bluuebunny/crossref_metadata_2025 huggingface dataset:
Relaxation of a two-species magnetofluid and application to finite-β flowing plasmas
Authors: Steinhauer L. C. , Ishida A.
Published: July 2002

The relaxation theory of a two-species magnetofluid is presented. This generalizes the familiar magnetohydrodynamic (single-fluid) theory. The two-fluid invariants are the self-helicities, one for each species. Their “local” invariance follows from the helicity transport equations, which are derived. The global forms of the self-helicities are examined in a weakly dissipative system. They are shown to pass three tests of ruggedness (“relative” invariance compared with the magnetofluid energy): the cascade test; the selective decay test; and the stability to resistive modes test. Once ruggedness is established, relaxed states can be found by minimizing the magnetofluid energy subject to constrained self-helicities. The Euler equations are found by a variational procedure. Example equilibria are presented that resemble field-reversed configurations (FRCs) and tokamaks. These states are characterized by finite pressure and significant sheared flows. Throughout the analysis it is shown how this more general theory reduces to the magnetohydrodynamic (single-fluid) theory for suitable reducing assumptions.
Model of enhanced energy deposition in a Z-pinch plasma
Authors: Velikovich A. L. , Davis J. , Thornhill J. W. , Giuliani J. L. , Rudakov L. I. , Deeney C.
Published: July 2002

In numerous experiments, magnetic energy coupled to strongly radiating Z-pinch plasmas exceeds the thermalized kinetic energy, sometimes by a factor of 2–3. An analytical model describing this additional energy deposition based on the concept of macroscopic magnetohydrodynamic (MHD) turbulent pinch heating proposed by Rudakov and Sudan [Phys. Reports 283, 253 (1997)] is presented. The pinch plasma is modeled as a foam-like medium saturated with toroidal “magnetic bubbles” produced by the development of surface m=0 Rayleigh-Taylor and MHD instabilities. As the bubbles converge to the pinch axis, their magnetic energy is converted to thermal energy of the plasma through pdV work. Explicit formulas for the average dissipation rate of this process and the corresponding contribution to the resistance of the load, which compare favorably to the experimental data and simulation results, are presented. The possibility of using this enhanced (relative to Ohmic heating) dissipation mechanism to power novel plasma radiation sources and produce high K-shell yields using long current rise time machines is discussed.
Resonant tunneling in GaAs/AlAs heterostructures grown by metalorganic chemical vapor deposition
Authors: Bonnefoi A. R. , Collins R. T. , McGill T. C. , Burnham R. D. , Ponce F. A.
Published: July 2002

We report the first observations of resonant tunneling in electronic transport perpendicular to two AlAs layers separated by a GaAs quantum well in GaAs/AlAs heterostructures grown by metalorganic chemical vapor deposition. Resonant tunneling can be observed as inflections in the I-V curves at room temperature. These inflections become more pronounced as the temperature is reduced, until negative differential resistance regions become visible for temperatures below 260 K. At low temperatures, the I-V curves not only reveal two large negative resistance regions corresponding to the first energy level in the GaAs quantum well but also a structure which shows evidence of resonant tunneling through the second and possibly the third energy states in the well. Second derivative (d2I/dV2) measurements confirm the existence of the resonances seen in the I-V curves.
Energy spread of ions from Ga liquid metal ion sources at low emission currents
Authors: Mayer H. P.
Published: July 2002

Measurements of the energy distribution of Ga liquid metal ion sources (LMIS) have been carried out using different emitters and tip currents between 0.5 and 3 μA. For LMIS operating at low emission voltages and with low tip currents, distributions as narrow as 2.3 eV full width at half-maximum have been observed. These narrow distributions can only be observed if the emitter tip is placed very close (0.5 mm) to the extraction electrode.
Analytical technique for deriving the distribution of critical currents in a superconducting wire
Authors: Warnes W. H. , Larbalestier D. C.
Published: July 2002

The derivation of the critical current or critical current density distribution from an analysis of the voltage-current characteristic of a composite superconductor is discussed. Critical current distributions have been obtained for three Nb-Ti composites in quite different metallurgical states. The distribution is shown to be markedly broadened when sausaged filaments produce an extrinsic limit on the composite critical current.
Non-Markovian quantum dynamical equations for modeling electron transport in ultrafast microdevices
Authors: Lin J. , Chiu L. C.
Published: July 2002

In ultrasmall devices where the relevant time scale is comparable to the dynamical time scale, the usual Markovian transport theory based on time coarse graining becomes untenable. We present a new non-Markovian quantum transport formalism that is not only valid in the dynamical regime, but also free from the energy runaway problem plaguing the Markovian theory. Apart from making practical calculations numerically stable, the theory provides the foundation for delineating the range of validity of the classical Boltzmann and Markovian quantum transport.
Indium exodiffusion in annealed GaAs:In crystals
Authors: Krawczyk S. K. , Khoukh A. , Olier R. , Chabli A. , Molva E.
Published: July 2002

In this work, we report on the effect of annealing on the distribution of indium in the surface region of In-alloyed GaAs crystals. Auger, secondary ion mass spectroscopy, and photoluminescence were used as the analytical tools. It is shown that In migrates and piles up over a depth of several tens or a few hundreds of angstroms from the surface leaving behind an In-depleted region. The In redistribution results in modifications of the band gap in the surface region of annealed GaAs:In substrates; these modifications take place even at temperatures as low as 400 °C.
Fluorescence probes for study of insulator damage
Authors: Menzel E. Roland , Hatfield Lynn L. , Agarwal Vijendra K.
Published: July 2002

