bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic theory study of steady evaporation from a spherical condensed phase containing inert solid particles
Authors: O/stmo Svend , Frezzotti Aldo , Ytrehus Tor
Published: July 2002

Steady evaporation from a spherical and heterogeneous condensed body into vacuum is considered. Inert solid particles, initially embedded in the condensed phase, are liberated and collisionally accelerated by the evaporating gas molecules. A simple mathematical model for the flow is proposed and executed by the Direct Simulation Monte Carlo (DSMC) method. For small Knudsen numbers, the results are compared with a continuum solution including Knudsen layer corrections obtained by a moment method, demonstrating that these corrections are leading order effects in the treatment.
Effect of a lateral gravitational field on the nonaxisymmetric equilibrium shapes of liquid bridges held between eccentric disks and of volumes equal to those of cylinders
Authors: Laverón-Simavilla Ana , Checa Elena
Published: July 2002

Bifurcation diagrams of nonaxisymmetric cylindrical volume liquid bridges held between nonconcentric circular disks subject to a lateral gravitational force are found by solving the Young-Laplace equation for the interface by a finite difference method. In the absence of lateral gravity, the primary family of liquid bridges that starts with the cylinder when the eccentricity of the disks, e, is zero first loses stability at a subcritical bifurcation point as e increases. Further loss of stability is experienced by the already unstable primary family as a turning point is encountered at yet higher values of the eccentricity. However, the introduction of lateral gravity gl changes entirely the structure of the solutions in that instability always occurs at a turning point with respect to e no matter how small the magnitude of gl. The stability limits calculated are compared with the ones obtained using asymptotic techniques by taking as base solution the cylinder of slenderness Λ=π.
Rarefied gas flow between two cylinders caused by the evaporation and condensation on their surfaces
Authors: Gramani Cumin Liliana M. , Sharipov Felix M. , Kremer Gilberto M.
Published: July 2002

The rarefied gas flow between two coaxial cylinders caused by the evaporation and condensation on their surfaces is investigated on the basis of the kinetic and hydrodynamical equations. It is assumed that the cylinders may rotate with equal angular velocity. The equilibrium is perturbed by the small density difference of evaporated particles on the inner cylinder. The hydrodynamical equation has been solved analytically and the kinetic equation has been solved by the discrete velocity method modified for the discontinuous distribution function. The fields of the density, the velocity and the temperature are presented for a wide range of the Knudsen number. An analysis of the influence of the rotation of the cylinders on the flow field is given.
Large growth rate instabilities in three-layer flow down an incline in the limit of zero Reynolds number
Authors: Weinstein Steven J. , Chen Kang Ping
Published: July 2002

In this paper, we examine the effect of viscosity stratification on wave propagation in three-layer flow down an inclined plane at vanishingly small Reynolds number and at finite wavelengths, for cases of negligible liquid–liquid interfacial tensions. We have found that the long-wavelength interface mode inertialess instability of Weinstein and Kurz [Phys. Fluids A 3, 2680 (1991)] persists into the finite wavelength domain in the form of nearly complex conjugate wave speed pairs; in certain limits, the interface modes are precisely complex conjugates. As in the case of Weinstein and Kurz, the physical configuration necessary to achieve inertialess instability is a low viscosity and thin internal layer with respect to the other layers in the film. The largest growth rate of the inertialess instability is found at finite wavelengths on the order of the total thickness of the film, and is orders of magnitude larger than the maximum growth rates identified by Lowenhurz and Lawrence [Phys. Fluids A 1, 1686 (1989)] for two-layer flows. We have also found an additional configuration exhibiting extremely large growth rates, also characterized by nearly complex conjugate behavior, that is not accessible via a long or short wavelength asymptotic limit; these three-layer structures have thin, high viscosity internal layers. The characteristic wavelengths associated with the largest growth rates are on the order of ten times smaller than those for the low viscosity internal layer cases. The influence of the deformable free surface on the growth rates of these interface modes is studied and found to be significant.
Fully nonlinear global modes in slowly varying flows
Authors: Couairon A. , Chomaz J.-M.
Published: July 2002

We study the existence of nonlinear solutions of the real Ginzburg–Landau amplitude equation, with varying coefficients when the solution is subject to a boundary condition at x=0. These solutions, called nonlinear global modes, are explicitly obtained from a matched asymptotic expansion when nonlinear effect dominates over the inhomogeneity. The dynamics of this model is believed to mimic the behavior of strongly nonlinear but weakly nonparallel basic flow (basic flow varying in the streamwise direction). For the model, we derive scaling laws for the amplitude of nonlinear global modes and for the position of the maximum that explain for the first time the experimental observations of Goujon-Durand et al. [Phys. Rev. E 50, 308 (1994)] and the numerical simulations of Zielinska and Wesfreid [Phys. Fluids 7, 1418 (1995)] of the wake behind bluff bodies.
Vacuum calculations in azimuthally symmetric geometry
Authors: Chance M. S.
Published: July 2002

A robustly accurate and effective method is presented to solve Laplace’s equation in general azimuthally symmetric geometry for the magnetic scalar potential in the region surrounding a plasma discharge which may or may not contain external conductors. These conductors can be topologically toroidal or spherical, and may have toroidal gaps in them. The solution is incorporated into the various magnetohydrodynamic stability codes either through the volume integrated perturbed magnetic energy in the vacuum region or through the continuity requirements for the normal component of the perturbed magnetic field and the total perturbed pressure across the unperturbed plasma–vacuum boundary. The method is based upon using Green’s second identity and the method of collocation. As useful by-products, the eddy currents and the simulation of Mirnov loop measurements are calculated.
Torque balance and rotational stabilization of the resistive wall mode
Authors: Gimblett C. G. , Hastie R. J.
Published: July 2002

