bluuebunny/crossref_metadata_2025 huggingface dataset:
Subthreshold electron velocity-field characteristics of GaAs and In0.53Ga0.47As
Authors: Haase M. A. , Robbins V. M. , Tabatabaie N. , Stillman G. E.
Published: July 2002

The electron drift velocities in GaAs and In0.53Ga0.47As have been measured at room temperature and at liquid-nitrogen temperature for electric fields up to the onset of the Gunn effect. The experiments were performed on samples with carrier concentrations from 4×1014 to 1×1018 cm−3. The results illustrate effects of ionized impurity scattering, polar optical phonon scattering, alloy scattering, and intervalley scattering on electron transport in this range of electric fields, and confirm the potential of In0.53Ga0.47As for high-speed device applications.
Fits for hydrogenic Stark-broadened line profiles for the elements carbon to argon
Authors: Lee R. W.
Published: July 2002

Using theoretical calculations to generate Lyman β and δ Stark-broadened line profiles, we have found a simple parameterization of the line intensity full width at half maximum over a broad range of the atomic species [Z∈(6,18)], electron density [NE∈(1019,1025) cm−3], and electron temperature (TE=250,500,1000 eV). The parameters of the fits are presented together with a discussion of the method.
Time-resolved proton focus of a high-power ion diode
Authors: Johnson D. J. , Leeper R. J. , Stygar W. A. , Coats R. S. , Mehlhorn T. A. , Quintenz J. P. , Slutz S. A. , Sweeney M. A.
Published: July 2002

An improved understanding of the factors that control the axial focus of applied-B ion diodes was obtained from time-resolved diagnostics of ion-beam trajectories. This resulted in a new selection of anode shape that produced a proton focus of 1.3-mm diameter from a 4.5-cm-radius diode, which is a factor of 2 improvement over previous results. We have achieved a peak proton power density of 1.5±0.2 TW/cm2 on the 1-TW Proto I accelerator. The radial convergence of this proton beam, defined as the ratio of the anode diameter to focused beam FWHM, is 70. Time-resolved information about virtual cathode evolution, the self- and applied-magnetic-field bending, and the horizontal focus of the beam was also obtained. In addition, the diffusion of the magnetic field into the anode plasma is estimated by measuring the horizontal focal position as a function of time. Finally, we discuss the effects of gas cell scattering on the beam focus.
Silicon-on-insulator structures formed by a line-source electron beam: Experiment and theory
Authors: Knapp J. A.
Published: July 2002

A line-source electron beam has been used to melt and recrystallize isolated Si layers to form Si-on-insulator structures. Heat flow calculations for these layered structures have been developed which correctly predict the observed recrystallization. Using sample sweep speeds of 100–600 cm/s and peak power densities up to 75 kW/cm2 in the 1×20-mm beam, we have obtained single-crystal areas as large as 50×350 μm. Seed openings to the substrate are used to control the orientation of the regrowth and the heat flow in the recrystallization film.
Thermomigration in indium and indium alloy films
Authors: van Gurp G. J. , de Waard P. J. , du Chatenier F. J.
Published: July 2002

Thermomigration in indium and indium alloy films of thickness between 0.3 and 3 μm was studied between 80 and 145 °C in a scanning electron microscope, using a newly developed test pattern with a stripe heater of 10 μm width. The amount of transported material was determined as a function of time and temperature by measuring the size of the holes appearing at the position of maximum temperature. The product of diffusion coefficient D and heat of transport Q* was determined, using calculated values of the temperature gradient. The DQ* product has an activation energy of 0.8 eV. Material is transported from hot to cold areas, so that Q* is positive. Transport is much faster for thinner films. Alloying indium with Ag, Ga, Pb, or Sb has little effect on thermomigration rate.
Diffusion of boron in heavily doped n- and p-type silicon
Authors: Willoughby A. F. W. , Evans A. G. R. , Champ P. , Yallup K. J. , Godfrey D. J. , Dowsett M. G.
Published: July 2002

The diffusion of 10B in the presence of high-concentration 11B and As doping has been studied. Dopants were introduced by ion implantation and profiles after annealing were obtained by secondary ion mass spectrometry. Diffusion coefficients were derived by comparing experimental profiles with those from a computer simulation program and results confirmed that diffusion of boron is enhanced in p+ silicon and depressed in n+ silicon. These results have been analyzed using the widely accepted vacancy model for boron diffusion and have produced values of the parameter β, which is related to the ratio of diffusivity for charged and uncharged vacancies, of 0.25 to 3.0 for the p+ and 3.0 to 7.7 for the n+ conditions. This difference cannot be ascribed to experimental error and suggests that further refinement of the vacancy model is required.
Analysis of current-voltage characteristics of metal-insulator composite films
Authors: Niklasson G. A. , Brantervik K.
Published: July 2002

We present a method for analyzing current-voltage relationships to obtain information on the dominant conduction mechanisms. The method is based on the analysis of the derivative of the logarithmic conductivity with respect to inverse applied electrical field. To illustrate the method we apply it to the study of Co-Al2O3 and Au-Al2O3 composite films. The former material displays space-charge-limited conduction, which is due to a high density of trap states in the oxide matrix. On the other hand, Au-Al2O3 shows evidence of percolation and tunneling between metal particles.
Magnetic diffusion smoothing with application to the hydromagnetic Rayleigh–Taylor instability
Authors: Roderick N. F. , Hussey T. W.
Published: July 2002

