bluuebunny/crossref_metadata_2025 huggingface dataset:
Semianalytic formula for the radio-frequency-induced alpha-particle current in a tokamak reactor
Authors: Van Eester D. , Chang C. S.
Published: July 2002

A simple semianalytic expression is obtained for energetic alpha-particle current induced by radio-frequency (rf) waves in a deutrium–tritium tokamak reactor. Using a new poloidal angle variable, which makes the Jacobian a constant along the unperturbed orbit, the expressions for alpha current and alpha power absorption are considerably simplified from those obtained in the previous analysis [C. S. Chang, Phys. Plasmas 2, 3696 (1995)]. A more realistic treatment of the quasilinear rf heating effect, including the tangential resonance effect, makes the present model not only simpler but also more accurate. This expression should have a practical value in a quick evaluation of rf-induced alpha current in an equilibrium or transport code, together with an existing formula for rf-induced electron current.
Magnetohydrodynamic ponderomotive forces generated about Alfvén resonance layers
Authors: Tataronis J. A. , Petržílka V.
Published: July 2002

The total ponderomotive force produced by radio frequency electric and magnetic fields about the spatial resonances of the shear Alfvén wave is derived. The time-averaged currents and plasma transport that result from these forces are also derived. The wave analysis is based on a resistive magnetohydrodynamic fluid. A relationship between the time-averaged rates of change of wave energy dissipation and wave momentum dissipation in the resonant layers is found. Since the deposited wave momentum in the Alfvén resonant layers alters the plasma transport locally, control of the density profile is a possible application of this theory.
Effect of induced spatial incoherence on flow induced laser beam deflection: Analytic theory
Authors: Ghosal Sandip , Rose Harvey A.
Published: July 2002

Analytic results are presented for the laser beam deflection rate in the case of spatial and temporal smoothing by induced spatial incoherence (ISI). It is shown that for flow perpendicular to the beam propagation direction with Mach number M, temporal smoothing decreases the beam deflection rate for M>1, but may increase it for M<1 and weak acoustic wave damping.
Observation of type-1 intermittency caused by current-driven ion acoustic instability
Authors: Taniguchi K. , Kuwae H. , Hayashi N. , Kawai Y.
Published: July 2002

Intermittent chaotic phenomena caused by the current-driven ion acoustic instability are experimentally observed using a Double Plasma device, in which two mesh grids are installed to excite the instability. When a dc potential is applied to one of the two mesh grids and exceeds a certain threshold, the system suddenly transits from a periodic state to a chaotic state. At the same time, the signals picked up as perturbation components of a current exhibit intermittent turbulent bursts. The calculations of the correlation dimension and the Lyapunov exponent indicate that the system reaches a chaotic state. Furthermore, it is found that the results of mathematical and statistical analysis of observed signals agree with the theoretical properties of the type-1 intermittency: the occurrence of 1/f-type low-frequency noise and the probability distribution of the duration between two bursts. Therefore, it is concluded that the present system reaches a chaotic state via the type-1 intermittency.
Intrinsic bending of a laser beam in a flowing plasma
Authors: Bezzerides B.
Published: July 2002

In this paper a simple analytic model for deflection of a laser beam in the presence of flowing plasma is presented. The model utilizes a nonlinear solution of the paraxial wave equation in the random phase approximation. This approximation excludes any contribution from hot-spot induced self-focusing, but allows for the effects of intensity fluctuations of the beam. For a speckled beam the solution for the beam intensity in wave number space depends sensitively on the properties of the incident beam. It is shown that for an incident beam whose initial spectrum in wave number space is Gaussian, the final spectrum is also Gaussian with the overall spectrum rotated in wave number space by a radius of curvature function that is an explicit expression of the Mach number of the flow, the local acoustic damping, and the local average intensity. This result is applicable to the case in which the speckle develops upon transmission of the beam through a random phase plate (RPP). The bending rate thus calculated for a RPP-smoothed beam is compared to the bending rate in the absence of the RPP. This comparison provides some insight into the efficacy of the RPP in reducing the bending of the laser beam.
Longitudinal permittivity of magnetospheric plasmas with dipole and circular magnetic field lines
Authors: Grishanov N. I. , de Azevedo C. A. , de Assis A. S.
Published: July 2002

Longitudinal permittivity elements of an axisymmetric magnetosphere are derived by solving the drift-kinetic equation for the trapped particles, in a two-dimensional plasma model with dipole and circular magnetic field lines. The drift-kinetic equation is solved for waves in the frequency range much larger than the drift frequencies. It is shown that the collisionless dissipation of such waves by the bounce-resonant interaction with the trapped particles differs substantially from one in a straight magnetic field. The estimations of the electron Landau damping for kinetic Alfvén waves in magnetospheric plasmas are presented. Imaginary part of the longitudinal permittivity is analyzed numerically in the wide range of wave frequencies and plasma parameters.
Time–space self-consistent dynamics of surface-wave produced discharges in pulsed regime operation
Authors: Kirov K. , Shivarova A.
Published: July 2002

A model for the dynamics of gas discharge production in a diffusion controlled regime by pulses carried by surface waves is presented. The model is within the fluid plasma theory. It combines ideas for a diffusion advance of the plasma and for a breakdown wave. A numerical solution of the problem is given. Results for the self-consistent time–space dynamics of plasma density and wave-field intensity are obtained from which values for the ionization front velocity are extracted.
Theoretical study on discharge-pumped soft x-ray laser in Ne-like Ar
Authors: Lan Ke , Zhang Yuquan , Zheng Wudi
Published: July 2002