A model is developed to analyze the stabilization of the resistive wall mode (RWM) by plasma rotation. Central to the model is a cylindrical plasma that is ideal magnetohydrodynamic unstable in the absence of a wall, and possesses an internal resonance [J. M. Finn, Phys. Plasmas 2, 198 (1995)]. This system is then a qualitative model for the actual toroidal external kink mode that is relevant in advanced tokamak scenarios. It has been shown in the past that the RWM can possess stability windows for modest rotation frequencies. However, the equilibrium parameter regime in which stabilization can take place is small. A nonlinear formulation of the problem is presented, with plasma rotation determined self-consistently by an equation of torque balance. It is found that, within the same small parameter regime, stability windows can be considerably extended at the expense of the growth of a magnetic island. On the other hand, depending on the initial rotation, the system can reduce the plasma rotation rate asymptotically to zero while the island continues to grow.
Photothermal modulation of the gap distance in scanning tunneling microscopy
Authors: Amer Nabil M. , Skumanich Andrew , Ripple Dean
Published: July 2002

We have employed the photothermal effect to modulate the gap distance in a tunneling microscope. In this approach, optical heating induces the expansion and buckling of laser-illuminated sample surface. The surface displacement can be modulated over a wide frequency range, and its height (typically <1 Å) can be varied by changing the illumination intensity and modulation frequency. This novel method provides an alternative means for performing tunneling spectroscopy and microscopy, and for determining work functions of materials.
High resolution scanning photoluminescence characterization of semi-insulating GaAs using a laser scanning microscope
Authors: Marek J. , Elliot A. G. , Wilke V. , Geiss R.
Published: July 2002

Spatially resolved photoluminescence properties of semi-insulating, liquid encapsulated Czochralski-grown GaAs substrates are analyzed with a laser scanning microscope. The improved resolution of the laser scanning microscope results in the observation of single dislocations within the subgrain boundaries of the polyganized dislocation cell network for the first time by photoluminescence. Both the cell structure and the Cottrell cloud are clearly resolved.
High power (2.1 W) 10-stripe AlGaAs laser arrays with Si disordered facet windows
Authors: Thornton R. L. , Welch D. F. , Burnham R. D. , Paoli T. L. , Cross P. S.
Published: July 2002

Silicon impurity induced disordering has been used to fabricate lasers with reduced facet absorption (facet windows) exhibiting enhanced catastrophic facet damage levels over comparable nonwindow devices. Power levels of 1.2 W cw were obtained from uncoated output facet devices and 2.1 W cw were obtained for a device with a coated output facet. Evidence is presented that the window region formed by silicon diffusion is a low-loss waveguide which confines the propagating wave, increasing the efficiency of the device.
Hydrogenation of boron acceptor in silicon during electron injection by Fowler–Nordheim tunneling
Authors: Chao Calvin Yi-Ping , Luo Marie Shiang-Chyong , Pan Samuel Cheng-Sheng , Sah Chih-Tang
Published: July 2002

Hydrogenation of the boron acceptor in silicon is observed during Fowler–Nordheim tunneling injection of electrons for the first time. Experiment is also presented which shows that the existence of free holes at the silicon surface is not important for boron hydrogenation.
Inherent memory effect in a SrS:Ce,K blue-emitting electroluminescent thin-film device
Authors: Tanaka Shosaku , Yoshiyama Hideki , Mikami Yoshiro , Nishiura Junichi , Ohshio Shozo , Deguchi Hiroshi , Kobayashi Hiroshi
Published: July 2002

The luminance-applied voltage hysteresis characteristic, so-called memory effect, has been found in the SrS:Ce,K blue-emitting electroluminescent thin-film device. The hysteresis voltage width is about 38 V with 1 kHz pulse drive. The origin of the memory effect is attributable to native defects of the SrS phosphors.
Amorphous silicon, germanium, and silicon-germanium alloy thin-film transistor performance and evaluation
Authors: Yan Philip , Lichtin Norman N. , Morel Don L.
Published: July 2002

The first hydrogenated amorphous germanium and hydrogenated amorphous silicon-germanium alloy field-effect transistors with appreciable field-effect response in n- and p-channel modes were developed by reducing the dihydride content in the films. Field-effect mobilities were derived from transistor characteristics. Hole mobilities are superior to those in pure hydrogenated amorphous silicon which offers the opportunity for improved thin-film devices.
Activation mechanism of zinc implants in GaAs
Authors: Bensalem Rachid , Sealy Brian
Published: July 2002

Rapid thermal annealing has been used to study the activation mechanism of zinc ions implanted into GaAs. The data divide into two parts, a time-dependent and a time-independent regime. Analysis of these regimes suggests that inactive zinc becomes electrically active by local diffusion to an unoccupied gallium vacancy, the energy for this process being 1.1 eV. The time-independent regime produces another energy of 0.37 eV which is suggested to be the energy required to place a zinc atom onto a gallium vacancy.
Electron density measurements of electron-beam-pumped XeF and KrF laser mixtures
Authors: Kimura W. D. , Guyer Dean R. , Moody S. E. , Seamans J. F. , Ford D. H.
Published: July 2002