An analytic model has been developed to quantify the effects of magnetic field diffusion on plasmas accelerated by magnetic J×B forces. We examine the penetration of equilibrium and perturbed magnetic fields into a conducting plasma. Analytic solutions are found for both fields for a power law time dependence of the equilibrium field at the field plasma interface. Results show that wavelengths longer than the magnetic field diffusion length penetrate the plasma shell faster than the equilibrium field. For wavelengths shorter than the magnetic diffusion length the perturbed field remains confined to the original field plasma interface and falls off rapidly inside the plasma. Application to imploding linear plasmas show good agreement with detailed two-dimensional magnetohydrodynamic simulations.
A photoluminescence and Hall-effect study of GaSb grown by molecular-beam epitaxy
Authors: Lee M. , Nicholas D. J. , Singer K. E. , Hamilton B.
Published: July 2002

Unintentionally doped gallium antimonide has been grown by molecular-beam epitaxy on gallium arsenide and gallium antimonide. Substrate temperatures in the range 480 to 620 °C and antimony to gallium flux ratios from 0.65 : 1 to 6.5 : 1 have been investigated. The deposition conditions have been related to growth morphology and to the electrical and optical properties of the epitaxial films. A strong correlation has been found between the quality of the layers and the degree of excess antimony flux; the best material in terms of both optical and electrical properties was obtained with the minimum antimony stable growth at a particular substrate temperature. All the material exhibited residual p-type behavior. The lowest hole concentration achieved was 7.8×1015 cm−3 with a corresponding room-temperature mobility of 950 cm2/V s. The narrowest PL (photoluminescence) features observed were peaks associated with bound exciton transitions with half-widths of 2–3 meV.
Distribution of charge carriers generated in a semiconductor by a focused convergent light beam
Authors: Wilson T. , McCabe E. M.
Published: July 2002

We calculate the three-dimensional light distribution in the focal region of a lens in the presence of absorption. The results are directly applicable to the optical generation of carriers in a semiconductor. A generation volume for these carriers is introduced and its dependence on focus position is investigated.
The effect of processing conditions on the GaAs/plasma-grown insulator interface
Authors: Hshieh F. I. , Borrego J. M. , Ghandhi S. K.
Published: July 2002

The effect of processing conditions on the interface state density was evaluated from C-V measurements on metal-oxide-semiconductor capacitors. The optimum processing condition for the minimum surface state density was found to be related to the postoxidation annealing temperature and time, and was independent of chemical treatments prior to oxidation. Annealing at the optimum condition (i.e., at 350 °C for 1 h in either nitrogen or hydrogen gas, with or without an aluminum pattern on the oxide) reduces the fast surface state density by about one order of magnitude. By using a nitrogen/oxygen plasma, the static dielectric constant of the oxide decreased as the N/O ratio was increased, and nitrogen was incorporated into the oxide. In addition, the fast surface state density was reduced as a result of this nitridation process.
Infrared absorption in indium nitride
Authors: Tansley T. L. , Foley C. P.
Published: July 2002

The room-temperature optical absorption spectra of indium nitride films in the subband-gap energy range 40 meV to 2.0 eV are surveyed. The major features are two broad absorption bands: a band-edge tail with a threshold energy of about 1 eV and a broad peak centered at about 0.3 eV. Both are strongly sample dependent and are identified with crystal defects associated with the observed electrical compensation of the shallow donor impurity. All samples show optical excitation of the 50–60-meV shallow donor seen in thermal excitation measurements, while some exhibit an absorption doublet, whose nature is not understood, around 0.15 eV.
Relation between crystallographic orientation and the condensation coefficients of Hg, Cd, and Te during molecular-beam-epitaxial growth of Hg1−xCdxTe and CdTe
Authors: Sivananthan S. , Chu X. , Reno J. , Faurie J. P.
Published: July 2002

We investigate here the influence of the crystallographic orientation of the CdTe substrate on the condensation coefficients of Hg, Cd, and Te during the growth of Hg1−xCdxTe and CdTe by molecular-beam epitaxy. We show that the Hg condensation coefficient is strongly influenced by the orientation. A CdTe (1̄1̄1̄)B face requires about one order of magnitude less mercury than a (111)A face when growth occurs at 185 °C. Whereas for a CdTe(100) face, the Hg condensation coefficient falls in between. Even though the effect is less dramatic for the condensation coefficient of cadmium, a similar tendency is observed. These results can be explained in terms of the bonding of the surface atoms and confirm once again that the surface plays an important role in the molecular-beam-epitaxial growth process.
Slowness surface measurements for zero- and five-degree [100]-cut GaAs
Authors: Hunt W. D. , Miller R. L. , Hunsinger B. J.
Published: July 2002

A modification to accommodate loss is made to a method developed by D. Murray and E. A. Ash [1977 Ultrasonics Symposium Proceedings, IEEE Cat. No. 77CH1264-1SU (IEEE, New York, 1977), p. 823] for computing the surface acoustic wave slowness surface of piezoelectric substrates. The resulting algorithm is used to determine the slowness surface for the leaky or pseudosurface wave which propagates on [100]-cut GaAs and for a cut 5° off from this. The data thus obtained are used in a diffraction theory computer program to predict the shape of beam profiles as they propagate in the substrate material and accurate predictions of beam shapes are obtained.
Barrier heights and electrical properties of intimate metal-AlGaAs junctions
Authors: Eizenberg M. , Heiblum M. , Nathan M. I. , Braslau N. , Mooney P. M.
Published: July 2002

