bluuebunny/crossref_metadata_2025 huggingface dataset:
Extended neoclassical transport theory for incompressible tokamak plasmas
Authors: Shaing K. C.
Published: July 2002

Conventional neoclassical transport theory is extended to include the effects of orbit squeezing, and to allow the effective poloidal Mach number UpM=[(V∥/vt)+(VEB/vtBp)] of the order of unity for incompressible tokamak plasmas. Here, V∥ is the parallel mass flow, vt is the ion thermal speed, VE is the poloidal E×B drift speed, B is the magnetic field strength, and Bp is the poloidal magnetic field strength. It is found that ion thermal conductivity is reduced from its conventional neoclassical value in both banana and plateau regimes if UpM>1 and S>1. Here, S=[1+cI2Φ′′/(Ω0B0)] is the orbit squeezing factor with c the speed of light, I=RBt, R the major radius, Φ the electrostatic potential, B0 the magnetic field strength on the axis, Ω0=eB0/Mc, M the ion mass, e the ion charge, Φ′′=d2Φ/dψ2, and ψ the poloidal flux function. However, there is an irreducible minimum for the ion thermal conductivity in the banana-plateau regime set by the conventional Pfirsch–Schlüter transport.
Vortex tube models for turbulent dynamo action
Authors: Bigazzi Alberto , Brandenburg Axel , Moss David
Published: July 2002

The possibility of dynamo action resulting from a pair of elongated vortex structures immersed in an electrically conducting fluid is investigated. For elongated vortex structures, the critical magnetic Reynolds number for dynamo action is about half that for the spherical rotors that have been studied previously. When applied to Kolmogorov turbulence with vortex structures of scale comparable to the dissipation length, this model can explain dynamo action only when the magnetic Prandtl number (=kinematic viscosity/magnetic diffusivity) exceeds a critical value that is larger than unity. It is argued that in astrophysical bodies where this condition is not satisfied (in stellar convection zones, for example), dynamo action must instead result from motions on all scales up to the size of the region.
Search for low-dimensional chaos in a reversed field pinch plasma
Authors: Sattin F. , Martines E.
Published: July 2002

An analysis of experimental data from the reversed field experiment (RFX) reversed field pinch machine [L. Fellin, P. Kusstatscher, and G. Rostagni, Fusion Eng. Des. 25, 315 (1995)] is carried out to investigate the possible existence of deterministic chaos in the edge plasma region. The mathematical tools used include Lyapunov exponents, Kaplan–Yorke dimension, minimum embedding dimension estimates and nonlinear forecasting. The whole analysis agrees in ruling out the possibility of low-dimensional chaos: The dimension of the underlying dynamical system is estimated to be >10. From a critical rereading of the literature it emerges that the findings of this work are likely to be common to all reversed field pinches.
Applied-B ion diode theory: The screening scale, relaxation of a Lagrangian invariant, and the diode stability
Authors: Gretchikha A. V.
Published: July 2002

The assumption of relaxation to uniformity for the electron drift Lagrangian invariant ne/B results in a voltage–current characteristic U(ji) of an ion diode. The effect of the electric field screening at the magnetic Debye scale rB=B/4πene causes the existence of a maximum in the U(ji) curve at a certain threshold ion current density ji=jcrit. The diode can be stable only at the rising part of the U(ji) curve (ji<jcrit). The theoretical threshold ion current density jcrit is in very good agreement with the ion current density at which the slow two-fluid mode arises in the three-dimensional, particle-in-cell (3D PIC) simulations. This can be an important key to suppression of this mode, which is the main source of the beam divergence.
Kinetic analysis of the plasma boundary layer in an oblique magnetic field
Authors: Daube Th. , Riemann K.-U.
Published: July 2002

A kinetic analysis is presented to study the influence of a strong oblique magnetic field on the plasma boundary layer in front of an absorbing wall. The ion transport is provided by (a) magnetic field lines intersecting the wall and (b) by charge exchange collisions with neutrals. The Debye length λD is small compared with the ion gyroradius ρi and the electrons are Boltzmann distributed. For the limiting case λD→0 and cold neutrals, an efficient method is developed to calculate the self-consistent stationary solution of the ion Boltzmann equation. The resulting ion distribution functions exhibit an involved structure. The kinetic Bohm-criterion is found to be fulfilled marginally. To investigate the stability of the solution, the analysis is supplemented by a particle simulation. It is shown that the involved structure of the stationary ion velocity distribution is smeared out (a) by an ion cyclotron instability (cold gas) and (b) by a finite gas temperature. The potential profiles and ion distributions resulting from the self-consistent kinetic analysis are compared with expectations based on a previous hydrodynamic model.
Calculations of wave excitation and dissipation in Tokamak Chauffage Alfvén wave heating experiment in Brazil
Authors: Amarante-Segundo G. , Elfimov A. G. , Ross D. W. , Galvão R. M. O. , Nascimento I. C.
Published: July 2002

The results of numerical calculations of Alfvén wave absorption are discussed for the experimental conditions foreseen for the Tokamak Chauffage Alfvén wave heating experiment in Brazil (TCABR) [Nucl. Fusion 30, 503 (1996)]. In particular, the effect of toroidal mode coupling on the power deposition of Global Alfvén Wave (GAW) eigenmodes is carefully investigated. Resonant absorption of the toroidally coupled sidebands causes a broad power deposition close to the plasma boundary which can surpass the power deposition of the main GAW at the plasma center. However, the wave absorption can be somewhat optimized by a proper choice of mode spectrum. The excitation of a pure mode spectrum centered at the toroidal mode numbers n=−4 and −6 leads to better plasma coupling than a spectrum centered at n=−2. Finally, it is shown that a small population of light impurities in a hydrogen plasma can strongly modify the dispersion of the GAW and the toroidal Alfvén continuum.
A tearing mode model for cascades of high-frequency modes
Authors: Hallatschek K.
Published: July 2002

