bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation and measurement of corona for electrostatic pulse powered precipitators
Authors: Salasoo Lembit , Nelson J. Keith , Schwabe Robert J. , Snaddon Robert W. L.
Published: July 2002

The use of pulse powering for electrostatic precipitators has shown several advantages but the underlying physics has been insufficiently understood to allow any optimization. A numerical model has been assembled which allows the controlling corona process to be simulated in both time and space to permit estimation of the ion densities and field distributions to be expected for a wide range of transient electrical parameters and gas properties. Supporting laboratory measurements have been undertaken under dc and pulse conditions both to verify the simulation and to provide corona spot density data not readily obtainable by other means.
Laser-based and thermal studies of stress corrosion in vitreous silica
Authors: Fisk G. A. , Michalske T. A.
Published: July 2002

Crack-propagation rates in vitreous silica were monitored as specimens were heated thermally or irradiated by a laser beam. The laser was tuned to the OH bond vibration to determine the role of OH stretching in the dissociative chemisorption mechanism for stress corrosion of silica in moist environments. Laser radiation heated the silica near the crack tip but did not generate any bond-specific changes in crack velocity. For samples maintained in moist air, the propagation velocity decreases as temperature increases. The temperature dependence of crack velocity indicates that physisorption is an important step in stress corrosion, and a simple model of the process is proposed.
Absolute efficiency of Y2O2S:Tb screens under fluoroscopy conditions
Authors: Giakoumakis G. E. , Nomicos C. D.
Published: July 2002

The absolute x-ray efficiency of Y2O2S:Tb phosphor screens was measured under fluoroscopy conditions as a function of the x-ray tube voltage and as a function of the screen’s weight. The experimental results are in very good agreement with the theoretical predictions obtained according to the Hamaker model.
Experimental observation of light trapping in hydrogenated amorphous silicon solar cells
Authors: Faughnan Brian W.
Published: July 2002

Experimental evidence for light trapping in glass/conductive transparent oxide/p-i-n/metal hydrogenated amorphous silicon solar cell structures is presented. A short-circuit current of 17.8 mA/cm2 has previously been reported for a cell made with this structure. The light trapping is treated by a modification of the Yablonovitch–Cody (YC) statistical theory of light trapping in textured layers [E. Yablonovitch and G. D. Cody, IEEE Trans. Electron. Devices ED-29, 300 (1982)]. Reflection measurements show that 80% of the incident light is trapped. Quantum efficiency measurements made on cells with back electrode metals of different reflectivity are shown to be in agreement with the predictions of the YC theory.
Levitation force acting on a three-dimensional static current source moving over a stratified medium
Authors: De Zutter D.
Published: July 2002

The levitation or suspension forces acting on an arbitrary three-dimensional dc current source moving over a stratified medium consisting of a track and the underlying earth are determined analytically for arbitrary relativistic velocities. The proposed method also allows the determination of the currents inside the track. As a first step towards the analysis of moving magnets, the obtained results are applied to a moving magnetic dipole.
Skin depth measurement in thin metal films by pulse nuclear-magnetic-resonance nutation technique
Authors: Reich S. , Vega A. J.
Published: July 2002

The rate of nutation of the magnetic moments of 2H and 1H nuclei in a pulsed NMR experiment is used to measure the skin depth in thin metallic films. This measurement yields values of skin depth which are in good agreement with those calculated from measured electric conductivity data. Also this new method is direct and contactless.
Propagation of quasifracture in viscoelastic media under low-cycle repeated stressing
Authors: Liu X. P. , Hsiao C. C.
Published: July 2002

The propagation of a craze as quasifracture under repeated cyclic stressing in polymeric systems has been under intensive investigation recently. Based upon a time-dependent crazing theory, the governing differential equation describing the propagation of a single craze as quasifracture in an infinite viscoelastic plate has been solved for sinusoidal stresses. Numerical methods have been employed to obtain the normalized craze length as a function of time. The computed results indicate that the length of a quasifracture may decelerate and decrease indicating that its velocity can reverse. This behavior may be consistent with the observed and much discussed craze healing and the enclosure model in fatigue and fracture of solids.
Determination of distribution of states in hydrogenated amorphous silicon from capacitance-voltage characteristics
Authors: Balberg I. , Gal E.
Published: July 2002

In this paper we present an experimental method for the derivation of the state distribution in the pseudogap of an amorphous material. The method is based on capacitance-voltage (C-V) measurements and on transient capacitance interpretation. Analysis of the frequency and temperature dependence of the C-V characteristics, obtained under deep depletion conditions, enables a differential determination of the density of states in part of the forbidden gap. This approach is shown to have advantages over other capacitance-based methods in particular for routine comparative studies. In the present work we have measured phosphorus-doped a-Si:H (hydrogenated amorphous silicon) materials which have been prepared under similar conditions in three different laboratories. The results indicate that the discrepancy found in the density-of-states maps derived in different laboratories are due more to the different data interpretations than to real variations between the materials. The map derived here is found to be in general agreement with results obtained by other transient capacitance methods. In particular, the presence of a wide peak in the density of states, the center of which is around midgap. The peak increases with increasing dopant concentration but the rise in the Fermi level and the doping efficiency appear to be associated with the fine details of the density-of-states dip which lies between the above peak and the sharply rising conduction band tail.
A simple qualitative model of surface versus bulk effects in gamma-ray irradiated p-n diodes
Authors: Hirsh I. , Hava S. , Kopeika N. S. , Alfassi Z. B. , Kushelevsky A. P.
Published: July 2002