The dependence of the Schottky barrier height of Mo-n:AlGaAs junctions, fabricated in situ by molecular beam epitaxy, on the Al mole fraction (x) was determined by internal photoemission measurements and by activation energy plots of the current versus voltage dependence on temperature. Both techniques yielded similar values. The difference in barrier height of Mo-AlGaAs as a function of x, compared to that of Mo-GaAs, was found to be equal to the conduction band discontinuity in AlGaAs-GaAs heterojunctions for Al concentrations in the range 0≤x≤0.4. For x>0.4, values of the barrier heights were somewhat lower than values of the band discontinuity; however, both dependencies on x were quite similar. The temperature dependence of the current-voltage characteristics showed that thermionic emission was the dominant transport mechanism at forward bias for temperatures higher than 250 K. At lower temperatures, current transport was governed by thermionic field emission.
Stability enhancement of a low initial density hollow gas-puff z pinch by e− beam preionization
Authors: Ruden E. , Rahman H. U. , Fisher A. , Rostoker N.
Published: July 2002

e − beam preionization of the initial gas column of the hollow gas-puff z pinch at the University of California, Irvine is shown to decrease the amplitude of Rayleigh–Taylor instabilities which disrupt the imploding plasma shell of low initial density (<1×1017 cm−3) helium pinches. A 5-ns pulsed nitrogen laser Mach–Zehnder interferometer compares the plasma density profile at various times during the implosion for preionized and unpreionized pinches. Also, a B-dot current probe compares the plasma induction fluctuations of the pinched state. Numerical calculations of the effects of the Rayleigh–Taylor growth for our geometry are discussed.
High-temperature stress measurement on chemical-vapor-deposited tungsten silicide and tungsten films
Authors: Shioya Yoshimi , Ikegami Kaoru , Maeda Mamoru , Yanagida Kimio
Published: July 2002

Stresses in chemical-vapor-deposited tungsten silicide and tungsten films at high temperatures were measured. Tungsten silicide films were formed from WF6 and SiH4 or Si2H6. Tungsten films were formed from WF6 and H2. The stress in tungsten silicide films is tensile and in the order of 109–1010 dynes/cm2. For a composition ratio of Si/W≤2.6, the stress of a film of more than 1000 Å has a maximum at about 500 °C. On the other hand, for a composition Si/W>2.9, the stress has no maximum. The maximum of the stress is caused by crystallization of the film. The stress has two components. One component is related to the difference of the thermal expansion coefficients between the film and the Si substrate. Another is related to the film crystallization. It was found that the stress concentrates in the portion of the film nearest the substrate. The stress in tungsten films also reaches a maximum at 550 °C, similar to the tungsten silicide films. However, the cause of this behavior is not clear.
Magnetic properties of Er2Fe14B and Nd2Fe14B thin films
Authors: Zasadzinski J. F. , Segre C. U. , Rippert E. D.
Published: July 2002

Thin films of Nd2Fe14B and Er2Fe14B have been synthesized by dc sputtering onto single-crystal sapphire substrates. X-ray diffraction revealed that the films were single phase and that the texture was sensitive to the substrate temperature. Films deposited onto substrates at 600 °C showed directed crystalline growth with the c axis of the tetragonal structure predominantly perpendicular to the film plane. Magnetization measurements of the Er2Fe14B films and Kerr rotation of the Nd2Fe14B films indicate an intrinsic anisotropy consistent with the preferred orientation. Electrical transport measurements of the Nd2Fe14B film display a change of slope near T=150 K which is interpreted as a consequence of the spin reorientation.
Electrical conduction mechanism in semi-insulating polycrystalline silicon films
Authors: Comizzoli R. B. , Opila R. L.
Published: July 2002

A scanning Auger microprobe (SAM) has been used to measure the equipotential lines and the potential profile across semi-insulating polycrystalline silicon (SIPOS) film structures, and the electron beam parameters required to prevent charging effects and to minimize beam current relative to sample current have been determined. The conduction process in these SIPOS films was related to Frenkel generation of carriers. This field-enhanced emission from a localized state results in a field-dependent current which is added to an ohmic current. The potential profiles obtained with the SAM are in reasonable agreement with those predicted by this model. The effects of potential screening by charge at the SiO2-SIPOS interface are discussed and related to location-dependent variations in the potential profile. A zero-field conductivity of 1.4×10−6 (Ω cm)−1 was obtained for our films.
Enhanced magnetism in amorphous Fe-based alloys
Authors: Liou S. H. , Ge S. H. , Taylor J. N. , Chien C. L.
Published: July 2002

Systematic investigations of binary amorphous Fe–T alloys (T=an early transition-metal elements Ti, Zr, Nb, Hf, Ta...) over wide composition ranges reveal depressed magnetic properties with anomalously low magnetic ordering temperature and magnetization. We show in this work, via a prototype amorphous Fe70Ti30 alloy, the substitution of Fe by Co, Ni, or Cu greatly enhances the magnetic ordering temperature and the magnetization. Our results indicate that this is primarily caused by the increased Fe moment upon alloying.
Effect of ion bombardment on the plasma-assisted etching and deposition of plasma perfluoropolymer thin films
Authors: Fracassi F. , Occhiello E. , Coburn J. W.
Published: July 2002

A study of the etching and deposition of plasma perfluoropolymer thin films has been carried out by using quartz-crystal microbalance methods for a range of feed gas mixtures.
Radiation-induced defect centers in high-purity GeO2 glass
Authors: Tsai Tsung-Ein , Griscom D. L. , Friebele E. J. , Fleming J. W.
Published: July 2002

