bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical simulation of laser–target interaction and blast wave formation
Authors: Giuliani John L. , Mulbrandon Margaret , Hyman Ellis
Published: July 2002

A numerical hydrodynamics chemistry model to simulate the laser–target interaction experiment at the Naval Research Laboratory’s PHAROS [Laser Interaction and Related Plasma Phenomena (Plenum, New York, 1986), Vol. 7, p. 857] is presented. Both laser–target and debris–background interactions are modeled, solving mass continuity, total momentum, and separate ion and electron internal energy equations. The model is appropriate for background densities≥1 Torr. To accurately treat both the early-time planar ablation and the later spherical expansion of the blast wave, as well as the rear-side shock front, an oblate spheroidal coordinate system was adopted. The aluminum target ablates into and interacts with an ambient nitrogen gas, filling the facility chamber. The simulation models the target continuously from the solid state to the state of a highly ionized nonequilibrium plasma, including all charge states of aluminum and all charge states of the nitrogen background. The laser beam has a wavelength of 1 μ, a ∼5 nsec full width at half-maximum (FWHM), an intensity at the target surface ∼1013 W/cm2, and total energy varying from 20–100 J. The model accurately reproduces the measured time-of-flight profile and the mass of ablated aluminum. Expansion of the blast wave in the model follows the ideal Sedov relation until radiation losses force a deviation due to a failure in the constant energy assumption. In the shock wave region the simulations show electron density of a few times 1018 cm−3, temperatures ranging from 10–20 eV, and dominant nitrogen species of N+3 and N+4, all in agreement with experimental measurement. A calculated profile of electron density both in the shock and in the cavity region agree closely with experiment and imply an average aluminum charge state of 11 times ionized in the cavity out to late times, as predicted by the simulation described in this paper.

The simulation suggests, also, that observed rear-side structuring is a result of a deceleration Rayleigh–Taylor instability. The model is capable of providing detailed predictions, which are presented, as to profiles of charge states, densities, and temperatures as a function of time; these predictions are not yet tested by experimental measurement.
Electron temperature gradient modes in tokamaks
Authors: Hirose A.
Published: July 2002

Effects of kinetic damping, resulting from electron magnetic and Landau resonances, have been investigated for the electron temperature gradient mode in tokamaks. Damping is strong, and the instability can occur only when the temperature gradient is very steep, LT/R<0.1, where LT is the temperature gradient scale length and R is the magnetic curvature radius.
Mode selection by priming in an overmoded electron cyclotron maser
Authors: McCurdy Alan H. , Armstrong Carter M.
Published: July 2002

It has been found that an externally injected signal can strongly influence the steady-state electromagnetic mode in which a pulsed electron cyclotron maser (ECM) operates. A careful experimental examination reveals that the process by which this occurs is similar to the oscillator phase priming noted previously in magnetron work. It is found here that the degree of mode control depends on the injected signal power level (relative to the ECM noise power level), frequency, and time of application. Mode control is obtained at power levels nearly four orders of magnitude below that of the steady-state ECM output power and over frequency bandwidths several times that of the cavity resonance band. The optimum input signal is a circularly polarized wave, corotating with the electron cyclotron motion. The experimental results are compared with a quasilinear coupled-mode theory. The theory is used to provide analytic predictions of the temporal mode evolution through third-order coupling. The comparison with experiment indicates that higher-order terms are non-negligible in some regimes of operation. However, this model suitably predicts ECM steady-state operation over much of the operating parameter space and gives a qualitative understanding of the role of the external signal and preoscillation noise in the mode selection process. Mode priming may enable stable and efficient single-mode operation of the ECM and other overmoded sources of coherent radiation.
Nonlinear coupling of tearing fluctuations in the Madison Symmetric Torus*
Authors: Sarff J. S. , Assadi S. , Almagri A. F. , Cekic M. , Den Hartog D. J. , Fiksel G. , Hokin S. A. , Ji H. , Prager S. C. , Shen W. , Sidikman K. L. , Stoneking M. R.
Published: July 2002

Three-wave, nonlinear, tearing mode coupling has been measured in the Madison Symmetric Torus (MST) reversed-field pinch (RFP) [Fusion Technol. 19, 131 (1991)] using bispectral analysis of edge magnetic fluctuations resolved in ‘‘k-space.’’ The strength of nonlinear three-wave interactions satisfying the sum rules m1+m2=m3 and n1+n2=n3 is measured by the bicoherency. In the RFP, m=1, n∼2R/a (6 for MST) internally resonant modes are linearly unstable and grow to large amplitude. Large values of bicoherency occur for two m=1 modes coupled to an m=2 mode and the coupling of intermediate toroidal modes, e.g., n=6 and 7 coupled to n=13. These experimental bispectral features agree with predicted bispectral features derived from magnetohydrodynamic (MHD) computation. However, in the experiment, enhanced coupling occurs in the ‘‘crash’’ phase of a sawtooth oscillation concomitant with a broadened mode spectrum suggesting the onset of a nonlinear cascade.
Steady particulate flows in a horizontal rotating cylinder
Authors: Yamane K. , Nakagawa M. , Altobelli S. A. , Tanaka T. , Tsuji Y.
Published: July 2002