A CO2 quadrature interferometer is used to measure the temporal evolution of the electron density in XeF and KrF electron-beam-pumped laser mixtures (nonlasing). Measurements are obtained using a 300-kV electron beam which delivers ≳10 A/cm2 at the foil for pulse durations ≤650 ns (FWHM). For typical XeF mixtures (99.35% Ne/0.5% Xe/0.15% F2 at 2888 Torr) the electron density varies between 3 and 4.5×1014 cm−3 during the pulse. The electron density is found to increase as the initial F2 concentration is decreased. Both 10% Kr in argon diluent and argon-free KrF mixtures are tested. The electron density for these mixtures has the same magnitude and behavior as the typical XeF mixture.
Ion beam generation by field ionization of laser-excited Rydberg atoms
Authors: Oomori T. , Ono K. , Fujita S. , Murai Y.
Published: July 2002

Sodium atoms (108–1011 cm−3) effused from an oven where excited by two pulsed dye lasers (∼8–15 ns, ∼100 μJ) from the ground state 3s, via an intermediate state 3p, to a Rydberg state ns or nd (20≤n≤25). About 50 ns after the laser irradiation, a pulsed electric field (0.5–5.5 kV/cm) was applied to the Rydberg atoms to ionize them and accelerate the resulting ions. Thus, a pulsed ion beam was obtained with a maximum total electric charge of ∼5 pC, corresponding to a peak current of ∼25 μA with an output pulse of ∼200 ns full width at half-maximum.
Very thin PbI2 single crystals grown by a hot wall technique
Authors: Nagamune Y. , Takeyama S. , Miura N. , Minagawa T. , Misu A.
Published: July 2002

A hot wall technique was applied to grow PbI2 thin films of about 100 nm thickness on cleaved surfaces of CdI2 single crystals. The band-edge exciton absorption spectra were investigated for the films grown in various conditions. A very sharp exciton absorption line of 8.8 meV half-width was obtained in a PbI2 single-crystal film grown at a 75 °C substrate temperature. The sharpness of the exciton line proved the excellent quality of the PbI2 film and the usefulness of the technique.
Observation of large quadratic electro-optic effect in GaAs/AlGaAs multiple quantum wells
Authors: Wood Thomas H. , Tkach Robert W. , Chraplyvy Andrew R.
Published: July 2002

We simultaneously measure the intensity modulation level and the optical spectrum of the output of a multiple quantum well modulator, and use these data to deduce the electro-optic coefficients. The effect is quadratic, with a measured ‖s33‖=4.6×10−13 cm2/V2 at a wavelength 12 meV below the band gap. This is approximately 800 times the coefficient measured further from the band gap. We are able to achieve a fractional change in the refractive index of 3.7%. Despite the size of this effect, when we operate the device as an intensity modulator, we observe a linewidth enhancement factor of α=1.0, which means the chirp induced in the device’s output will be small.
Electronic properties of In0.53Ga0.47As-InP single quantum wells grown by chemical beam epitaxy
Authors: Frei Michel , Tsui D. C. , Tsang W. T.
Published: July 2002

In0.53Ga0.47As-InP single quantum well (SQW) structures grown by chemical beam epitaxy (CBE) were studied using low-field magnetotransport, the quantum Hall effect, and far-infrared cyclotron resonance measurements at 4.2 K. We compare results on the two-dimensional electron gas (2DEG) in the SQW’s and the single interface heterojunctions. These results confirm the high quality of the material grown by CBE and demonstrate conclusively that the use of the SQW’s for 2DEG confinement can effectively eliminate the parallel conduction often present in single interface structures.
Development of a formed-ferrite flash plasma light source for gas laser applications
Authors: Watanabe K. , Kashiwabara S. , Fujimoto R.
Published: July 2002

A new type of plasma light source using amorphous filaments formed on ferrite substrates has been developed for application to gas laser excitation and preionization. A formed filament acts as a leading guide to produce a long-distance, high-current discharge plasma which emits hard ultraviolet photons. The plasma production mechanism and technological advantages over conventional ways of producing plasmas of the formed-ferrite flash are described.
Study of structural faults in Ti-diffused lithium niobate
Authors: Twigg M. E. , Maher D. M. , Nakahara S. , Sheng T. T. , Holmes R. J.
Published: July 2002

Transmission electron microscope studies of Ti-doped, congruent lithium niobate (LiNbO3) have shown that extended structural faults are only present within the Ti-diffused layer (i.e., the wave guiding region). Structural faults have also been observed in undoped Li-deficient LiNbO3, though not in undoped control crystals of congruent and stoichiometric LiNbO3. In both Ti-doped and Li-deficient LiNbO3, crystal chemistry predicts an increase in the concentration of the point defects V′′′′′Nb and Nb....Li and therefore it is appealing to suggest that these defects are responsible for the creation of structural faults. Since the extent of these structural faults is tens of microns, they are clearly potential scattering sites for photons. In this regard, a systematic understanding of their origin and thermal stability is crucial to integrated optical device technologies based on LiNbO3 and on the Ti-doped waveguide fabrication technique.
Optical tristability using a twin-stripe laser diode
Authors: Watanabe Masanobu , Itoh Hideo , Mukai Seiji , Yajima Hiroyoshi
Published: July 2002

Optical tristability is demonstrated with a positive feedback circuit composed of a twin-stripe laser diode, a p-i-n photodiode, and a transistor. A novel nonlinearity in the current/light characteristics of the twin-stripe laser diode is the key point in realizing the tristability. By changing the circuit parameters, optical bistability and differential gain characteristics can also be performed.
Ultrasonic study of mechanically alloyed Co40Sn60
Authors: Hikata A. , McKenna M. J. , Elbaum C.
Published: July 2002