We present an innovative approach to the study of electrical damage in insulators, involving laser excited fluorescence probes. Specimens first subjected to surface flashover in vacuum were stained with highly fluorescent dyes, chosen to have varied chemical properties, and examined under laser excitation. Surface flashover tracks, locations of corona discharge, and other features were readily revealed, even when no damage was visible to the naked eye. Our results indicate that chemical changes, charge distributions, and structural features arising from electrical, mechanical, and thermal stresses can be probed.
Inverse noncollinear Compton laser as a device for acceleration of electrons
Authors: Apollonov V. V. , Kalachev Yu. L. , Prokhorov A. M. , Fedorov M. V.
Published: July 2002

A new method of laser acceleration of electrons is proposed. The method is based on stimulated Compton scattering in a noncollinear geometry. The saturation length is found to be rather small. The scheme with a varying geometry is suggested to prevent the process from saturating and to achieve high energies of the accelerated electrons.
Avalanche photomultiplication in the far infrared
Authors: Brown Fielding , Parker David R. , Heyman James , Newbury Nathan
Published: July 2002

We identify a process of avalanche photomultiplication in n-germanium initiated by pulsed far-infrared radiation at λ=151 μm. The sample at 4 K is biased above breakdown so that electrons populate the conduction band and excited states of donors as well as the ground state. Primary photoexcitation between 1s(3) and 2p± states alters the dynamic equilibrium between impact ionization and recombination and leads to photomultiplication by a factor M>105. Signals as low as 10−11 W have been detected with system bandwidth 20 MHz and response time τ∼1 ns. The relationship between detector current response and incident power has the unusual form is∝P0.5.
Planar, embedded InP/GaInAs p-i-n photodiode with very high-speed response characteristics
Authors: Miura S. , Kuwatsuka H. , Mikawa T. , Wada O.
Published: July 2002

A surface-illuminated InP/GaInAs p-i-n photodiode with a planar, embedded structure has been fabricated. By minimizing the stray capacitance and by using semi-insulating substrates, the capacitance has been reduced to 0.08 pF for a diode with a diameter of 20 μm. It has been demonstrated that this photodiode has a very high-speed response of greater than 10 GHz. The present structure is suitable not only as a discrete p-i-n photodiode but also for optoelectronic integration.
Direct electron spin resonance determination of dangling bond energies in rf sputtered hydrogenated amorphous silicon
Authors: Jousse D.
Published: July 2002

The energy positions within the gap of the dangling bond levels are deduced from the variations in intensity of the equilibrium electron spin resonance signal as a function of Fermi level positions in undoped and doped rf sputtered hydrogenated amorphous silicon (a-Si:H). The measurements of optically induced spin signals are used to detect any changes in the dangling bond concentration induced by doping. The results place the singly occupied level at 0.05 eV below the middle of the gap, i.e., at 0.95 eV below the conduction band, in agreement with one of the two values proposed for glow discharge a-Si:H and give an effective correlation energy of +0.3 eV.
Comparison of diamondlike coatings deposited with C+ and various hydrocarbon ion beams
Authors: Anttila A. , Koskinen J. , Lappalainen R. , Hirvonen J-P. , Stone D. , Paszkiet C.
Published: July 2002

The mechanical properties of the diamondlike coatings deposited with mass-separated C+, CH+3, CH+4, and C2H+2 ion beams have been compared. The hardness, abrasive wear resistance, and adhesion of the coatings prepared with the C+ ion beam were superior to those of the coatings prepared with other ions. The most serious drawback of the films prepared with hydrocarbon beams was their brittleness and weak adhesion.
Nitridation of iron by pulsed excimer laser treatment under liquid ammonia: Mössbauer spectroscopic study
Authors: Ogale S. B. , Patil P. P. , Roorda S. , Saris F. W.
Published: July 2002

Iron is nitrided by pulsed excimer laser treatment under liquid ammonia. Conversion electron Mössbauer spectroscopy and small-angle x-ray diffraction measurements reveal formation of γ-austenite in the as-treated sample and its transformation to γ′-Fe4N upon thermal annealing.
Optical intensity modulation to 40 GHz using a waveguide electro-optic switch
Authors: Korotky S. K. , Eisenstein G. , Tucker R. S. , Veselka J. J. , Raybon G.
Published: July 2002

We report the intensity modulation of an optical carrier at frequencies as high as 40 GHz using a Ti:LiNbO3 optical waveguide switch. The device is shown to exhibit a small-signal electrical 3 dB bandwidth of >22 GHz and −8 dB response at 40 GHz. A high-speed self-electro-optic-sampling arrangement based on a mode-locked injection laser is used to observe the modulation in the time domain.
Current spreading and carrier diffusion in zinc-diffused multiple-stripe-geometry lasers
Authors: Papannareddy R. , Ferguson W. , Butler J. K.
Published: July 2002

Numerical estimates of lateral current spreading and carrier diffusion in multiple-stripe-geometry AlGaAs lasers, both with and without zinc diffusion, are presented. This is the first analysis of the effect of zinc diffusion on the injected current and carrier density profiles. Results show that with a higher zinc diffusion depth, these lasers have significantly reduced current spreading, lower operating currents, and improved carrier density profiles. However, the higher zinc diffusion depths may lead to some undesirable dips in the injected current density profiles.
Demonstration of dual gain mechanism in an InGaAs/InAlAs superlattice photodiode
Authors: Li W-Q. , Bhattacharya Pallab K. , Juang F-Y.
Published: July 2002