A model for cascades of high-frequency modes found in the ASDEX Upgrade (Axially Symmetric Divertor Experiment) tokamak [Plasma Physics and Controlled Nuclear Fusion Research 1993 (International Atomic Energy Agency, Vienna, 1994), Vol. 1, p. 127] is described. In a cascade, modes of the form (m,n), m=n+1 are sequentially excited and stabilized. Mode numbers up to 23 can be reached by a domino effect, where each mode excites a mode with m,n increased by one and is extinguished subsequently. Despite the high mode numbers these modes can be interpreted as tearing modes destabilized by a region of very low magnetic shear and high current gradient. Their instability can be shown by a cylindrical estimate, the cascade process has been investigated in a quasilinear model. The onset of the cascade phenomenon is shown to be caused by an inverse resistivity profile during the activity of a (1,1) mode.
Quasilinear evolution of the ion cyclotron beam-anisotropy instability in a current carrying plasma
Authors: Chaston C. C. , Hu Y. D. , Fraser B. J.
Published: July 2002

The evolution of particle velocity moments and wave spectra during the quasilinear saturation of the proton beam-anisotropy instability in a current carrying plasma is studied. For initial plasma moments characteristic of the near-Earth plasma sheet boundary layer, it is found that the saturation of the ion beam-anisotropy instability drives a field-aligned current, which self-consistently excites a kink-like mode. The driven current allows the wave fields of current driven mode to grow to amplitudes comparable to that of the anisotropy instability and facilitates more rapid isotropization of the unstable anisotropic beam components and saturation of the beam-anisotropy instability. This work has general relevance to the study of field-aligned instabilities in plasmas where the excited waves carry a net momentum density away from the source of instability.
Chaos and chaos control in a strongly driven thermionic plasma diode
Authors: Mausbach T. , Klinger T. , Piel A.
Published: July 2002

In a periodically driven thermionic diode period doubling cascades, period adding and low-dimensional chaos are found. Some dynamical properties of the driven discharge are comparable to strongly driven diode resonant circuits. The chaotic oscillations of the discharge current are controlled using occasional proportional feedback and an improved difference feedback method. Feedback constants are predetermined by the local analysis of the first return map.
Asymptotic theory of spherical electrostatic probes in large Debye length plasmas containing negative ions
Authors: Bektursunova Rimma M.
Published: July 2002

The problem of a spherical electrostatic probe in negative ion containing oxygen plasmas is treated by the matching asymptotic expansions technique [A. H. Nayfeh, Perturbation Methods (Wiley, New York, 1973)]. Assuming that the energy relaxation length is much smaller than the local characteristic length, explicit results are obtained in the asymptotic limits, (rp/rD)2≪1,(rp/rS)2≪1, where rD is the Debye radius, rS is the recombination length and rp is the probe radius. The perturbation region divides naturally into a thin space charged sheath, a transitional sheath, and a quasineutral chemically equilibrium plasma. The potential and charged particle density distributions are obtained. The calculated probe characteristic is presented in an analytical form.
Parallel velocity shear instability, Alfven waves and the formation of the transport barrier
Authors: Sen S. , Cairns R. A.
Published: July 2002

It is suggested that the ponderomotive force induced by radio frequency (rf) waves in the range of the Alfven frequency can create a transport barrier in a tokamak. The linear and nonlinear behavior of the driftlike perturbation with a parallel velocity shear is studied in the presence of rf waves. It is shown if the radial profile of the rf field energy is properly chosen the linear mode is stabilized and turbulent momentum transport reduces. The rf power required for this stabilization is found to be rather modest and hence should be easily obtained in actual experiments.
Three-dimensional modeling of capsule implosions in OMEGA tetrahedral hohlraums
Authors: Schnittman J. D. , Craxton R. S.
Published: July 2002

Tetrahedral hohlraums have been proposed as a means for achieving the highly uniform implosions needed for ignition with inertial confinement fusion (ICF) [J. D. Schnittman and R. S. Craxton, Phys. Plasmas 3, 3786 (1996)]. Recent experiments on the OMEGA laser system have achieved good drive uniformity consistent with theoretical predictions [J. M. Wallace et al., Phys. Rev. Lett. 82, 3807 (1999)]. To better understand these experiments and future investigations of high-convergence ICF implosions, the three-dimensional (3-D) view-factor code BUTTERCUP has been expanded to model the time-dependent radiation transport in the hohlraum and the hydrodynamic implosion of the capsule. Additionally, a 3-D postprocessor has been written to simulate x-ray images of the imploded core. Despite BUTTERCUP’s relative simplicity, its predictions for radiation drive temperatures, fusion yields, and core deformation show close agreement with experiment.
Reversal of contrast for infrared absorption of deep levels in semi-insulating GaAs
Authors: Queisser Hans J.
Published: July 2002

A new interpretation is offered for the observed reversal of contrast in the infrared absorption of nonuniformly distributed deep centers, related to EL2, in large-diameter, liquid-encapsulation-grown, semi-insulating GaAs. In the photoquenched state, having reversed contrast, the absorption originates in electrons, having been transferred from spatially clustered deep centers onto shallow centers adjacent to these clusters. Transfer is achieved by photon absorption and subsequent removal via the built-in electric fields, generated by the clustering of the deep centers.
Epitaxial growth of ZrSi2 on silicon with an ion beam mixing assisted scheme
Authors: Cheng H. C. , Chen L. J.
Published: July 2002