Results of discrete element method (DEM) simulation and magnetic resonance imaging (MRI) experiments are compared for monodisperse granular materials flowing in a half-filled horizontal rotating cylinder. Because opacity is not a problem for MRI, a long cylinder with an aspect ratio ∼7 was used and the flow in a thin transverse slice near the center was studied. The particles were mustard seeds and the ratio of cylinder diameter to particle diameter was approximately 50. The parameters compared were dynamic angle of repose, velocity field in a plane perpendicular to the cylinder axis, and velocity fluctuations at rotation rates up to 30 rpm. The agreement between DEM and MRI was good when the friction coefficient and nonsphericity were adjusted in the simulation for the best fit.
The excitation of obliquely propagating fast Alfvén waves at fusion ion cyclotron harmonics
Authors: Dendy R. O. , Lashmore-Davies C. N. , McClements K. G. , Cottrell G. A.
Published: July 2002

The theory of the magnetoacoustic cyclotron instability, which has been proposed as a mechanism for suprathermal ion cyclotron harmonic emission observed in large tokamaks, is generalized to include finite parallel wave number k∥. This extension introduces significant new physics: the obliquely propagating fast Alfvén wave can undergo cyclotron resonant interactions with thermal and fusion ions, which affects the instability driving and damping mechanisms. The velocity–space distribution of the fusion ions is modeled by a drifting ring, which approximates the distribution calculated for the emitting region in tritium experiments on the Joint European Torus (JET) [Cottrell et al., Nucl. Fusion 33, 1365 (1993)]. Linear instability can occur simultaneously at the fusion ion cyclotron frequency and all its harmonics when the fusion ion concentration is extremely low, because the finite k∥ gives rise to a Doppler shift, which decouples cyclotron damping due to thermal ions from wave growth associated with fusion ions. Doppler shifts associated with finite k∥ may also be related to the observed splitting of harmonic emission lines.
Magnetohydrodynamic Vlasov simulation of the toroidal Alfvén eigenmode
Authors: Todo Y. , Sato T. , Watanabe K. , Watanabe T. H. , Horiuchi R.
Published: July 2002

A new simulation method has been developed to investigate the excitation and saturation processes of toroidal Alfvén eigenmodes (TAE modes). The background plasma is described by a magnetohydrodynamic (MHD) fluid model, while the kinetic evolution of energetic alpha particles is followed by the drift kinetic equation. The magnetic fluctuation of n=2 mode develops and saturates at the level of 1.8×10−3 of the equilibrium field when the initial beta of alpha particles is 2% at the magnetic axis. After saturation, the TAE mode amplitude shows an oscillatory behavior with a frequency corresponding to the bounce frequency of the alpha particles trapped by the TAE mode. The decrease of the power transfer rate from the alpha particles to the TAE mode, which is due to the trapped particle effect of a finite-amplitude wave, causes the saturation. From the linear growth rate the saturation level can be estimated.
A model realization of self-organized criticality for plasma confinement
Authors: Carreras B. A. , Newman D. , Lynch V. E. , Diamond P. H.
Published: July 2002

A model for plasma transport near marginal stability is presented. The model is based on subcri- tical resistive pressure-gradient-driven turbulence. Three-dimensional nonlinear calculations based on this model show effective transport for subcritical mean profiles. This model exhibits some of the characteristic properties of self-organized criticality. Perturbative transport techniques are used to elucidate the transport properties. Propagation of positive and negative pulses is studied. The observed results suggest a possible explanation of the apparent nonlocal effects ob- served with perturbative experiments in tokamaks.
Rayleigh–Taylor instability of steady ablation fronts: The discontinuity model revisited
Authors: Piriz A. R. , Sanz J. , Ibañez L. F.
Published: July 2002

A new model for the instability of a steady ablation front based on the sharp boundary approximation is presented. It is shown that a self-consistent dispersion relation can be found in terms of the density jump across the front. This is an unknown parameter that depends on the structure of the front and its determination requires the prescription of a characteristic length inherent to the instability process. With an adequate choice of such a length, the model yields results, in excellent agreement with the numerical calculations and with the sophisticated self-consistent models recently reported in the literature.
The influence of fast ions on the magnetohydrodynamic stability of negative shear profiles
Authors: Helander P. , Gimblett C. G. , Hastie R. J. , McClements K. G.
Published: July 2002

The influence of energetic ions on the stability of ideal double kink modes in a tokamak plasma with negative magnetic shear is investigated. It is found that the fast ions play a similar role as for the ordinary m=n=1 internal kink. In particular, phenomena analogous to sawtooth stabilization and fishbone excitation are possible.
Heat flux driven ion turbulence
Authors: Garbet X. , Waltz R. E.
Published: July 2002

This work is an analysis of an ion turbulence in a tokamak in the case where the thermal flux is fixed and the temperature profile is allowed to fluctuate. The system exhibits some features of self-organized critical systems. In particular, avalanches are observed. Also the frequency spectrum of the thermal flux exhibits a structure similar to the one of a sand pile automaton, including a 1/f behavior. However, the time average temperature profile is found to be supercritical, i.e., the temperature gradient stays above the critical value. Moreover, the heat diffusivity is not the same for a turbulence calculated at fixed flux than at fixed temperature gradient, with the same time averaged temperature. More precisely the diffusivity at fixed temperature is found to be larger in the edge and smaller close to the heat source.
Symmetry forbidden Raman scattering from (100) surfaces of oxidized Si and Ge
Authors: Tsang J. C.
Published: July 2002

Raman scattering excited by light absorbed within 200 Å of the semiconductor surface has been used to characterize changes introduced at (100) surfaces of Si and Ge by oxidation. Oxidation dependent, broad band, first order Raman spectra similar in appearance to the spectra obtained from the amorphous phases of Si and Ge have been observed. These results are obtained for oxide thicknesses up to 1.7 μm without any special sample preparation, suggesting that Raman scattering can be a useful probe of such interfaces.
Growth of selective tungsten films on self-aligned CoSi2 by low pressure chemical vapor deposition
Authors: van der Putte P. , Sadana D. K. , Broadbent E. K. , Morgan A. E.
Published: July 2002