Ultrasonic velocity changes of mechanically alloyed Co40Sn60 are investigated as a function of temperature at low temperatures. It is found that the velocity increases logarithmically with temperature below ∼1 K, indicating the existence of features characteristic of the glassy state. With the two level tunneling system (TLS) model developed for amorphous materials, factors nM2 and K̃ are determined, where n is the density of states of TLS, M and K̃ are TLS coupling constants for phonons and electrons, respectively.
Formation of epitaxial NiSi2 of single orientation on (111) Si inside miniature size oxide openings
Authors: Chang C. S. , Nieh C. W. , Chen L. J.
Published: July 2002

Epitaxial NiSi2 of single orientation was grown on (111) Si inside miniature size oxide openings. Striking oxide opening size effects on the growth of NiSi2 epitaxy were observed. The formation temperature of NiSi2 on (111) Si was found to be as low as 550 °C inside oxide openings 1.8 μm or smaller in size. Epitaxial NiSi2 of single orientation which is identical to that of (111) Si substrate was formed inside oxide openings of or smaller than 1.8, 1, and 0.8 μm in size in samples annealed at 550–750, 800, and 850–900 °C, respectively. The results are discussed in terms of the variation in tensile stress exerted by oxide near the silicon surface and small free-energy difference between type A and type B NiSi2 epitaxy inside small size oxide openings.
Ion beam enhanced magnetron reactive ion etching
Authors: Chinn J. D.
Published: July 2002

A new dry etching technique is described which allows for decoupling of the chemical etch component from the ionic (physical) component which cannot be achieved in other conventional plasma processing methods. A magnetically confined rf plasma of SF6 was used to contribute a reactive chemical flux with ion bombardment energies of less than 50 eV. In conjunction with this reactive plasma, a broad beam ion source was used to independently deliver an Ar+ ionic flux to the substrate. It was observed that the ion enhanced etch rates of silicon were greater than the individual magnetron reactive ion etch and the argon ion milling rates combined. However, the structure profiles were observed to be directly related to the separately controllable etch components.
Hydrogenated amorphous silicon prepared by ArF and F2 excimer laser-induced photochemical vapor deposition
Authors: Toyoshima Yasutake , Kumata Ken , Itoh Uichi , Matsuda Akihisa
Published: July 2002

Hydrogenated amorphous silicon (a-Si:H) films were prepared by laser-induced photochemical vapor deposition using ArF and F2 excimer lasers. Disilane (Si2H6) and trisilane (Si3H8) diluted with helium were used as the reaction gases for the ArF laser and monosilane (SiH4), disilane, and trisilane for the F2 laser. A good linear correlation was found between the estimate of deposition rate derived from gas phase photoabsorption and the observed deposition rate, indicating that one-photon process governs the film deposition rate. Density of excited molecules in the gas phase was found to be an important factor in controlling the film properties. Laser irradiation onto the growing surface also affects the film properties through a decrease in the hydrogen incorporated in the film.
Heterointerface stability in GaAs-on-Si grown by metalorganic chemical vapor deposition
Authors: Pearton S. J. , Malm D. L. , Heimbrook L. A. , Kovalchick J. , Abernathy C. R. , Caruso R. , Vernon S. M. , Haven V. E.
Published: July 2002

The stability of the electrical and structural properties of GaAs directly deposited on Si by metalorganic chemical vapor deposition is examined. Extended annealing at 900 °C leads to substantial diffusion of Si across the heterointerface while under the same conditions there is no significant motion of Si incorporated as a dopant into the GaAs surface region. The degree of enhancement of Si diffusion ranges from a factor of ∼250 for 0.5-μm-thick GaAs films to ∼5 for 4-μm-thick films. The annealing time and GaAs layer thickness dependence of Si diffusivity near the interface is consistent with a defect-modulated mechanism. A large fraction of this mobile Si is electrically inactive.
Beneficial effect of Co substitution on the magnetic properties of rapidly quenched Nd-Fe-B
Authors: Wecker J. , Schultz L.
Published: July 2002

Isotropic Nd15(Fe1−xCox)77B8 ribbons are produced by conventional melt spinning. For moderate Co additions the coercivity HcI increases while the remanence Jr remains almost constant. Co contents above x=0.3 lead to decreasing HcI and Jr values. The beneficial effect of Co on coercivity is ascribed to the occurrence of a Nd-Fe-Co minority phase which serves as pinning center for domain walls. The temperature characteristic of the coercivity and the remanence is substantially improved due to the increased Curie temperature Tc and the pinning-type behavior of the material.
Low-threshold gain-guided coupled-stripe quantum well diode lasers by laser-assisted processing
Authors: Epler J. E. , Burnham R. D. , Paoli T. L.
Published: July 2002

The first coupled-stripe laser diodes fabricated by a laser-assisted process are reported. In this process, a focused laser beam is scanned across AlGaAs-GaAs heterostructure material to pattern a shallow resistive region in the GaAs cap layer. In this manner, the distribution of the injected current is patterned to fabricate gain-guided four-stripe diode lasers. The devices operate continuously (cw) at room temperature with a low threshold current (36 mA) and high differential quantum efficiency (80%). A maximum cw power efficiency of 48% is obtained at 350 mA. The gain-guided structure favors the lower order array modes, thus the far-field pattern is dominated by a central lobe.
Acoustoelectric effects in superlattices using a separate-medium structure
Authors: Tabib-Azar M. , Das P.
Published: July 2002

The interaction of the surface acoustic wave (SAW) with the GaAs/AlAs superlattice is investigated using a separate-medium convolver structure. The magnitude and polarity of the acoustoelectric voltages exhibit strong temperature and SAW frequency dependences, a phenomenon that is not observed in homogeneous semiconductors. Possible SAW-superlattice interaction models that tentatively explain the observed data are discussed.
Si3N4-Si interface formation by catalytic nitridation using nitrogen exposures on alkali metal overlayers and removal of the catalyst: N2/Na/Si (100) 2×1
Authors: Soukiassian P. , Gentle T. M. , Schuette K. P. , Bakshi M. H. , Hurych Z.
Published: July 2002