Ion beam mixing has been demonstrated to play a critical role in growing refractory silicide epitaxially on silicon for the first time. Epitaxial ZrSi2 has been successfully grown on (111) and (001) Si. Best epitaxy was obtained in samples irradiated by As+ with an ion range close to the original Zr/Si interface to a dose of 1×1016/cm2 followed by 1100 °C annealing. The breaking of metal–oxygen bonds, dissolution of native silicon dioxide, as well as dispersion of impurities present at the interface by ion beam are thought to be beneficial in inducing the epitaxial growth of ZrSi2 on Si. The orientation relationships between epitaxial ZrSi2 and Si were found to be [010]ZrSi2//[001]Si, (002̄)ZrSi2//(22̄0)Si (with about 1° misorientation), [31̄0]ZrSi2//[112]Si, and (130)ZrSi2//(111̄)Si. Hexagonal and square networks of interfacial dislocations were observed. They were identified to be of edge type with (1)/(6) 〈112〉 or 1/2 〈110〉 Burgers vectors. The average spacings were measured to be 140 and 800 Å correspondingly. The results represent the first successful attempt to grow orthorhombic structure refractory silicide epitaxially on silicon.
Instability in a relativistic electron layer with a strong azimuthal magnetic field
Authors: Hughes T. P. , Godfrey B. B.
Published: July 2002

A thin relativistic electron layer immersed in a strong azimuthal magnetic field between two concentric cylindrical conductors is shown to be unstable. The instability is caused by the curvature of the walls, which modifies the interaction between particles in such a way that the inductive (attractive) forces are greater than the electrostatic (repulsive) forces. The growth rate of the instability peaks at long axial wavelengths.
Asymptotic estimates of diffusion times for rapid thermal annealing
Authors: Fehribach J. D. , Ghez R. , Oehrlein G. S.
Published: July 2002

Temperature profiles for rapid thermal annealing of ion implanted material are analyzed using asymptotic methods. Although only rapid thermal annealing is discussed, these methods are also applicable to many other annealing processes. Formulas for effective diffusion distance and effective annealing time are given which correct for the deviations of actual annealing profiles from ideal annealing profiles. The three major deviations considered are (1) ramp terms, (2) rising plateaus, and (3) plateau overshoots. The analysis shows that even relatively small deviations can have sizable effects.
Fiber-optic logic gate
Authors: Kitayama Ken-ichi , Kimura Yasuo , Seikai Shigeyuki
Published: July 2002

Operation of a fiber-optic logic gate is demonstrated for the first time. The principle of operation is based upon the intensity-dependent polarization rotation in birefringent fibers. Using a birefringent fiber combined with polarizers in the crossed state, the ON/OFF state of an AND operation is clearly observed with an extinction ratio of approximately 10 dB. The fiber-optic logic gate would be a promising device for optical information processing in the future because of the feasibility of compact configuration and very fast-speed operation.
Nonlinear single-mode fiber coupler using liquid crystals
Authors: Goldburt E. S. , Russell P. St. J.
Published: July 2002

The operation of a new nonlinear optical waveguide coupler, fabricated in single-mode fibers and using a liquid crystal as the nonlinear medium, is described. Strongly intensity-dependent coupling and associated bistability are observed to occur in the intensities of the light in the uncoupled and coupled fibers, plotted as a function of the intensity in the input fiber. The effects of applying a dc electric field are also reported. Criteria for the development of liquid crystals suitable for the construction of various types of nonlinear optical devices in single-mode optical fibers are proposed.
Carrier trapping in room-temperature, time-resolved photoluminescence of a GaAs/AlxGa1−xAs multiple quantum well structure grown by metalorganic chemical vapor deposition
Authors: Fouquet J. E. , Siegman A. E. , Burnham R. D. , Paoli T. L.
Published: July 2002

The time decay of the room-temperature photoluminescence from the n=1 transition in a multiple quantum well structure grown by metalorganic chemical vapor deposition is observed to depend strongly on excitation energy density. For low excitation (0.2 μJ/cm2) an exponential 3-ns decay is observed, while for high excitation (120 μJ/cm2) the decay lengthens to 45 ns. In the case of higher excitation, the photoluminescence decay rate is observed to increase after excitation and initial decay. The excitation energy dependence of the initial decay can be explained by saturation of carrier traps, and the later speedup of photoluminescence decay can be explained by the release of carriers from the traps and subsequent refilling. Time-integrated photoluminescence data qualitatively support the trapping interpretation. This is the first report, to the best of our knowledge, of time-resolved photoluminescence in a metalorganic chemical vapor deposition grown GaAs/AlxGa1−x As quantum well structure.
Electron heating and free-carrier absorption in GaAs/AlGaAs single heterostructures
Authors: Höpfel R. A. , Weimann G.
Published: July 2002

We observe far infrared broadband emission from the hot two-dimensional electron plasma in GaAs/AlGaAs single heterostructures grown by molecular beam epitaxy. The radiation is analyzed in two different frequency regimes (around 35 and 100 cm−1). From the relative dependence of the intensities on the applied longitudinal electric field the hot-electron temperatures are determined. From the absolute emission intensities values of the free-carrier absorption coefficient (down to 10−5 in ultrahigh mobility samples) are measured.
Experimental evaluation of low-frequency oscillations in undoped GaAs to probe deep level parameters
Authors: Maracas G. N. , Johnson D. A. , Goronkin H.
Published: July 2002