A high-gain photodiode in which the internal gain can result from either potential barrier lowering or mass filtering action, depending on device geometry and bias conditions, is proposed and demonstrated. The photodiode structure is similar to a modulated barrier diode and uses In0.53Ga0.47As and InGaAs/InAlAs superlattice absorption regions. The superlattice helps to reduce the dark current and aids in mass filtering. The devices reported here were made with multilayered InP-based materials grown by molecular beam epitaxy and exhibit responsivity as high as 1000 A/W.
Improved electron mobility by AlAs spacer in one-sided selectively doped AlxGa1−xAs/GaAs multiple quantum well heterostructures
Authors: Ploog K. , Fronius H. , Fischer A.
Published: July 2002

One-sided selectively Si-doped n-AlxGa1−xAs/GaAs multiple quantum well heterostructures were grown by molecular beam epitaxy, which exhibit an enhanced mobility of more than 6×105 cm2/V s at 4 K using a binary AlAs spacer as narrow as 4.5 nm. In this heterostructure the two-dimensional electron gas is formed at the all-binary GaAs/AlAs interface of the constituent asymmetric GaAs quantum wells. The periodic sequence of electrically not coupled electron channels of high mobility with a spacing of about 133 nm is attractive for fundamental investigations; e.g., coupled-layer plasmon modes have been studied which give important information on the carrier density profile.
Two-photon absorption in ZnS calculated by an empirical pseudopotential method
Authors: White W. T. , Yee J. H. , Orvis W. J.
Published: July 2002

Using an empirical pseudopotential method, we have computed the spectrum of two-photon absorption (2PA) in cubic ZnS. The 2PA coefficients obtained this way agree better with experimental data than 2PA coefficients obtained from simpler band-structure calculations.
Planar avalanche photodiode with a low-doped, reduced curvature junction
Authors: Chi G. C. , Muehlner D. J. , Ostermayer F. W. , Freund J. M. , Pawelek R. , McCoy R. J. , Peticolas L. J. , Mattera V. D.
Published: July 2002

A planar InP/InGaAsP avalanche photodiode with a reduced junction curvature and low p-type doping was fabricated by Be+ implantation through a photoelectrochemically etched InGaAs mask. A uniform gain as high as 15 was obtained without edge or surface breakdown. The device had a separated absorption and multiplication structure grown by vapor phase epitaxy. The n−-InP top layer and guard ring conventionally used for planar devices were not needed. Two-dimensional device modeling indicates that the reduced junction curvature and low doping can prevent edge breakdown and greatly suppress the surface field.
Steady-state self-consistent analysis of diode-laser arrays
Authors: Kumar Tribhawan
Published: July 2002

A diode-laser array model, solving the two-dimensional Laplace equation in the passive layer and the carrier diffusion equation in the active layer in a self-consistent manner, is presented. The model is general and does not make use of the usual one-dimensional approximation to the current spreading problem. The beam-propagation method used in solving the wave equation eases the inclusion of any axial variations.
Charge injection through Langmuir–Blodgett films into organic polymers
Authors: Yuh Huoy-Jen , Chen Cindy C. , Chen Inan
Published: July 2002

The steady-state current-voltage characteristics resulting from charge injection from a metal into an organic charge transporting polymer are found to deviate significantly from the space-charge-limited values when a Langmuir–Blodgett film of cadmium stearate is interposed between the metal and the organic polymer. A phenomenological model of charge injection is proposed to account for the observed features, and to quantify the injection level of a non-Ohmic contact.
Dislocation transport in shock-loaded single crystals
Authors: Johnson J. N.
Published: July 2002

It has been previously observed that the impact surface of [100] shock-loaded lithium fluoride is a strong source of dislocations. These dislocations, on one side of the impact surface, are nearly all of the same sign and move in the same direction when the driving (impact) stress is maintained. This produces an excess of like-signed dislocations between the impact surface and the advancing planar shock front. It is shown that inclusion of dislocation transport effects in the equation for dislocation regeneration is required when surface sources are present. A derivation of the general expression of dislocation transport is presented along with some specific results for [100] loaded lithium fluoride. These results have important consequences regarding proper analysis of elastic precursor decay and rate-dependent plastic deformation in shock-loaded solids.
Growth and dissolution of oxide films during laser-assisted combustion of Ti and Zr
Authors: Ursu I. , Mihailescu I. N. , Nistor L. C. , Teodorescu V. S. , Prokhorov A. M. , Konov V. I. , Ralchenko V. G.
Published: July 2002

cw CO2 laser-assisted combustion of Ti and Zr in Xe:O2 and N2:O2 gaseous mixtures was studied. Total dissolution of oxide films and/or formation of oxynitride layers on both metals were evidenced and the growth of giant oxide nuclei of up to 100×10×10 μm3 was observed upon burning Zr samples.
Field-assisted bonding below 200 °C using metal and glass thin-film interlayers
Authors: Lee W. Y. , Sequeda F. , Salem J. , Chapman D.
Published: July 2002

Bonding between similar or dissimilar surfaces with metal and glass thin-film interlayers as well as bulk glass plates using an electric field assisted bonding technique at 160 °C or less is described. This low-temperature field-assisted bonding is achieved using, e.g., few μm thick glass films rf magnetron sputter deposited from Na or Li silicate glasses, and 0.05–1.0 μm thick Al, Sn, Mg, and Hf films. The bond strength thus achieved is found to be greater than the cohesive strength of the glass used. Results from x-ray photoelectron spectroscopy analyses confirm the migration across the glass layer and the plating out on the cathode surfaces of mobile ions such as Na+ or Li+ during field-assisted bonding. The migration and plating out of mobile ions can be detected in 10 s after the potential is applied and whether actual bonding between the metal and glass occurs or not. The possible bonding mechanism based on these XPS results is proposed.
Determination of band offsets using the photovoltaic effect: Application to the PbS/PbSe heterostructure
Authors: Chu T. K. , Agassi D. , Martinez A.
Published: July 2002