A one-dimensional Lagrangian magneto-hydrodynamics code coupled to an atomic kinetics code was developed. In this code, the ablation and ionization of the wall material were taken into account, the coupled rate equations were solved by using the matrix-block method, and the effect of the reabsorption of the resonant lines was calculated by using an approximate expression of the escape-factor in a cylindrically expanding plasma. The numerical results obtained from this code on a discharge-pumped J=0−1 transition 46.9 nm laser line in Ne-like Ar were in good agreement with experimental observations. The physical schemes in the 46.9 nm laser line were studied.
An analytical expression of plasma density at electrical discharge in high-pressure gas
Authors: Uhm Han S. , Choi Eun H. , Cho Guangsup , Ko Jae J.
Published: July 2002

Plasma properties during the Townsend discharge and also at electrical breakdown were investigated. A simple analytical expression of plasma generation in a high-pressure gas provides important scaling laws in the dc electrical discharge system. It was found that the logarithm of the electron density at the breakdown is proportional to the discharge time τb, and is inversely proportional to the pulse risetime and gap distance d between the two electrodes. The plasma density at breakdown is also an increasing function of the gas ionization energy εi.
Ion diffusion in a velocity space induced by Alfvén ion cyclotron mode observed in a mirror plasma
Authors: Goto T. , Ishii K. , Goi Y. , Kikuno N. , Katsuki Y. , Yamanashi M. , Nakamura M. , Ichimura M. , Tamano T. , Yatsu K.
Published: July 2002

Ion distributions in a loss cone are measured in the GAMMA 10 tandem mirror [Phys. Rev. Lett. 55, 939 (1985)]. When Alfvén ion cyclotron (AIC) modes are excited in the central cell, enhanced end-loss of ions is observed for a characteristic energy region which agrees well with the resonant ion cyclotron condition with the AIC wave. From measurements of pitch angle distributions of end-loss ions, it is found that the loss cone is filled for this characteristic energy region, indicating an ion diffusion in a velocity space induced by the AIC wave. Magnitude of the observed additional end-loss increases with increase in the amplitude of the AIC modes. In the present experimental parameters in GAMMA 10, the AIC wave effect on the axial ion confinement is not serious.
Moderate-convergence inertial confinement fusion implosions in tetrahedral hohlraums at Omega
Authors: Bennett G. R. , Wallace J. M. , Murphy T. J. , Chrien R. E. , Delamater N. D. , Gobby P. L. , Hauer A. A. , Klare K. A. , Oertel J. A. , Watt R. G. , Wilson D. C. , Varnum W. S. , Craxton R. S. , Glebov V. Yu. , Schnittman J. D. , Stoeckl C. , Pollaine S. M. , Turner R. E.
Published: July 2002

A highly uniform thermal x-radiation field for indirect-drive inertial confinement fusion implosions may be obtained by irradiating a four-hole, tetrahedral geometry, spherical hohlraum with all 60 Omega laser beams. Implosion studies and calculations [J. M. Wallace et al., Phys. Rev. Lett. 82, 3807 (1999)] indicate a drive uniformity comparable to that expected for the National Ignition Facility [J. A. Painser et al., Laser Focus World 30, 75 (1994)]. With 60 beams distributed over the cavity wall, tetrahedral hohlraums have a natural insensitivity to power balance and pointing errors. Standard, smooth Nova capsules imploded with this drive indicate that moderate convergence-ratio implosions, Cr∼18, have measured-neutron yield to calculated-clean-one-dimensional-neutronyield ratios similar to those previously investigated using the comparatively poor drive uniformity of Nova cylindrical hohlraums. This may indicate that a nonsymmetry-related neutron yield degradation mechanism, e.g., hydrodynamic mixing of cold, dense ablator material with the hot-spot region or some combination of nonsymmetry effects, is dominating in this Cr regime.
Gigavolt pulsed power by magnetic levitation
Authors: Winterberg F.
Published: July 2002

A magnetically levitated and insulated torus of meter-size dimensions can be charged up to gigavolt potentials. Discharging the torus through a breach made by a plasma jet or spark gap, an intense relativistic ion beam can be extracted from a magnetically insulated diode. Because of its self-magnetic field, the beam can be transported over large distances, a property well suited for thermonuclear microexplosion ignition.
Theory of negative differential conductivity of electrons caused by electron–electron scattering in low-temperature plasma
Authors: Chiflikyan R. V.
Published: July 2002

A simplified quantitative analysis of the mechanism of negative differential conductivity (NDC) of electrons in low-temperature plasma due to electron–electron scattering (EES) is presented for the first time. On the basis of an analytical treatment of the Boltzmann equation, it is shown that with the constraint νε≪νee≪νm the necessary condition for displaying of the N- and S-type NDC induced by EES can be written as ν̂mU=δ̂U>0.5 and <−0.5, respectively, where νε=νε(U), νee=νee(U), and νm=νm(U) are the total electron energy exchange, effective electron–electron, and momentum transfer collision frequencies, respectively [U is the electron mean energy, δ=(E/N)/W, where E/N is the reduced electric field (E=E(U) is the intensity of the electric field, N is the gas number density), W=W(U) is the drift velocity of electrons, and ŷx=d ln y/d ln x]. Simple analytical criteria for prediction of the EES induced NDC are obtained. It is shown that the EES induced NDC may be responsible for triggering of a broad category of spatial and temporal instabilities taking place in various gases and gas mixtures in glow-discharge plasma. The validity of the proposed theory is confirmed by comparison with numerous experimental and numerical works of other authors.
Self-consistent simulation of electron cyclotron resonance plasma discharge
Authors: Liu Minghai , Hu Xiwei , Wu Qinchong , Yu Guoyang , Pan Yuan
Published: July 2002