The selective deposition of tungsten films onto CoSi2 and onto Co by low pressure chemical vapor deposition and their material properties have been investigated with Auger electron spectroscopy, transmission electron microscopy, and Rutherford backscattering. When using WF6 and H2, uniformly thick tungsten films can be deposited onto CoSi2 without substrate alteration. In patterned structures, however, void formation was found at the perimeters of CoSi2 contacts to silicon, indicating encroachment of WF6 down the edge of the silicide-Si interface. In WF6 and Ar, the film thickness was limited to 10 nm and some Si was locally consumed from the upper part of the CoSi2 film. Transmission electron diffraction showed evidence of Co2Si formation in these areas.
One-third (period three) harmonic generation in microwave-driven Josephson tunnel junctions
Authors: Hansen J. Bindslev , Clarke J. , Mygind J. , Ovsyannikov G. A. , Svensmark H.
Published: July 2002

One-third harmonic signals have been generated in the zero voltage state of a Josephson tunnel junction driven with a microwave current in the frequency range 8–20 GHz. The signal was as much as 50 dB above the noise level of the detector with a linewidth of less than 100 Hz. The junction parameters and microwave current were measured in situ in separate experiments. The subharmonic generation occurred for ranges of microwave current and frequency that were in reasonable agreement with the results of digital computer simulations.
Experimental verification of the improved coupled-mode equations
Authors: Marcatili E. A. J. , Buhl L. L. , Alferness R. C.
Published: July 2002

The responses of specially designed directional couplers built with Ti:LiNbO3 in-diffused guides were measured and found to be substantially better predicted by an improved version of the coupled-mode theory than by the traditional one.
Long term storage of inversion holes at a superlattice/GaAs interface
Authors: Melloch M. R. , Qian Q-D. , Cooper J. A.
Published: July 2002

We report an investigation of the long term retention characteristic of a hole inversion layer at the interface between an AlAs/GaAs superlattice and GaAs in the dark. The retention time constant at 77 K is measured to be 34 h. From the temperature dependence of the retention time constant, an effective valence-band discontinuity of 0.17 eV is obtained.
Phase conjugate signal from Bi12SiO20 crystal at elevated temperatures
Authors: Jo Jae Heung , Lee Sang Soo
Published: July 2002

In a degenerate four wave mixing system, the phase conjugate signal from a transmission grating recorded in a Bi12SiO20 crystal is measured at various temperatures and the results are compared with theory. The diffraction efficiency η has a maximum value at a temperature above room temperature. The dynamic range in η vs It improves with increasing temperature, where It is the total intensity of the laser beam incident on the crystal. The experimental results are interpreted in terms of the temperature dependence of the effective modulation depth of the transmission grating and the diffusion field in the crystal.
Ultrasonic imaging of layered structures utilizing nondestructive subnanosecond photoacoustic pulse generation
Authors: Tam A. C. , Ayers G.
Published: July 2002

We describe a photoacoustic ultrasonic imaging system that can provide separate acoustic information on a thick substrate and a thin coating simultaneously. This is achieved by generating an ultranarrow longitudinal pulse on the opaque layered sample, and detecting the series of substrate and coating echoes in high time resolution. The echo times, attenuations, and acoustic dispersions in each series provide information on the substrate or coating separately. New photoacoustic images of coatings and of substrates for coated ceramic substrates are presented.
TiC, Ti, and C as a mixing barrier for Ni-Si ion beam mixing
Authors: Nastasi M. , Hirvonen J-P. , Caro M. , Rimini E. , Mayer J. W.
Published: July 2002

The effect of thin titanium carbide layer on the ion beam mixing of Ni and Si was studied. No mixing was observed following the ion beam bombardment at 600 keV to the fluence of 8×1015 Xe++/cm2. Furthermore, it was also found that Ti and C layers alone could prevent an ion beam mixing between Ni and Si, although in the Ti case mixing did occur between Ti and Ni. These results were compared to a thermodynamic model of ion mixing and found to be in qualitative agreement but relative quantitative agreement was poor.
cw phase-locked array Ga0.25In0.75As0.5P0.5-InP high power semiconductor laser grown by low-pressure metalorganic chemical vapor deposition
Authors: Razeghi M. , Blondeau R. , Krakowski M. , de Cremoux B. , Duchemin J. P. , Lozes F. , Martinot M. , Bensoussan M. A.
Published: July 2002

Continuous and pulsed phase-locked operation of a high power GaInAsP-InP semiconductor laser emitting at 1.3 μm has been achieved. The laser consists of a seven-striped array of ridge-island lasers fabricated by a two-step low-pressure metalorganic chemical vapor deposition growth technique. Linear output powers greater than 300 mW (pulsed) and 120 mW (cw) have been obtained with no facet coatings. The far-field full widths at half power, both parallel and perpendicular to the junction plane, were 3° and 45°, respectively, at 10 mW (at 20 °C) which is evidence for strong stripe-to-stripe coupling.
Laser-induced gratings in nematic/cholesteric mixtures
Authors: Espinet Héctor , Lesiecki Michael , Ramsburg Michael
Published: July 2002