Defect centers induced in GeO2 glass by either 100-KeV x rays at 77 K or γ rays at room temperature were studied by electron-spin resonance. The model of a singly charged oxygen vacancy defect center for the Ge E′ center (g∥ =2.0012, g⊥ =1.9945) was confirmed by the observation and computer simulation of the 73Ge hyperfine structure associated with this center. The evolutions of the Ge E′, peroxy radical, and nonbridging oxygen hole centers were studied by isochronal thermal annealing. Surprisingly, the Ge(2) center, a defect previously known only in Ge-doped silica, and an additional center with a hyperfine coupling constant half that of the Ge E′ center were found in pure GeO2 samples irradiated at 77 K; these, too, were studied by isochronal thermal annealing and computer simulation. Structural models for these centers are presented.
Current transport in p-type CdIn2Te4 Schottky diodes
Authors: Kianian S. , Eshraghi S. A. , Stafsudd O. M. , Gentile A. L.
Published: July 2002

Schottky diodes were fabricated on p-type CdIn2Te4 using evaporated aluminum dots. The forward and reverse current-voltage characteristics of these Schottky barrier devices were studied as a function of temperature. An analysis of this data allows the determination of the barrier height, the behavior of traps, and the current transport mechanism of the devices. The forward conduction mechanism appears to be a multistep tunneling process. The reverse transport is dominated by a diffusion process. The height of the barrier associated with the junction as revealed by the reverse I-V characteristics is 0.4 eV. The conductivity type of the crystals can be changed from n type to p type in a manner similar to CdTe.
Determination of electron density and temperature in non-LTE plasmas from spectral lines of impurity ions
Authors: Kunc Joseph A.
Published: July 2002

An approach to determination of populations of the excited lithiumlike ions C iv, N v, O vi, and Ne viii in stationary nonequilibrium plasmas is presented. Each of these ions produces several dipole-allowed spectral lines so that the number of the available line intensity ratios is large. Consequently, the electron density and temperature can be determined by comparing some of the measured intensity ratios with their calculated values. The populations of several ionic levels, electronic partition functions, and the intensity ratios for 3 2D→2 2P/2 2P→2 2S, 3 2P→2 2S/2 2P→2 2S, 3 2S→2 2P/2 2P→2 2S, 3 2D→2 2P/3 2P→2 2S, 3 2D→2 2P/3 2S→2 2S→2 2P, and 3 2P→2 2S/3 2S→2 2P transitions are calculated in a broad range of electron density and temperature. The approach is especially useful for diagnostics of systems where nonintrusive spectroscopic techniques must be used (e.g., astrophysical and fusion plasmas).
Modeling of pyrolytic laser-assisted chemical vapor deposition: Mass transfer and kinetic effects influencing the shape of the deposit
Authors: Skouby D. C. , Jensen K. F.
Published: July 2002

The laser-assisted chemical vapor deposition of metals is modeled. The case of pyrolytic deposition induced by a continuous laser source is considered. The heat transfer in the solid substrate is considered to be transient, while the gas-phase heat and mass transfer are assumed to be in the quasi-steady state. The model accommodates the use of temperature-dependent physical properties and the occurrence of irregularly shaped deposits. The modeling equations are solved by a finite element approach which is briefly described. Volcanolike deposits are predicted under certain conditions of gas pressure and laser intensity. Model predictions show that depletion effects and adsorption-desorption phenomena are major factors in influencing the occurrence of volcanolike deposits.
Digital filter design approach for SQUID gradiometers
Authors: Bruno A. C. , Ribeiro P. Costa
Published: July 2002

A review of the traditional method for designing gradiometers is made. A nonrecursive digital filter model for the gradiometer is presented, giving a new set of parameters for the gradiometer identification. Some designs are analyzed using the proposed set. As an example, a true differentiator is designed to be used as the SQUID input coil. It is shown that the differentiator has the same noise rejection as the conventional gradiometer but provides more signal sensitivity.
Amorphous iron particles in cosputtered Fe-SiO2 films
Authors: Holtz R. L. , Edelstein A. S. , Lubitz P. , Gossett C. R.
Published: July 2002

Small silicon-stabilized amorphous iron particles in a silica matrix have been produced by cosputtering under conditions that apparently disturb the Si:O stoichiometry obtained from the SiO2 source. The amorphous iron particles can be converted to α-Fe by annealing in vacuum at high temperatures. As-deposited films with iron volume fractions around 45% have small coercive force and exhibit a magnetic switching phenomena.
A thermodynamic phenomenology for ferroelectric tungsten bronze Sr0.6Ba0.4Nb2O6 (SBN:60)
Authors: Oliver J. R. , Neurgaonkar R. R. , Cross L. E.
Published: July 2002

The tetragonal tungsten bronze ferroelectrics in the strontium barium niobate system have been extensively studied over many years. As for many of the bronzes, a crude interpretation of the experimental data has been attempted in the past using the simple Landau-Ginsburg-Devonshire expansion of the Gibbs free energy as a Taylor series in powers of the polarization, lumping all the temperature dependence into the lowest order term. In this paper new measurements are presented for the temperature dependence of dielectric polarization, permittivity, and the E-field dependence of the permittivity. It is shown that for a realistic fitting of the data, the Taylor expansion must be taken to at least the eighth power term, and that the coefficients of terms up to the sixth power must be taken as functions of temperature. Since the phenomenology describes equilibrium behavior, it is the total static polarizability that is being explored in this treatment. The nature of this temperature dependence strongly suggests that the phase transition from a macropolar to a macrononpolar state is tetracritical.
WxN1−x alloys as diffusion barriers between Al and Si
Authors: So F. C. T. , Kolawa E. , Zhao X.-A. , Pan E. T-S. , Nicolet M.-A.
Published: July 2002