Microwave fields in an extended electron cyclotron resonance (ECR) plasma reactor were analyzed in the resonant cavity from Maxwell’s equations, and a formalism of microwave absorption was investigated at the resonance zone with plasma kinetic theory and simulated using a two-dimension computer hybrid-code. The results indicated that there are three typical power deposition profiles over the entire parameter range: (1) the parabolic shape: peaking on axis and decreasing slowly along the radius, (2) the trumpet shape: peaking on axis and decreasing quickly along the radius, and (3) the camel shape, i.e., a hollow distribution. The spatial distributions of plasma parameters (plasma density, electron temperature, ionization rate, etc.) would be significantly influenced by the microwave power absorption profile.
Growth of ultrapure and Si-doped InP by low pressure metalorganic chemical vapor deposition
Authors: Di Forte-Poisson M. A. , Brylinski C. , Duchemin J. P.
Published: July 2002

Low pressure metalorganic chemical vapor epitaxial growth and characterization of high purity and Si-doped indium phosphide on semi-insulating (100) InP:Fe substrate are presented in this letter. Electrical characteristics of the layers were determined from Hall measurements. Hall mobilities as high as 145 000 cm2 V−1 s−1 at 77 K have been achieved on high purity layers with net donnor density ND−NA≂2×1014 cm−3. High resolution photoluminescence measurements were performed with the as-grown layers at temperatures down to 1.7 K. Carrier concentration and the resulting mobility of intentionally Si-doped low pressure metalorganic chemical vapor deposition grown InP layers were also studied.
Resonant tunneling oscillations in a GaAs-AlxGa1−xAs heterostructure at room temperature
Authors: Shewchuk T. J. , Chapin P. C. , Coleman P. D. , Kopp W. , Fischer R. , Morkoç H.
Published: July 2002

This letter reports the first observation of resonant tunneling negative differential resistance (NDR) through a double barrier GaAs-AlxGa1−xAs -GaAs-AlxGa1−x As-GaAs structure at room temperature. The NDR yields radio frequency oscillations at 300 K in a coaxial cable circuit that compare closely to those of a standard 1N3716 tunnel diode.
Vacancy-Zn complexes in InP studied by positrons
Authors: Dlubek G. , Brümmer O. , Plazaola F. , Hautojärvi P. , Naukkarinen K.
Published: July 2002

Positron lifetime measurements have been performed in various InP crystals. The crystal doped with Zn to a concentration of 4.5×1018 cm−3 shows strong positron trapping by vacancy defects, but no vacancies are found in crystals doped with Zn to a lower concentration of 2×1018 cm−3 or doped with Sn, S, or Fe. The concentration of vacancy defects agrees well with the estimated number of neutral Zn atoms thus supporting strongly the idea that neutral Zn atoms are bound to complexes with P vacancies. The Zn-vacancy complexes start to disappear above 400 °C.
Lithium quench-condensed microstructures and the Aharonov–Bohm effect
Authors: Bishop D. J. , Licini J. C. , Dolan G. J.
Published: July 2002

We describe an apparatus and our method for fabricating and measuring in situ lithium quench condensed microstructures at dilution refrigerator temperatures. We then discuss our observation of normal-metal flux quantization in these structures.
I
n s
i
t
u chemical information at the semiconductor/electrolyte interface from infrared vibrational spectroscopy
Authors: Tardella A. , Chazalviel J.-N.
Published: July 2002

We have investigated the n-Si/acetonitrile electrolyte interface using attenuated total reflection spectroscopy in the 1.2–5-μm spectral region. Characteristic information from the surface has been extracted by using modulation of the electrode potential and lock-in detection of the optical signal. When the modulated potential is kept positive with respect to the flatband potential, vibrational lines can be observed that are characteristic of the Si–H, (Si–)O–H, C–H, and C–N chemical bonds. The shapes and magnitudes of the various lines are qualitatively well understood. Upon electrode aging, the Si–H signal decreases and the (Si–)O–H signal increases, which provides direct in situ evidence for slow oxidation of the silicon surface.
Fluorescence thermometry of shocked water
Authors: Justus B. L. , Huston A. L. , Campillo A. J.
Published: July 2002

We describe a fluorescence probe thermometer for measuring shock heating directly in transparent solvents. As a demonstration of this scheme, the temperature of shocked water was measured in a previously inaccessible pressure regime, 0–9 kbar, by observing the fluorescence enhancement from a fluorescein dye additive following 527-nm excitation and laser driven shock loading. A ring-up shock temperature increase of 33 °C was observed at 8.4 kbar with an accuracy of ±4 °C.
Energy loss of two-dimensional electron gas in GaAs-AlGaAs multiple quantum wells by screened electron-polar optic-phonon interaction
Authors: Basu P. K. , Kundu Sudakshina
Published: July 2002

Experimental data on the variation of the rate of energy loss of two-dimensional electrons with electron temperature in GaAs-AlGaAs multiple quantum wells have been found to be substantially lower than the values calculated from available theory. We have modified the theory to include overlap function, degeneracy, and screening of electron-polar optic-phonon coupling. The Landau damping of the plasma by single particle excitations and coupling between phonons and plasma are, however, neglected. It is found that inclusion of overlap and screening leads to good agreement between theory and experiment.
Self-limiting mechanism in the atomic layer epitaxy of GaAs
Authors: Tischler M. A. , Bedair S. M.
Published: July 2002

A self-limiting mechanism has been observed in the atomic layer epitaxy (ALE) of GaAs deposited by alternate exposure to AsH3 and trimethylgallium (TMG). The thickness of the deposited film was found to be independent of the mole fractions of both TMG and AsH3 in the gas phase. These results will allow the use of ALE to deposit III-V compounds with growth rates which are insensitive to the input partial pressures of the reactive gases.
Low defect densities in molecular beam epitaxial GaAs achieved by isoelectronic In doping
Authors: Bhattacharya Pallab K. , Dhar Sunanda , Berger Paul , Juang Feng-Yuh
Published: July 2002