Various Si and Ge rectifier diodes are tested at frequent intervals of γ-radiation doses for changes in ideality factor η and minority carrier lifetime τ. Although both parameters are well known to decrease with dosage, here they are probably for the first time measured to also subsequently increase, decrease, increase, etc., at higher dosages. Examination of diodes in vacuum prior to and following even modest irradiation levels indicates experimentally that noticeable changes in surface properties have been induced by the irradiation. Such experimental techniques permit greater insight into the basic structure of surface phenomena long suspected to play a significant role in diode changes brought about by nuclear irradiation. Utilization of such surface changes leads to a broad general concept to explain the reversals and changes in the dosage dependences of η and τ in terms of bulk versus surface effects.
A mathematical study of general analytical models for step p-n semiconductor junctions
Authors: Ruan Ying-Chao , Paranjape B. V. , Tang Jing-Qing
Published: July 2002

Three generalized models covering a wide range of ionized impurity densities, NA and ND, have been put forward for undegenerate semiconductor step p-n junctions at equilibrium. They contain the exact electric field and the potential at the interface of a junction, and give a satisfactory field distribution and potential distribution. In limiting cases they reduce to the traditional depletion model given by Shockley and the one-side junction model by van de Wiele and Demoulin. The proposed models can be applied to low-injection junctions. The electric field and the potential as functions of position given in this paper can also be used in other step junctions.
Magnetic study of carbon chars in the transition range
Authors: Sarachik M. P. , Michelman F. , Li W. , Smith F. W. , Remeika J. P.
Published: July 2002

Using static techniques, we have measured the susceptibility and magnetization of carbon chars heat treated at temperatures between 1000 and 1500 °C, the so-called ‘‘transition range,’’ where equivalent information is unavailable by electron spin resonance measurements due to severe line broadening effects. A small increase is observed in the Curie contribution to the susceptibility as a function of heat-treatment temperature, indicating the appearance of unpaired spins possibly associated with structural changes which occur in the transition range. The diamagnetism of these chars increases rapidly with increasing heat-treatment temperature, and a strong temperature dependence appears which is consistent with behavior expected for a two-dimensional gas of charged carriers. The latter can be ascribed to the formation and growth of microcrystalline graphitic regions.
Low-temperature direct nitridation of silicon in nitrogen plasma generated by microwave discharge
Authors: Moslehi M. M. , Fu C. Y. , Sigmon T. W. , Saraswat K. C.
Published: July 2002

Plasma nitridation of silicon has been performed at low temperatures (at ≊500 °C and also lower temperatures) in nitrogen plasma generated by microwave discharge. The effects of various growth parameters such as microwave power, nitrogen gas pressure, anodization current and polarity, growth time and substrate temperature on the thickness, surface morphology, uniformity, composition and stoichiometry, and electrical and physical characteristics of the grown films have been studied. The thickness of the grown films varied between 30 and more than 100 Å depending on the growth conditions. Based on the grazing-angle Rutherford-backscattering data, the grown films were silicon nitride with some oxygen and carbon contamination. A typical breakdown field of ≊10 MV/cm was measured for these films. The preliminary results obtained indicate that these nitride films can be considered as potential candidates for ultrathin gate, tunnel, and dram memory insulators for very large scale integration devices.
Effects of hydrogenlike fine structure on Balmer alpha gain
Authors: Tallents G. J.
Published: July 2002

The effects on the plasma and other conditions required to achieve population inversions between the quantum states n=3 and n=2 of hydrogenlike ions caused by nonstatistical equilibrium fine-structure sublevel densities are examined. Collisional and radiative transitions into and out of each of the fine-structure sublevels (up to principle quantum number n=5) are taken into account in a comprehensive collisional-radiative code. Population inversions produced by both recombination and by photopumping from the 1s to 3p quantum states are examined. For electron densities Ne ≲1012 Z7 cm−3 (where Z is the atomic number of the hydrogenlike ion), it is shown that inversions can be much more difficult to produce than is predicted by simple calculations assuming all sublevels are populated statistically.
Boundary-layer flow in a magnetohydrodynamic channel
Authors: Rao B. Nageswara
Published: July 2002

Magnetohydrodynamic boundary-layer flow with tensor electrical conductivity and transpiration number has been examined. The resulting nonlinear partial differential equations are solved using a local nonsimilarity solution method. It is found that suction will cause an increase in wall-shearing stress and a decrease in the thicknesses of the boundary layer.
Mechanism of phosphorus diffusion gettering of cobalt in silicon studied by Mössbauer spectroscopy
Authors: Shaikh A. G. , Schröter W. , Bergholz W.
Published: July 2002

