bluuebunny/crossref_metadata_2025 huggingface dataset:
Close spatial correlation and chemical effects in annealing of paramagnetic oxygen vacancies (E′1 centers) in ion-implanted amorphous SiO2
Authors: Golanski A. , Pfister J. C. , Nicolle T.
Published: July 2002

Electron paramagnetic resonance has been used to study the isochronal and isothermal irreversible annealing of E1 defects induced in amorphous SiO2 by implantation of He+, N+, O+, and Bi+ ions. The annealing behavior observed is successfully compared to predictions based on two models for diffusion-limited thermally activated processes: a simple model of a first-order unimolecular recombination, and Simpson and Sosin’s model for bimolecular recombination of closely spatially correlated Frenkel pairs. In both cases it has been assumed that the diffusion process is controlled by a Gaussian distribution of the activation energy for diffusion. It is shown that both models offer a consistent interpretation of the annealing behavior observed, indicating that for the temperature range between 500–800 °C, the irreversible thermal annealing of E′1 defects in ion-implanted amorphous SiO2 is controlled by unimolecular recombination. A new enhanced annealing effect has been observed in amorphous SiO2 implanted with chemically active N+ and O+ impurities.
Activity coefficient calculations for the Hg and Cd components in a tellurium-rich (Hg,Cd)Te liquid-phase-epitaxy growth solution containing Hg and Cd
Authors: Vydyanath H. R.
Published: July 2002

Activity coefficients of the Hg and Cd components have been qualitatively calculated for a tellurium-rich Hg-Cd-Te ternary liquid-phase-epitaxy growth solution for the growth of (Hg,Cd)Te. A comparison of these values with the corresponding values for HgTe(s), CdTe(s), and binary Hg-Cd alloys indicates that the activity coefficient for the Cd component is closer to the value for tellurium-rich CdTe(s), while that for the Hg component lies between the value for Te-rich HgTe(s), and binary Hg-Cd alloy of a similar composition.
Refractive indices of In0.49Ga0.51−xAlxP lattice matched to GaAs
Authors: Tanaka Hidenao , Kawamura Yuichi , Asahi Hajime
Published: July 2002

The refractive indices of In0.49Ga0.51P, In0.49Al0.51P, and In0.49Ga0.29Al0.22P, lattice matched to GaAs grown by molecular-beam epitaxy, are determined from double-beam reflectance measurements for photon energies ranging from 0.6 to 1.3 eV. Variation of the In0.49Ga0.51−xAlxP, refractive index with Al composition x and photon energy is calculated according to the single-effective-oscillator model. These analytical results are then compared with experimental data.
Extrapolated and projected ranges of electrons in metals
Authors: Pal P. B. , Varshney V. P. , Gupta D. K.
Published: July 2002

The extrapolated range Rex and the projected range Rpr of electrons in metal absorbers have been calculated using the Wilson expression for mean range of high-energy electrons. The results are in good agreement with experimental values reported by Tabata, Ito, and Okabe [J. Appl. Phys. 42, 3361 (1971)]. Schematic comparison of the calculated values with experimental data is made.
Magnetic-field extraction and filamentation of high-current electron beams
Authors: Freeman J. R. , Poukey J. W. , Wagner J. S. , Coats R. S.
Published: July 2002

Beam extraction simulations for high-voltage, immersed source accelerators are compared with analytic theory and experiment. dynadisc, a new nonlinear beam propagation code, is described and applied to the initial few meters of propagation in 1 atm air. The dynadisc results indicate that filamentation is the fastest growing instability. The filamentation changes the beam current density profile from an annular to a quasi-uniform distribution.
A lead-on-sapphire superconducting cavity of superior quality
Authors: Thakoor S. , Strayer D. M. , Dick G. J. , Mercereau J. E.
Published: July 2002

A cavity consisting of a superconducting lead film on a sapphire substrate has been fabricated to obtain the enhanced frequency stability possible with this configuration. The cavity exhibits a quality value Q exceeding 2×109 in its TE011 mode with a resonant frequency of 2.689 GHz. Methods of fabrication and testing of the cavity are presented in this article. Since the interface between the film and substrate is exposed to the full value of the resonant magnetic field, our experiment is the most sensitive test to date for enhanced losses at the interface itself. We find no evidence of such losses. In fact, the measured values of the surface resistance match very well predictions for rf losses based on the BCS theory.
Measurement of the intrinsic signal-to-noise ratio for high-performance rigid recording media
Authors: Belk Nathan R. , George Peter K. , Mowry Greg S.
Published: July 2002

Electrical measurements of the intrinsic media signal-to-noise ratio are made to examine the future impact of increasing recording density. Intrinsic media signal-to-noise measurements are made on oxide, on several thin-film-plated and sputtered longitudinal media, and on sputtered CoCr vertical media. Integrated spectrum noise versus write frequency and performance data are presented and contrasted for the different media. The character of the oxide and vertical media noise are shown to be produced by a uniformly distributed source whereas the noise of the thin-film longitudinal media is shown to be caused by localized fluctuations in the zig-zag transition region.
Profiles and annealing of thermally generated electron traps in boron-implanted phosphorus-doped silicon
Authors: Jackson Daniel B. , Sah C. T.
Published: July 2002