We have studied the effects of adding small amounts of In (0.2–1.2%) to GaAs grown by molecular beam epitaxy. The density of four electron traps decreases in concentration by an order of magnitude, and the peak intensities of prominent emissions in the excitonic spectra are reduced with increase in In content. Based on the higher surface migration rate of In, compared to Ga, at the growth temperatures it is apparent that the traps and the excitonic transitions are related to point defects. This agrees with earlier observations by F. Briones and D. M. Collins [J. Electron. Mater. 11, 847 (1982)] and B. J. Skromme, S. S. Bose, B. Lee, T. S. Low, T. R. Lepkowski, R-Y. DeJule, G. E. Stillman, and J. C. M. Hwang [J. Appl. Phys. 58, 4702 (1985)].
Widely separate wavelength switching of single quantum well laser diode by injection-current control
Authors: Tokuda Yasunori , Tsukada Noriaki , Fujiwara Kenzo , Hamanaka Koichi , Nakayama Takashi
Published: July 2002

It is demonstrated for the first time that by injection-current control, the lasing wavelength was able to be switched from the lowest (n=1) quantized state transition to the second (n=2) transition for a single quantum well laser diode. The separation in energy was as wide as >50 meV. This novel function of a laser was realized as a result of appropriately increased threshold gain. This diode, moreover, acted as a multiple wavelength-emitting laser.
X-ray observation of twin faults in (1,1,1) CdTe epitaxial layers and in (1,1,1) Hg1−x
X
xTe/CdTe superlattices
Authors: Horning R. D. , Staudenmann J.-L.
Published: July 2002

This letter describes x-ray precession photographs of (1,1,1) CdTe epitaxial layers on GaAs, CdTe, and Cd0.96Zn0.04Te substrates. The precession method is further applied to some (1,1,1) Hg1−xXxTe/CdTe superlattices where X=Cd or Mn. More than half of the samples used in this study were grown by molecular beam epitaxy, others by metalorganic chemical vapor deposition, and a few by liquid phase epitaxy. The results unambiguously show that the common (1,1,1) face centered cubic twin fault, or stacking disorder, seen in bulk growth methods also exhibits its effects with the mentioned layer deposition growth techniques, except when liquid phase epitaxy is used. It seems that the twinning is intrinsic to the (1,1,1) growth in face centered cubic systems. In addition, devices with twin domains may have lower electronic mobilities. It further means that more experimental work is needed to produce untwinned single-crystal materials deposited by molecular beam techniques.
Probe pressure effect on tunneling current through a GaAs-(Al,Ga)As-GaAs heterojunction barrier
Authors: Solomon P. M. , Wright S. L. , La Tulipe D.
Published: July 2002

We have observed a remarkable increase of current through GaAs/(Al,Ga)As/GaAs barrier structures on the application of probe pressure. The increase in current is by many orders of magnitude, and is reversible on removal of the pressure. A rough calculation based on the probe geometry gives a local pressure of tens of kbar over an area of several square micrometers. The phenomenon may be understood in terms of the pressure dependence of the band edges of GaAs and AlGaAs.
Phased-array lasers with a uniform, stable supermode
Authors: Streifer W. , Osiński M. , Scifres D. R. , Welch D. F. , Cross P. S.
Published: July 2002

A phased-array semiconductor laser with identical coupled waveguides is designed to favor a uniform, stable supermode. All but the two outermost waveguides are equally spaced with the placement of the first and Nth guides chosen so as to increase their coupling coefficient by √2. The lowest and highest order supermodes have a uniform near-field intensity envelope and utilize the injected charges more efficiently. Whichever of these is favored at threshold should remain stable with increasing pumping or under modulation.
Physics of the enhancement of impact ionization in multiquantum well structures
Authors: Brennan Kevin , Hess Karl , Capasso Federico
Published: July 2002

We present an analytical theory of the experimentally observed enhanced impact ionization rate in multiquantum well structures, which is based on a modification of Schockley’s [Solid State Electron. 2, 35 (1961)] lucky electron theory. The general expression always predicts an enhancement in the ionization rate over the corresponding bulk value. The model is compared to both Monte Carlo calculations and recent experimental results. It is concluded that owing to the nonlinear aspects of impact ionization, the ionization rate can be significantly enhanced by the superposition of a uniform electric field and any spatially periodic electric field.
High-speed integrated heterojunction field-effect transistor photodetector: A gated photodetector
Authors: Taylor G. W. , Simmons J. G.
Published: July 2002

A new concept for a high-speed photodetector is described which promises very low noise with avalanche gain. The detector is constructed as an integrated circuit element in the heterojunction field-effect transistor technology and utilizes a unique n-n heterojunction interface formed by either metalorganic chemical vapor deposition or molecular beam epitaxy growth techniques. The degree of avalanching is controlled via an electrical third terminal.
Low threshold buried heterostructure quantum well diode lasers by laser-assisted disordering
Authors: Epler J. E. , Burnham R. D. , Thornton R. L. , Paoli T. L.
Published: July 2002