The energy-band offsets at a semiconductor heterointerface can be determined by measuring the temperature and wavelength dependence of the photovoltaic response. Results for the PbS/PbSe structure show a type I band alignment with a conduction-band offset ΔEc of ∼48 meV. The method is sensitive to small band offsets and can be applied to the study of other semiconductor systems, especially narrow band-gap materials.
Interface roughness scattering in GaAs/AlAs quantum wells
Authors: Sakaki H. , Noda T. , Hirakawa K. , Tanaka M. , Matsusue T.
Published: July 2002

We study experimentally and theoretically the influence of interface roughness on the mobility of two-dimensional electrons in modulation-doped AlAs/GaAs quantum wells. It is shown that interface roughness scattering is the dominant scattering mechanism in thin quantum wells with a well thickness Lw<60 Å, where electron mobilities are proportional to L6w, reaching 2×103 cm2/V s at Lw∼55 Å. From detailed comparison between theory and experiment, it is determined that the ‘‘GaAs-on-AlAs’’ interface grown by molecular beam epitaxy has a roughness with the height of 3–5 Å and a lateral size of 50–70 Å.
Radiation induced interface states in metal-aluminosilicate (Al2O3⋅SiO2) insulator-Si capacitors
Authors: Ishida Makoto , Sakamoto Hikaru , Shirotori Haruo , Nakamura Tetsuro
Published: July 2002

Aluminosilicate (Al2O3⋅SiO2) thin films were prepared on a (100) Si wafer by pyrolysis of Al(CH3)3, SiH4, and N2O gases at the deposition temperature of 850 °C. From the high-frequency and the quasi-static capacitance-voltage measurements, the initial interface state densities of capacitors with Al2O3⋅SiO2 gate insulators were 1.3–2.2×1011 cm−2 eV−1, and hysteresis characteristics were not present. Distribution of interface states of Al2O3⋅SiO2/Si was different from that of SiO2/Si. Even after exposure to 1×105 rads (Si) of Co60 γ-ray irradiation, the interface states were not affected. The interface state density showed a slight increase after exposure to 1×106 rads.
Use of the Meissner effect to separate, purify, and classify superconducting powders
Authors: Barsoum Michel , Patten Daniel , Tyagi Somdev
Published: July 2002

A separation technique, based on the Meissner effect, to purify and classify superconducting powders was developed. Powders of the Y1Ba2Cu3O7−x composition were sealed in a glass tube, cooled to liquid-nitrogen temperature, and passed over the pole of a magnet. The superconducting phase responded to the field and moved away from the magnet, whereas the nonsuperconducting phases, impurities, especially magnetic, and unreacted phases did not move. X-ray diffraction revealed that the separated powder was single phase with all impurity phases eliminated. Furthermore, the powder particles separated along the length of the tube according to their size and applied magnetic field: the larger the particles and/or the field the farther the movement and the smaller the particles that moved.
Model of a nonlinear directional coupler in gallium arsenide
Authors: Gibbons Wayne M. , Sarid Dror
Published: July 2002

We have calculated the response of a nonlinear directional coupler fabricated in an AlGaAs/GaAs structure using a realistic model for the optical nonlinearities. The model takes into account carrier-density-dependent index of refraction and absorption, and lateral carrier diffusion in each of the two coupled channel waveguides. Our results differ considerably from those obtained using a Kerr model for the optical nonlinearities.
Superconducting thin films based on La2−xSrxCuO4
Authors: de Lima O. F. , Mattson J. , Sowers C. H. , Brodsky M. B.
Published: July 2002

Superconducting films (300–400 nm thick) of La2−xSrxCuO4 have been prepared by a combined evaporation-reaction method. Amorphous films of the oxide are formed initially on sapphire substrates at deposition temperatures of 25–400 °C. Crystallized films can then be obtained with the desired tetragonal structure and show superconducting resistive transitions, with onsets between 23–28 K and zero resistivities near 4.2 K. A diamagnetic transition consistent with the onset-resistive transition is seen for different samples and a critical current density of 0.4 A/cm2 is obtained.
Electron beam recrystallization of plasma-sprayed silicon substrates
Authors: Suryanarayanan R. , Akani M. , Gauthier R. , M’Ghaieth R. , Pinard P.
Published: July 2002

Polycrystalline silicon substrates of 5–8 cm2 area and 0.5–3 mm thickness have been recrystallized by electron beam glazing. The grain size as well as the Hall mobility increases dramatically from 50 μm to 1 mm or more and from 5 to 320 cm2/V s, respectively.
Single-crystal preparation and some characterizations of the superconducting Y-Ba-Cu oxide
Authors: Haneda Hajime , Isobe Mitsumasa , Hishita Shunichi , Ishizawa Yoshio , Shirasaki Shin-ichi , Yamamoto Taisei , Yanagitani Takagimi
Published: July 2002

Single crystals of Ba2YCu3O7−δ were prepared from melts of a BaO-Y2O3-CuO mixture and characterized by the x-ray microprobe analyzer and x-ray diffraction. Electrical resistivity was measured by the standard four-terminal method. Some crystals have the critical temperature above 77 K. After annealing in oxygen, the crystals behave like a semiconductor.
Comment on ‘‘Interface charge polarity of a polar on nonpolar semiconductor GaAs/Si with Ga and As prelayers’’ [Appl. Phys. Lett. 4
9, 1257 (1986)]
Authors: Won T. , Munns G. , Houdré R. , Morkoç H.
Published: July 2002