Observations of the concentration profiles of four electron traps formed by annealing boron-implanted, phosphorus-doped silicon at temperatures near 400 °C is reported. Isothermal annealing data is also presented for three of the traps. From the concentration profiles it is concluded that the lattice vacancies left behind by the recoiled atoms during the implantation dominate formation of the four traps.
Microstructure of fine-grained Pb-alloy films for Josephson integrated circuits
Authors: Hasumi Yuji , Waho Takao
Published: July 2002

The microstructure of Pb-In-Au alloy films is studied using transmission electron microscopy (TEM), Auger-electron spectroscopy (AES), and x-ray diffraction (XD) in order to obtain fine-grained films for high-reliability Josephson integrated circuits (ICs). TEM and XD observations are made to determine the film structure dependence on deposition technique. The techniques tested are molecular-beam condensation (MBC) and sequential deposition. Furthermore, AES analysis is performed to study the effect of the distribution of AuIn2 particles on the film structure. By using the MBC technique, fine-grained films are obtained with average grain sizes of 0.05–0.08 μm for about 0.2-μm-thick films. This result indicates that the MBC technique is promising for fabrication of high-reliability Pb-alloy Josephson ICs.
Optical constants and associated functions of metastable diamondlike amorphous carbon films in the energy range 0.5–7.3 eV
Authors: Savvides N.
Published: July 2002

The complex refractive index N(ω)=n+ik and the complex dielectric constant ε(ω)=ε1+iε2 are presented for diamondlike amorphous carbon (a-C) films in the photon energy range 0.5–7.3 eV. The effective number of valence electrons neff per carbon atom, the static dielectric constant ε0,eff, and the energy loss function Im[−1/ε(ω)] are deduced via the use of sum rules and are used to interpret the optical data. The a-C films were deposited using an unbalanced magnetron gun to sputter a graphite target (effective sputtering area of 20 cm2) in ultrapure argon gas. The magnetron is characterized by a high deposition flux of condensing atoms (1.5×1014–1.2×1016 cm−2 s−1) and a concomitant high ion flux (6×1014–2.5×1016 cm−2 s−1). A series of films were prepared by sputtering at different power levels in the range 5–500 W. Insulating substrates were used which allowed the films to self-bias negatively with respect to the plasma, so that the films were bombarded during their growth by Ar+ ions of energy 16–13 eV at an Ar+/C arrival rate ratio varying from about 4 to 2. A transition in the optical properties, physical properties (density, conductivity, microhardness), and microstructure is observed with the most rapid changes occurring at low sputtering power. The optical data are discussed in terms of interband transitions appropriate to amorphous semiconductors, and by comparison with the optical constants and the band structure of crystalline graphite and diamond. We find that films possess a metastable bonding configuration of a mixture of sp3 (tetrahedral) and sp2 (trigonal) bonds with the average coordination of the carbon atoms varying from 3.76 to 3.44. This fourfold-to-threefold transition in bonding is attributed to ion-induced structural modification of the amorphous carbon matrix. Weak plasma peaks at about 5 eV and the trends in neff and ε0,eff indicate that the π electron is localized leading to a hopping conductivity and a large optical gap, E0=0.40–0.74 eV.
Microstructural studies of the growth of aluminum films with water contamination
Authors: van der Kolk G. J. , Verkerk M. J.
Published: July 2002

Al films were grown at three different water partial pressures. The structure of the films at various thicknesses was observed with transmission electron microscopy. It was found that all three cases grew initially by island formation. (i) At greater thicknesses the film grown at the lowest pressure has large grains and a uniform thickness. (ii) The medium contaminated film has relatively clean regions with large grains and heavily contaminated regions with small grains. Furthermore, the film is not uniform in thickness; the clean regions are much thicker than the contaminated ones. Contamination of Al nucleates at discontinuous regions. Starting at the boundary Al substrate vacuum the contamination extends up to the Al surface. The contaminant layer prevents coalescence and recrystallization of Al, explaining the small grain size in certain areas. (iii) The heavily contaminated film has small grains and a uniform thickness. It is observed that at relatively small thicknesses (50 nm) the Al surface is already contaminated, preventing the growth of large grains.
Microparticles and their effects in vacuum diodes
Authors: Gray Eoin W.
Published: July 2002

There has been considerable interest over the last few years in high-voltage vacuum devices for pulsed power applications in inertial confinement fusion and weapons related areas. This paper describes both the microparticles created in vacuum diodes and the impact craters that are formed when these microparticles collide at high and hypervelocities with the diode components. Particles formed from molten electrodes can have field enhancement factors greatly above that for a spherical particle on the electrode surface. This enhancement of the local electric field on the particles can lead to the high velocities encountered. Velocities of the particles are calculated to be in the range 104–106 m/s, and these compare favorably with those found in the literature. The presence of microparticles in high-voltage diodes can lead to lower breakdown voltages and premature degradation of insulator and other diode components.
New method to measure low Schottky barriers on n-type silicon
Authors: Suu H. V. , Pászti F. , Mezey G. , Petö G. , Manuaba A. , Fried M. , Gyulai J.
Published: July 2002

To overcome difficulties which arise when either the series resistance is too high or the Schottky barrier height is too low, a new and simple method was developed to measure barrier height. Crucial point is the application of a ‘‘one-sided’’ configuration. This method was successfully applied to the GdSi2 system, where φB =0.38±0.005 eV was measured.
Thallium incorporation in molecular-beam-epitaxial InSb
Authors: Wood C. E. C. , Noreika A. , Francombe M.
Published: July 2002