The first buried heterostructure laser diodes fabricated by laser-assisted disordering, a direct-write process, are described. In laser-assisted disordering a focused laser beam is scanned across the AlGaAs-GaAs heterostructure material to induce local melting and thereby incorporate Si from an encapsulation layer into the regrown crystal. A subsequent thermal anneal (850 °C, 0.7 h) is used to diffuse the Si deeper into the sample to enlarge the disordered region. This combination of patterned crystal regrowth and impurity-induced disordering is used to fabricate quantum well devices with lasing threshold currents as low as 6 mA (pulsed) and 8 mA (continuous). These devices have a narrow 4.5-μm-wide waveguide region and operate with a single longitudinal and spatial mode. They are the first optoelectronic devices fabricated with a direct-write laser-assisted process.
Optical bistability and gating in metalorganic vapor phase epitaxy grown GaAs étalons operating in reflection
Authors: Sahlén Olof , Olin Ulf , Masseboeuf Eric , Landgren Gunnar , Rask Michael
Published: July 2002

Nonlinear Fabry–Perot étalons of GaAs have been fabricated with metalorganic vapor phase epitaxy technology. The étalons operate in reflection mode, and have an epitaxially grown, rear dielectric mirror consisting of a stack of alternating AlAs/GaAlAs layers. Optical logic functions using a HeNe laser and optical bistability at room temperature are reported. Low switching powers and improved étalon uniformity are obtained.
Ultraviolet light stimulated thermal oxidation of silicon
Authors: Young E. M. , Tiller William A.
Published: July 2002

The photon-stimulated oxidation enhancement efficiency is shown to increase by an order of magnitude when the photon energy is raised from the visible range to the UV range just above the SiO2 to Si conduction-band energy difference. An additional order of magnitude in oxidation enhancement efficiency occurs when the UV photon energy is raised to just above the O2 dissociation energy. A critical UV pulse energy density threshold was found above which major morphological oxidation features developed at the laser beam spot location on the sample surface.
Coupling of diode laser arrays with photorefractive passive phase conjugate mirrors
Authors: Segev Mordechai , Weiss Shimon , Fischer Baruch
Published: July 2002

An experimental study of the coupling of diode laser arrays to various photorefractive phase conjugate mirrors is presented. We demonstrate frequency locking of arrays as well as the control of their emitted light patterns.
Observation of deep levels in cubic silicon carbide
Authors: Zhou Peizhen , Spencer M. G. , Harris G. L. , Fekade Konjit
Published: July 2002

In this work, a deep level transient spectroscopy (DLTS) study on n-type epitaxial cubic silicon carbide grown on Si substrates has been performed. The results of this study indicate the presence of at least two majority-carrier traps. One trap (SCE1) is located 0.34 eV from the conduction-band edge; the other trap (SCE2) is located 0.68 eV from the conduction-band edge. These two traps have concentrations of approximately 1×1015 cm−3. The DLTS spectrum as a function of the surface treatment of the SiC has been investigated. The results of this investigation indicate that one of the levels (SCE2) appears to be formed as a result of high-temperature thermal oxidation.
Experimental determination of the edge depletion width of ahe two-dimensional electron gas in GaAs/AlxGa1−xAs
Authors: Choi K. K. , Tsui D. C. , Alavi K.
Published: July 2002

A new method based on one-dimensional localization theory is introduced to determine the width of the two-dimensional electron gas (2DEG) in narrow conducting channels of GaAs/AlxGa1−xAs heterojunctions. The edge depletion width of the 2DEG, measured by the difference between this width and the metallurgical width of the channel, is ∼0.5 μm±0.2 μm for a 2DEG density ns=1.5×1011/cm2.
Influence of a constant current on Raman spectra of high mobility superlattices
Authors: Kempa K.
Published: July 2002

A constant current in a semiconductor high mobility superlattice is shown to lead to a shift and broadening of the intrasubband plasmon loss peaks in the Raman spectrum. By a model calculation for GaAs-AlGaAs we find that the simple homogeneous drift approximation is not valid in the high current regime where the drift velocity of electrons is of the order of the Fermi velocity.
Evidence for Si diffusion through epitaxial NiSi2 grown on Si(111)
Authors: Hinkel V. , Sorba L. , Haak H. , Horn K. , Braun W.
Published: July 2002

Epitaxial nickel silicide films grown on Si(111)-(2×1) surfaces have been studied by valence and core level photoemission using synchrotron radiation. The different chemical binding states of the nickel atoms were clearly identified in the valence-band spectra, and our data demonstrate that NiSi2 forms at lower temperatures than previously assumed. The growth of these epitaxial layers is always accompanied by the outdiffusion of silicon atoms, which exhibit an epitaxial arrangement on the silicide surface. By means of depth profiling using tunable synchrotron radiation we were able to determine the thickness of the topmost silicon layer.
Comparison of carrier profiles from spreading resistance analysis and from model calculations for abrupt doping structures
Authors: Casel A. , Jorke H.
Published: July 2002

Very abrupt doping structures grown by Si molecular beam epitaxy are investigated by spreading resistance (SR) analysis. The corresponding SR profiles reveal strong carrier spilling effects. To calculate the ‘‘on bevel’’ carrier concentrations of these structures, a formalism is developed which is based on the Poisson–Boltzmann equation. Qualitative agreement between the model calculation and the SR data is established.
Continuous (300 K) photopumped laser operation of AlxGa1−xAs-GaAs quantum well heterostructures grown on strained-layer GaAs on Si
Authors: Kaliski R. W. , Holonyak N. , Hsieh K. C. , Nam D. W. , Lee J. W. , Shichijo H. , Burnham R. D. , Epler J. E. , Chung H. F.
Published: July 2002