Reactively sputtered tungsten nitride (WxN1−x) layers are investigated as diffusion barriers between Al overlayers and Si shallow n+ -p junctions. Both amorphous W80 N20 and polycrystalline W60 N40 films were found to be very effective in preserving the integrity of the n+ -p diodes for 30-min vacuum annealing up to 575 °C. Diode failure at higher temperatures is caused by localized penetration of Al into 〈Si〉 through the WxN1−x barriers. The effectiveness of the barrier decreases for polycrystalline W90 N10 and is worse for pure W.
Dislocation structure, formation, and minority-carrier recombination in AlGaAs/InGaAs/GaAs heterojunction bipolar transistors
Authors: Fitzgerald E. A. , Ast D. G. , Ashizawa Y. , Akbar S. , Eastman L. F.
Published: July 2002

The defect structure in lattice-mismatched Al0.25Ga0.75As/InxGa1−xAs/GaAs heterojunction bipolar transistors (HBTs) was investigated using cathodoluminescence (CL), planar and cross-sectional transmission electron microscopy (TEM), and electron-beam-induced current images of the emitter-base and base-collector junctions. It was found that the individual techniques listed above cannot lead to a complete understanding of the defect structure; however, by combining techniques, we are able to derive a detailed knowledge of the dislocation structure, formation, and nonradiative recombination properties in the HBT structures. We find that misfit dislocations predominately form at the mismatched interface located most deeply in the structure. For noninverted HBT structures, which have the AlGaAs emitter/InGaAs base junction on top, we find the majority of misfit defects near the base-collector junction at the bottom InGaAs/GaAs interface. At low dislocation density interfaces, dark line defects observed in CL and misfit dislocations seen in TEM micrographs correlate one to one, but at high densities the dark lines correspond to groups of misfit dislocations. At high In concentrations, a dense network of defects forms at the bottom InGaAs/GaAs interface. The dislocations that are expelled by interdislocation forces from this interface propagate into the GaAs side of the interface, leaving the base region and the emitter-base interface relatively free of misfit dislocations. The relaxation of the strained base by misfit dislocation formation at the InGaAs/GaAs interface is much slower than that predicted using mechanical equilibrium theory. Utilizing the above results, we describe a method for obtaining dislocation-free interfaces in mismatched multilayer structures. This method can be incorporated in lattice-mismatched HBT structures to obtain dislocation-free emitter-base junctions.
Photothermoelastic imaging at a flexural resonance frequency of a clamped plate sample
Authors: Hane K. , Kanie T. , Hattori S.
Published: July 2002

Photothermal technique is studied for nondestructive imaging of irregularity in a platelike sample partially clamped circumferentially. By using a flexural resonance of the sample itself, the sensitivity for obtaining the image has been improved. The excitation efficiency for the resonant vibration at different positions of the heating laser beam is dependent on the resonance mode as well as the clamp condition.
Stimulated luminescence in rare-earth-doped MgS
Authors: Chakrabarti K. , Mathur V. K. , Rhodes Joanne F. , Abbundi R. J.
Published: July 2002

Optically stimulated luminescence and thermally stimulated luminescence in MgS:Ce,Sm and MgS:Eu,Sm have been investigated. It appears that samarium in the form of Sm3+ ion acts as a thermally stable electron trap in MgS:Ce,Sm and MgS:Eu,Sm. A Sm3+ ion becomes a Sm2+ ion capturing an electron when these materials are exposed to UV radiation at room temperature, while the free hole is captured by a Ce3+ (or Eu2+). On optically stimulating an UV treated sample, the trapped electrons are released from Sm2+ ions and are recaptured by Ce4+ (or Eu3+) ions leading to the luminescence which is characteristic of Ce3+ (or Eu2+) emission. However, thermal stimulation of these UV treated samples results in luminescence which is characteristic of Sm3+ emissions, indicating that the thermoluminescence results from the release of holes from Ce4+ (or Eu3+) and Sm3+ acts as a luminescence center.
Interface-roughness and island effects on tunneling in quantum wells
Authors: Liu H. C. , Coon D. D.
Published: July 2002

An effective-mass envelope function approach is applied to tunneling in quantum wells with nonplanar heterointerfaces. Epitaxial-growth-related interface roughnesses and islands complicate electron-tunneling processes and degrade resonant tunneling in double-barrier structures. Basic theoretical techniques are developed and applied to both single- and double-barrier cases.
High population inversion in the soft-x-ray band observed in a laser-irradiated microtube
Authors: Tan Weihan , Lin Zunqi , Yu Wenyan , Gu Min , Chen Wenhua , Zheng Yuxia , Wang Guanzhi , Cui Jixiu , Deng Ximing
Published: July 2002

A new microtube target has been adopted for high population inversion of Mg+10 ions between 1s3p level and 1s4p or 1s5p levels for the first time. The mechanism for inversion is discussed.
Magnetic and structural properties of Nd2Fe14B permanent-magnet films and multilayers with Fe and Ag
Authors: Aylesworth K. D. , Zhao Z. R. , Sellmyer D. J. , Hadjipanayis G. C.
Published: July 2002