The incorporation of thallium in molecular-beam-epitaxial indium antimonide has been studied by secondary-ion mass spectrometry. At temperatures above 300 °C desorption competes with incorporation. Increasing incorporation and surface accumulation is observed below 300 °C. The incorporation rate is also affected by the surface stoichiometry in a manner consistent with thallium occupying indium sublattice sites.
Localized epitaxial growth of WSi2 on silicon
Authors: Lin W. T. , Chen L. J.
Published: July 2002

Epitaxial growth of both tetragonal and hexagonal WSi2 in silicon was investigated by transmission electron microscopy. Eight different modes of WSi2 epitaxy were found to grow in (001), (111), and (011) Si. Variants of WSi2 epitaxy were also observed. Crystallographic analyses were performed to find possible matches between atoms in overlayer and silicon at WSi2/Si interfaces. Interfacial structures were analyzed. The roles of the lattice match in the growth of epitaxial WSi2 and MoSi2, which are similar in various aspects, are explored. The effects of anharmonicity in the interatomic force of overlayer on the heteroepitaxial growth and pseudomorphism are discussed.
Whistler instability in a magnetic trap
Authors: Singh Raghvendra , Singh D. P. , Das Salil
Published: July 2002

The eigenvalue problem of whistler propagation in a magnetic trap is analyzed in the slab model. The plasma is comprised of three regions: (I) a≤x<∞, (II) 0≤x≤a, and (III) −∞<x≤0. Region II contains a hot-electron component and possesses a smaller magnetic field. The hot electrons have a temperature anisotropy and tend to destabilize the whistler mode. The dip in the magnetic field tends to confine the mode to region II.
Optical absorption in a thin nickel wire
Authors: Inagaki T. , Goudonnet J. P. , Arakawa E. T.
Published: July 2002

Absorption of a 633-nm photon in a cylindrical nickel wire with diameter 13 μm was measured by a photoacoustic method as a function of angle of photon incidence θ. A good photoacoustic signal was obtained with a 6-mW He-Ne laser as a light source without employing focusing optics. The absorption measured for p-polarized photons was found to be in good agreement with geometrical optics calculation. For s-polarized light, however, significant excess absorption was found for θ>35°.
Deuterium location and migration in metals: Comparison of implantation and solid solution
Authors: Ligeon E. , Danielou R. , Fontenille J. , Eymery R.
Published: July 2002

The lattice location of deuterium has been investigated by channeling in fcc, hcp, and bcc metals. Implanted deuterium is studied in the range 15 K up to the release temperature and its site is compared to that of dissolved deuterium (α phase). After implantation, the octahedral and tetrahedral sites are distorted and deuterium can be displaced inside these cells. This distortion explains why implanted deuterium occupies a displaced site within the tetrahedral cell in bcc metals and not the pure tetrahedral site as for dissolved deuterium. The vacancy-deuterium interaction cannot account for all the experimental results. The trapping of implanted deuterium is described in terms of the stress induced by extended implantation defects.
Self-aligned ohmic contacts technology using Ti plasma etching for GaAs metal Schottky field-effect transistors
Authors: Debrie F. , Chaplart J. , Chevrier J.
Published: July 2002

Bimetal ‘‘T-gate’’ structures have been obtained by selective Ti-Al plasma etching. These structures have been used as self-aligned masks for ohmic contact metallizations. Titanium Schottky diodes exhibit a barrier height of 720 mV with an ideality factor of 1.17. By using only the optical lithographic process, normally on GaAs metal Schottky field-effect transistors (MESFET) of 1.3-μm gate length have been fabricated. Transconductance up to 142 mS mm−1 and pinchoff voltage around −2 V have been measured.
Electroreflectance studies above the fundamental gap on InxGa1−xAs layers deposited on GaAs
Authors: Wrobel J. M. , Aubel J. L. , Reddy U. K. , Sundaram S. , Salerno J. P. , Gormley J. V.
Published: July 2002

Interband transitions E1 and E1+Δ1 were investigated using the electrolyte electroreflectance technique for various compositions of InxGa1−xAs layers deposited on GaAs by molecular-beam epitaxy. A discrepancy in the results for layers deposited with lattice mismatch and bulk materials was noticed. The results were compared with the predictions of the scaled-virtual-crystal-approximation method for transition energy dependence on composition.
Hindering of hydrogen diffusion in stoichiometric yttrium iron garnet
Authors: Balestrino G. , Gerard P. , Lagomarsino S. , Tucciarone A.
Published: July 2002

Stoichiometric and nonstoichiometric yttrium iron garnet (YIG) films, both virgin and neon implanted, have been annealed in H2 atmosphere at temperatures up to 450 °C. The samples were measured by double-crystal x-ray diffraction, ferromagnetic resonance, and conversion electron Mössbauer spectroscopy. No evidence was found of reduction processes in the stoichiometric films. In particular, an evaluation of the upper limit δH for atomic hydrogen in the films after annealing gives δH∼10−2 afu. It is proposed that impurities have a central role in the problem of hydrogen diffusion. In particular Pb4+ → Pb2+ reduction may be a mechanism activating diffusion in nonstoichiometric YIG films.
Nature of photoconductivity in amorphous SixHy alloy films prepared by planar rf magnetron sputtering
Authors: Sun Y. Z. , Das S. R. , Williams D. F. , Webb J. B.
Published: July 2002