Laser-induced gratings are produced in thin films of mixtures of nematic and cholesteric liquid crystals doped with a dye. A transient grating regime is found which decays on the order of seconds; additionally, a ‘‘persistent’’ grating with lifetimes up to 16 h has been found. Mechanisms for creation and decay are discussed.
Pentavacancies in plastically deformed silicon
Authors: Brohl M. , Kisielowski-Kemmerich C. , Alexander H.
Published: July 2002

High-pressure/low-temperature plastic deformation of silicon leads to the appearance of new electron spin resonance active centers. One of them could be identified to be the pentavacancy Si-P1, which also can be produced by irradiation. Depending on the deformation axis the defect occurs in several homologous orientations. Spin-lattice relaxation time measurements performed on both plastically deformed and neutron-irradiated silicon show the existence of an Orbach-type relaxation with an activation energy of about 23 meV corresponding to the thermal excitation energy of the resonant electron into its high-temperature state.
Effect of a buried superlattice on the dynamic storage of electrons at the AlGaAs/GaAs heterojunction
Authors: Melloch M. R. , Qian Q-D. , Cooper J. A.
Published: July 2002

A buried five-period 94 Å Al0.3Ga0.7As/ 56 Å GaAs superlattice is employed to improve the dynamic retention of electrons at an AlGaAs/GaAs heterojunction. The improvement is attributed to the impurity trapping and gettering properties of this superlattice and the amount of time our molecular beam epitaxy system had been closed. Electron retention time constants of 29 s were obtained at a temperature of 77 K. This is more than 200 times longer than previously reported time constants and more than adequate for dynamic logic or memory applications compatible with AlGaAs/GaAs heterojunction field-effect transistors.
Influence of conductor linewidth on short-circuit failure
Authors: Towner Janet M.
Published: July 2002

A study was made on the influence of conductor linewidth on electromigration-induced short-circuit failure in layered TiW/Al-1% Cu conductors. Experimental results suggest that the median time to failure is constant for conductors wider than a critical dimension.
Effective elastic constants of thin-film tungsten-silicide from surface acoustic wave analysis
Authors: Crean G. M. , Golanski A. , Oberlin J. C.
Published: July 2002

The dispersion of surface acoustic waves propagating on single-crystal (100) silicon substrates covered by thin films of tungsten-silicide has been investigated using an acoustic material signature technique at a frequency of 339 MHz. The tungsten-silicide layers (500–2500 Å) were deposited using a co-sputtering technique, isochronally annealed at temperatures of 700 and 850 °C for 45 min in an argon atmosphere and examined using Rutherford backscattering spectrometry. Dispersion curves were calculated using a Tiersten model [J. Appl. Phys. 40, 2 (1969)] and fitted to the experimental dispersion data. The effective elastic constants for annealed and ‘‘as-deposited’’ layers were determined as best-fit parameters.
Nitrogen implantation for local inhibition of oxidation
Authors: Berruyer Pascale , Bruel Michel
Published: July 2002

Nitrogen implantation for local oxidation is a way of forming a silicon nitride film directly sealed to the silicon surface. (N2)+ implantation in silicon was performed through a thin film of oxide at low energy (10–40 keV) and high dose (1016–1017 at/cm2). Oxidation resistance as a function of dose and energy was investigated using step height measurements. Forming a layer which was an efficient oxidation mask required a minimum dose at a given energy. For a (N2)+ implant energy of 20, 25, and 40 keV the minimum doses are respectively 5×1016, 6.5×1016, and 7×1016 at/cm2. In addition the layers formed at a dose of 1017 at/cm2 and a (N2)+ energy above 55 keV do not put up a complete oxidation resistance. Using these results, simple devices were developed in order to examine the profile of the transition region between field oxide and implanted area. It turned out that the length of this region (commonly known as the bird’s beak) is largely reduced. A length of 50 nm was obtained for an oxide thickness of 550 nm. The ratio of the bird’s beak length to field oxide was less than 0.1.
Transient spectroscopy using the Hall effect
Authors: Kachwalla Z. , Miller D. J.
Published: July 2002

The Hall effect is used to measure the transient change in the carrier concentration in a semiconductor sample due to the thermal emission from states filled by a pulsed perturbation. This method has several advantages over other methods based on measuring the capacitance transient or the current transient. The identity of the released carriers can be determined from the sign of the Hall voltage. The new method is applied to the measurement of traps in epitaxial GaAs.
Spectroscopic evidence that oxygen suppresses Si incorporation into vapor phase epitaxial InP
Authors: Iwata Naotaka , Inoshita Takeshi
Published: July 2002

Photothermal ionization spectroscopy is employed to monitor the residual donor impurities in InP grown by vapor phase epitaxy, and study the effect of adding O2 to the carrier gas. The dominant donor species are found to be Si and S, irrespective of the O2 addition, and their concentrations are obtained with the aid of Hall measurements. The result shows that the O2 addition reduces the incorporation of Si into InP but does not affect the incorporation of S.
Oxygen implantation for internal gettering and reducing carrier lifetime
Authors: Weiner David H. , Wong S. Simon , Drowley Clifford I.
Published: July 2002

Implantation of oxygen into Si wafers has been studied as a method to create a defect region for gettering impurities. An epitaxial layer is subsequently deposited to bury the defects. The nature of the defects as well as the effects on the quality of epitaxy, carrier lifetime, and diode leakage current is characterized.
Carrier-induced phase shift and absorption in a semiconductor laser waveguide under current injection
Authors: Liu J. M. , Chen Y. C. , Newkirk M.
Published: July 2002