Data are presented demonstrating continuous (cw) room-temperature photopumped laser operation of an AlxGa1−xAs-GaAs quantum well heterostructure (QWH) grown on a Si substrate. The QWH is grown in a two-step process with first the GaAs grown on the Si substrate by molecular beam epitaxy (MBE) and second the QWH grown by metalorganic chemical vapor deposition (MOCVD). The MBE GaAs contains a thin 600-Å layer at the Si/GaAs interface that is rich in defects, ‘‘absorbs’’ much of the mismatch, and provides a good surface (specular surface) for the MOCVD growth of the QWH. Although cw 300 K laser operation is obtained, it occurs at high threshold and is short lived, agreeing with earlier results on the cw 300 K laser operation of mismatched III-V QWH’s.
Perforation seed structure in electron beam recrystallized silicon-on-insulator films
Authors: Horita Susumu , Ishiwara Hiroshi
Published: July 2002

A novel perforation seed structure in electron beam recrystallization of silicon-on-insulator (SOI) films has been proposed, in which seed regions typically with rectangular shapes are separately arranged along a line, so that voids are not generated in the films during the melting and recrystallization process. The structure was designed based on investigation of the void generation mechanism and its optimum dimensions were determined experimentally from viewpoints of the void suppression effect and the crystalline quality of the SOI films.
Molecular beam epitaxial growth of high-purity AlGaAs
Authors: Cunningham J. E. , Tsang W. T. , Chiu T. H. , Schubert E. F.
Published: July 2002

We report molecular beam epitaxial (MBE) growth of AlGaAs in the previously unexplored temperature range exceeding 800 °C for which excellent material can be achieved. Photoluminescence reveals bound excitonic linewidth as sharp as 3.6 meV, which is among the narrowest ever reported for material of equivalent Al mole fraction. In this temperature range carbon impurity concentrations are found to be dramatically reduced while temperature-dependent data provide information from which an understanding of carbon incorporation during MBE growth emerges.
Improved bremsstrahlung radiation uniformity from an indented-anode diode
Authors: Sanford T. W. L. , Halbleib J. A. , Poukey J. W. , Wright T. P. , Heath C. E. , Mock R. , Spence P. W. , Proulx G. , Bailey V. , Fockler J. , Kishi H.
Published: July 2002

Use of an indented anode in a cylindrical-cathode, planar anode diode placed at the exit of a coaxial magnetically insulated transmission line on the helia accelerator results in improved radiation uniformity. Measurements of the uniformity made on the accelerator at 3 MV, 150 kA are compared and shown to agree with theoretical calculations. The advantage of this scheme over that of the planar anode is that the diode impedance, pinch angle, and radial impact position at the anode can be partially decoupled.
Influence of boron on tin induced interdiffusion in GaAs-Ga0.72Al0.28As superlattices
Authors: Rao E. V. K. , Ossart P. , Alexandre F. , Thibierge H.
Published: July 2002

By performing different annealing treatments on variously tin-doped molecular beam epitaxially grown GaAs-Ga0.72Al0.28As quantum well structures, we show here the following: (i) tin, like other donor atoms silicon and sulfur, also induces disordering by enhancing interdiffusion coefficients, and (ii) a voluntary introduction of boron atoms in a tin-doped structure prior to annealing leads to a retardation in tin enhanced interdiffusion.
Hg1−xMnxTe-CdTe superlattices grown by molecular beam epitaxy
Authors: Chu X. , Sivananthan S. , Faurie J. P.
Published: July 2002

Molecular beam epitaxial growth of Hg1−xMnxTe-CdTe superlattices is reported here for the first time. They have been characterized by electron and x-ray diffraction, infrared transmission, and Hall measurements. The presence of satellite peaks in the x-ray spectra shows that Hg1−xMnxTe-CdTe superlattices have narrower band gaps than the equivalent quaternary Hg1−x−yMnxCdyTe. These superlattices exhibit a band-gap energy in the 0.1–0.3 eV range, demonstrating that they are a new infrared material. All these superlattices are n type even though their HgMnTe layers have been grown to be p type. Thus the type III-type I superlattice transition could not be investigated for hole mobility.
Piezomodulated electronic spectra of semiconductor heterostructures: GaAs/AlxGa1−xAs quantum well structures
Authors: Lee Y. R. , Ramdas A. K. , Chambers F. A. , Meese J. M. , Ram Mohan L. R.
Published: July 2002

Optical transitions associated with the electronic levels of a single quantum well in GaAs/AlxGa1−xAs heterostructures are observed with exceptional clarity in the piezomodulated reflectivity spectrum measured down to liquid helium temperature. The splitting of such transitions in multiple quantum well structures due to the coupling of the electronic levels in the adjacent wells is illustrated with results on a double quantum well.
Noncritically phase-matched sum frequency generation and image up-conversion in KNbO3 crystals
Authors: Baumert Jean-Claude , Günter Peter
Published: July 2002

Tunable and continuous wave (cw) near infrared up-conversion into the dark blue wavelength range (410–465 nm) has been achieved in KNbO3 crystals using the nonlinear optical coefficient d32 (ω1+ω2; ω1,ω2)=20.4 pm/V. High efficiencies have been reached due to the large nonlinearity and the possibility of temperature-tuned noncritical 90° phase matching. Using a neodymium:yttrium aluminum garnet laser (1064.2 nm) as the signal source and a krypton laser (676.4 nm) as the pump source, a sum signal (413.6 nm) power of over 0.1 mW was reached at a pump power of only 26.2 mW. cw image up-conversion into the blue wavelength range has been demonstrated using a noncritically phase-matched configuration in the same crystals at T=−4 °C.
Spectral dependence of propagation loss in InP/InGaAsP antiresonant reflecting optical waveguides grown by chemical beam epitaxy
Authors: Koch T. L. , Tsang W. T. , Corvini P. J.
Published: July 2002