A new method for characterizing undoped, semi-insulating GaAs is presented. The low-frequency current oscillations on undoped liquid encapsulated Czochralski GaAs substrates are used to determine deep level energies, cross sections, and concentrations. A Fourier transform is used to resolve the various frequency components of the signal. The frequency is seen to vary almost four orders of magnitude in a 50-K temperature range. Plotting the temperature dependence of each frequency component in an Arrhenius plot gives activation energies and cross sections corresponding to the deep levels responsible for the oscillations. It is seen that two closely spaced levels cause the low-frequency oscillations. In addition, this technique allows the determination of trap parameters as a function of electric field at values much less than the critical field for intervalley transfer in GaAs.
Magnetic structure for a microundulator
Authors: White R. M.
Published: July 2002

A scheme is proposed for the fabrication of an undulator having a magnetic period in the millimeter range.
Laser chemical vapor deposition of copper
Authors: Houle F. A. , Jones C. R. , Baum T. , Pico C. , Kovac C. A.
Published: July 2002

The first laser-induced deposition of copper has been demonstrated using a volatile copper coordination complex. The technique is characterized by reasonable rates and by the high quality of copper produced.
A novel GaInAsP/InP distributed feedback laser
Authors: Liau Z. L. , Flanders D. C. , Walpole J. N. , DeMeo N. L.
Published: July 2002

GaInAsP/InP distributed feedback lasers have been fabricated with a simple new design in which the grating is etched into the top of a mass-transported buried heterostructure. Single-frequency operation with sidemodes lower than −32 dB and threshold currents as low as 16 mA have been achieved.
Laser-initiated microchemistry: Dynamic probes of metallopolymer thin-film decomposition
Authors: Fisanick G. J. , Hopkins J. B. , Gross M. E. , Fennell M. D. , Schnoes K. J.
Published: July 2002

Transient absorption has been used as a probe of the reaction kinetics in the laser-initiated thermal decomposition of Au metallopolymers. Feature sizes are considerably larger than the dimensions of the laser spot due to the propagation of a reaction front driven by the heat release from the highly exothermic reaction. Front velocities in the range of 30–50 cm/s are measured using spatially separated generating and probe lasers. These effects should be generalizable to any laser-driven thermal reaction in the condensed phase with sufficient heat release, and, as such, constitute a major limitation on feature size obtainable in these systems.
Reduced dynamic linewidth in three-terminal two-section diode lasers
Authors: Coldren L. A. , Boyd G. D. , Bowers J. E. , Burrus C. A.
Published: July 2002

The dynamic wavelength chirping observed in modulated semiconductor lasers can be reduced in three-terminal coupled-cavity structures by appropriately splitting the modulation signal to the two cavities. In a 1.3-μm wavelength GaInAsP/InP cleaved-coupled-cavity laser, the 90% modulation-depth linewidth was reduced to ∼0.2 Å for modulation frequencies up to 1.7 GHz.
Dilute magnetic semiconductor (Cd1−xMnxTe) quantum well laser
Authors: Bicknell R. N. , Giles-Taylor N. C. , Blanks D. K. , Schetzina J. F. , Anderson N. G. , Laidig W. D.
Published: July 2002

In this letter we report the first observation of stimulated emission from an optically pumped multilayer structure in which Cd1−xMnxTe, a dilute magnetic semiconductor (DMS), serves as the active quantum well material. The DMS laser structure was grown by molecular beam epitaxy with an active region consisting of 25 Cd0.81Mn0.19Te quantum wells of thickness LZ=125 Å alternating with 24 Cd0.64Mn0.36Te barrier layers of thickness LB=40 Å. The DMS lasers operate in the visible (red) spectral region at 665–670 nm when pumped at T=15 K with a pulsed argon ion laser. The threshold for laser action occurs at a peak pump power density of about 2.0×104 W/cm2.
Holographic-grating acoustic devices
Authors: Oates D. E. , Gottschalk P. G. , Wright P. V.
Published: July 2002

We report observations of acoustic wave reflections by an optically produced holographic grating within iron-doped LiNbO3. The stored hologram, through the electroacoustic effect, causes a spatially varying acoustic velocity change which can serve to reflect acoustic waves. We have demonstrated the reflection of bulk acoustic waves from a 4-μm period grating in LiNbO3 with an iron doping of 0.015%. The acoustic frequency was 0.9 GHz. A strong interaction with a reflection coefficient of 4×10−4 per grating element was found. Memory retention exceeds the three months over which we have observed the effect. The reflections can be exploited to produce practical filters and resonators.
Low-temperature characteristics of electron and hole ionization coefficients in (100) oriented Ga1−xInxAsyP1−y
Authors: Osaka Fukunobu , Mikawa Takashi , Kaneda Takao
Published: July 2002

Low-temperature characteristics of electron and hole ionization coefficients, α and β, in four kinds of (100) oriented Ga1−x Inx Asy P1− y crystals have been derived from photomultiplication data measured on Ga1−x Inx Asy P1− y/InP diodes with arsenic compositions of 0, 0.28, 0.39, and 0.70 over the temperature range from room temperature (293 K) to liquid nitrogen temperature (77 K). It has been found that the increase rates of α and β in GaInAsP with lowering temperatures are 20–50% smaller than those in InP, and that the increase rate of β in a GaInAsP crystal is 15–25% smaller than that of α in the same crystal. These low-temperature characteristics of α and β have been indicated to be explained by assuming alloy scattering influencing impact-ionizing electrons and holes in quaternary alloy crystals in this temperature range.
Long wavelength InGaAsP (λ∼1.3 μm) modified multiquantum well laser
Authors: Dutta N. K. , Napholtz S. G. , Yen R. , Wessel T. , Shen T. M. , Olsson N. A.
Published: July 2002