The effects of injected carriers on the refractive index of an AlGaAs/GaAs semiconductor laser waveguide are investigated through measurements of the carrier-induced phase shift and free-carrier absorption of a guided probe laser beam at a wavelength below the band gap of the GaAs waveguide. The carrier densities and carrier lifetimes at various injection current levels can be deduced directly from these measurements. A carrier-induced phase shift of more than π/2 is observed.
Stable quasi 0° phase mode operation in a laser array diode nearly aligned with a phase shifter
Authors: Taneya M. , Matsumoto M. , Matsui S. , Yano S. , Hijikata T.
Published: July 2002

The phase shift of the 180° out of phase mode to the 0° phase mode is an efficient means for producing a stable high power laser output in a coherent single beam. We fabricated laser array diodes which are operated in a very stable 180° out of phase mode, and a phase shifter in which accurate optical phase shift control is possible. These two devices are nearly aligned and a stable quasi 0° phase mode operation is achieved up to 200 mW without any other optical equipment. This fact indicates that it would be possible for these two devices to be integrated.
Theoretical study of the optimum performance of a two-phase flow CO2 gasdynamic laser
Authors: Thulasiram R. K. , Reddy K. P. J. , Reddy N. M.
Published: July 2002

Theoretical optimization studies of the performance of a combustion driven premixed two-phase flow gasdynamic laser are presented. The steady inviscid nonreacting quasi-one-dimensional two-phase flow model including appropriate finite rate vibrational kinetic rates has been used in the analysis. The analysis shows that the effect of the particles on the optimum performance of the two-phase laser is very small. The results are presented in graphical form.
X-ray photoelectron spectroscopy study of Schottky barrier formation and thermal stability of the LaB6/GaAs(001) c (4×4) interface
Authors: Yokotsuka Tatsuo , Narusawa Tadashi , Uchida Yoko , Nakashima Hisao
Published: July 2002

Schottky barrier formation and thermal stability of the LaB6/GaAs(001) c (4×4) interface were investigated by x-ray photoelectron spectroscopy. Results show an excellent thermal stability without any appreciable interface reactions such as interdiffusion. Band bending induced by LaB6 deposition is found to depend on the evaporation condition. However, the Fermi level pinning position does not change due to heat treatments between 300 and 700 °C. This indicates that LaB6 is a promising gate material for GaAs integrated circuits.
Determination of spatial potential fluctuations in Si and GaAs inversion layers by weak localization
Authors: Mensz P. M. , Wheeler R. G. , Foxon C. T. , Harris J. J.
Published: July 2002

Drawing upon our current understanding of the weak localization correction to the Drüde conductivity in quasi-two-dimensional systems, a method of measuring the random motion of charge carriers perpendicular to the plane of the quantum confinement is demonstrated. This technique has been applied to silicon inversion layers and a GaAs heterojunction to determine, with subangstrom resolution, the mean fluctuation of the average perpendicular position of the electron wave function during transport parallel to the potential barrier.
Integrated external cavity distributed Bragg reflector laser
Authors: Dutta N. K. , Cella T. , Zilko J. L. , Piccirilli A. B. , Brown R. L. , Napholtz S. G.
Published: July 2002

The fabrication and performance characteristics of single frequency integrated external cavity distributed Bragg reflector lasers are described. The current is confined to the active region of these lasers using semi-insulating Fe-doped InP layers. The semi-insulating layer also provides lateral index guiding to the lasing optical mode both in the active and the passive cavity sections. The lasers emit near 1.52 μm. The threshold currents of these lasers are in the range 70–120 mA. dc linewidth of 2.2 MHz has been obtained for a 5-mm-long laser at an output power of 6 mW. Lasers with longer external cavity and higher mode coupling between the active and the passive cavity sections should exhibit lower dc linewidth.
Chemical effects in ion mixing of a ternary system (metal-SiO2)
Authors: Banwell T. , Nicolet M-A. , Sands T. , Grunthaner P. J.
Published: July 2002

The mixing of Ti, Cr, and Ni thin films with SiO2 by low-temperature (−196–25 °C) irradiation with 290 keV Xe has been investigated. Comparison of the morphology of the intermixed region and the dose dependences of net metal transport into SiO2 reveals that long range motion and phase formation probably occur as separate and sequential processes. Kinetic limitations suppress chemical effects in these systems during the initial transport process. Chemical interactions influence the subsequent phase formation.
Spatial light modulation and filtering effects in photorefractive wave mixing
Authors: Fischer Baruch , Weiss Shimon , Sternklar Shmuel
Published: July 2002

A study of photorefractive wave mixing with image bearing beams reveals unique capabilities in spatial modulation, filtering, and cleanup of amplitude and phase modulated beams. We study and explain the negligible image crosstalk in various photorefractive oscillators.
Raman scattering from rapid thermally annealed tungsten silicide
Authors: Kumar Sandeep , Dasgupta Samhita , Jackson Howard E. , Boyd Joseph T.
Published: July 2002

Raman scattering as a technique for studying the formation of tungsten silicide is presented. The tungsten silicide films have been formed by rapid thermal annealing of thin tungsten films sputter deposited on silicon substrates. The Raman data are interpreted by using data from resistivity measurements, Auger and Rutherford backscattering measurements, and scanning electron microscopy.
Reduction of the field spectrum linewidth of a multiple quantum well laser in a high magnetic field—spectral properties of quantum dot lasers
Authors: Vahala Kerry , Arakawa Yasuhiko , Yariv Amnon
Published: July 2002