The gettering of cobalt in silicon during phosphorus diffusion under high surface concentrations (PDG) has been investigated by Mössbauer spectroscopy between 825 and 1000 °C. It has been found that cobalt, distributed uniformly in the specimen before PDG, is concentrated within a highly phosphorus doped Si-surface layer thinner than 0.5 μm after PDG. It is also shown that PDG suppresses surface gettering and that the residual cobalt concentration in the bulk can be lower than the cobalt solubility. Mössbauer spectra of this layer show that cobalt occurs as two species there. The first of these has nearly cubic symmetry and is transformed into the second species upon annealing at 600 °C. This species is stable under the conditions of PDG. Neither the formation of phosphorus-cobalt pairs nor the presence of CoSi2 can provide a comprehensive explanation of all experimental facts.
Current oscillation in modulation-doped GaInAs/n-GaAs strained-layer superlattices
Authors: Kubota K. , Ohnishi T. , Shiomoto T.
Published: July 2002

The current oscillation was observed in modulation-doped GaInAs/n-GaAs strained-layer superlattices when a high electric field was applied parallel to the layers. The critical voltage for the threshold of oscillation depended on the layer thickness. Observation of the propagation of a high-electric-field domain in the GaInAs layers shows that this phenomenon is the Gunn effect. Comparing with the high-field effects in GaAs/n-AlGaAs superlattices, we consider the role of the interface dislocations.
Method of ion reaction time amplification in time-of-flight mass and energy analysis
Authors: Tsong T. T.
Published: July 2002

Very fast ion reactions can be studied with a time resolution better than 10−13 s in a time-of-flight spectrometer by using a time amplification method. This is done by separating the system into a very short ion acceleration-reaction section and a very long field-free-flight section. An example drawn from a study of field dissociation by atomic tunneling of RhHe2+ is presented.
Indium-doped zinc oxide thin films prepared by rf magnetron sputtering
Authors: Shih I. , Qiu C. X.
Published: July 2002

Indium-doped zinc oxide films have been prepared by rf magnetron sputtering, using ZnO targets containing up to 10 wt. % In2O3. Room temperature resistivity of the deposited films was found to decrease by about four orders of magnitude as the In2O3 content was increased from 0 to 10 wt. %.
Raman scattering study of rapid thermal annealing of As+-implanted Si
Authors: Kirillov D. , Powell R. A. , Hodul D. T.
Published: July 2002

Rapid thermal annealing of Si after implantation with 60-keV 75As+ ions was studied using Raman scattering. Spectra were measured at different stages of annealing. It was found that the as-implanted amorphous phase was first transformed into the higher-order amorphous phase before the transformation into the crystalline phase. Regrowth of the crystalline phase occurred only from the substrate side, and no polycrystalline regions could be detected at the intermediate stages of annealing. Electrical activation of the implanted As dopant proceeded simultaneously with crystal regrowth, and complete activation coincided with the disappearance of the amorphous phase. Changes in the Raman spectra of the implanted and annealed crystalline layer caused by the contribution of free electrons were found, allowing the concentration of activated free carriers to be determined.
Properties of Au/oxide/InP metal-interfacial layer-semiconductor junctions
Authors: Eberspacher Chris , Fahrenbruch Alan L. , Bube Richard H.
Published: July 2002

The properties of Au/thermal oxide/p-InP metal-interfacial layer-semiconductor (MIS) junctions have been investigated. Thin InP thermal oxides are stable and in the dark are positively charged so as to increase the band bending and reduce the forward leakage currents in MIS junctions. Under illumination, photogenerated electrons are trapped in the oxide or near the oxide/InP interface such that MIS junctions exhibit photosuppression and hysteresis effects.
New technique for excitation of bulk and surface spin waves in ferromagnets
Authors: Bogacz S. A. , Ketterson J. B.
Published: July 2002

A meander-line magnetic transducer is discussed in the context of bulk and surface spin-wave generation in ferromagnets. The magnetic field created by the transducer was calculated in closed analytic form for this model. The linear response of the ferromagnet to the inhomogenous surface disturbance of arbitrary ω and k was obtained as a self-consistent solution to the Bloch equation of motion and the Maxwell equations, subject to appropriate boundary condition. In particular, the energy flux through the boundary displays a sharp resonantlike absorption maximum concentrated at the frequency of the magnetostatic Damon–Eshbach (DE) surface mode; furthermore, the energy transfer spectrum is cut off abruptly below the threshold frequency of the bulk spin waves. The application of the meander line to the spin diffusion problem in NMR is also discussed.
Mechanism of hydrogen sensing in Pd-Si metal-insulator-semiconductor diodes
Authors: Butler M. A.
Published: July 2002

Capacitance, conductance, and photoinduced current measurements have been made on Pd-Si metal-insulator-semiconductor diodes to define the mechanism by which these devices sense hydrogen. The results have been used to construct a model which is capable of describing the major features of the response of these diodes to hydrogen. The current flow is found to be majority carrier dominated, through interface states at the SiO2-Si interface. Changes in current under reverse bias upon exposure to hydrogen result from lowering of both the Schottky barrier and the oxide barrier height but not from changes in the interface density of states.
Threshold conditions for the air plasma initiation near solid surfaces under the action of powerful pulsed CO2 laser radiation
Authors: Ursu I. , Apostol Ileana , Dinescu Maria , Hening A. , Mihǎilescu I. N. , Prokhorov A. M. , Chapliev N. I. , Konov V. I.
Published: July 2002