The effects of sputtering conditions on the structure and magnetic properties of Nd2(Fe0.9Co0.1)14B films and multilayers are reported. The samples were sputtered onto temperature-controlled mica and Ta substrates, at temperatures between 20 and 620 °C. X-ray diffraction results indicate that films deposited directly onto 500–600 °C substrates with Fe buffer layers are nearly single-phase materials with the c axis of the grains largely perpendicular to the film plane. Room-temperature magnetization measurements to 17.4 kOe indicate that these films have strong perpendicular anisotropy with coercivities in excess of 10 kOe and magnetizations greater than 100 emu/g. Results for Nd2 (Fe0.9 Co0.1 )14 B/Fe multilayers show that films can be produced with either in-plane or perpendicular anisotropy depending on the layer thicknesses. The Fe multilayers were found to have coercivities similar to those for the single layer films. Multilayers made with Ag were found to have significant interdiffusion and secondary phases.
Investigation of the negative peak in photoinduced transient spectra of semi-insulating gallium arsenide
Authors: Blight S. R. , Thomas H.
Published: July 2002

A common observation in the photoinduced transient (PITS) spectra of semi-insulating GaAs is the appearance of a negative peak, which is anomalous in that both electron and hole traps should give rise to positive peaks. In this paper, it is shown that the negative peak can be explained in terms of charge exchange with the GaAs surface and only occurs in material which displays particular types of current-voltage and current-temperature characteristics. The dependence of this peak on the processing effects of surface passivation, etching, and baking and polishing has been investigated and its sensitivity to variations in incident light intensity is demonstrated. A new variation of PITS, namely gated-PITS has been employed. This technique suppresses the negative peak in the spectrum, allowing transients corresponding to emission from EL2 to be detected in particular undoped liquid encapsulated Czochralski GaAs substrates for the first time.
Determination of crystallographic orientations in silicon films by Raman-microprobe polarization measurements
Authors: Mizoguchi Kohji , Nakashima Shin-ichi
Published: July 2002

Local crystallographic orientations of semiconductors have been determined by a scanning Raman microprobe combined with polarization measurements. We present a method of Raman scattering determination of crystallographic orientations in silicon crystals which allows rapid determination with an accuracy of ±2°. It is found that surface morphology affects the Raman polarization analysis. For laser-annealed silicon layers capped with silicon nitride films, unpolarized scattered light is superimposed on polarized scattered light, because incident light beams entering rough surfaces are directed into random orientations and produce the unpolarized scattered light. The degree of the surface roughness is estimated by assuming that the rough surface consists of periodically arranged spherical segments.
Relaxation and rocking-curve broadening of strained (Ga,In)As single layers on (001) GaAs
Authors: Wie C. R.
Published: July 2002

We have measured the lattice relaxation of various strained Ga1−xInxAs layers which are thicker than the equilibrium critical thickness. Samples with a thickness near the energy balance model critical thickness exhibited a large relaxation. We have analyzed the strain relaxation data in a GaInAs/GaAs system using the Dodson–Tsao plastic flow model [Appl. Phys. Lett. 52, 852 (1988)]. It was found that the model provides a reasonably good fit to the data, however, the model parameters have widely different values for the GaInAs/GaAs samples with different mismatches. One parameter of the model shows an approximate inverse-square-law dependence on the misfit. The rocking-curve linewidths are presented for the GaInAs layers. The measured linewidths are discussed in terms of the theoretical linewidth, dynamical x-ray diffraction, and defect density depth distribution.
On the thermodynamical driving force during ion mixing of the Co-Si system
Authors: Xia W. , Hewett C. A. , Fernandes M. , Lau S. S. , Poker D. B.
Published: July 2002

The relative importance between the thermodynamical driving force and kinetics in thermal annealing and ion mixing in the thermally activated regime has not been clarified. To probe the role of the thermodynamical driving force in reactions between metals and silicon, the Co-Si system was chosen for investigation. In general, three silicide phases are formed during thermal annealing of samples consisting of Co thin films deposited on Si substrates, i.e., Co2Si (the first phase to form with a heat of formation, ΔHf=−9 kcal/g atoms), CoSi (ΔHf=−12 kcal/g atoms), and CoSi2 (the last phase to form, with ΔHf=−8.2 kcal/g atoms). Previous experiments have shown that annealing a sample of Si/CoSi/Co converts CoSi into Co2Si instead of a continuous growth of CoSi. This type of reaction is apparently unrelated to the magnitude of the thermodynamical driving force since ΔHf of CoSi is significantly larger than those of Co2Si and CoSi2, but is kinetically restricted instead. Under ion mixing conditions the kinetic restriction is expected to relax due to enhanced atomic mobilities under ion irradiation; the ion-induced reactions should then be driven by thermodynamics; i.e., growth of the phase with the largest ΔHf is favored. In this work, phase formation induced thermally and with ion mixing in the Co-Si system was investigated using Rutherford backscattering spectrometry and x-ray diffraction (Read camera). It was found that in thermal annealing, Co2Si is the first phase to form and Co is the dominant moving species in the formation of Co2Si, in agreement with previous results. In ion mixing, both CoSi and Co2Si are observed to form. At low temperatures, the formation of CoSi dominates. As the substrate temperature is increased, the formation of Co2Si becomes more significant. Co and Si are found to be the dominant moving species in the ion-beam-assisted formation of Co2Si and CoSi, respectively. By introducing the concept of an effective heat of formation, initial phase formation in both ion mixing and thermal annealing can be rationalized in terms of the thermodynamical driving force.
Nonlinear analyses for optimized short-period-wiggler free-electron laser oscillators
Authors: Booske J. H. , Serbeto A. , Antonsen T. M. , Levush B.
Published: July 2002