The field spectrum linewidth of a multiple quantum well laser immersed in a high magnetic field is measured at room temperature and at 165 K. The low-temperature measurements show a decrease of linewidth with increasing magnetic field. We believe this behavior results from the formation of a totally discrete electronic state space. Measurements of the low-temperature luminescence spectrum show that the emission is split into two peaks by the high field with the higher energy peak responsible for lasing action.
X-ray topography of growth striations in Czochralski-grown Si wafers
Authors: Imai Masato , Noda Hiroyuki , Shibata Masahiro , Yatsurugi Yoshifumi
Published: July 2002

Growth striations in Czochralski-grown Si wafers have been observed by a scanning x-ray double-crystal method. We confirmed that the striations on the topographs relate to the variation of oxygen concentration.
Dependence of radiation-induced interface traps on silicide gate stoichiometry in silicide/SiO2/Si devices
Authors: Buchner S. , Natan M. , Kang K. , Gill D.
Published: July 2002

The density of radiation-induced traps at the Si/SiO2 interface in TiSix and WSix gate metal-oxide-semiconductor capacitors is shown to depend on the stoichiometry (x value) of the silicide. The dependence is such that capacitors with metal-rich silicide gates exhibit a smaller increase in interface traps than do capacitors with silicon-rich gates. These results can be qualitatively explained by the dependence of the silicide stress on stoichiometry—metal-rich films are under large tensile stress that inhibits the generation of radiation-induced interface traps.
Observation of valence-band discontinuity of hydrogenated amorphous silicon/hydrogenated amorphous silicon carbide heterojunction by photocurrent-voltage measurements
Authors: Okayasu Yoshinobu , Fukui Keitaro , Matsumura Mitsuo
Published: July 2002

Photocurrent-voltage measurements at different wavelengths exhibit the valence-band discontinuity of a hydrogenated amorphous silicon/hydrogenated amorphous silicon carbide heterojunction. A band discontinuity of ∼100 meV is deduced based on a tunneling model for a hole barrier. This energy gap is relatively small compared to that for the conduction band, but significantly affects the characteristics of heterojunction p-i-n solar cells.
Permanent magnet helical wiggler for free-electron laser and cyclotron maser applications
Authors: Bekefi G. , Ashkenazy J.
Published: July 2002

A permanent magnet, ‘‘bifilar’’ helical wiggler for use in free-electron lasers and cyclotron masers has been designed, assembled, and measured. It is composed of a cylindrical array of staggered samarium-cobalt bar magnets, transversely magnetized and held in place in an axially grooved hollow metal cylinder. High-quality helically polarized fields of several kilogauss can be readily achieved.
Reduction of interfacial tunnel defects in silicon due to chemical vapor deposition of tungsten
Authors: De Blasi J. M. , Delfino M. , Sadana D. K. , Ritz K. N. , Norcott M. H.
Published: July 2002

A method is reported for reducing tunnel formation in p+-n Si, and a correlation is shown between tunnel defects and junction leakage. 11B+-implanted Si annealed for 30 min at 900 °C in N2 and subsequently deposited with W forms a high density of filamentary tunnel defects extending on the order of 0.1 μm from the W/Si interface. Reverse-bias leakage of 0.33-μm-deep junctions is −90 nA/cm2 at −5 V and the forward-bias ideality is 1.24 over eight decades of current. By contrast, for 11B+-implanted Si oxidized for 7 min in steam, tunnels if present are less than 0.01 μm in length. The reverse-bias leakage is −0.3 nA/cm2 at −5 V and the forward-bias ideality is 1.00. The 2×1019 cm−3 interfacial carrier concentration is the same for both deposits.
Supermode discrimination in diffraction-coupled laser arrays with separate contacts
Authors: Wilcox J. Z. , Jansen M. , Yang J. , Peterson G. , Silver A. , Simmons W. , Ou S. S. , Sergant M.
Published: July 2002

We show that in-phase lasing is favored in diffraction-coupled arrays with separate electrical contacts for the common unguided diffraction zone and for the waveguide section, if the common unguided section is biased above a critical level. Below that level, out-of-phase lasing will be favored. By varying the current about the critical level, the far-field intensity switches from a wide far-field pattern characterized by the admixture of several supermodes, to a near-diffraction-limited single peak.
Critical current of Y1Ba2Cu3O7 in strong applied fields
Authors: Dai Uri , Deutscher Guy , Rosenbaum Ralph
Published: July 2002

Critical currents of the new high-temperature superconductor Y1Ba2Cu3O7 have been measured in applied fields of up to 7 T and for temperatures down to 70 K. We find that the critical current is drastically reduced by the application of magnetic fields much smaller than the upper critical field of the samples, Hc2. This anomalous behavior might be due to very weak pinning, or to a very strong anisotropy of Hc2. Hc2 is found to follow a linear temperature dependence that however extrapolates to a critical temperature higher than that measured directly. This might result from the existence of a percolative structure, or from the presence of a small volume fraction of high critical temperature, high critical field regions.
Rapid thermal oxidation of silicon monoxide
Authors: Fogarassy E. , Slaoui A. , Fuchs C. , Regolini J. L.
Published: July 2002

Silicon monoxide and silicon dioxide form insulating films that are commonly used in microelectronic devices. In the technology of devices containing silicon, the insulating silicon dioxide films are formed on the silicon wafers using conventional methods of thermal oxidation. This technique, which requires long periods of annealing (30–60 min) and high temperature (≂1000 °C), is known to induce different types of physical degradation in the device. In this letter, we demonstrate the possibility of converting silicon monoxide deposited at room temperature to silicon dioxide by rapid thermal annealing. Although the annealing temperature is high (700–1100 °C) the time is very short (within seconds), so that this process may still be compatible with the requirements of low-temperature processing.
Improved magnetic fine-structure analysis by simultaneous observation of domains and walls
Authors: Hartmann U.
Published: July 2002