We present direct measurement of low propagation loss in InP-core antiresonant reflecting optical waveguides (ARROW’s) at wavelengths that are strongly absorbed in the directly adjacent InGaAsP reflector layers. With 1.54-μm luminescence peak InGaAsP reflector layers, losses range from a low value of ∼0.9 dB/cm at 1.67 μm to ∼6.5 dB/cm at a wavelength of 1.515 μm for which the reflector layer losses approach 104 dB/cm. This proves the suitability of the ARROW geometry for providing large mode, low propagation loss guides for wavelengths that may either be generated, experience gain, or absorption within the reflector layers.
Plasma-enhanced deposition of high-quality epitaxial silicon at low temperatures
Authors: Comfort James H. , Reif Rafael
Published: July 2002

The use of a plasma during the deposition of epitaxial silicon from 750 to 800 °C is explored. Emphasis is placed on enhancement of the deposition process as opposed to the predeposition surface clean. Plasma enhancement of the deposition process is observed without a change in the apparent activation energy, and the mild ion bombardment (plasma) exposure during deposition introduced no additional defects observable by cross-sectional transmission electron microscopy. Plasma enhancement is also shown to facilitate deposition of high-quality epitaxial silicon films with low levels of unintentional impurity incorporation.
Laser etching of metals in neutral salt solutions
Authors: Datta M. , Romankiw L. T. , Vigliotti D. R. , von Gutfeld R. J.
Published: July 2002

We report new findings that relate to rapid maskless laser etching of steel and stainless steel in neutral solutions of sodium chloride, sodium nitrate, and potassium sulfate. Etch rates have been determined as a function of laser power, laser on-time, and solution concentration. The morphology of laser-etched holes obtained in these solutions was compared with holes obtained in pure water. Results indicate that some controlled melting occurs under certain laser conditions in addition to the metal dissolution process induced by the locally intense heat of the laser beam.
Energy requirements in communication
Authors: Landauer Rolf
Published: July 2002

The accepted view maintains that at least kT loge2 must be dissipated per transmitted bit. This is the result of prevalent assumptions that communication is done by waves, in linear systems, and that the energy in the message must be dissipated. It is shown, through counterexamples, that there is no minimal dissipation per transmitted bit. The simplest counterexample is physical transport of bistable systems. As in computation and measurement, unavoidable minimal dissipation occurs only when information is discarded.
Very low temperature (250 °C) epitaxial growth of silicon by glow discharge of silane
Authors: Baert K. , Symons J. , Vandervorst W. , Vanhellemont J. , Caymax M. , Poortmans J. , Nijs J. , Mertens R.
Published: July 2002

Epitaxial growth of phosphorus-doped silicon deposited at 250 °C from a radio-frequency glow discharge from SiH4 is demonstrated by high-resolution electron microscopy (HREM) and spreading resistance profile measurements. Thin epitaxial films are present at the interface between (100) Si substrates and hydrogenated amorphous silicon. After recrystallization at 700 °C, single-crystal layers are obtained, in which HREM reveals extensive twinning. The fact that epitaxial growth can take place at 250 °C in a system with a background pressure of only 5×10−6 mbar can be attributed to the presence of species in the SiH4 plasma that reduce the native oxide and the use of HF in the cleaning procedure.
Abnormal outdiffusion behavior of the deep level EL2 at the surface layer of undoped semi-insulating GaAs
Authors: Matsui Masayoshi , Kazuno Tadao
Published: July 2002

p-type thermal conversion of high-purity undoped semi-insulating GaAs after annealing at 850 °C in H2 gas has been investigated. It has been found that the p-type carrier concentration at the surface layer quantitatively matches the residual carbon concentration in the bulk. The concentrations of the other acceptor impurities (Mn, Zn, Cu, Cr) in the sample are confirmed to be negligibly small. The depth profile of the carrier concentration indicates that the concentration of the EL2 level increases as the sixth power of the depth near the surface region and that it exhibits a linear dependence on depth in the deeper region. A possible mechanism for this abnormal behavior of the EL2 level is discussed.
Two-electrode distributed feedback injection laser for single-mode stabilization and electro-optical switching
Authors: Liou K.-Y. , Burrus C. A. , Koren U. , Koch T. L.
Published: July 2002

By utilizing two electrodes on a conventional uniform-grating distributed feedback (DFB) injection laser, the usual two-mode DFB laser degeneracy has been removed to permit (1) single-frequency operation with 33-dB side-mode suppression and (2) current-controlled switching between the two modes, separated by a 10–25 Å stop band, in less than 1 ns.
EuBa2Cu3Ox produced by oxidation of a rapidly solidified precursor alloy: An alternative preparation method for high T
c ceramic superconductors
Authors: Haldar R. , Lu Y. Z. , Giessen B. C.
Published: July 2002

High-temperature ceramic superconductors such as RE1Ba2Cu3O∼7 are usually prepared by reacting the constituent metal oxides (RE=rare-earth metal). We have prepared RE1Ba2Cu3O∼7 by an alternate method, first combining three metals into an alloy by rapid solidification processing, followed by oxidation to form the cuprate. Only Eu (or Yb) yields single phase RE-Ba-Cu liquids as required for melt processing, because their valency changes from two in the metal (assuring complete miscibility with Ba) to three in the oxide. The superconducting properties of the oxidized alloys are similar to those of EuBa2Cu3Ox prepared by the standard ceramic reaction route.
Temporary laser damage threshold enhancement by laser conditioning of antireflection-coated glass
Authors: Frink M. E. , Arenberg J. W. , Mordaunt D. W. , Seitel S. C. , Babb M. T. , Teppo E. A.
Published: July 2002