In this comment we report new experimental results for the capacitance voltage measurement of p−GaAs/n−Si heterojunction diodes and point out the inappropiate assumption used in our previous letter that the boundaries of the depletion layer do not change much despite the presence of the prelayer. (AIP)
Neutron diffraction as a rapid screening method for semiconductor wafers
Authors: Martel P. , Rogers D. , Stephens A. E.
Published: July 2002

Measurements are presented which illustrate advantages of thermal neutron scattering for rapid screening of Si and GaAs semiconductor wafers. Regions of high dislocation density are found to cause localized decreases in extinction that are readily observable by a detector set to measure a diffracted beam with a cross-sectional area comparable to typical wafer areas. Significant variations in reflected intensity are found by scanning small beams across GaAs wafers. Comparisons are made with x-ray scattering techniques.
Integrate-and-fire infrared detectors
Authors: Coon D. D. , Perera A. G. U.
Published: July 2002

The effect of infrared radiation on spontaneous pulsing of forward biased silicon p+-n-n+ diodes (injection mode devices) at 4.2 K is studied as a means of detecting infrared radiation in the wavelength range of 20–32 μm. A model based on space-charge buildup of phosphorus donors in the i region is developed to explain the integration and the sudden firing as well as the dependence of firing frequency on infrared flux. Experimentally, a dynamic range of about a million and responsivities of 9×109 Hz/W (9.6 A/W) have been found in nonoptimized detectors. Theory indicates the possibility of even larger dynamic ranges. Dark pulse rates as low as 10−5 Hz have been observed.
Superconducting properties of the Ba1−xYxCuO3−y system
Authors: Togano K. , Kumakura H. , Fukutomi K. , Tachikawa K.
Published: July 2002

Superconductivity of the pseudobinary Ba1−xYxCuO3−y oxide system has been studied. A zero-resistance state has been achieved at 92.5 K for Ba0.6Y0.4CuO3−y. The critical curent density estimated from the magnetization curve is >102 A/cm2 at 77 K in a magnetic field less than 0.1 T.
Inhibition of charge packet broadening in GaAs charge-coupled devices
Authors: Song J. I. , Fossum E. R.
Published: July 2002

Computer simulation of charge transport in GaAs resistive-gate charge-coupled devices is reported. The simulation has been performed for 10 μm finger spacings, doping concentrations in the range of 1×1016–1×1017 cm−3, effective channel thicknesses 0.1–1.0 μm, lateral applied fields 3–10 kV/cm, and charge packet sizes 5%–100% of full bucket capacity. Inhibition of charge packet broadening due to transferred electron effects has been observed. Charge transfer time of 99.9% charge transfer efficiency across the intermediate phase finger was investigated and found to decrease monotonically with increasing electric field despite the turnaround in average carrier velocity. This may be attributed to a combination of improved initial charge confinement and inhibition of charge packet broadening.
Infrared absorption of epitaxial NiSi2 layers on Si(111)
Authors: Flohr Th. , Schulz M. , Tung R. T.
Published: July 2002

Infrared absorption of epitaxial type A and type B NiSi2 layers on Si(111) has been measured with photoacoustic spectroscopy. Type A silicides showed identical absorption as type B layers with corresponding thicknesses. The observed dependence of absorption on silicide thickness agrees with calculations based on no-interface absorption, in sharp contrast to previous studies of nonepitaxial silicide interfaces. These results suggest that the densities of electronic states at epitaxial NiSi2 interfaces are below the detection limit of this technique, ∼1014 cm−2.
Hybrid aligned cholesteric: A novel liquid-crystal alignment
Authors: Lewis M. R. , Wiltshire M. C. K.
Published: July 2002

A hybrid aligned cholesteric (HAC) liquid-crystal (LC) structure is reported. The LC director tilt varies from a small angle at one surface to almost 90° at the other, while incorporating a helical twist. Cells having one surface treated with rubbed polyvinyl alcohol and the other with the organosilane octadecyltriethoxysilane, adopt the HAC structure when filled with a long pitch chiral mixture. The presence of the HAC structure was confirmed by studies of the variation of the optical rotation, first with thickness in a wedge cell and second with temperature for a compensated cholesteric mixture. Use of the HAC structure in a wedge cell is characterized by an absence of the pitch breaks seen with conventional alignments.
Space group and chemical analysis of Y2BaCuO5−x by convergent beam electron diffraction and x-ray energy-dispersive spectroscopy
Authors: Mansfield John F. , Chevacharoenkul Sopa , Kingon Angus I.
Published: July 2002

The results of analyses of chemistry and microstructure of one of the secondary phases commonly observed in samples of the new high-temperature superconductors are reported. The crystal structure has been examined by convergent beam electron diffraction and is confirmed to be orthorhombic, with space group Pbnm and lattice parameters a=0.71 nm, b=1.22 nm, and c=0.56 nm. The stoichiometry of the metal components was found by x-ray energy-dispersive spectroscopy to be Y1.0Ba0.5Cu0.5, which leads us to postulate that this phase is Y2BaCuO5−x.
Novel electromagnetic effects in high-temperature superconductors
Authors: Macfarlane J. C. , Driver R. , Roberts R. B.
Published: July 2002

We report the first observations at liquid-nitrogen temperatures of parametric inductance behavior, signal up-conversion, and the nondestructive read-out of persistent supercurrent states in a superconductor. These observations have been made using a toroidal transformer with a core of the high-temperature superconductor YBa2Cu3O6.8. The effects arise from the field-dependent behavior of the magnetic susceptibility of this superconductor.
Fabrication of Y-Ba-Cu-O mixed phase superconductors
Authors: Garland M. M.
Published: July 2002