Procedures to determine the parameters of optimized (for maximum efficiency) experimental short-period-wiggler free-electron laser (FEL) oscillators are presented. The calculations are based on a normalized set of nonlinear equations which describe a one-dimensional FEL oscillator. Scaling formulas relating the normalized theoretical parameters to dimensional experimental quantities are obtained. The physics of such realistic effects as waveguide dispersion, wiggler field dependence on magnet gap, beam energy spread, and the frequency tunability of tapered wigglers are considered. Finally, specific examples for both tapered and untapered 300-GHz, 1.0-MW FEL oscillators are calculated and discussed.
Photoionization cross section of electron traps in thin oxynitride films of metal-oxynitride-oxide-silicon devices
Authors: Xu Dan , Kapoor Vik J.
Published: July 2002

The flat-band voltage monitored photodepopulation technique in combination with photoinjection was used to investigate the first-order kinetics of a trap emptying in low-pressure chemical vapor deposited thin films of silicon oxynitride (SiOx Ny ) of metal-oxynitride-oxide-silicon devices. An effective photoionization cross section associated with deep electron traps was determined to be 4.9–18.9×10−19 cm2 over the photon energy range of 2.06–3.1 eV for oxynitride films containing 7–17 at. % of oxygen. At a fixed oxygen concentration, the photoionization cross section decreased from 8.3×10−19 to 4.9×10−19 cm2 as the photon energy was lowered from 2.06 to 2.48 eV. However, the photoionization cross section at a fixed photon energy within this range showed an average decrease of 18% for a 10% increase in the amount of oxygen content in the oxynitride film. The photoionization cross section increased from 4.9×10−19 to 18.9×10−19 cm2 as the photon energy was increased from 2.48 to 3.1 eV. Over this higher photon energy range, a 28% decrease in photoionization cross section was observed for the same 10% increase of oxygen content in the oxynitride films.
High-speed video observation of laser recrystallization for semiconductor-on-insulator fabrication
Authors: Ogura Atsushi , Aizaki Naoaki , Terao Hiroshi
Published: July 2002

An in situ observation system, using a high-speed video attached to a conventional cw-Ar laser annealer for semiconductor-on-insulator (SOI) fabrication, was constructed. This system provided 25-ns time resolution and had a 2-μm or better spatial resolution. The effects of intentionally induced laser power changes and of the existence of underlying devices were studied. The results of these observations indicated that the crystal quality for fabricated SOI was strongly affected by the shape of solidification interfaces. Frequently changing solidification interfaces were observed at times, and such might be the cause of defect generation in SOI.
A Monte Carlo simulation of primary and secondary electron trajectories in a specimen
Authors: Kotera M.
Published: July 2002

A new Monte Carlo calculation model is presented to simulate not only the primary electron behavior but also the secondary electron cascade in a specimen bombarded with an electron beam. Electrons having energy greater than 0.1 keV are treated as ‘‘fast electrons’’ and the previous single scattering Monte Carlo model is adopted. Electrons having energy smaller than 0.1 keV are treated as ‘‘slow electrons’’ and the electron cascade Monte Carlo model is used. The calculated results for the energy distribution of secondary electrons, and primary electron energy dependence of the total secondary yield and the backscattering yield are in good agreement with experimental results.
Photoluminescence characterization of ZnSe doped with Ga by bulk and planar doping techniques in molecular-beam epitaxy
Authors: Skromme B. J. , Shibli S. M. , de Miguel J. L. , Tamargo M. C.
Published: July 2002

Room-temperature and low-temperature (1.7-K) photoluminescence (PL) characteristics of heteroepitaxial ZnSe layers on GaAs which are doped with Ga by either conventional (bulk) or planar doping techniques are described. Low-temperature PL peaks at 2.27 and 2.0 eV involving deep acceptor levels are introduced by Ga doping, as well as newly reported shallow acceptor levels with binding energies of approximately 68 and 85 meV. The behavior of these peaks and the excitonic transitions is studied as a function of Ga-doping level and, for the case of the planar-doped layers, surface stoichiometry during doping. The exciton peaks exhibit substantially greater broadening for doping on Zn-rich surfaces than for Se-rich surfaces, corresponding to the higher carrier concentrations observed by electrical measurements in the former case. The deep acceptor levels are found to be incorporated to a lesser degree for doping on Zn-rich surfaces, while the incorporation of the 85-meV acceptor is enhanced in this case. The net electrical compensation is evidently dominated by the behavior of the deep levels. The results are explained by assuming that both deep levels involve donor-Zn vacancy complexes, whose formation is suppressed by the excess Zn flux supplied during the planar-doping process. A comparison of the exciton spectra of nominally undoped and bulk Ga-doped samples is used to demonstrate that the residual donor in the undoped material is Ga.
A comprehensive study on the optical properties of thin-film CuInSe2 as a function of composition and substrate temperature
Authors: Tuttle J. R. , Albin D. , Matson R. J. , Noufi R.
Published: July 2002