An optical technique is presented which permits a simultaneous observation of domains and domain boundaries in transparent and opaque magnetic specimens. The Faraday or Kerr contrast combined with Bitter pattern agglomerations yields a maximum information transference for an investigation of magnetic fine structures. Some results obtained for a uniaxial ferrimagnetic film are discussed.
Low-threshold 1.55-μm InGaAsP/InP buried heterostructure distributed feedback lasers
Authors: Chinen K. , Gen-ei K. , Suhara H. , Tanaka A. , Matsuyama T. , Konno K. , Muto Y.
Published: July 2002

An extremely low-threshold current of 6 mA in cw mode at 22 °C was achieved in 1.55-μm InGaAsP/InP buried heterostructure distributed feedback lasers with a first-order grating and a normal cavity length of 300 μm. These lasers exhibited an average differential efficiency of 30% total at 4 mW without any coating on the facets, and a T0 (25–70 °C) value of 55 K. A spectral linewidth as low as 8 MHz at cw mode was obtained. The lasers showed high-speed pulse modulation response to 2.4 Gb/s (NRZ).
Raman scattering study of low dose Si±-implanted GaAs used for metal-semiconductor field-effect transistor fabrication
Authors: Wagner J. , Frey Th. , Jantz W.
Published: July 2002

The annealing of the lattice damage introduced by Si+ implantation into GaAs as well as the electrical activation of the dopant has been studied by Raman scattering. Implantation doses (4×1012–1×1013 cm−2) and annealing conditions (800–1040 °C for 5 s) were used which are typical for GaAs metal-semiconductor field-effect transistor fabrication. The normalized peak intensity of the longitudinal optical (LO) phonon-plasmon coupled mode is found to correlate with the sheet of conductivity, i.e., it probes the electrical activation. The lattice perfection, in contrast, is most sensitively measured by resonant 2LO-phonon scattering.
New fabrication method for 1.3-μm GaInAsP/InP buried crescent lasers using a reactive ion beam etching technique
Authors: Kasukawa Akihiko , Iwase Masayuki , Hiratani Yuji , Matsumoto Narihito , Ikegami Yoshikazu , Irikawa Michinori , Kashiwa Susumu
Published: July 2002

A 1.3-μm GaInAsP/InP buried crescent laser on a p-type InP substrate was demonstrated. An active region width narrower than 1.5 μm was achieved with good controllability and reproducibility using the newly introduced reactive ion beam etching technique for the etching process. Stable fundamental transverse mode operation with low threshold currents of 15–25 mA was obtained. Less than 5% degradation in threshold current at 50 °C was achieved with a constant driving current of 150 mA at 70 °C for 100 h.
Semiconductor laser logic gate suitable for monolithic integration
Authors: Grande W. J. , Tang C. L.
Published: July 2002

A new semiconductor laser optical logic gate based on quenching and capable of performing the not, nor, and nand functions is described. The device can be operated both pulsed and cw at room temperature. In addition, the new logic gate can be monolithically integrated.
Photoconduction dynamics in a GaAs/AlGaAs superlattice photoconductor
Authors: Minot C. , Le Person H. , Alexandre F. , Palmier J. F.
Published: July 2002

We report on room-temperature measurements of electron and hole mobilities perpendicularly to the layers of a GaAs/AlGaAs superlattice inserted in a n-i-n photoconductor as the intrinsic region. The dynamical behavior of the structure is described by means of a numerical simulation which solves the classical drift-diffusion transport equations. We discuss the electron and hole mobilities, μn=120 cm2/(V s) and μp=12.5 cm2/(V s) respectively, by referring to the two distinct mechanisms of Bloch and hopping conduction, as well as to the peculiar electronic properties of the superlattices.
Measurement of small rotations by eigenvector flips in a quasi-isotropic Fabry–Perot
Authors: Le Grand Y. , Medjaou M. , Le Floch A. , Le Naour R.
Published: July 2002

A novel small rotation or small birefringence measurement scheme based on the dynamics of the helicoidal eigenstates of a passive Fabry–Perot cavity with two quarter-wave plates is described. When the system is inserted between two crossed polarizers, the sensitivity of the method is shown to be proportional to the square of the finesse of the cavity. For a finesse of 50, the observed noise floor corresponds to an estimation of the minimum detectable small rotation of 3×10−8 rd. We discuss possible improvements and potential possibilities of the method.
Optical amplification by monolithically integrated distributed-feedback lasers
Authors: Inoue H. , Tsuji S.
Published: July 2002

Optical amplification gain up to 17.7 dB has been realized in monolithically integrated distributed-feedback lasers. Master laser lasing wavelength and slave laser amplified spontaneous emission wavelength must be tuned within 0.03 nm.
Reduction of Hg1−xCdxTe native oxide during the SiNx deposition process
Authors: Sudo G. , Kajihara N. , Miyamoto Y. , Tanikawa K.
Published: July 2002