New data are reported concerning the plasma initiation in front of metallic and dielectric surfaces under the action of pulsed CO2 laser radiation.
Influence of Cu as an impurity in Al/V thin-film reactions
Authors: Colgan E. G. , Palmstro/m C. J. , Mayer J. W.
Published: July 2002

Thin-film reactions of Al/V with and without 4 at. % Cu in the Al have been studied by Rutherford backscattering, x-ray diffraction, scanning electron microscopy, and Auger electron spectroscopy after vacuum annealing in the temperature range 300–500 °C. In the Al/V system, the intermetallic phase VAl3 grows as (time)1/2 with an activation energy of 2.1±0.2 eV. The presence of Cu in the Al retards the VAl3 growth and alters the phase sequence.
Effect of the presence of Ge in Er compound on the barrier height formation of Er-Si contacts
Authors: Wu C. S. , Ghaemmaghami A. , Lau S. S.
Published: July 2002

The barrier heights of Er and ErSi2 on oxide-free p-Si have been reported to be identical (φpB ∼0.8 eV), suggesting that the stoichiometry of the metallic contact does not appear to affect the barrier heights as long as a specific metal is present at the interface. In this work, the effects of Ge in the Er film on the barrier height have been investigated. Our results show that the ratio of Ge to Er in an Er/(GexSi1−x)2 compound layer in contact with p-Si affects the barrier heights significantly. A linear relationship between φpB and x has been found and can be expressed as φpB =0.778 −(2x) (0.098). This experimental finding indicates that the barrier height of a metallic compound on Si may depend not only on the metal species, but also on the composition of the compound.
Laser stimulated thermoluminescence
Authors: Abtahi A. , Bräunlich P. , Kelly P. , Gasiot J.
Published: July 2002

Experimental and computational methods are presented for the complete characterization of the thermoluminescence response obtained from thermoluminescent phosphors upon exposure to localized Gaussian laser heating beams. A number of different phosphor configurations are described as examples. These include LiF:Mg,Ti (TLD-100, Harshaw Chemical Corporation) in form of chips, which are widely used in the dosimetry of ionizing radiation, and thin-layer dosimeters prepared either as self-supporting films or powder in a polyimide matrix, or on substrates of LiF single crystals or borosilicate glass. It is demonstrated that all relevant optical and thermal properties of the dosimeters can be determined by these methods and that, based on this knowledge, the expected thermoluminescence response of a given configuration can be simulated as a function of a number of experimental parameters.
Low-threshold, high quantum efficiency stop-cleaved InGaAsP semiconductor lasers
Authors: Antreasyan A. , Chen C. Y. , Napholtz S. G. , Wilt D. P.
Published: July 2002

InGaAsP double-channel–planar-buried-heterostructure lasers with stop-cleaved mirrors emitting at 1.3 μm have been fabricated. Threshold currents as low as 18 mA and differential quantum efficiencies as high as 39% have been obtained. Furthermore, we have achieved a yield greater than 50% in obtaining good quality facets utilizing the stop-cleaving technique. Our result represents one of the lowest threshold currents obtained so far at 1.3-μm wavelength among the structures designed for monolithic optoelectronic integration.
Theory of lifetime measurement with the scanning electron microscope in a semiconductor containing a localized defect: Transient analysis
Authors: Jakubowicz A.
Published: July 2002

This paper presents a transient analysis of electron-beam induced current in a semi-infinite semiconductor containing an individual pointlike defect. A focused electron beam positioned in the vicinity of the defect is cut off and the resulting current versus time decay is calculated. It is shown that the time constant of this decay is a complex function of geometrical aspects of the system, bulk properties of the material, and strength of the defect. Computational results are given for a dislocation line parallel to the charge collection plane.
Comparative study of radiotracer and secondary-ion mass spectrometry profiling of gold diffused CdxHg1−xTe
Authors: Palfrey H. D. , Blackmore G. W. , Courtney S. J.
Published: July 2002

Radiotracer and secondary-ion mass spectrometry (SIMS) diffusion profiling techniques in CdxHg1−xTe (CMT) have been compared in order to provide a sounder basis for dopant characterization in this material. Au diffusion profiles were determined by the radiotracer and SIMS techniques after a diffusion anneal of 168 h at 225 °C in a flowing Ar ambient. The profiles obtained using the two different techniques were very similar, indicating the same Au diffusion behavior. It was shown that the radiotracer technique can be used for SIMS calibration of Au in CMT. It was also demonstrated that the two techniques give equally valid diffusion profiles.
Admittance frequency dependence of Schottky barriers formed on dc triode sputtered amorphous silicon: Hydrogen influence on deep gap state characteristics
Authors: Mencaraglia D. , Amaral A. , Kleider J. P.
Published: July 2002

The admittance of Schottky diodes formed on dc triode sputtered amorphous hydrogenated silicon has been measured as a function of frequency at zero dc bias. The electrical behavior of the device is modeled with an equivalent circuit taking into account the thermal response time of gap states and the transport of carriers in the conduction band. The theoretical frequency dependence of the admittance of the Schottky diode is derived in two limiting cases: whether the occupancy of the gap states is controlled mainly by their interaction kinetics with the extended states or by the transport of electrons in the conduction band. We reach the conclusion that, in our samples, the response to an ac modulation is limited by the interaction kinetics of the localized states with the extended states of the conduction band. We apply this analysis to samples exposed to different sputtering conditions. The results show that, with these samples, not only the density of deep gap states at the Fermi level but also their efficiency for the capture of electrons decreases with hydrogen incorporation. These variations correlate well with the evolution of the electron mobility-lifetime product obtained from independent photoconductivity measurements.
Minority-carrier diffusion and recombination in CdZnS/CuInSe2 solar cells
Authors: Ahrenkiel R. K. , Matson R. J. , Osterwald C. R. , Dunlavy D. J. , Kazmerski L. L.
Published: July 2002