Mixed phase superconductors have been fabricated from Y2O3, BaCO3, and Cu2O which show an onset temperature of 96 K. The presence of superconductivity is found to depend on cooling rate, the presence of oxygen, and temperature.
Annealing induced strain in 31P+-implanted Si (111) and Si (100)
Authors: Zsoldos L. , Petó G. , Zsoldos E. , Brogren G. , Kanski J.
Published: July 2002

The thermal annealing of (100) and (111) oriented Si crystals after high dose implantation with 80 keV 31P+ ions was followed by double-crystal x-ray diffractometry. Analysis of the rocking curves shows that at higher temperature annealings after regrowth at 630 °C, P atoms may leave their substitutional position at temperatures higher than 700 °C, depending upon the implantation dose and surface orientation.
Electrical characteristics of Al/ZnS/p-p+ Si diodes
Authors: Thomas C. B. , Sands D. , Brunson K.
Published: July 2002

The electrical characteristics of Al/ZnS/p-Si diodes have been investigated. The behavior is shown to be very similar to that of the tin oxide /ZnS/p-n+ diodes used previously for electroluminescent diodes indicating that current through the ZnS is limited by the rate of generation of minority carriers in the p-Si. The fact that the current is limited is the surest indication that no breakdown is occurring either in the ZnS or the silicon. These results are discussed, both in the context of device manufacture and in the context of a recent theory of breakdown in electroluminescent diodes.
High current Cu3P liquid metal ion source using a novel extractor configuration
Authors: Higuchi-Rusli R. H. , Corelli J. C.
Published: July 2002

It has been found that by utilizing a sharp needle for the extractor electrode in close proximity to the source tip wetted with Cu3P liquid alloy, a large increase (factor ∼300) in ion current is observed in comparison to standard liquid metal ion sources (LMIS’s). In standard previously used LMIS’s the extractor electrode was a flat plane with a circular hole centered on the source needle tip. This new high current source has important applications in focused and broad ion beam deposition systems.
Promethium-doped phosphate glass laser at 933 and 1098 nm
Authors: Krupke W. F. , Shinn M. D. , Kirchoff T. A. , Finch C. B. , Boatner L. A.
Published: July 2002

A promethium (Pm3+) laser has been demonstrated for the first time. Trivalent promethium 147 doped into a lead-indium-phosphate glass étalon was used to produce room-temperature four-level laser emission at wavelengths of 933 and 1098 nm. Spectroscopic and kinetic measurements have shown that Pm3+ is similar to Nd3+ as a laser active ion.
Low-frequency noise measurements on n-InGaAs/p-InP junction field-effect transistor structures
Authors: Kugler S. , Steiner K. , Seiler U. , Heime K. , Kuphal E.
Published: July 2002

Deep level analysis in the ohmic regime of ungated n-InGaAs/p-InP junction field-effect transistor structures was made by low-frequency noise measurements. The noise spectra exhibit two deep trap levels in the n-InGaAs channel with activation energies of 0.49 and 0.37 eV. The related capture cross sections are 7×10−15 and 4×10−16 cm2, respectively.
Electron-beam-pumped two-dimensional semiconductor laser array with tilted mirror resonator
Authors: Tong F. , Osgood R. M. , Sanchez A. , Daneu V.
Published: July 2002

The spatial and spectral emission characteristics of a two-dimensional CdS laser array, pumped by a high-energy electron beam, have been experimentally investigated. The near-field emission from each cell or array element is found to arise from a virtual line located behind the cell. The results are consistent with a geometric ray model of a tilted mirror resonator.
Two-dimensional behavior of molecular beam epitaxy grown HgTe
Authors: Justice R. J. , Seiler D. G. , Zawadzki W. , Koestner R. J. , Goodwin M. W.
Published: July 2002

Two-dimensional electronic properties of HgTe films (∼2 μm thick) grown by molecular beam epitaxy on CdTe substrates have been investigated by using the Shubnikov–de Haas effect. Electron densities, effective masses, and Dingle temperatures of three electric subbands in an accumulation layer near the HgTe-CdTe interface have been determined for two samples with different total densities. The results exhibit behavior typical of an asymmetric triangular potential well and a pronounced band nonparabolicity.
Two-step barrier diodes
Authors: Schulz P. A. , Gonçalves da Silva C. E. T.
Published: July 2002

Transmission probabilities and current densities of a two-step barrier heterostructure are calculated within the effective-mass approximation as a function of electron energy and applied bias. This system shows negative differential resistance under forward bias, because of a quasibound state in a triangular well, and no resonance under reverse bias, in the current density. The two-step barrier diode may show negative resistance in an ac field in the absence of a dc bias.
Enhancement of carrier lifetime in silicon-doping superlattices
Authors: Landheer D. , Denhoff M. W. , Buchanan M. , Jackman T. E. , McKinnon G. H. , Teo K. H. , Jackman J. A.
Published: July 2002

Silicon-doping superlattices have been grown by molecular beam epitaxy by using a Knudsen cell with boron oxide for p doping and an ion beam doper with arsenic for n doping. Depositions were done through an etched silicon mask to create nini and pipi regions at the edges of mesas to which selective contacts were made with the use of AuSb and PtSi. Recombination lifetimes as long as 14 ms have been measured at 77 K by carrier injection from 503 nm light pulses.
Modification of interfacial charge between SiO2 and silicon
Authors: Aronowitz S. , Anand K. , Riga G.
Published: July 2002