The fabrication and performance characteristics of InGaAsP (λ∼1.3 μm) double channel planar buried heterostructure lasers with multiquantum well (MQW) active layers are reported. The MQW structure has λg∼1.3 μm InGaAsP active wells and λg∼1.03-μm InGaAsP barrier layers. The lasers have threshold current of ∼20 mA at 30 °C and external differential quantum efficiencies of ∼0.2 mW/mA/facet at 30 °C. The temperature dependence of threshold current is characterized by T0∼100 K both under electrical and optical pumping. The lasers have been operated to 110 °C and up to ∼30 mW/facet at 25 °C. The measured dynamic linewidth under modulation is ∼2 smaller than that for conventional double heterostructure lasers. The lower temperature dependence of threshold current and smaller dynamic linewidth makes real index-guided InGaAsP MQW active layer lasers potentially attractive for many system applications.
Electric field dependent cathodoluminescence of III-V compound heterostructures: A new interface characterization technique
Authors: Magnea N. , Petroff P. M. , Capasso F. , Logan R. A. , Alavi K. , Cho A. Y.
Published: July 2002

A new method for the analysis of heterostructures is described and applied to the characterization of InP-InGaAs and AlInAs-InGaAs interfaces. The technique’s principle relies on the selective quenching of the cathodoluminescence of each layer induced by application of an electric field. The cathodoluminescence quenching curves as a function of reverse bias voltage give the position of the interfaces in good agreement with the capacitance versus voltage profile, and hysteresis in the luminescence behavior is ascribed to deep levels at or near the interfaces.
Epitaxial growth of (100)CdTe on (100)GaAs induced by pulsed laser evaporation
Authors: Dubowski J. J. , Williams D. F. , Sewell P. B. , Norman P.
Published: July 2002

Epitaxial (100) CdTe films were grown on the (100) GaAs surface by pulsed laser evaporation. The growth was achieved on substrates held at 260 °C and under a pressure of about 8×10−8 Torr. High-energy electron diffraction, x-ray diffraction, and UV reflectivity studies have shown that epilayers of high crystalline quality were obtained. The surface morphology of films thicker than about 0.4 μm approached atomic smoothness. No incorporated impurities, including oxygen and carbon, were found by Auger electron spectroscopy in the films studied.
High quality silicon on insulator structures formed by the thermal redistribution of implanted nitrogen
Authors: Hemment P. L. F. , Peart R. F. , Yao M. F. , Stephens K. G. , Chater R. J. , Kilner J. A. , Meekison D. , Booker G. R. , Arrowsmith R. P.
Published: July 2002

Silicon wafers have been implanted with 200-keV 14N+ ions to doses between 0.25 and 1.4×1018 N+ cm−2 at a temperature of 500 °C and have been annealed at 1200 °C for 2 and 8 h. Rapid redistribution of the implanted nitrogen occurs, against the macroscopic concentration gradient, in samples implanted with doses below that required to directly synthesize stoichiometric Si3N4. This leads to the formation of a continuous buried layer of either amorphous or polycrystalline Si3N4. The surface layer is high quality single crystal silicon (χmin =0.043) containing no polycrystalline material nor precipitates. The Si-Si3N4 interfaces are extremely abrupt but with an irregularity of ∼100 and ∼50 Å at the upper and lower interfaces, respectively.
Photoluminescence of organometallic vapor phase epitaxial GaInAs
Authors: Fry K. L. , Kuo C. P. , Cohen R. M. , Stringfellow G. B.
Published: July 2002

The low-temperature photoluminescence (PL) characteristics of undoped organometallic vapor phase epitaxial GaInAs lattice matched to InP have been studied and related to different growth conditions. By varying the excitation intensity, PL transitions due to excitons and donor-acceptor pairs have been identified. Analysis of the two donor-acceptor pair peaks yields acceptor activation energies of 13 and 24 meV, which are attributed to C and Zn, respectively. Carbon incorporation is seen to decrease markedly, accompanied by a substantial increase in mobility (10 000 and 40 000 cm2/Vs at 300 and 77 K, respectively) when the growth temperature is increased to 650 °C and the V/III ratio is kept above ∼30. The importance of accounting for lattice mismatch in interpreting PL half-widths is evidenced by the doubling of the 77-K PL half-width for a lattice mismatch of only ∼10−3.
Enhancement of intensity-dependent absorption in InP and GaAs at 1.9 μm by doping
Authors: Li Nien-Lou , Bass Michael , Swimm Randall
Published: July 2002

Dopants giving rise to deep level states in InP and GaAs were found to significantly enhance the process of intensity-dependent absorption at 1.9 μm. Such dopants also beneficially alter the laser damage threshold of the host materials.
High efficiency, high modulation bandwidth (Ga,Al)As:Te,Zn light-emitting diodes with graded band gap
Authors: Leibenzeder S. , Rühle W. , Hoffmann L. , Weyrich C.
Published: July 2002

A new (Ga,Al)As light-emitting diode (λmax =660–880 nm) is presented which has several advantages: simple processing, high external quantum efficiencies (up to 12%), and short decay times (down to 12 ns). The importance of photon recycling and reduced self-absorption in the graded band gap is demonstrated.
Organometallic vapor phase epitaxial growth and characterization of high purity GaInAs on InP
Authors: Carey Kent W.
Published: July 2002