The absorption coefficient (α) and fundamental transition energies of thin-film CuInSe2 were determined by spectrophotometry in the near-infrared (NIR) and visible wavelength regions from 500 to 2000 nm for a wide range of compositions. The results suggest a relationship between the constituent specie fluxes and substrate temperature, and the resulting polycrystalline nature of the film which dominates the optical properties. Near-stoichiometric and Cu-rich films appear to crystallize in larger grain sizes in comparison with Cu-poor films, with a Cu2−δ Se secondary phase at grain boundaries and free surfaces. Correspondingly, significant variations in the absorption coefficient among different film compositions exist in the neighborhood of the band edge. At energies well above the gap, all films behave similarly with α’s of (1–2)×105 cm−1 at 500 nm. Similarly, continuous dispersion curves for the index of refraction have only been derived for single phase Cu-poor material by an iterative technique. The absorption data are substantiated through spectral response simulations that accurately reproduce measured device data. The range of primary and secondary transition energies, respectively, is 0.95–1.01 and 1.17–1.22 eV. These values indicate a valence-band splitting of 0.20–0.24 eV, in good agreement with single-crystal values.
Low-cost technique for preparing Cd1−xZnxTe films and solar cells
Authors: Basol Bulent M. , Kapur Vijay K. , Ferris Michael L.
Published: July 2002

Cd1−xZnxTe films of various stoichiometries have been prepared by the two-stage process. The technique involves sequentially depositing thin layers of Cd, Zn, and Te on a substrate and reacting these elemental layers to form the compound. Both electrodeposition and evaporation techniques have been used in this work to deposit the elemental films. Properties of the electroplated elemental films, as well as the structural, optical and electrical characteristics of the reacted compounds, have been studied. Transparent ZnTe films of low resistivity have been obtained. Cd1−xZnxTe/CdS solar cells using films processed by the two-stage technique are demonstrated.
Plasma waves in a bounded anisotropic plasma: Influence of the electron density inhomogeneity
Authors: Pasquiers S.
Published: July 2002

The influence of a radial electron density inhomogeneity on plasma modes propagating in a cylindrical bounded plasma immersed in an axial static magnetic field, and the variations of the wave characteristics induced by a dielectric layer surrounding the plasma have been studied. The computations show that the electromagnetic-field radial distribution can be very sensitive to the electron density gradient, with or without the presence of the dielectric.
Spin dynamics of amorphous Fe90−xNixZr10 (invited)
Authors: Fernandez-Baca J. A. , Rhyne J. J. , Fish G. E. , Hennion M. , Hennion B.
Published: July 2002

Amorphous Fe90−xNixZr10 is a system that exhibits a relatively high degree of magnetic exchange frustration, which becomes stronger as the system approaches the composition of amorphous pure iron. Thus, while samples with moderate amounts of iron (x≥5) are ferromagnetic, the samples with the highest concentration of iron (x≤1) behave like reentrant spin glasses. We have performed a detailed neutron scattering study of the spin-wave excitations in this system for x=1, 5, 10, 20. In all cases, well-defined spin-wave excitations were observed below a transition temperature Tc that decreased from 455 K (for x=20) to 250 K (for x=1). For x=5, 10, 20 the spin-wave stiffness coefficient follows the temperature dependence expected for a conventional ferromagnet but the spin-wave excitations broaden considerably at low temperatures. For x=1 the spin-wave stiffness coefficient softens at low temperatures and an elastic component of the scattering, associated with the development of a spin-glass order parameter, appears below T≊0.28Tc. A coexistence of propagating spin-wave excitations and spin freezing phenomena is observed below this temperature down to T=0.09Tc. These results are discussed in terms of the relevant current theories.
Correlation between the photoreflectance impurity peak in semi-insulating GaAs and the bulk acceptor concentration
Authors: Brierley Steven K. , Lehr Deborah S.
Published: July 2002

We have measured the strength of the first-derivative peak observed below the band gap in photoreflectance spectra of semi-insulating GaAs and found that it is correlated with the bulk residual acceptor concentration. The apparent energy separation of the impurity peak is not fixed, but varies from sample to sample.
The role of hydrogen in diamond synthesis using a microwave plasma in a CO/H2 system
Authors: Muranaka Yasushi , Yamashita Hisao , Sato Kouji , Miyadera Hiroshi
Published: July 2002

In order to clarify the role of hydrogen in diamond synthesis using a microwave plasma in a CO/H2 system, carbon films were grown by varying hydrogen mole fractions in a CO/H2/He microwave plasma. The correlation between film properties and plasma species was investigated through film characterization and plasma emission spectroscopy. C and C2 were formed in the gas phase of the CO/He system and only sootlike carbon was deposited. Hydrogen additions to the CO/He system were found to enhance diamond growth by suppressing the formation of C and C2, which inhibited diamond growth by blocking the nucleation sites. The complicated structure of amorphous hydrogenated carbon, diamond microcrystallites having a diameter of 100 Å, and graphitic carbon was formed in the CO(5%)/H2 (30%)/He system, while columnar polycrystallites were grown in the CO(5%)/H2 system. Almost the same amount of atomic hydrogen in the ground state was found to exist in both systems, whereas a larger amount of electronically excited atomic hydrogen existed in the CO/H2/He system than the CO/H2 system. The atomic hydrogen in the ground state enhanced diamond growth by removing the amorphous carbon deposits, while the electronically excited atomic hydrogen exhibited no contribution to diamond growth and reacted with the amorphous carbon deposits to form the amorphous hydrogenated carbon. Finally, oxygen-containing species and hydrocarbons were suggested to be important precursors for diamond crystallization.