Core level photoemission spectroscopy using synchrotron radiation was performed to study the activity of sodium on the nitridation of the (100) face of silicon. At room temperature, the exposition to molecular nitrogen of a Si (100) surface modified by a sodium monolayer induced the formation of a SiNx compound. The sodium catalyst is removed from the surface by thermal desorption at moderate temperature. Subsequently, a clean (sodium free) Si3N4-Si interface was formed at a much lower temperature than without the alkali metal.
Measurements of the optical properties of liquid silicon and germanium using nanosecond time-resolved ellipsometry
Authors: Jellison G. E. , Lowndes D. H.
Published: July 2002

The optical properties of liquid silicon and germanium have been determined at several laser wavelengths from 1.96 to 3.71 eV, using time-resolved ellipsometric measurements during pulsed laser melting. The results from these transient melting experiments are compared with results from the literature for materials held above their melting temperatures for long periods of time. The results for liquid germanium agree well with those of J. N. Hodgson [Philos. Mag. 6, 509 (1961)], but the results for liquid silicon disagree with the results of K. M. Shvarev, B. A. Baum, and P. V. Gel’d [High Temp. 15, 548 (1977)].
Unlubricated friction and wear of an ion beam mixed, nitrogen-implanted Fe50Ti50 surface alloy on AISI 304 stainless steel
Authors: Hirvonen J-P. , Nastasi M. , Mayer J. W.
Published: July 2002

Nitrogen implantation was observed to significantly improve the dry sliding properties of an ion beam mixed Fe50Ti50 surface alloy on AISI 304 stainless steel. Implantation to the fluence of 1.7×1017 N/cm2 at 50 keV increased the wear resistance but a decreased friction coefficient was obtained only after few hundred cycles at the beginning of the pin-on-disk test. When nitrogen was implanted to the fluence of 3×1017 N/cm2 an improved wear resistance and decreased friction were detected throughout the test of 1000 cycles. In addition, good sliding properties were also found at higher loads in the high fluence, nitrogen-implanted samples. These results differ from those obtained following a nitrogen implantation into Ti-implanted iron or iron-based alloys and are attributed to higher titanium and nitrogen concentrations.
Modulation of light by an electrically tunable multilayer interference filter
Authors: Yoffe G. W. , Schlom D. G. , Harris J. S.
Published: July 2002

We describe the structure and performance of a new, nonabsorbing, perpendicular geometry light modulator based on an electrically tunable, multilayer interference filter. The device consists of a GaAs/AlAs quarter-wave stack with aluminum contacts, grown by molecular beam epitaxy. A strong, applied electric field changes the refractive indices through the Franz–Keldysh effect, shifting the transmission spectrum and modulating the intensity of light tuned to the edges of the high reflectance band. Modulation ratios up to 2.5:1 have been obtained for photon energies 0.05–0.2 eV below the GaAs band gap. The device has applications in arrays and for modulation of high power light.
New approach to growth of high-quality GaAs layers on Si substrates
Authors: Varrio J. , Asonen H. , Salokatve A. , Pessa M. , Rauhala E. , Keinonen J.
Published: July 2002

GaAs films were grown by molecular beam epitaxy (MBE) on Si (100) substrates using a two-step growth process of a 300 °C GaAs buffer layer followed by a 600 °C device layer. The films were examined by Rutherford backscattering and x-ray diffraction methods. A significant reduction in the defect density near the GaAs/Si interface and in the bulk of these films was observed when the buffer layer was deposited by alternately supplying Ga atoms and As4 molecules to the substrate, rather than applying conventional MBE. Possible reasons for this reduction of crystal defects are discussed.
Diffraction effects in a diode array traveling-wave amplifier
Authors: Andrews John R. , Paoli T. L. , Burnham R. D.
Published: July 2002

The far-field pattern of a traveling-wave amplifier made from a gain-guided laser diode array consists of a nearly diffraction-limited principal lobe with one or two side lobes when injected with a plane wave from a single-mode diode laser. The observed patterns for varying angle of incidence and amplifier pump current are consistent with a model that treats the array as a diffracting aperture containing a complex volume grating having an amplitude that depends on the current. Some internal parameters of the array are extracted and the implications to broad area amplifiers and laser arrays are discussed.
Mechanism of alkali-promoted oxidation of silicon
Authors: Asensio M. C. , Michel E. G. , Oellig E. M. , Miranda R.
Published: July 2002

Photoelectron spectroscopy data suggest that the mechanism of enhanced oxidation of Si promoted by multilayers of K deposited on its surface is based on the formation of potassium oxides, identified as K2O2 and KO2, that transfer oxygen efficiently to the Si substrate upon annealing at 900 K.
Influence of oxygen incorporation on beryllium-doped InGaAs grown by molecular beam epitaxy
Authors: Le Corre A. , Caulet J. , Gauneau M. , Loualiche S. , L’Haridon H. , Lecrosnier D. , Roizes A. , David J. P.
Published: July 2002

InGaAs epitaxial layers have been doped with beryllium with concentrations ranging from 1016 to 5×1019 cm−3 as measured by secondary ion mass spectroscopy (SIMS). From electrical measurements we have observed that p-type layers presented a high degree of compensation, and for a doping level below 5×10−7 cm−3, they are often found to be n type. SIMS analysis shows that oxygen is responsible for such behavior. Beryllium doping leads to incorporation of a large amount of oxygen in the epitaxial layers. Investigations on the origin of oxygen incorporation show that it is extremely sensitive to the residual vacuum during the growth and can be reduced by decreasing arsenic pressure.
Spectral photoconductivity in n-modulation-doped GaAs/AlGaAs quantum well structures
Authors: Höpfel R. A.
Published: July 2002