Reduction of the net positive charge at the interface between SiO2 and silicon has been achieved by implanting calcium in the SiO2 near the interface and annealing. Comparison between initial calcium implant profiles and calcium profiles obtained after a high-temperature (950 °C) anneal showed that the calcium was basically immobile. A theoretical approach also was employed. Calculations using a model SiO2 structure yielded that among the atomic species examined, calcium was most likely to contribute an effective net negative charge density to the interface when placed randomly at various sites in the model structure.
Optical waveguide lens measurement using an image processing system
Authors: Miki A. , Okamura Y. , Yamamoto S.
Published: July 2002

An image processing system was used to evaluate optical waveguide lens performance. The focal length, the focal spot size, and the efficiency of geodesic lenses formed on ion-exchanged waveguides were measured nondestructively, and beams propagating along the curved guiding surface of the waveguide lens were observed.
Electron beam source molecular beam epitaxial growth of analog graded AlxGa1−xAs ballistic transistors
Authors: Malik Roger J. , Levi Anthony F. J.
Published: July 2002

A new method has been developed for the growth of graded band-gap AlxGa1−xAs alloys by molecular beam epitaxy which is based upon electron beam evaporation of the group III elements. The metal fluxes are measured and feedback controlled using a modulated ion gauge sensor. The system is computer controlled which allows precise programming of the Ga and Al evaporation rates. The large dynamic response of the metal sources enables growth of variable band-gap III-V alloys with arbitrary composition profiles. This new technique is demonstrated by synthesis of analog graded AlxGa1−xAs unipolar ballistic electron transistors.
Real-time image subtraction with the use of wave polarization and phase conjugation
Authors: Tomita Yasuo , Yahalom Ram , Yariv Amnon
Published: July 2002

We demonstrate, using a double-phase conjugate mirror, image subtraction, addition, and intensity inversion by two orthogonally polarized image-bearing phase conjugate waves.
Diffusion suppression of photolytic fragments on laser-induced chemical vapor deposition
Authors: Arai Yoshimitsu , Yamaguchi Satoru , Ohsaki Takaaki
Published: July 2002

Diffusion suppression of Al fragments formed in a trimethylaluminum atmosphere by an ArF excimer laser during photolytic laser-induced chemical vapor deposition is investigated. Heavier molecular weight base gas such as Ar is found to act as a diffusion buffer which suppresses the diffusion of Al radicals and atoms. Furthermore, biasing the upper electrode positive relative to the stage is also effective in suppressing photolytic fragment diffusion.
High-efficiency, one-sun (22.3% at air mass 0; 23.9% at air mass 1.5) monolithic two-junction cascade solar cell grown by metalorganic vapor phase epitaxy
Authors: Chung B-C. , Virshup G. F. , Werthen J. G.
Published: July 2002

A high-efficiency monolithic two-junction solar cell consisting of an Al0.37Ga0.63As (Eg =1.93 eV) upper cell and a GaAs lower cell has been grown by metalorganic vapor phase epitaxy. Since both component cells have the n-on-p configuration, the unwanted p-n junction has been eliminated with the use of metal-interconnect contact during post-growth processing. As a two-terminal device, an efficiency of 22.3% has been achieved under 1 sun, air mass 0 illumination conditions, whereas an efficiency of 23.9% was obtained when the cascade cell was operated as a three-terminal device under 1 sun, air mass 1.5 illumination. This result represents the highest 1 sun efficiency ever reported. The advantages of utilizing this multijunction solar cell for terrestrial and space applications are also described.
Dynamics of phase-locked semiconductor laser arrays
Authors: Wang S. S. , Winful H. G.
Published: July 2002

Time-dependent coupled mode theory is used to investigate the stability of phase-locked semiconductor laser arrays. The output of individual array elements is dynamically unstable and exhibits large amplitude chaotic pulsations. The total output initially exhibits damped relaxation oscillations and then settles down to a quasi-steady state characterized by small amplitude fluctuations. The theory predicts both the pulsation frequency and the phase lock-in time of the array.
Erasable optical memory media with thermoplastic/absorbent double layer
Authors: Kobayashi M. , Yabe A. , Maeno Y. , Oishi K. , Kawamura K. , Ohno S.
Published: July 2002

A thermoplastic/absorbent double layer type optical memory was developed. The thermoplastic was monodispersed polystyrene of which the molecular weight was 800–110 000, and the absorbent was Cu phthalocyanine. The erasing properties were dependent on the molecular weight. The medium was best when the molecular weight was 2000 and the record/erase repetition could be more than 350. The dye addition to the polystyrene increased the recording sensitivity but decreased the maximum limit of record/erase repetition, so the dye content was preferable to be less than 10 wt. %.
Origin of modulation-induced mode partition and Gb/s system performance of highly single-mode 1.5 μm distributed feedback lasers
Authors: Choy M. M. , Liu P. L. , Sasaki S.
Published: July 2002

Modulation-induced mode partition in distributed feedback lasers was investigated by photon statistics and bit-error-rate measurements. Its origin is explained for the first time in terms of the transient index changes and the resulting corrugation dephasing. We also propose device screening and desirable parameters for error-free operation.
Linear electro-optic effect in barium metaborate
Authors: Nakatani H. , Bosenberg W. , Cheng L. K. , Tang C. L.
Published: July 2002