Amorphous SixHy alloy films have been prepared by planar rf reactive magnetron sputtering with a wide range of electrical, optical, optoelectronic, and microstructural characteristics. The photoconductivity of the films is observed to depend sensitively on the microstructure. In particular, the interrelationship between the dark conductivity (σdark), the photoconductivity (σph), the photoconducting gain (σph/ σdark), and the optical band gap (Eg) of a film is strongly influenced by the microstructure. It is shown that films with a particular combination of σdark, σph, σph/ σdark, and Eg values can only be prepared with a specific type of microstructure.
A zooming lens for acoustic microscopy applications
Authors: Nongaillard B. , Rouvaen J. M. , Logette P. , Bridoux E. , Torguet R.
Published: July 2002

The application of acoustic microscopy to the nondestructive evaluation of mechanical parts in their bulk is somewhat limited by the need for a great number of lens probes (in order to analyze the sample over its whole thickness). A zooming device is proposed here, which enables the continuous testing over the whole volume of bulky samples. A simplified theoretical analysis of the focusing properties of this device is given and the experimental results obtained in the detection mode are reported.
Particle trajectories from simulation of a relativistic electron pinch diode
Authors: Turnbull A. D. , Maron Y. , Quintenz J. P.
Published: July 2002

Recently, experiments have shown that relativistic electrons in a pinch diode, which strike the anode near the axis, have an angular distribution that is almost entirely within 30° of the normal. Analysis of numerical simulation results provides an explanation of the observed angular distribution. The small angles result from the fact that the electrons are strongly decelerated by a large potential gradient that exists just below the anode center. The resulting population of cool electrons can then be swept up by the axial electric field and redirected to the anode with small angles of incidence.
Behavior of ion-implanted As atoms in Si during molybdenum disilicide formation
Authors: Ohdomari Iwao , Chikyow Toyohiro , Kawarada Hiroshi , Konuma Kazuo , Kakumu Masakazu , Hashimoto Kazuhiko , Kimura Itsuro , Yoneda Kenji
Published: July 2002

The behavior of ion implanted As atoms during MoSi2 formation has been investigated by I-V measurement and neutron activation analysis. I-V characteristics of the MoSi2/Si interface was rectifying indicating that the impurity concentration in Si is very low. Arsenic atoms implanted in the Si substrate were found to redistribute toward the MoSi2/Si interface, but not into the underlying Si. The reason for no enhanced diffusion of As during MoSi2 formation has been discussed in terms of point defects which are not likely to be generated for the silicides in which Si is the dominant diffusing species.
Interface reactions at Cu-Hg1−xCdxTe contacts
Authors: Ehsani H. , Bené R. W.
Published: July 2002

In this study we report the results of structural studies of the interfaces between sputter-deposited copper (Cu) thin films and Hg0.8Cd0.2Te, CdTe substrates. In both cases, Cu2Te was formed even though the heat of reaction (ΔHR) would be positive as determined by calculation of the bulk reaction of Cu thin films with the substrates. This phase may disappear after several hours, gradually leaving a CdTeO3 phase in its place.
Photoexcitation effects in semi-insulating GaAs as revealed by electron paramagnetic resonance
Authors: Goltzené A. , Meyer B. , Schwab C.
Published: July 2002

A set of semi-insulating bulk GaAs samples of various specifications and origins has been studied under illumination conditions proper to reveal quenchable paramagnetic signals behaving like the metastable electrical defect EL2. Whereas In-alloyed crystals are almost free of any defect, all other materials display photosensitive signals which are either a quenchable quadruplet constrainable to the As4+Ga configuration or two enhanceable singlets not yet fully identified; the preferred occurrence of either type of spectrum is seemingly linked to the growth method.
Investigation of localization in a 10-well superlattice
Authors: Littleton R. K. , Camley R. E.
Published: July 2002

It is shown in semiconductor superlattices that slight fluctuations in layer thicknesses will result in localization of electronic states. It has been previously argued that this localization will hinder the formation of minibands. We show that these localized states have energy differences of much less than the thermal energy at room temperature. Therefore, the overall electronic state is a thermal average of the localized states. Because of this, slight fluctuations in layer thickness will not hinder the formation of minibands, except at low temperatures.
Electron orbits in combined rotating quadrupole and dipole magnetic fields
Authors: Levush B. , Antonsen T. M. , Manheimer W. M.
Published: July 2002

The single-particle trajectories of relativistic electrons in a magnetic field configuration which consist of a periodic wiggler field produced by a helical winding of two wires (‘‘dipole’’ magnetic field) superimposed on a helical winding of four wires (continuously rotating ‘‘quadrupole’’ magnetic field) are studied. The orbit equations can be reduced to a system of linear, inhomogeneous differential equations for variables related to transverse velocities. These equations are solved exactly and the stability region for the electron orbits in wide range of the parameters is obtained.
Si incorporation probabilities and depth distributions in Ga1−xAlxAs films grown by molecular-beam epitaxy
Authors: Rockett A. , Klem J. , Barnett S. A. , Greene J. E. , Morkoç H.
Published: July 2002