Minority-carrier diffusion has been investigated in as-grown CdZnS/CuInSe2 solar cells. Capacitance-voltage (C-V) and photoconductivity measurements are combined to determine diffusion and interface recombination processes. Diffusion lengths of about 2 μm and a small interface recombination velocity are determined from biased photoconductivity, biased spectral response, and photoluminescence studies. Photoluminescence studies also indicate that a much lower interface recombination velocity occurs at the CdZnS/CuInSe2 interface than that at a bare CuInSe2 surface.
Arsenic segregation to silicon/silicon oxide interfaces
Authors: Wong C. Y. , Grovenor C. R. M. , Batson P. E. , Isaac R. D.
Published: July 2002

Arsenic segregation at polycrystalline silicon/silicon and polycrystalline silicon/silicon oxide interfaces was examined directly by transmission electron microscopy (TEM) and scanning transmission electron microscopy(STEM). Segregation occurring precisely at these interfaces was identified. A simple model was proposed based on arsenic segregation to structural units containing dangling bonds and consequent bond saturation. The removal of these dangling bonds will then play an important role in the electrical properties of these interfaces. Furthermore substitutional arsenic segregation at a degenerate level at these interfaces was also proposed. The subsequent dopant ionization and localized charges at the interfaces was discussed.
Short-pulse, multiline energy extraction from a transversely excited atmospheric CO2 laser amplifier
Authors: Rooth R. A. , Witteman W. J.
Published: July 2002

Data are presented on the energy extraction from a transversely excited atmospheric CO2 laser amplifier by a 1.1-ns pulse consisting of an adjustable number of lines which are generated by a multiline oscillator of a new design. An increase in energy extraction of 95% with respect to single-line extraction was achieved with a pulse consisting of up to six lines in the 10.6-μm branch. Energy extraction at a fixed number of lines was not very sensitive to their spectral distribution. We observed a maximum increase of about 8% when the lines were spread over the 00°1–10°0 vibrational band. This indicates a slight preference for small Δj values in the rotational relaxation processes.
Interdiffusion and chemical ordering in composition-modulated Fe70Si30/Si amorphous thin films
Authors: Bruson A. , Piecuch M. , Marchal G.
Published: July 2002

The interdiffusivity and chemical ordering in compositionally modulated (Λ=20 to 40 Å) amorphous Fe70Si30/Si thin films have been measured from the decay of the satellite intensities of the (000) x-ray scattering peak during isothermal anneals in the temperature range 373–473 K. Diffusivities as low as 10−26 to 10−25 m2 s−1 have been measured. A linear dependence of D̃Λ on 1/Λ2 has been observed, providing the evidence of chemical ordering in Fe-Si alloy and leading to the determination of a critical wavelength.
Transient annealing as a tool for the investigation of thin-film–substrate solid-phase reactions
Authors: Bentini G. G. , Nipoti R. , Berti M. , Drigo A. V. , Cohen C.
Published: July 2002

The solid-phase reaction of a thin film and a substrate induced by a transient annealing in the solid phase is analyzed in detail. The technique is based on the scanning of a line-shaped energy beam. At a given point on the sample the transient process can be considered equivalent to an isothermal one at an effective temperature for an effective time. Whatever the assumed reaction process is, it has an exponential dependence on the temperature; moreover, the real annealing time of the transient treatment is quite short so that the effective temperature can be chosen equal to the maximum value reached and the effective time can be computed by solving the heat equation numerically. The beam scanning induces a temperature gradient on the sample along the scanning direction so that each irradiated point is annealed at slightly different effective temperatures. In the present work the annealing temperatures range from 600 °C up to 1100 °C and the effective times from 0.7 to 1.5 sec, owing to the different experimental conditions. Such ranges make the transient annealing a powerful tool for the investigation of reaction processes on a time scale which is not accessible in a furnace treatment. As an application, the early stages of the reaction between a clean titanium film and a silicon substrate are described in the temperature range 700–900 °C. In this temperature range, the kinetics are first dominated by diffusion through the Ti-rich silicides which are formed. This process, with presumably high activation energy and large preexponential factor, cannot be observed in standard furnace annealing where a continuous TiSi2 layer is formed at the interface during the temperature rise time and the silicon supply is limited by the diffusion through this layer.
Laser-assisted chemical vapor deposition of Si: Low-temperature (<600 °C) growth of epitaxial and polycrystalline layers
Authors: Suzuki K. , Lubben D. , Greene J. E.
Published: July 2002