We report the first measurement of the linear electro-optic coefficients of crystalline barium metaborate. The largest electro-optic coefficient r22 was found to be 2.5 pm/V, about four times smaller than the r63 of potassium dihydrogen phosphate (KDP). The dispersion of the electro-optic coefficient was also measured and found to be in excellent agreement with predicted values using the anharmonic oscillator model. Implications of the result on the point group symmetry of barium metaborate are also discussed.
Enhancement of transport critical current density by Gd substitution in YBa2Cu3O7
Authors: Sastry P. V. P. S. S. , Gopalakrishnan I. K. , Yakhmi J. V. , Iyer R. M.
Published: July 2002

Samples with composition Y1−xGdxBa2Cu3O7 (x=0.001–0.005) are prepared and TC, ΔTC, JC, ρ(300 K) are measured. It is shown that upon substituting yttrium by small amounts of gadolinium, JC can be improved significantly. The anticorrelation of JC with ΔTC and ρ(300 K) is established. The possible role of gadolinium in enhancing JC is discussed. General guidelines for getting high JC values are gathered.
Mass-dispersive recoil spectrometry studies of oxygen and nitrogen redistribution in ion-beam-synthesized buried oxynitride layers in silicon
Authors: Whitlow Harry J. , Petersson C. Sture , Reeson Karen J. , Hemment Peter L. F.
Published: July 2002

Mass-dispersive recoil spectrometry has been employed to study the influence of annealing conditions in ion-beam-synthesized silicon oxynitride structures prepared by implantation of 1.8×1018 and 1×1017 200 keV 16O+ and 14N+ ions cm−2, respectively, at approximately 600 °C. Subsequent annealing at 1200 and 1300 °C leads to redistribution of the implanted oxygen to form a buried oxide layer with nitrogen segregation to the buried SiO2/Si interfaces. Implantation with N+ subsequent to O+ followed by annealing at 1200 °C for 2 h was found to lead to both a lower oxygen content and lower channeling detectable defect concentration in the overlying silicon film than if the order of implantation was reversed. No significant dependence on order of implantation was observed after annealing at 1300 °C for 5 h.
Low-loss GaAs/AlGaAs waveguide phase modulator using a W-shaped index profile
Authors: Deri R. J. , Kapon E. , Harbison J. P. , Seto M. , Yun C. P. , Florez L. T.
Published: July 2002

We demonstrate a low-loss semiconductor optical waveguide phase modulator for the 1.5 μm wavelength region. The device, based on a p-i-n diode/heterostructure waveguide, utilizes a novel epilayer structure to reduce propagation losses associated with doped electrode layers. Propagation loss below 1 dB/cm, significantly lower than previously reported values for conventional semiconductor waveguide phase modulators, was achieved without sacrificing modulator efficiency.
Efficient, long pulse XeF(C→A) laser at moderate electron beam pump rate
Authors: Mandl A. , Litzenberger L. N.
Published: July 2002

Efficient, long pulse lasing on the XeF(C→A) electronic transition has been demonstrated in an electron beam pumped device at a moderate pump rate of ∼250 kW/cm3 . A mixture of F2, NF3, Xe, Kr, and Ar at a total gas pressure of 1.6 atm was excited with a 700-ns pulse. Lasing occurred for 400 ns during the excitation pulse. The laser spectrum showed a peak wavelength of 483 nm and a bandwidth of 16 nm. An intrinsic efficiency of 0.7% was determined. The laser output energy was 1 J. Further improvements in laser performance are expected under fully optimized conditions.
Studies of the coherence properties of a diode-pumped Nd:YAG ring laser
Authors: Bush S. P. , Güngör A. , Davis C. C.
Published: July 2002

The coherence properties of a diode-pumped Nd:YAG ring laser have been studied by a self-heterodyne autocorrelation technique using a very long path difference Mach–Zehnder interferometer and by homodyne interferometry in a Michelson interferometer. Results show the laser to have a linewidth of Δf=6.1±0.7 kHz at a power output of 5 mW.
High-accuracy post-fabrication trimming of surface acoustic wave devices by laser photochemical processing
Authors: Dolat V. S. , Sedlacek J. H. C. , Ehrlich D. J.
Published: July 2002

Laser direct writing reactions for molybdenum etching and Cr/Cr2O3 cermet conductivity transformation have been developed for concurrent phase and amplitude trimming of surface acoustic wave devices on LiNbO3. The molybdenum etching reaction utilizes photolytic decomposition of Cl2 with 488 nm light as a means to achieve low process temperature and avoid substrate damage. The cermet reaction utilizes a solid-state transformation in an O2 environment to render the film highly nonattenuating to surface acoustic waves with no underlying substrate damage. These techniques have been applied to trimming of reflective array compressors and have provided order-of-magnitude improvement in phase and amplitude accuracy over devices compensated by lithographic processing.
Hot-electron transport in a graded band-gap base heterojunction bipolar transistor
Authors: Hayes J. R. , Harbison J. P.
Published: July 2002

In this letter we report the direct observation of electron heating in an electric field using hot-electron spectroscopy. The device structure used for the study was a graded band-gap base heterojunction bipolar transistor, fabricated in the GaAs/AlGaAs semiconductor alloy system. A thermal electron distribution at 4.2 K was injected from the emitter into the base of a transistor that was compositionally graded to yield a quasielectric field of 20 kV cm−1 . The equilibrium electron distribution was heated by the electric field and could be characterized at the end of the 900 Å base region by an effective electron temperature of 650 K.
All-optical bistability in nematic liquid crystals at 20 μW power levels
Authors: Lloyd A. D. , Wherrett B. S.
Published: July 2002

Optical switches at power levels as low as 14 μW, allowing bistable operation with compact disk laser systems, are reported in optimized cavities containing planar-aligned nematic liquid crystals.