The Si incorporation probability σSi of Si and the segregation-induced broadening Δs of nominally abrupt Si doping modulations during the deposition of Ga1−xAlxAs films grown by molecular-beam epitaxy (MBE) have been measured as a function of film growth temperature Ts, alloy composition x and As2 overpressure. Si depth distributions were obtained using secondary ion mass spectrometry (SIMS) calibrated with internal standards. The inherent broadening due to the SIMS sputter profiling Δ0 was ∼6.5±1 nm. Dopant modulations generated by abrupt changes in the incident Si flux were found to exhibit broadening which varied, after subtracting the instrumental effects, from Δs≂7 nm at 600 °C to 25 nm at 725 °C. Thus, Si segregation during Ga1−xAlxAs MBE, while quite small compared to other dopants such as Sn, was still measurable. The fact that Δs increased with increasing Ts indicates that the segregation rate was kinetically limited over the temperature range investigated in these experiments. There was a slight tendency for an increase in Si segregation with increasing Al content in the film. However, increasing the As2 overpressure by a factor of 3 above that required to obtain an As-stabilized surface had no measurable effect on Si segregation. A lower limit for the Gibbs free energy of segregation was found to be ∼0.4 eV. The Si-incorporation probability σSi in Ga1−xAlxAs was unity at Ts≲600 °C and decreased to ∼0.5 at 725 °C. Varying x had no detectable effect on Si incorporation. The surface binding energy of Si on Ga1−xAlxAs (100) was estimated from the above results to be 3±0.1 eV.
Dark-field stigmatic ion microscopy for structural contrast enhancement
Authors: Bernius Mark T. , Ling Yong-Chien , Morrison George H.
Published: July 2002

Dark-field images are observed with a stigmatic (immersion objective lens) secondary ion mass spectroscopic ion microscope by means of an eccentric objective aperture, and are a useful extension of shadow contrast imaging. The spatial resolution in these images is comparable with conventional bright-field imaging, provided that a narrow energy bandpass is selected to minimize chromatic aberrations. It is demonstrated that the dark-field method is useful for correlating surface relief with chemical contrast in the compositional secondary ion mass spectroscopic mapping of conventional ion microscopy. Further, based on the information acquired in the dark-field imaging mode, digital techniques to compensate for asperity artifacts in conventional ion microscopy are proposed.
Effect of ionic electromigration on Cu2−αS/CdS solar cell
Authors: Allen Leslie H. , Buhks Ephraim
Published: July 2002

Lateral electromigration of Cu+ in a Cu2−αS/CdS solar cell induced by light generated current causes variation in composition of copper sulfide leading to increased sheet resistance and power losses of the device. These effects have been studied in short-circuit mode by fine probe measurements of lateral potential distribution and are clearly evident in I-V characteristics. The theory of mixed ionic-electronic transport in copper sulfide explains steady-state logarithmic potential distribution between grid wires and correctly predicts its kinetics which depend on Cu+ diffusion coefficient in Cu2−αS and grid density. The effects of grid defects on cell degradation are also demonstrated.
Near- and far-field observations of transient behavior in pulsed graded barrier quantum well lasers
Authors: Mawst L. J. , Givens M. E. , Zmudzinski C. A. , Emanuel M. A. , Coleman J. J.
Published: July 2002

The pulsed behavior of both gain-guided and index-guided graded barrier quantum well lasers has been studied with near- and far-field lateral mode measurements at different pulse widths. Above threshold, gain-guided devices show a transition to predominantly index-guided operation as a result of thermally induced waveguiding. Similar devices with built-in real index guiding exhibit low threshold, stable mode operation, with no observable variations with pulse width.
Defects created in ion-implanted Ga1−xAlxAs alloys
Authors: Sela I. , Beserman R. , Morkoç H.
Published: July 2002

Alloys of Ga1−xAlxAs were implanted with As and Be ions at room temperature, and the implant damage was studied as a function of the depth from the surface by Raman scattering. The arsenic implant led to the amorphization of the AlAs and GaAs constituents of the mixed crystal. The Be implant, on the other hand, amorphized the AlAs constituent only while damaging the GaAs.
The effects of vacuum conditions on epitaxial Al/GaAs contacts formed by molecular-beam epitaxy
Authors: Missous M. , Rhoderick E. H. , Singer K. E.
Published: July 2002

The effects of the quality of the vacuum on the epitaxy of aluminum on (100) gallium arsenide have been investigated. It was found that leaving the ion gauge running during the cooling down of the GaAs prior to the deposition of the Al and the presence of a helium cryopump both affected the nature of the epitaxy and the height of the resulting Schottky barrier. Reproducible results were only obtained with the ion gauge off and the cryopump on. The Al film was found to take up the (100) orientation irrespective of the reconstruction of the GaAs surface [c(2×8), c(4×4), or (4×6)]. The height of the Schottky barrier on n-type GaAs was 0.77±0.01 eV, and was independent of the GaAs reconstruction. The I-V characteristics were the most nearly ideal that have been reported, a plot of log{I/[1−exp(−qV/kT)]} vs V being linear over the whole voltage range from +0.5 to −1.0 V, with an ideality factor of 1.01 which can be explained solely in terms of image-force lowering. The barrier height on p-type GaAs was 0.64±0.01 eV, also irrespective of the GaAs reconstruction, so that φbn+φbp is equal to the band gap within the experimental error.
Laser melting of solids—An exact solution for time intervals less or equal to the transit time
Authors: El-Adawi M. K.
Published: July 2002

The thickness of the molten layer and the rate of melting induced by constant laser irradiance in a solid slab is studied. The study is carried out for time intervals less than or equal to the transit time, defined as the time taken for the temperature of the rear surface to change from ambient. The integral form of the heat conduction equation with the boundary condition at the interfacial surface between the liquid and solid phases together with a suggested model for the melting process is used to obtain an exact solution for the considered problem. Computations for a slab of aluminum of thickness 3×10−4 m subjected to laser irradiance of value q0=1014 W/m2 are carried out. It is found that the rate of melting after a certain delay time attains a constant value.
High-temperature annealing of implanted buried oxide in silicon
Authors: Mogro-Campero A. , Love R. P. , Lewis N. , Hall E. L. , McConnell M. D.
Published: July 2002