Pulsed KrF laser irradiation (248-nm or 5-eV photons) during the chemical vapor deposition of Si from SiH4 has been used to periodically melt and rapidly resolidify thin layers of continuously deposited material. From one-dimensional heat-flow calculations, the increase in the average film growth temperature for the conditions used in these experiments was less than 1° C, the melt depth ranged from ∼5 to 40 nm, and the resolidification velocity was 2 to 3 ms−1. By proper choice of laser energy density E, pulse repetition rate f, and film deposition rate R, the melt depth was adjusted to correspond to a value slightly larger than the film thickness deposited between pulses. Using this procedure, we have grown polycrystalline Si films on SiO2 and Si single crystals on (100)Si substrates at average growth temperatures Ts between 535 and 650 °C. The polycrystalline films had average grain sizes of 1 to 2 μm with a (111) preferred orientation. Films grown without laser irradiation, but otherwise under the same conditions, were amorphous at Ts<580 °C and fine-grained polycrystalline at higher temperatures. The room-temperature conductivity of irradiated In-doped polycrystalline films grown at Ts=565 °C was ∼5 orders of magnitude higher than the conductivity of unirradiated films. Irradiated single-crystal films doped with B exhibited room-temperature hole mobilities which were near the maximum theoretical bulk values for the corresponding carrier concentrations (∼1018 cm−3).
Current transport across the emitter-base potential spike in AlGaAs/GaAs heterojunction bipolar transistors
Authors: Lee Si-Chen , Kau Jau-Nan , Lin Hao-Hsiung
Published: July 2002

The recent observation of an emitter-base potential spike explains the origin of the high offset voltage of the Npn Al0.5Ga0.5As/GaAs heterojunction bipolar transistor. A new model is proposed in the paper to explain the higher turn on voltage of the emitter-base junction caused by the potential spike. This model treats the current transport mechanism across a p-n heterojunction to be a balanced two-step process, i.e., thermionic emission followed by Shockley diffusion, instead of the conventionally believed one-step diffusion process. The correct procedures to extract the potential spike height from the measured offset voltage are also established.
Low power nonlinear effects in the ferromagnetic resonance of yttrium iron garnet
Authors: McKinstry Kevin D. , Patton Carl E. , Kogekar Milind
Published: July 2002

Ferromagnetic resonance (FMR) absorption was observed in a spherical single-crystal sample of Y3Fe5O12 (YIG) at 9.5 GHz and room temperature. Resonance absorption curves were obtained as a function of microwave power level and duty cycle for different static field directions relative to the crystal axes. Foldover effects and other nonlinear behavior were seen at microwave field amplitudes (hrf) between 9 and 50 mOe with the applied static field in the (110) plane. When FMR absorption is observed with a high power cw signal (hrf=50 mOe) with the biasing field along either the [100] or the [110] directions and decreasing in magnitude, an absorption curve is obtained that has a long broad shoulder which is shifted below the low power FMR biasing field position. With increasing field in these directions, the absorption curve develops a cusp below the low power biasing field position. With the bias field in the [111] direction the absorption curve shows cusps for both increasing and decreasing fields at this power level. Field shifts in the observed resonance spectra do not converge to the zero anisotropy resonance field value, but to a field value below the low power [110] direction FMR field position. These effects disappear when the experiments are carried out using pulsed microwaves with a pulse width of 100 μsec and duty cycles below 1%. These phenomena are therefore attributed to the effects of heating on the magnetocrystalline anisotropy properties of single-crystal YIG. The quantitative results, however, are not in accord with simple heating considerations.
Transmission and reflection of a surface wave plate mode through a transverse boundary separating two isotropic media
Authors: Shen T. P. , Maradudin A. A. , Wallis R. F. , Stegeman G. I.
Published: July 2002

The transmission and reflection of guided acoustic waves by a transverse boundary separating two isotropic plates has been studied by two numerical methods, viz. the pointmatching (collocation) method and the least-squares boundary residual method. In both cases, normal mode expansions are made on both sides of the interface, and both propagating and evanescent modes are used to match the usual boundary conditions along the boundary. The plate thicknesses are chosen sufficiently large that the lowest-order modes correspond very closely to Rayleigh waves and hence information is gained about the reflection and transmission of Rayleigh waves at material discontinuities. We have investigated the influence of the material properties and plate thicknesses on the guided wave reflection and transmission coefficients, as well as the conversion efficiency into higher order guided wave modes that approximate the bulk waves that would be excited in the two semi-infinite media case.
Relationship between the stationary-state and first-order transfer-Hamiltonian tunneling models
Authors: Whiteley S. R. , Haas D. , Gustafson T. K.
Published: July 2002

An equivalence of the expectation of the flux operator for the structure eigenstates of a tunneling junction to the square of the matrix elements of the flux operator evaluated between different structure eigenstates is discussed. The results are employed to elucidate the relationship between the stationary-state model and the transfer-Hamiltonian model of the junction current.
Effective index of refraction of isotropic media containing layered spheres
Authors: Poularikas A. D.
Published: July 2002

The effective index of refraction of isotropic media containing homogeneous and layered spheres was developed. The obtained results apply to small concentration of inclusions, to different sets of particles, i.e., particles of different shapes, and each set can have Ki types of inclusions.
Deviations from Arrhenius behavior in the dark conductance of In-doped CdS films
Authors: Hurd C. M.
Published: July 2002