Electron cyclotron resonance plasma chemical vapor deposition enables low-temperature SiNx deposition on Hg1−xCdxTe (MCT). The SiNx film has an excellent interface on MCT with a low surface state density of 1.0×1011 cm−2 eV−1 and a low fixed charge of −1.4×1011 cm−2. A detailed analysis by x-ray photoelectron spectroscopy and Auger electron spectroscopy spectra of Te, Cd, and Si at the SiNx/MCT interface indicated that the SiNx deposition reduces the naturally grown MCT native oxide. The oxygen taken from Te oxidizes SiH4 and produces silicon oxides which remain in the SiNx film. Since a chemical shift caused by oxidized Cd at the fresh surface of MCT is very slight, intentionally oxidized samples were used to confirm the above reaction. The analysis of the shape of the Si(2p) peak at the interface indicated that the silicon oxides are composed of SiO and SiO2. Thermodynamic considerations support such a mechanism.
Birefringence-induced polarization counter rotation in a semiconductor laser
Authors: Fujita T. , Schremer A. , Tang C. L.
Published: July 2002

The effects of a birefringence in a semiconductor laser are reported. We demonstrate Nπ (where N is an odd integer) phase retardation between the TE and TM modes in the laser output beam resulting in the phenomenon of counter rotation of the output polarization. A numerical value for the birefringence is estimated.
Contrast enhancement pattern transfer etching of phosphorus-doped polycrystalline silicon
Authors: Hayasaka N. , Nakahara H. , Okano H. , Horiike Y.
Published: July 2002

Pattern transfer etching of heavily phosphorus-doped polycrystalline silicon has been developed using a KrF excimer laser through a 1:1 reflective optics and a new contrast enhancement scheme employing methylmethacrylate. With laser power at more than 0.5 mJ/cm2 and Cl2 gas as etchant, etching of n+ poly-Si proceeded in the illuminated (bright) region, while the dark region was protected from etching by a polymer film formed from methylmethacrylate. As a result, a 0.9-μm resolution pattern has been achieved.
All-optical guided-wave Mach–Zehnder switching device
Authors: Thylen L. , Finlayson N. , Seaton C. T. , Stegeman G. I.
Published: July 2002

We propose and analyze an all-optical switching device on a nonlinear Mach–Zehnder waveguide interferometer. The nonlinear medium is modeled as a two-level system to take saturation and attenuation effects into account.
Digital optical switch
Authors: Silberberg Y. , Perlmutter P. , Baran J. E.
Published: July 2002

We propose and demonstrate a novel polarization- and wavelength-independent digital electro-optic switch in Ti:LiNbO3. This four-port integrated optics switch is characterized by a steplike response to the applied voltage. Switching is achieved through adiabatic eigenmode transformation in an asymmetric waveguide junction. We demonstrate switching of both polarization components at two wavelengths (1.32 and 1.52 μm) with a crosstalk of −20 dB.
Measurement of Au/GaAs/AlxGa1−xAs hetero-Schottky barrier height and GaAs/AlxGa1−xAs conduction-band discontinuity
Authors: Chen H. Z. , Wang H. , Ghaffari A. , Morkoç H. , Yariv A.
Published: July 2002

A new hetero-Schottky structure for the study of Schottky barriers and heterojunctions is discussed. Photoelectric measurements have revealed a correlation between Au/GaAs and Au/AlxGa1−xAs Schottky barrier heights and GaAs/AlxGa1−xAs heterojunction band offsets. The conduction-band discontinuity ΔEc in the GaAs/AlxGa1−xAs system is determined, and the ratio ΔEc:ΔEg is found to vary between 69±5% and 58±5% for x=0.15–0.48.
Molecular beam epitaxial growth of III-V compound semiconductor in the presence of a low-energy ion beam: A Monte Carlo simulation study
Authors: Ogale S. B. , Madhukar A. , Thomsen M.
Published: July 2002

Monte Carlo simulation study of molecular beam epitaxial growth of III-V compound semiconductor in the presence of a low-energy ion beam is performed to examine the role of such physical parameters as beam induced preferential desorption and enhanced surface migration on the growth front morphology. It is demonstrated that the smoothness of the growth front can be controlled by appropriate choice of ion type, its energy, angle of incidence, and flux. Thus smooth morphology can be realized at temperatures significantly lower than normal epitaxial growth temperatures.
High-pressure study of solid phase epitaxial regrowth in implanted amorphous GaAs
Authors: Licoppe C. , Savary H.
Published: July 2002

A new in situ technique for determination of solid phase epitaxial regrowth kinetics under high-pressure conditions is described. It is applied to the study of pressure effects on recrystallization kinetics of amorphous implanted GaAs. The results show that the epitaxial growth rate is enhanced with pressure. An empirical formalism is developed describing the effect of pressure as a softening of the acoustic modes and a consequent decrease of the activation energies. Good agreement is obtained with the experimental data.
Multiple quantum well coupling element with losses
Authors: Cada M. , Gauthier R. C. , Paton B. E. , Glinski J. M.
Published: July 2002

A nonlinear directional coupling element consisting of a GaAs-based multiple quantum well (MQW) heterostructure sandwiched between two slab optical waveguides is analyzed numerically with optical absorption losses in the MQW included. Optical waveguides are designed to be made of lossless AlGaAs slabs of an appropriate composition corresponding to the wavelength of operation. Calculations indicate an improvement in the element’s overall propagation attenuation by about two orders of magnitude when compared to previous results dealing directly with MQW optical waveguides. Promising element performance characteristics are reported.
Observation of electroluminescence of ZnS:TbF3 under various gaseous atmospheres
Authors: Arakawa Tsuyoshi , Suezawa Nobuya , Adachi Gin-ya , Shiokawa Jiro
Published: July 2002

The intensity of the electroluminescence (EL) of ZnS:TbF3 changed after gas adsorption. The threshold voltage of EL after gas adsorption is correlated to the specific dielectric constant of adsorbates.