A silicon-on-insulator structure was formed by implanting 2×1018 oxygen ions cm−2 into crystalline silicon at 150 keV. A systematic investigation of the effect of annealing temperature was carried out by annealing for 6 h at temperatures of 1150, 1200, 1250, and 1295 °C. The microstructure and oxygen-concentration profile were investigated by using cross-sectional transmission-electron microscopy and Auger analysis. Changes were observed to occur throughout this annealing-temperature regime. After the highest annealing temperature, a single-crystal top silicon-layer of 150 nm with 4×109 dislocations cm−2 and no oxide precipitates was obtained. The 500 nm of buried oxide has very sharp interfaces, and contains crystalline-silicon inclusions near the interface with the substrate silicon.
Quantum-statistical theory of microwave detection using superconducting tunnel junctions
Authors: Devyatov I. A. , Kuzmin L. S. , Likharev K. K. , Migulin V. V. , Zorin A. B.
Published: July 2002

A quantum-statistical theory of microwave and millimeter-wave detection using superconducting tunnel junctions is developed, with a rigorous account of quantum, thermal, and shot noise arising from fluctuation sources associated with the junctions, signal source, and matching circuits. The problem of the noise characterization in the quantum sensitivity range is considered and a general noise parameter ΘN is introduced. This parameter is shown to be an adequate figure of merit for most receivers of interest while some devices can require a more complex characterization. Analytical expressions and/or numerically calculated plots for ΘN are presented for the most promising detection modes including the parametric amplification, heterodyne mixing, and quadratic videodetection, using both the quasiparticle-current and the Cooper-pair-current nonlinearities. Ultimate minimum values of ΘN for each detection mode are compared and found to be in agreement with limitations imposed by the quantum-mechanical uncertainty principle.
Biot waves in layered media
Authors: Allard Jean-F. , Bourdier Renaud , Depollier Claude
Published: July 2002

A description of the propagation of compression Biot waves in layered porous media in normal incidence with transfer matrices is given. An application of this model to prediction of surface impedance for a partially reticulated foam is given, with comparison with measured values.
Surface polaritons on an array of rectangular grooves
Authors: Seshadri S. R.
Published: July 2002

The interaction of surface polaritons on an interface having the profile of a periodic array of rectangular grooves is investigated. The technique used constitutes a large-amplitude grating theory of nonsmooth surfaces since the relative depth of the grooves is not assumed to be small. The wave characteristics near the location of the first band gap occurring at the boundary of the first Brillouin zone for gratings of different profiles with the same first harmonic content are the same in the limit of shallow grooves but become different for deeper grooves. As the depth of the grooves is increased, the width of the first band gap occurring at the boundary of the first Brillouin zone asymptotically approaches a constant value for a groove depth approximately equal to one half the groove period.
Recrystallization-driven migration of implanted ions in sapphire and resultant-oriented precipitation
Authors: Ohkubo Masataka , Hioki Tatsumi , Kawamoto Jun-ichi
Published: July 2002

The migration of Cr, Mn, Ni, and Xe implanted in sapphire during post-implantation thermal annealing is investigated by Rutherford backscattering (RBS)/channeling studies. Thermal annealing was performed in air or in vacuum. It is shown that the epitaxial recrystallization of the implantation-damaged region dominantly causes the migration of the implanted ions when there is little or no solid solubility of the ion species in sapphire. This migration mechanism strongly relates to the formation of oriented precipitates. When the implanted ions migrate toward the surface, surface precipitates of oxides are formed with annealing in air. On the other hand, when the implanted ions concentrate around the projected range at an elevated temperature, metals mainly precipitate in the substrate. The following crystallographic relations are found between the precipitates and the substrates: (111) MnAl2O4, (111) NiAl2O4, (111) Ni or (110) Cr∥(0001) Al2O3, and (103) Mn3O4∥(112̄0) Al2O3.
Sputtered silicon as a new etching mask for GaAs devices
Authors: Wu X. S. , Omura E. , Huang T. C. , Coldren L. A. , Merz J. L.
Published: July 2002

The use of a sputtered silicon film as a new type of etching mask is reported for the first time. Its desirable properties arise because of similar material characteristics (thermal expansion coefficient, crystal structure, smaller misfit factors) and different etching behavior as compared to gallium arsenide. These properties are studied and utilized in the fabrication of GaAs/GaAlAs double heterostructure (DH) ridge waveguide devices.
Interactions of four metallic compounds with Si substrates
Authors: Hung L. S. , Mayer J. W.
Published: July 2002

Interactions of PtTi, NiTi, AlPt, and AlNi compounds with Si substrates were analyzed by a combination of backscattering spectrometry and transmission electron microscopy. The reaction occurs via the migration of Si into the alloy matrix at temperatures between 500 and 600 °C. Uniform mixing rather than phase separation is observed in all the systems investigated. Ternary compounds (PtTiSi, NiTiSi2, AlPtSi, and Al2Ni2Si) are formed in the reacted layer and exhibit a high stability to heat treatment at elevated temperatures. These reactions were rationalized in terms of the free energy change of the reacted systems and the mobilities of various atoms.
Field-enhanced conductivity in semi-insulating GaAs
Authors: Pistoulet B. , Abdalla S.
Published: July 2002