GaInAs grown on InP at atmospheric pressure using organometallic vapor phase epitaxy is characterized by x-ray diffraction, transmission electron microscopy (TEM), and Hall measurements. The sources used are TMIn, TMGa, AsH3, and PH3 in a carrier gas of H2. Double crystal x-ray diffraction is used to evaluate the mismatch and crystal quality of the GaInAs epitaxial films. Full widths at half-maximum intensity (ω1/2) of the double crystal diffraction peak as small as 50 arc s are obtained. The average ω1/2 is less than 80 arc s for all films grown at deposition temperatures between 520 and 540 °C and with mismatch strains between −4×10−3 and +1×10−3. Standard TEM is used to image Ga0.47In0.53As on InP in cross section. No planar defects and few dislocations are present. High resolution TEM of the Ga0.47Ino.53As/InP interface shows that no strain or mismatch related defects are present for nearly lattice-matched films. Hall mobilities of 10 500 and 47 500 cm2/Vs at 300 and 77 K are measured at n=2×1015 cm−3. These values are comparable to those of good liquid phase epitaxial layers.
Fine structure of frequency chirping and FM sideband generation in single-longitudinal-mode semiconductor lasers under 10-GHz direct intensity modulation
Authors: Lin Chinlon , Eisenstein G. , Burrus C. A. , Tucker R. S.
Published: July 2002

The fine structure of the dynamically broadened spectral line of a single-longitudinal-mode InGaAsP laser under large-signal direct intensity modulation at 10 GHz was studied. It is shown that the frequency-chirped spectral line has a characteristic FM modulation spectrum with many sidebands at 10-GHz intervals and with an asymmetry due to the superposition of the a.m. modulation.
X-ray emission from KrF laser-produced Al plasmas
Authors: Matsumoto Y. , Shaw M. J. , O’Neill F. , Partanen J. P. , Key M. H. , Eason R. , Ross I. N. , Hodgson E. M. , Sakagami Y.
Published: July 2002

A high power (200 J, 50 ns) 249-nm KrF laser has been focused onto solid Al targets in vacuum at a peak irradiance of 3×1013 W cm−2. High-temperature (>200 eV) plasmas are produced and x-ray measurements show intense emission of the resonance spectra of Al XII and Al XIII in the wavelength range 0.6–0.8 nm. Absolute x-ray intensity measurements indicate a maximum source brightness of 1.1×1017 erg cm−2 s−1 sterad−1 in Δν/ν=10−3 (Al XII, 1 1S0–2 1P1, 0.776 nm) and a conversion efficiency from laser power to x-ray power of 0.2% for 1.5 keV<hν<2.5 keV.
Etched-groove coupled-cavity vapor-phase-transported window lasers at 1.55 μm
Authors: Coldren L. A. , Koch T. L. , Bridges T. J. , Burkhardt E. G. , Miller B. I. , Rentschler J. A.
Published: July 2002

The fabrication and characterization of a new two-section etched-groove laser that uses vapor phase regrowth are given. A single undoped InP regrowth forms the buried heterostructure laser sidewalls and facilitates the formation of high-quality single-material etched-mirror facets. Low threshold (∼30 mA), tunable single-wavelength operation results at 1.55 μm.
Monolithic integration of AlGaAs/GaAs laser and external mirrors
Authors: Berger J. , Fekete D.
Published: July 2002

A monolithic integration of AlGaAs/GaAs Be-implanted laser and external mirrors was demonstrated. The mirrors of the laser and the external mirrors were produced using a microcleaving facets process. Results emphasize stabilization of the longitudinal mode spectrum by the external cavity action.
Ultraviolet (193 nm) laser-induced oxygen exchange and bulk diffusion in gallium arsenide native oxides: 18O experiments
Authors: Siejka J. , Perriere J. , Srinivasan R.
Published: July 2002

Pulsed laser irradiation (193 nm, t=14 ns) at low fluence (0.045 J/cm2) of GaAs 18O enriched native oxides leads to a very efficient oxygen exchange between 18O in the oxides and 16O coming from the surrounding atmosphere. 1000 laser pulses caused a complete exchange of oxygen from an oxide layer of ∼30-nm thickness. This showed a very high rate of oxygen self-diffusion under laser irradiation although the total oxygen content in the oxide was preserved. As this process is believed to have a threshold fluence, a model based on the hole-pair mechanism of Itoh and Nakayama [Phys. Lett. A 92, 471 (1982)] is suggested. Preferential loss of As and preferential oxidation of Ga are also observed to some extent.
Determination of minority-carrier generation lifetime in beam-recrystallized silicon-on-insulator structure by using a depletion-mode transistor
Authors: Vu D. P. , Pfister J. C.
Published: July 2002

We describe a technique for measuring minority-carrier lifetime on a very small area of material and apply this technique to recrystallized silicon layers on an insulating substrate where the localization of the crystalline defects gives rise to small defect-free regions actually used for devices. The method uses a depletion-mode transistor in which drain-source conductance yields a signal equivalent to capacitance signal, thus allowing measurements equivalent to conventional Zerbst transient capacitance to be made in the defect-free regions.
Interface disorder in GaAs/AlGaAs quantum wells grown by molecular beam epitaxy at high substrate temperature
Authors: Hayakawa T. , Suyama T. , Takahashi K. , Kondo M. , Yamamoto S. , Yano S. , Hijikata T.
Published: July 2002

The interface disorder of quantum wells grown by molecular beam epitaxy at high substrate temperature is investigated by low-temperature photoluminescence. The excitonic emission from a single quantum well is a single sharp peak, and the well width precisely determined from the emission peak energy does not equal to integral multiples of one-monolayer width in almost all samples. These results indicate that the lateral size of growth islands with a one-monolayer height is much smaller than the exciton diameter and a one-monolayer interface acts as a layer with smaller AlAs mole fraction than the barrier layer.
Blue luminescence of a ZnSe-ZnS0.1Se0.9 strained-layer superlattice on a GaAs substrate grown by low-pressure organometallic vapor phase epitaxy
Authors: Fujita Shigeo , Matsuda Yoshinobu , Sasaki Akio
Published: July 2002