The in-plane photoconductivity of n-modulation-doped quantum well structures of GaAs/AlGaAs is experimentally studied as a function of the incident photon energy. Negative photoconductivity with surprising dependences on background illumination, temperature, and electric field is observed for photon energies slightly below the band gap of GaAs. The effect may be due to optical filling of ionized deep donors in AlGaAs as well as to an optical backgating effect. High positive photoconductivity is present above the band gaps—in contrast to theoretical expectations from previous optical transport experiments.
Scan speed effects on enhanced disordering of GaAs-AlGaAs superlattices by focused Si ion beam implantation
Authors: Ishida Koji , Matsui Kazunori , Fukunaga Toshiaki , Kobayashi Junji , Morita Tetsuo , Miyauchi Eizo , Nakashima Hisao
Published: July 2002

We studied compositional disordering of GaAs-AlGaAs superlattices induced by focused Si ion beam implantation and subsequent annealing with different doses and scan speeds by secondary ion mass spectrometry and Rutherford backscattering spectrometry. The results indicate that the Al-Ga intermixing is enhanced by substitutional exchange of Si-Si pairs with vacancies as in the case of the unfocused implantation. However, with a slow scan implantation, it is confirmed that the implantation-induced defects suppress the Si diffusion and consequently Al-Ga interdiffusion.
Ion beam amorphization of YBa2Cu3Ox
Authors: Clark G. J. , LeGoues F. K. , Marwick A. D. , Laibowitz R. B. , Koch R.
Published: July 2002

The microstructure of ion-implanted thin films of the superconductor YBa2Cu3Ox has been investigated by transmission electron microscopy. The superconducting properties of the films were dominated by large pancake-shaped grains of YBa2Cu3Ox with their c axis perpendicular to the substrate. Other grains of YBa2Cu3Ox whose c axis was parallel to the substrate formed spherulites. Irradiation with 500 keV O+ ions caused amorphous zones to appear on the grain boundaries between the pancake grains, which initially were free of amorphous or second phases. At higher dose a continuous amorphous layer 150 Å thick was formed. However, the interior of the grains showed no irradiation-induced microstructural features until they became amorphous at a dose of 3×1014 ions/cm2. The appearance of the amorphous layer on the grain boundaries at low doses accounts for the reduction in the superconducting transition temperature observed in these films.
Electron spin resonance observation of the creation, annihilation, and charge state of the 74-Gauss doublet in device oxides damaged by soft x rays
Authors: Takahashi T. , Triplett B. B. , Yokogawa K. , Sugano T.
Published: July 2002

The E′ related defect called the 74-Gauss doublet is shown to be produced by reaction of E′ with hydrogen and is positively charged like the E′. The doublet is easily annihilated by exposure to ultraviolet light in contrast to the E′ which is comparatively stable. The new positive defect identified here appears to be the third paramagnetic ‘‘trivalent silicon’’ apparently generally responsible for damage and repair of damage to thermal oxides on silicon.
New evidence of small lattice relaxation for the D
X center in AlxGa1−xAs
Authors: Talwar D. N. , Manasreh M. O. , Suh K. S. , Covington B. C.
Published: July 2002

Local structure of isolated Si impurity in GaAs and AlAs is studied using a parameter-free semi-empirical tight binding method. It is predicted that nearest neighbor As atom around the impurity moves toward SiGa(Al) causing a 6.54% (5.73%) change in GaAs(AlAs) bond length. An estimation of lattice distortion energy 0.02±0.003 eV (0.025±0.003 eV) for GaAs:Si (AlAs:Si) is found in good qualitative agreement with the value obtained by J. C. M. Henning and J. P. M. Ansems [Semicond. Sci. Technol. 2, 1 (1987)] from the photoionization of the DX center in lightly doped Si impurities in Al0.33Ga0.67As. The fits for the observed maxima in the optical cross section and the calculation of the pressure-dependent thermal barrier energy lend support for the small lattice relaxation models and cast doubt on the validity of those with the large lattice relaxation usually recommended for this class of centers.
Crater formation in Langmuir–Blodgett films induced by electronic sputtering with fast heavy ions
Authors: Säve G. , Håkansson P. , Sundqvist B. U. R. , Johnson R. E. , Söderström E. , Lindquist S. E. , Berg J.
Published: July 2002

Secondary ion formation by fast heavy ion impact (electronic sputtering) on Langmuir–Blodgett films of fatty acids has been studied. The results show unambiguously that molecular ions originate from molecules in layers other than the surface layer. Furthermore, the results indicate that craters may be formed in electronic sputtering of such films. The depth of the craters depends on the stopping power of the incident ion and lower limits of the order of 100–200 Å are obtained from the ion data.
Novel physical effects in intersecting waveguides
Authors: McCaughan L. , Agrawal Niraj , Bogert G. A.
Published: July 2002

Previous theory of intersecting waveguides (optical) based on the idea of composite modes is unable to explain a variety of important experimental observations. We have developed a systematic theory which is in good agreement with the experiment. In addition, our theory points out the novel physical effects associated with this geometry. It is found that the crosstalk vanishes for an intersection angle which is twice the angle of rays in the individual waveguides. A sharply peaked radiation pattern from the intersection region of the two waveguides is both predicted and observed for the first time.
Enhanced ballistic transport in InGaAs/InAlAs hot-electron transistors
Authors: Chen J. , Reddy U. K. , Mui D. , Peng C. K. , Morkoç H.
Published: July 2002