Data on ac and dc field dependence of the conductivity of semi-insulating GaAs crystals are reported. The existence of long-range potential fluctuations in these samples has been previously reported. Field-enhanced conductivity results from the decrease of the maximum depth of the wells due to barrier lowering, up to a critical field at which the effect of potential fluctuations disappears. The transient behavior is also discussed.
Effect of velocity operator on acoustic-harmonic generation in n-type piezoelectric semiconductors
Authors: Wu Chhi-Chong , Tsai Jensan
Published: July 2002

Using the velocity operator derived from the Heisenberg equation of motion, we have investigated second-harmonic generation of acoustic waves propagating in nondegenerate piezoelectric semiconductors with a uniform dc magnetic field B directed along the waves. Since we are interested in both high-and low-frequency regions, an electron relaxation time due to the scatterings in solids is taken into account. Results show that the second-harmonic generation due to the piezoelectric polarization is insignificant in the very low-frequency region. However, when the frequency is coming into the microwave region, the second-harmonic generation increases quite rapidly with the sound frequency up to some maximum points at the range of frequency ω=1011–2×1011 rad/s, and then decreases. There are two maximum points in this range of frequency at very low temperatures. When the temperature increases, these two maximum points will be reduced to only a single maximum point. It is also found that the second-harmonic generation can be influenced by the dc magnetic field due to the nonlinear nature of energy bands in piezoelectric semiconductors.
Effects of D
X center and spatial distribution of electrons on the density of two-dimensional electron gas in modulation-doped AlGaAs/GaAs heterojunction structure
Authors: Lee D. H. , Li S. S.
Published: July 2002

The equilibrium density of two-dimensional electron gas in a modulation-doped AlGaAs/GaAs heterojunction structure has been studied by considering the deep electron traps (i.e., DX center) in doped AlGaAs layer, the spatial distribution of electrons in three conduction-band minima (Γ, L, and X), and the heavy doping effect. It is shown that the amount of conduction band-bending increases and the equilibrium density of two-dimensional electron gas decreases significantly as a result of incorporating these effects.
Gain models for source-flow chemical lasers
Authors: Batteh Jad H. , Smith Wilford
Published: July 2002

Four gain models are developed for use in analyzing source-flow chemical laser resonators. The first is a rotational nonequilibrium (RNE) model which traces the evolution of each vibrational-rotational state of the lasing molecule. The second is a less detailed model based on the assumption that each vibrational level is in rotational equilibrium (RE). In the third model, in addition to the rotational equilibrium assumption, the gain is assumed to be the same for all the vibrational transitions. The equations then become identical in form to those describing single-line (SL) lasing from a two-level system. The RE and RNE models solve the chemical kinetics equations for the gain self-consistently with the gasdynamic equations describing the flow field. In the SL model coupling between the gasdynamics and the laser kinetics is eliminated by using the gasdynamics from a simple Fabry–Perot calculation at a representative value of the threshold gain to provide the flow field conditions for the resonator calculation. A fourth gain model investigates the effect of using the gasdynamic calculation from the simpler SL model in a rotational nonequilibrium kinetics model. The objectives of the study are to determine how well the more computationally efficient RE and SL models can reproduce the predictions of the RNE model, and to determine the error introduced by decoupling the solutions to the gasdynamic and laser kinetic equations. The impact of rotational nonequilibrium phenomena on lasing performance is also assessed. Comparisons for the specific case of a HF laser indicate that both the RE and SL models predict output powers and peak-power mode widths which are in good agreement with those predicted by the RNE model over a wide range of values for the resonator gain. Furthermore, the RE model well approximates the power distribution among the vibrational levels, although only the RNE model is capable of providing detailed spectral information. We also find that decoupling the gasdynamic and kinetic equations does not significantly impact the accuracy of the resonator calculation. The utility of the more computationally efficient models in the design of source-flow chemical laser resonators is discussed.
Hydrogenation and annealing kinetics of group-III acceptors in oxidized silicon exposed to keV electrons
Authors: Pan Samuel Cheng-Sheng , Sah Chih-Tang
Published: July 2002

Group-III acceptors are deactivated by hydrogen released by 8 keV electrons in metal-oxide-silicon capacitors. The decay of the acceptor density during keV electron beam irradiation shows three conjoined phases: an initial delay, a short-time transient, and a long-time transient. This overlapping temporal characteristic is related to comparable rates of hydrogen bond breaking at the gate–oxide interface, hydrogen migration across the oxide, and emission and capture of proton at the group-III acceptor. Isothermal annealing data showed clearly two distinct annealing phases: an initial exponential rise and the long-time second-order recovery kinetics. The hydrogenation and annealing rate coefficients from these electron beam irradiated oxides are different from those obtained from avalanche electron injection (AEI) experiments. The difference suggests that the atomic structure surrounding the hydrogen-acceptor complex depends on the hydrogenation energetics. Compared with those electrons in the AEI experiments (tens eV), the higher-energy (keV) electrons can create more extended interfacial dangling bonds which are hydrogen or proton traps.
Calculated moments for the implantation of boron into silicides
Authors: Parkes Linda J. , Lavine J. P.
Published: July 2002