The ZnSe-ZnS0.1Se0.9 strained-layer superlattice (SLS) with an average lattice parameter equal to that of GaAs has been grown on a (100)GaAs substrate at a growth temperature of 400 °C by a low-pressure organometallic vapor-phase epitaxy using dimethylzinc, H2Se, and H2S as sources. The SLS’s exhibited strong blue photoluminescence with a single emission peak, while ZnSe epitaxial layers grown directly on the GaAs substrates showed several peaks related to some defects or impurities together with excitonic emission lines at a near band edge region. Intense blue emission was also observed in ZnS0.05Se0.95 layers grown on the top of the SLS structures. Low-temperature photoluminescence has been investigated to examine the influence of the structural variation on the properties of these layers.
Identification of EL2 in GaAs
Authors: von Bardeleben H. J. , Stievenard D. , Bourgoin J. C. , Huber A.
Published: July 2002

Combining electron paramagnetic resonance under optical excitation, deep level transient spectroscopy, electron irradiation, annealing, and quenching on LEC semi-insulating GaAs and lightly Si-doped material grown in the same way as the semi-insulating material, we have shown that (i) the irradiated material contains two types of defects related to the antisite AsGa, one As∇Ga, present before irradiation, identified to EL2 from its characteristic photoquenching behavior and the other As*Ga, created by the irradiation, stable under photoexcitation; (ii) As∇Ga anneals partially under a 850 °C thermal treatment followed by a quench and the remaining defects are transformed into As*Ga; (iii) further annealing around 120 °C converts As*Ga into As∇Ga, the process being thermally activated (0.5±0.2 eV). From these results and using observations of absorption on vibrational modes of the C-As interstitial pair in electron irradiated material, we are able to conclude that As*Ga is the isolated antisite and As∇Ga, i.e., EL2, is a complex of an As antisite and an As interstitial.
Continuously tunable distributed feedback laser diode
Authors: Dutta N. K. , Wessel T. , Cella T. , Brown R. L.
Published: July 2002

The fabrication and performance characteristics of a monolithically integrated thermoelectric controlled single frequency distributed feedback laser diode are reported. The emission frequency of the laser can be continuously tuned by ∼±5 Å using a 50-mA controller current. This fine tuning is useful for coherent system applications and for resonant optical amplifiers used as repeaters. We also report a multiwavelength laser array, each emission frequency of which can be independently tuned. Such sources are potentially useful for closely spaced wavelength multiplexed systems.
Photon echoes from two-dimensional excitons in GaAs-AlGaAs quantum wells
Authors: Schultheis L. , Sturge M. D. , Hegarty J.
Published: July 2002

We report photon echoes from two-dimensional (2D) excitons in a GaAs-AlGaAs quantum well structure at 2 K. We analyze our data with a theoretical model of the generation of photon echoes by pulses of finite length which includes phase relaxation during excitation. A line shape analysis yields the phase relaxation time of 2D excitons. We find that the phase coherence near the line center decays, together with the resonant population, within 4 ps, whereas well below line center the phase coherence is conserved for times up to 20 ps.
Supersonic gas injection valve for beam neutralization from Applied-B pulsed ion diodes
Authors: Horioka K. , Ohbayashi K. , Yoneda H. , Kasuya K.
Published: July 2002

In place of conventional sonic injection gas puff valves, a supersonic gas injection nozzle has been developed to neutralize the pulsed ion beams extracted from Applied-B magnetically insulated diodes. This valve is driven by the magnetic pressure produced by the diode field coil. The features of this nozzle are its simple geometry, repetition capability, and easy timeable operation. Amounts of gas introduced in the diode section depend on the plenum pressure. Preliminary results of beam neutralization are described briefly.
Reduction of background doping in metalorganic vapor phase epitaxy of GaAs using triethylgallium at low reactor pressures
Authors: Kuech T. F. , Potemski R.
Published: July 2002

The mechanism of background impurity incorporation in the metalorganic vapor phase epitaxy of GaAs using triethylgallium and arsine was investigated over a wide range of growth parameters. The growth temperature, total reactor pressure, AsH3/Ga(C2H5)3 ratio, and the linear gas velocity were altered in order to ascertain the primary determinants of the background impurity incorporation in the ethyl based chemistry. The GaAs electrical and optical properties are, in general, independent of AsH3/Ga(C2H5)3 ratio but strongly dependent on growth temperature and reactor pressure. Reductions in the reactor pressure, at a constant mass flow rate, result in a linear decrease in the unintentional impurity incorporation, while not changing the growth rate. Substantial improvements in the layer purity with greatly reduced AsH3 consumption can be achieved. A general model of impurity incorporation which relates the effect of reactor pressure and impurity incorporation is presented.
Microstructural, chemical, and electrical characterization of the beta silicon carbide thin-film silicon substrate interface
Authors: Ryu J. , Kim H. J. , Davis Robert F.
Published: July 2002

The epitaxial β-SiC monocrystalline thin-film Si substrate interface region has been studied using cross-section transmission electron microscopy and chemical and charge carrier concentration profiling. Interface dip and interface rise phenomena involving changes in the carrier concentration have been observed in unintentionally doped and Al-doped samples, respectively. The primary cause of the interface dip is believed to be the interaction of the charge carriers with the high density of dislocations present in the interface region. The reason for the interface rise is the progressive accumulation of Al in the interface region which is facilitated by pipe diffusion in the dislocations.
Pair-groove-substrate GaAs/AlGaAs multiquantum well lasers by molecular beam epitaxy
Authors: Mannoh Masaya , Yuasa Tonao , Naritsuka Shigeya , Shinozaki Keisuke , Ishii Makoto
Published: July 2002