Hot-electron transistors fabricated using a 600-Å InGaAs base and a 500-Å InAlAs barrier have shown a peak ballistic common base current gain of 0.82 at 77 K despite the large injection energies. Reduction of injection energies by lowering the emitter and collector barriers should lead to an even higher ballistic transport ratio due to the reduced Γ-L scattering.
Effects of trichloroethane during oxide growth on radiation-induced interface traps in Metal/SiO2/Si capacitors
Authors: da Silva Eronides F. , Nishioka Yasushiro , Ma T.-P.
Published: July 2002

The radiation-induced interface traps in Metal/SiO2/Si capacitors where the oxides are grown in dry O2+1.1.1.-trichloroethane (TCA) have been studied. Among all the samples tested, a peak in the interface trap distribution above midgap (centered at ∼Eν +0.70–0.75 eV) appears immediately after irradiation, and the magnitude of this peak is a function of the amount of TCA during oxide growth. After the termination of the irradiation, this peak will either increase or decrease with time at room temperature for a few hours, followed by a continuous decrease over a long period of time (up to several months) before saturation, and this time-dependent behavior also appears to be a function of the TCA concentration. In the case when this peak decreases with time, a second peak located below midgap (centered at ∼Eν +0.35 eV) will develop, and the rate of growth of the second peak is correlatable to the reduction of the first peak. A closer examination of the data reveals that it is the initial damage level that determines the post-radiation time-dependent behavior, and the apparent dependence on the TCA concentration arises from its effect on the radiation sensitivity of the SiO2/Si interface.
Picosecond measurement of chirp in gain-switched, single-mode injection lasers
Authors: Wiesenfeld J. M. , Tucker R. S. , Downey P. M.
Published: July 2002

Wavelength shifts caused by chirp in pulses generated from a gain-switched InGaAsP distributed-feedback laser have been measured with 0.5 ps resolution. The applicability of a simple, two-term analytical expression to describe the chirp is evaluated. For the pulses from the gain-switched laser, the power-dependent ‘‘wavelength-offset’’ term in the formula is the most important.
Performance characteristics of InGaAs/GaAs and GaAs/InGaAlAs coherently strained superlattice photodiodes
Authors: Das Utpal , Zebda Yousef , Bhattacharya Pallab , Chin Albert
Published: July 2002

The properties of In0.24Ga0.76As/GaAs and GaAs/In0.05Ga0.58Al0.37As superlattice photodiodes grown by molecular beam epitaxy have been investigated. From the temporal response characteristics, deconvolved rise times ∼60–100 ps are obtained. The measured responsivities of the photodiodes with dark currents of 5–10 nA at 10 V are ∼0.4 A/W, which correspond to peak external quantum efficiencies of ∼60%. These results indicate that very high performance photodiodes can be realized with strained layers.
Characterization of GaAs grown by metalorganic chemical vapor deposition on Si-on-insulator
Authors: Pearton S. J. , Vernon S. M. , Short K. T. , Brown J. M. , Abernathy C. R. , Caruso R. , Chu S. N. G. , Haven V. E. , Bunker S. N.
Published: July 2002

Epitaxial GaAs layers were grown by metalorganic chemical vapor deposition on Si-on-insulator structures formed by high dose oxygen implantation. The quality of the GaAs films was examined as a function of layer thickness (0.01–4 μm). The surface morphology, ion backscattering yield, x-ray diffraction peak width, and Si implant activation efficiency all improve substantially with GaAs thickness. At a film thickness of 4 μm many of these properties are comparable to bulk GaAs, but some cracking of the epitaxial film is evident. Cross-sectional transmission electron microscopy reveals an average defect density of ∼108 cm−2 in the GaAs layer, which is similar to the density in GaAs films grown directly on Si.
Fabrication of dense Ba2YCu3O7−δ superconductor wire by molten oxide processing
Authors: Jin S. , Tiefel T. H. , Sherwood R. C. , Kammlott G. W. , Zahurak S. M.
Published: July 2002

Fabrication of high Tc ceramic superconductors by an oxide melting method in place of a conventional sintering method has been attempted. Using three different processes, i.e., melt drawing, melt spinning, or preform-wire melting, it is demonstrated that the Ba2YCu3O7−δ type superconductors can successfully be fabricated into a desired geometry such as wire and ribbon. Tc’s for R=0 were about 92 K. The density of the melt-processed compound was measured to be as high as 6.2 g/cm3, or ∼98% of the theoretical density 6.3 g/cm3 as compared to the value of 80–85% density for sintered samples. The increased density is likely to be responsible for the noted improvements in fracture resistance and in the Jc value of the melt-processed compound.
YBaCuO superconducting thin films with zero resistance at 84 K by multilayer deposition
Authors: Bao Z. L. , Wang F. R. , Jiang Q. D. , Wang S. Z. , Ye Z. Y. , Wu K. , Li C. Y. , Yin D. L.
Published: July 2002

YBaCuO superconducting thin films were prepared by multilayer deposition on different kinds of substrates. High Tc with an onset of 94 K and a zero resistance at 84 K has been obtained by deposition on pure ZrO2 substrates. The nature of zero resistance as well as the dR/dT characteristic above Tc and the influence of substrates are discussed.
Characterization of multilayers for extended ultraviolet optics
Authors: Fernández Félix E. , Falco Charles M. , Dhez P. , Khandar-Shahabad A. , Névot L. , Pardo B. , Corno J. , Vidal B.
Published: July 2002

