing solutions with charge injection from the inner and outer electrodes. As in past work with parallel-plate geometries, the method of characteristics is used to convert the governing partial differential equations into a set of first-order ordinary differential equations which are easily numerically integrated by the Runge-Kutta method. For current-source excitations the equations can be integrated exactly. Special cases examined include the charging transients to a step voltage or current excitation from rest under space-charge-limited conditions and the discharging transients for systems in the dc steady state which are instantaneously open or short circuited.