The Monte Carlo computer program trim is used to calculate the projected range, the standard deviation, the skewness, and the kurtosis of implanted boron ion distributions in silicon, silicon dioxide, molybdenum disilicide, tantalum disilicide, titanium disilicide, and tungsten disilicide. The boron implantation energy ranges from 10 to 500 keV.
Layered magnetic domains in Fe-Cu multilayer films imaged by Schlieren–Lorentz microscopy
Authors: den Broeder F. J. A.
Published: July 2002

Multiple magnetic films composed of alternating magnetic and nonmagnetic layers may have a layered domain structure when there is no exchange coupling through the nonmagnetic layers. As demonstrated for an Fe-Cu multilayer thin film, this structure can be made visible in Schlieren images using a particular variant of Foucault–Lorentz transmission electron microscopy.
Characteristics of laser metalorganic vapor-phase epitaxy in GaAs
Authors: Aoyagi Yoshinobu , Kanazawa Manabu , Doi Atsutoshi , Iwai Sohachi , Namba Susumu
Published: July 2002

Growth characteristics of a laser metalorganic vapor-phase epitaxy (laser MOVPE) and the electrical and optical properties of the epitaxial layer grown by the technique are examined. The growth rate under laser MOVPE decreases with increasing substrate temperature in contrast with conventional MOVPE. The growth rate also depends on the type of the substrate, total gas flow rate and the incident laser power. The mechanism of laser MOVPE seems not to be a photothermal effect but a surface photochemical effect. The intensity of the photoluminescence at room temperature for the epitaxial layer grown by the laser MOVPE is found to be stroger than that of the epitaxial layer grown without the laser irradiation under the same growth condition. The carrier concentration is also found to be modified by the laser irradiation. It is emphasized that the laser MOVPE is very useful as a new crystal growth technology.
Deposition of the unreactive metal Au onto sputtered and cleaved Hg1−xCdxTe surfaces
Authors: Davis G. D. , Beck W. A. , Kelly M. K. , Tache N. , Margaritondo G.
Published: July 2002

The interaction between thin layers of Au and both cleaved and sputtered p-type Hg0.72Cd0.28Te and sputtered p-type Hg0.79Cd0.21Te surfaces has been investigated with ultraviolet photoelectron spectroscopy using synchrotron radiation. Only a small loss of Hg from the interface was observed during Au deposition, in contrast to that seen during Al and In deposition reported elsewhere. The retention of Hg is explained by the lower stability of AuTe2 compared with HgTe, which makes the exchange reaction between Au and Hg unfavorable. Small differences in the Hg/Cd ratio following Au deposition with different surface preparations and material were noted. They were attributed to reduced stability of the ion-bombarded surface caused by sputter-induced defects and reduced strength of the Hg–Te bond, which resulted from the increased local CdTe concentration. Although Au diffused into the semiconductor to partially compensate for the cleavage-induced defects (which act as donors), it was not able to compensate appreciably for the larger number of sputter-induced defects.
Properties of zinc-phosphide junctions and interfaces
Authors: Casey M. Sean , Fahrenbruch Alan L. , Bube Richard H.
Published: July 2002

The phenomena occurring at the surface of bulk polycrystalline zinc phosphide and at interfaces of zinc-phosphide-based devices have been investigated. Electrical measurements of magnesium/zinc-phosphide junctions formed on annealed zinc-phosphide surfaces, and analyses of similar surfaces by Auger electron spectroscopy, indicate that loss of phosphorus from a very thin surface region is sufficient to severely degrade diode characteristics. Surface photovoltage measurements show that at the surface of as-etched or as-polished zinc phosphide, the energy bands are nearly flat. High-frequency capacitance measurements of aluminum/aluminum-oxide/zinc-phosphide structures indicate that a high interface state density, greater than 1013 eV−1 cm−2, prevents barrier formation by pinning the surface Fermi level. These properties severely limit the applicability of zinc phosphide to electronic devices.
Surface temperature rise in multilayer solids induced by a focused laser beam
Authors: Kodas Toivo T. , Baum Thomas H. , Comita Paul B.
Published: July 2002

Surface temperatures of a laser-heated structure consisting of intersecting gold and nickel lines on a Si substrate with a SiO2 surface layer were determined experimentally and theoretically. Temperatures were measured with micron-sized thin-film thermocouples formed from intersecting gold and nickel lines. Temperature profiles were calculated using a finite difference method which took into account the optical and physical properties of the thermocouple metal lines, the silicon dioxide layer, and the silicon substrate. For a 0.2-μm SiO2 layer, maximum surface temperatures were much higher with the metal lines than without because of the lower reflectivity of the gold relative to the silicon and the limited ability of the thin metal lines to conduct heat away from the irradiated region. Calculated maximum temperatures on the metal lines depended strongly on the thicknesses of the insulating SiO2 layer and the metal lines. Application of these results to the dynamics of laser-induced chemical vapor deposition is discussed.
Crystalline defects in heteroepitaxial GaAs/(Ca,Sr)F2 grown by molecular-beam epitaxy
Authors: Fontaine C. , Munoz-Yague A. , H́eral H. , Bernard L. , Rocher A.
Published: July 2002

The crystallinity of GaAs/(Ca,Sr)F2 structures grown by molecular-beam epitaxy on (100) and (111) B-oriented GaAs substrates is studied by transmission electron microscopy. The main defects found in the GaAs heteroepitaxial layers were microtwins and dislocations. The geometry and the origin of these defects are discussed in terms of growth and stress relaxation mechanisms, and placed within the framework of published results on similar heteroepitaxial systems. The results obtained on (111)-oriented layers suggest the preeminent role played by stress at growth temperature.