We describe an extensive characterization procedure developed to study multilayers for extended ultraviolet (XUV, 1 Å≲λ≲1000 Å) optics. We present results of this procedure applied to sputtered Si/W multilayers designed as normal-incidence XUV reflectors for ∼200 Å. Techniques used were low-angle x-ray diffraction, Bragg–Brentano and Seemann–Bohlin diffraction, wide-film Debye–Scherrer (Read) camera, Rutherford backscattering spectroscopy, and transmission electron microscopy. Reflectances at several incidence angles were measured with synchrotron radiation and found to agree very well with reflectance curves calculated without adjustable parameters. The information obtained from the different techniques forms a coherent picture of the structure of these materials.
Growth of high-quality GaxIn1−xAsyP1−y by chemical beam epitaxy
Authors: Tsang W. T. , Schubert E. F. , Chiu T. H. , Cunningham J. E. , Burkhardt E. G. , Ditzenberger J. A. , Agyekum E.
Published: July 2002

GaxIn1−xAsyP1−y epilayers closely lattice matched, Δa/a≲5×10−4, have been reproducibly grown over the whole range of composition (y=2.2x, 1>y>0) by chemical beam epitaxy. The relative sticking coefficient (or equivalently the incorporation efficiency into the solid) of arsenic to phosphorus, i.e., SAs/SP was between 1.5 and 3 depending on the material composition. Such values indicate a very efficient incorporation of phosphorous in this process. Very intense efficient luminescence peaks due to excitonic transitions with linewidths full width at half-maximum as narrow as 3 meV were obtained. Such a linewidth corresponds closely to the intrinsic linewidth due to alloy broadening in GaInAsP alloys. Furthermore, the photoluminescence spectra revealed that the donor-to-acceptor pair recombination was nearly absent. Hall measurements on GaxIn1−xAsyP1−y epilayers lattice matched into InP at 300 and 77 K yielded electron mobility values that agreed closely with theoretical values calculated by using the one-phonon model and the electronegativity difference as the alloy scattering potential for layers with doping levels between 1×1015 cm−3 and 1×1016 cm−3. The 77 K electron mobilities ranged from 2.2×104 to 6.7×104 cm2/V s depending on the quaternary composition.
Control of hydrogen content of boron thin films produced in a dc toroidal discharge
Authors: Toyoda H. , Sugai H. , Isozumi T. , Okuda T.
Published: July 2002

Hydrogenated amorphous boron films have been produced by a toroidal glow discharge of B2H6/He mixtures at low pressures (10−2 Torr). Chemically stable pure films with a low hydrogen content can be formed at a moderate substrate temperature (∼200 °C) when the diborane flow rate is raised above 10 sccm with the discharge power lowered below 100 W. The controllability of H content is potentially interesting for applications in the coating of nuclear fusion devices, as well as for use in electronic devices.
Superconducting and structural properties of sputtered thin films of YBa2Cu3O7−x
Authors: Makous J. L. , Maritato L. , Falco Charles M. , Cronin J. P. , Rajendran G. P. , Uhlmann E. V. , Uhlmann D. R.
Published: July 2002

We have fabricated thin films of YBa2Cu3Ox by dc triode sputtering from two metallic targets. Post-annealing in pure O2 after sputtering resulted in superconducting films with a Tc onset as high as 89 K and a midpoint Tc of 75 K. We report preliminary results of films deposited on sapphire, MgO and sol-gel coatings of ZrO2 on sapphire, with and without buffer layers of Ag. The chemical and physical structures of these films were analyzed by using several x-ray diffraction techniques and Rutherford backscattering spectroscopy.
Resolved structure in the quenching band of the EL2 center in GaAs, studied by infrared spectroscopy
Authors: Fuchs F. , Dischler B.
Published: July 2002

Infrared measurements at low temperature on undoped semi-insulating GaAs reveal additional details in the photoresponse of the EL2 center. In the continuous spectral recording of the optical cross section for the bleaching of the EL2 absorption the zero phonon line (ZPL) at 1.039 eV and six phonon replicas with 11 meV separation have been observed. A modified Huang Rhys calculation is necessary to reproduce both the relative intensity of the ZPL and the maximum of the broad band at 1.17 eV. Using the intensity of the resolved structure for calibration, we calculate the contribution of the intracenter transition to the total EL2 absorption spectrum. Comparison with the known time constants for photoionization and quenching yields a probability of (1.2±0.3)% for transformation to the metastable state after intracenter excitation. The ZPL in the absorption spectrum shows considerable broadening and a decrease in energy by 3 meV in the temperature range 10–65 K.
Low-loss short-wavelength optical waveguides using ZnSe-ZnS strained-layer superlattices
Authors: Yokogawa Toshiya , Ogura Mototsugu , Kajiwara Takao
Published: July 2002

Low-loss short-wavelength optical ridge waveguides using ZnSe-ZnS strained-layer superlattices (SLS’s) were successfully fabricated on GaAs substrates by low-pressure metalorganic vapor phase epitaxy. A propagation loss α as low as 0.71 cm−1 was obtained for the SLS waveguide composed of 80 periods of ZnSe(50 Å)-ZnS(50 Å) at the 0.633-μm wavelength TE fundamental mode. Therefore, this waveguide may be suited for optoelectronic integrated circuits composed of II-VI and III-V compound semiconductor devices. Furthermore, these waveguides exhibited a large difference in the propagation loss between TE and TM polarizations which may be related to the birefringence for TE and TM polarizations due to the slight anisotropy of the refractive index in the ZnSe-ZnS superlattice structure. This birefringence effect will be very useful for a polarizing optical device.