The dark electrical conductivity σ of In-doped CdS films does not show a simply activated behavior. Appreciable curvature is seen in graphs of log σ vs T−1. This has been attributed to a temperature-dependent activation energy or to a tendency of σ towards saturation at low temperatures. We suggest that it arises because, as the doping is reduced, the data tend to follow log σ=constT rather than log σ=const T−1. This linear temperature dependence of log σ has also been seen for off-stoichiometric SiO2 films, among other low-conductivity solids, and we point out that it is a characteristic behavior which was anticipated more than 20 years ago in a model of quantum tunneling through a vibrating barrier.
Steady-state and transient capacitance of a p-n junction in the presence of high density of deep levels
Authors: Eron Murat
Published: July 2002

Static and transient capacitance of a n+-p junction is analyzed when a large density of deep levels are present. The model has a single level but the analysis can be easily extended to more complicated systems. The effect of the presence of such deep levels to measured junction capacitance, diffusion potential, and carrier density profiles are estimated. Relevant relations for steady-state and transient measurements are derived. The possibility of obtaining deep-level energy experimentally without making temperature measurements is pointed out.
Series array of highly hysteretic Josephson junctions coupled to a microstrip resonator
Authors: Costabile G. , Andreone D. , Lacquaniti V.
Published: July 2002

We have tested a new device based on a 12 junction array coupled to a resonator. We have explored the feasibility of the phase lock for all the junctions at the same biasing current, which yields voltage quantization across each junction, eliminating the need to individually bias the junctions. The whole rf structure has been realized by stripline technology. The resonator is fed by a 50-Ω line and is decoupled from the dc circuit by elliptical low-pass filters inserted in the bias leads.
Interpretation of multiple-pulse laser-induced damage in metal mirrors
Authors: Loh Eugene
Published: July 2002

The multiple-pulse laser-induced damage in metal mirrors investigated experimentally and theoretically by Lee, Koumvakalis, and Bass [Opt. Eng. 22, 419 (1983)] can be described by N≂exp[I(N)/I(Nmax)]. This exponential relation between the number of pulses N required to cause failure and the corresponding laser intensity I(N) can be interpreted readily in terms of the accumulative effect of plastic deformation induced by thermal stresses as outlined by the above authors.
Effects of deep Fe acceptors on the impedance of a semi-insulating n-type Fe-doped InP Schottky barrier
Authors: Hattori K. , Uraoka U. , Fujii T.
Published: July 2002

The capacitive response of deep Fe acceptors in a semi-insulating n-type Fe-doped InP Schottky barrier has been investigated. The capacitance-voltage (C-V) and conductance-voltage (G-V) characteristics over the frequency range 0.06–100 kHz are measured at 300, 317, and 335 K. Great frequency dispersion is observed in C and G. The reverse bias dependencies of C and (G−G0) are shown to be very weak at high frequencies, where G0 is the dc conductance. As measuring frequency is lowered, (G−G0) decreases but C increases considerably. At low frequencies, the bias dependencies of C and (G−G0) are observed and measured 1/C2 versus reverse bias curves are found to be straight lines. It is shown that at low frequencies, C and (G−G0) take maxima near zero bias and rapidly decrease in a forward bias region. As temperature increases, the frequency region in which such low-frequency characteristics are found extends more widely into a high-frequency range. Theoretical calculations of C and (G−G0) are also carried out. The results are compared with experimental ones. Observed variations of C and G with frequency, bias voltage, and temperature are well explained in terms of the delayed response of deep Fe acceptors.
II-VI infrared superlattices
Authors: Kinch M. A. , Goodwin M. W.
Published: July 2002

Superlattice materials systems have recently been proposed to overcome the inherent problems of large tunnel and dark currents that limit the operation of infrared detectors at longer wavelengths (≥10 μm). We have utilized the envelope function approximation and a simple two-band Kane model to calculate the dependence of cutoff wavelength and effective mass on specific layer thicknesses for the HgTe-CdTe materials system. Infrared absorption coefficient calculations have been carried out on this system (with Eg =0.1 eV) and compared with both HgTe and 0.1-eV HgCdTe alloy. Infrared device performance for various proposed superlattice systems is predicted from a consideration of effective mass and absorption coefficient values. Superlattice systems involving materials with the inverted gray tin band structure are seen to offer the greatest potential for future infrared devices.
Discharge-pumped gold-vapor laser operating in a low-temperature range using chloroauric acid as a lasant
Authors: Taniguchi Hiroshi , Saito Hiroshi
Published: July 2002

Laser oscillation has been obtained from a discharge-pumped gold vapor at 627.8 nm of a neutral gold atom in a low-temperature range of about 70 –150 °C by using chloroauric acid as a lasant. A laser is operated by successive pulsed discharges of a storage capacitor through a spark-gap switch. Excitation is done in an aperiodic pulse train with a compact device by a boosted-ac (50 Hz) high voltage of up to 5.4 kV rms. A maximum laser peak power of about 1.3 W and a laser-pulse energy of 27 nJ are obtained.
Acoustic observation of a welded steel block
Authors: Toda Kohji , Hayama Masaru , Miki Chitoshi
Published: July 2002

Imaging results are described by observing acoustically a welded region in a steel block. An obvious difference between the original state and the annealed state is recognizable, which indicates that the elastic discontinuity around the welded region produced by welding is diminished by annealing.
Influence of intense laser field on the tunneling current in semiconductors
Authors: Tronconi A. L. , Nunes O. A. C.
Published: July 2002