We investigated molecular beam epitaxial growth characteristics on (001) GaAs substrates with a pair of etched grooves along the 〈11̄0〉 direction. It is found that, as the growth proceeds, the mesa width between the pair of grooves gradually decreases and that the grown mesa surface becomes slightly concave. These results offer great advantages for precisely defining the lateral width of index guided lasers during growth. A pair-groove-substrate GaAs/AlGaAs multiquantum well laser has been newly developed, which shows stable fundamental transverse mode oscillation and a high external differential quantum efficiency of 68% as well as a low threshold current of 23 mA.
Corona-plasma cathode for high-energy electron beams
Authors: Shields H. , Sandstrom R. L. , Levatter J. I.
Published: July 2002

A new type of cold cathode for high-energy electron beam generators is described. A surface discharge, occurring at a metal-dielectric-vacuum ‘‘triple point,’’ acts as a plasma electron source. For a cathode area of 10 cm×10 cm, a maximum current density of 24 A cm−2 in a 1.3-μs pulse has been demonstrated at 400 kV applied voltage.
Seeding lateral epitaxy of silicon on insulator with improved seed and cap structure by pseudoline shaped electron beam annealing
Authors: Suguro K. , Inoue T. , Hamasaki T. , Yoshii T. , Yoshimi M. , Takahashi M. , Taniguchi K. , Kashiwagi M. , Tango H.
Published: July 2002

Seeding lateral epitaxy for silicon films on an insulator, using pseudoline shaped electron beam annealing, has been investigated. Higher oscillation frequency, higher beam scanning velocity, and suitable oscillation amplitude were effective to achieve large uniform silicon on insulator (SOI) films with the aid of simulating temperature distribution in silicon substrate. Furthermore, improved seed with tapered edge and capping layer of tungsten/insulator were employed to obtain 300 μm×1.3 mm single-crystal SOI films on a 1.3-μm SiO2 layer. Stacked SOI devices were successfully fabricated with low-temperature planarization process. 218 ps/stage propagation delay and 17 pJ power-delay product were obtained.
Spectral linewidth broadening due to self-modulation of the refractive index of semiconductor lasers
Authors: Sato H. , Fujita T.
Published: July 2002

We propose a new mechanism for the spectral linewidth broadening of semiconductor lasers, which is self-modulation of the refractive index of the semiconductor cavity caused by interference between the lasing modes. It is shown that the broadening of the main-mode linewidth due to submodes is explained reasonably well by the self-modulation term. A new interpretation of the power-independent linewidth problem is also suggested.
Low threshold current AlGaAs/GaAs distributed feedback laser grown by two-step molecular beam epitaxy
Authors: Kojima Keisuke , Noda Susumu , Mitsunaga Kazumasa , Kyuma Kazuo , Nakayama Takashi
Published: July 2002

AlGaAs/GaAs distributed feedback lasers with oxide-stripe structure were fabricated by two-step molecular beam epitaxy (MBE) growth for the first time. The large coupling coefficient of 90 cm−1 was obtained by controlling precisely the thickness of each layer. As a result, the threshold current of 165 mA, which is the lowest ever reported, was obtained at room temperature. The characteristic temperature T0 was as high as 210 K. Single longitudinal mode oscillation over the temperature range of 50 K was observed without mode hopping. Due to the uniformity of the thickness and composition of the layers grown by MBE, uniform oscillation wavelengths were observed.
Formation of a silicon-carbide layer during CF4/H2 dry etching of Si
Authors: Coyle George J. , Oehrlein Gottlieb S.
Published: July 2002

Silicon specimens which had been reactive ion etched in CF4/x% H2 (0≤x≤40) have been characterized by x-ray photoelectron emission spectroscopy. Angular rotation was used to study films deposited by the plasma process onto the Si surface. In agreement with previous studies it is found that plasma exposure of Si specimens leads to the deposition of a fluorocarbon film. An intriguing new finding was the discovery of a silicon-carbide layer localized near the fluorocarbon-film/Si interface. The existence of this carbide layer was found to be independent of gas composition from 0–40% H2 for a 1-min plasma exposure.
Light-induced excess conductivity and the role of argon in the deposition of doping-modulated amorphous silicon superlattices
Authors: Su F.-C. , Levine S. , Vanier P. E. , Kampas F. J.
Published: July 2002

Amorphous silicon pnpn ... structures that exhibit the phenomenon of light-induced excess conductivity (LEC) have been deposited in a single-chamber glow discharge deposition system by simple control of gas flows. This phenomenon is negligible when the doped silane is undiluted but clearly evident when the silane is diluted in argon. Experiments were performed in which argon dilution was only used for specific regions of the structure. The LEC effect was found to occur if argon dilution was used during the deposition of any fraction of the superlattice layers. These experiments rule out mechanisms requiring phosphorus-boron defect complexes or interface states.
Photoluminescence of very dilutely C+ ion-implanted GaAs
Authors: Makita Yunosuke , Nomura Toshio , Yokota Masaki , Matsumori Tokue , Izumi Tomio , Takeuchi Yoshinori , Kudo Kazuhiro
Published: July 2002

Very dilute C+ (carbon) ion implantations were carried out for extremely pure GaAs wafers grown by molecular beam epitaxy (MBE). Low-temperature photoluminescence measurements revealed that at least five sharp new emission lines are commonly formed near bound exciton emission region by the introduction of C for the dose range between 1015 and 1017 cm−3. It was for the first time demonstrated that the most dominant line among the above emission is identical to the g line in defect-induced bound exciton emission series which are frequently observed in rather impure MBE-grown or metalorganic chemical vapor deposition (MOCVD)-grown GaAs samples.