Laser irradiation at fluences below the damage threshold level of antireflection-coated BK7 (grade A borosilicate crown glass) samples temporarily increases the measured laser-induced damage threshold by about 40%. Because the surface damage threshold is sensitive to the irradiation history, it is necessary to control the test procedure to ensure reproducible and accurate measurements. Preliminary results indicate that adsorption of water is a principal factor involved in the deactivation of the conditioning enhanced laser damage thresholds.
Ohmic contacts to n-GaAs using In/Pd metallization
Authors: Allen L. H. , Hung L. S. , Kavanagh K. L. , Phillips J. R. , Yu A. J. , Mayer J. W.
Published: July 2002

Ohmic contacts to n-GaAs (Si doped at 2×1018 cm−3) with contact resistances of 0.7–1.5×10−6 Ω cm2 have been formed with deposited layers of In and Pd. The layers were sequentially evaporated and then annealed at 500 °C for 20 s to form In3Pd and a top layer of In. In addition a thin (≊200 Å) reacted layer was formed at the GaAs interface. Uniform interface morphology was observed with no evidence of localized reaction.
Orthorhombic-tetragonal phase transition in high-temperature superconductor YBa2Cu3O7
Authors: Eatough M. O. , Ginley D. S. , Morosin B. , Venturini E. L.
Published: July 2002

We have determined the effect of elevated temperature on the crystal structure and lattice parameters of the single-phase high-temperature superconductor YBa2Cu3O7 using high-temperature x-ray powder diffractometry. This compound is orthorhombic below about 550 °C (depending on oxygen partial pressure) and transforms to a tetragonal polymorph at higher temperatures. The reversibility of this transition depends on the oxygen partial pressure. An oxygen ‘‘hopping’’ mechanism with possible oxygen loss, which appears consistent with the known structural details, is proposed for the transition.
Melt-processible rare earth-Ba-Cu-O superconductors based on molten Ba-Cu oxides
Authors: Hermann A. M. , Sheng Z. Z.
Published: July 2002

Ba-Cu oxides with certain compositions were found to be meltable or partly meltable at a relatively low temperature of 950 °C. High-quality, dense, and void-free high-temperature superconductors based on rare earth(RE)-Ba-Cu oxides of the form REBa2Cu3O6.5+x have been made by reactions between molten Ba-Cu oxides and solid RE-containing materials at the same temperature. This has allowed superconductive components to be made in a wide variety of shapes. This melt process will significantly alter oxide superconductor preparation procedures, and will allow growth of large single crystals aiding in the understanding of the mechanism of superconductivity and in the search for superconductivity at even higher transition temperatures.
Rapid lattice expansion and increased x-ray reflectivity of a multilayer structure due to pulsed laser heating
Authors: Zigler A. , Underwood J. H. , Zhu J. , Falcone R. W.
Published: July 2002

The spacing of layers in a sputtered, multilayer structure was rapidly and permanently increased by heating with a nanosecond laser pulse. During laser heating, the Bragg angle decreased and the peak reflectivity increased for diffraction of soft x-ray radiation at 4.4 nm. Measurements were made using a time and space resolving x-ray streak camera detector.
High power, high efficiency window buried heterostructure GaAlAs superluminescent diode with an integrated absorber
Authors: Kwong Norman S. K. , Lau Kam Y. , Bar-Chaim Nadav , Ury Israel , Lee Kevin J.
Published: July 2002

A superluminescent diode (SLD) based on a proven high power, high efficiency ‘‘window-’’ type index-guided buried heterostructure laser is demonstrated. Lasing is suppressed for SLD operation by antireflection coating and by incorporating an unpumped absorber section. The resulting device emits high optical power (14 mW) in the SLD mode at very low injection current (50 mA). The spectral modulation depth is below 14% over the entire emission spectral bandwidth of 20 nm, with a symmetrical beam divergence (20°×40°) and a stable transverse mode.
Substrate temperature dependence of GaAs, GaInAs, and GaAlAs growth rates in metalorganic molecular beam epitaxy
Authors: Kobayashi N. , Benchimol J. L. , Alexandre F. , Gao Y.
Published: July 2002

The substrate temperature (Ts) dependence (350–700 °C) of GaAs and Ga1−y InyAs growth rates was investigated in metalorganic molecular beam epitaxy (MOMBE), using triethylgallium (TEG), trimethylindium (TMI), and solid arsenic (As4) sources. For GaAs growth, four distinct Ts dependent regions are observed, including a weak desorption process (500–650 °C) characteristic of MOMBE, preceding atomic Ga desorption (Ts >650 °C). When adding a TMI flux to grow Ga1−yInyAs, this desorption process was much enhanced up to 550 °C, and then decreased above 550 °C when the In desorption phenomenon takes place. Correlatively, the In alloy composition peaks at 550 °C. The same dependence was observed in Ga1−yInyAs growth using solid In and TEG sources. However, in Ga1−xAlxAs growth using solid Al or triethylaluminum (TEA) and TEG sources, the weak desorption observed in GaAs MOMBE was strongly minimized. From these results, possible growth mechanisms are discussed.
Extremely low-intensity optical nonlinearity in asymmetric coupled quantum wells
Authors: Little J. W. , Whisnant J. K. , Leavitt Richard P. , Wilson R. A.
Published: July 2002

We have observed an intensity-dependent shift in the exciton absorption features for a system of coupled quantum wells in which a thin barrier separates two wells of unequal widths. We found that for a fixed external bias on the sample, the normal quantum Stark shift of the excitons in the wells was suppressed when light of 1 μW/cm2 intensity was used to measure the absorption. The shift became systematically larger as the light intensity was decreased to as low as 100 pW/cm2. This extremely low-level nonlinearity may be due to internal fields that arise when free electrons and holes are separated within the coupled-well system.