The influence of an intense laser field on the quasienergy gap of a semiconducting crystal as developed in the presence of an exciting laser field is discussed. It is shown that the effect of the strong laser is of ‘‘dressing’’ the quasienergy gap in that it becomes modulated by the strong field amplitude. The consequence of this latter effect on the tunneling current between a semiconductor-semiconductor junction is discussed. An application is made for a GaAs sample.
Isomerically selective photoionization of mercury-197
Authors: Dyer P. , Baldwin G. C. , Sabbas A. M. , Kittrell C. , Schweitzer Eric L. , Abramson E. , Imre Dan G.
Published: July 2002

We report the second of a series of experiments on selective photoionization of mercury isotopes in which we show that radioactive atoms containing either isomeric form of the radionuclide 197Hg can be selectively ionized in the presence of natural mercury isotopes by doubly resonant three-step laser photoionization, and discuss its implications as a test case for nuclear-isomer separation.
Time-resolved optical emissions from high-current relativistic electron beams propagating in 150-mTorr air
Authors: Hughes R. H.
Published: July 2002

Results of a time-resolved study of optical emissions from high-current relativistic (6.5 MeV) electron beams propagating in air at a pressure of 150 mTorr are presented. The emissions included N+ lines at λλ4803, 4630, 4552, and 4530 Å. Data were obtained on a single-shot basis by simultaneously recording the temporal history of all four ion lines. For propagating electron beam pulses, each ion line exhibited peak intensity a few microseconds after the passage of the 80-ns-wide electron pulse. This behavior is explained on the basis of inductive (magnetic) energy storage in the return current plasma channel. Spatially integrated plasma temperatures are measured to be in the 20 000–30 000 K range, reaching a maximum when the inductive energy storage has gone to zero.
A photothermal radiometer for concentrator solar cell measurements
Authors: Birkeland Joel D. , Kaufman Irving , Backus Charles E.
Published: July 2002

A photothermal technique for measuring the intensity of concentrated sunlight is described. In this technique chopped concentrated sunlight is allowed to impinge on a black metal plate, to produce a time-varying surface temperature, which is measured by an infrared radiometer followed by a lock-in amplifier. By calibrating this system with a solar cell in the range in which the cell short-circuit current is known to vary linearly with light intensity, high ratios of solar concentration can be determined. Using this technique, we found the short-circuit current of an n+p solar cell to be linear with concentration up to 410 suns.
Majority-carrier capture cross-section determination in the large deep-trap concentration cases
Authors: Morante J. R. , Samitier J. , Cornet A. , Herms A. , Cartujo P.
Published: July 2002

A method to determine the thermal cross section of a deep level from capacitance measurements is reported. The results enable us to explain the nonexponential behavior of the capacitance versus capture time when the trap concentration is not negligible with respect to that of the shallow one, and the Debye tail effects are taken into account. A figure of merit for the nonexponential behavior of the capture process is shown and discussed for different situations of doping and applied bias. We have also considered the influence of the position of the trap level’s energy on the nonexponentiality of the capture transient. The experimental results are given for the gold acceptor level in silicon and for the DX center in Al0.55 Ga0.45As, which are in good agreement with the developed theory.
(FeCo)-Nd-B permanent magnets by liquid dynamic compaction
Authors: Chin T. S. , Hara Y. , Lavernia E. J. , O’Handley R. C. , Grant N. J.
Published: July 2002

A new rapid solidification processing technique, liquid dynamic compaction (LDC), has been used to make bulk permanent magnets of composition Fe57 Co20 Nd15 B8. In this process, molten metal is spray atomized onto a cooled substrate in a protective atmosphere. Oxidation is minimal. Subsequent heat treatment at 450 °C of the LDC’d material has resulted in isotropic permanent magnets with intrinsic coercivity and remanance approaching 8000 Oe and 6000 G, respectively.
Formation of charged N1 centers in KCl and KBr
Authors: Schneider Irwin
Published: July 2002

This paper reports the results of studies on charged N1 centers, produced using a technique in which additively colored KCl and KBr crystals are exposed to near ultraviolet excitation at low temperatures. In undoped crystals, absorption and emission data are presented showing several new charged N1 transitions along with information relating to the nature of the defects. In addition, this work demonstrates that in sodium-doped crystals, N1 centers can be ionized through electron transfer to FA centers. This technique has already been used in stabilizing (F+2)A centers in laser-active crystals and may have future application for lasing ionized N1 centers.
Photochromic silver complex oxide thin films synthesized by anodic oxidation
Authors: Hirono Takushi , Yamada Tomoaki , Nishi Toshihiro
Published: July 2002

Silver complex oxide thin films, which contain V, Cr, Mo, W, Si, Sn, P, Te, and I as constituent elements, are synthesized by anodic oxidation of silver metal films. It is found that Ag3VO4, Ag4SiO4, and Ag3PO4 films show good photochromic properties. An x-ray photoelectron spectroscopy study on a Ag3PO4 film shows that the silver ions are reduced and PO4 tetrahedra are condensed by visible light irradiation and that the inverse reaction is produced by heating.