bluuebunny/crossref_metadata_2025 huggingface dataset:
Shock-induced mixing of nonhomogeneous density turbulent jets
Authors: Hermanson J. C. , Cetegen B. M.
Published: July 2002

An experimental study of the mixing enhancement and changes in flow structure arising from the interaction of weak normal shock waves with turbulent jets was conducted. The experimental configuration was an axisymmetric jet processed by weak normal shock waves propagating in a shock tube along the jet axis. Experiments involved three different jet gases: helium, air, and carbon dioxide, each in a coflowing air stream, with nominal jet fluid to ambient density ratios of 0.14, 1.00, and 1.52, respectively. The jet local Reynolds number was Reδ≈25 000 and the nominal oncoming shock Mach numbers were 1.23 and 1.45. Planar laser Mie light scattering from mineral oil smoke was utilized for flow visualization and for obtaining jet fluid concentration distributions across diametric planes of jets. Analysis of the spatial probability density function (pdf) of jet fluid concentration indicates that the average helium jet fluid concentration levels decrease and become more uniform in the regions processed by the shock waves. The degree of mixing enhancement increases with increasing shock strength, and amounts to nearly 30% for the stronger shock (M=1.45). The passage of a shock through low-density (helium) jets induces the formation of a flow structure that resembles a large-scale, toroidal vortex. The air and carbon dioxide jets exhibit neither a vortex-like structure or a significant change in mixing upon shock passage, unlike the helium jets. A comparison of the results for the helium and carbon dioxide jets indicates that the reversal of the density ratio between the jet and the surroundings, and the consequent change in the sign of baroclinic vorticity does not yield similar effects in terms of flow structure or mixing enhancement. The average concentration behind the shock wave decreases for both air and helium jets with increasing distance behind the shock. These features are explained qualitatively in terms of a simple characteristic time scale argument. The spatially averaged scalar dissipation calculated from the concentration data decreases for both the air and helium jets due to shock passage. The change is less marked for the air jet than for the helium jet for a given shock strength.
Resonant coupling between ion bounce in a potential well and the potential relaxation instability
Authors: Popa G. , Schrittwieser R.
Published: July 2002

When in a double plasma machine (DP-machine) plasma is produced solely in the source chamber, not only ions but also electrons can leak through the separating grid into the target chamber, so that a low-density plasma forms there. The electrons are trapped by the traveling ion space charge and can thereby overcome the strongly negative grid bias. The investigations presented here show that a positive space-charge forms behind the grid in the target chamber and a deep potential well is formed around the grid. When the anode of the target chamber is biased positively, under certain conditions a low-frequency instability is observed in the target chamber, the properties of which indicate a potential relaxation oscillation, somewhat similar to the potential relaxation instability in a quiescent plasma machine (Q machine). The frequency of the instability is determined by the ion transit time through a thin layer of the target chamber plasma. In addition, resonant coupling occurs between this frequency and the bounce frequency of ions in the potential well around the grid.
X-ray spectroscopy of hot solid density plasmas produced by subpicosecond high contrast laser pulses at 1018–1019 W/cm2
Authors: Jiang Z. , Kieffer J. C. , Matte J. P. , Chaker M. , Peyrusse O. , Gilles D. , Korn G. , Maksimchuk A. , Coe S. , Mourou G.
Published: July 2002

Analysis is presented of K-shell spectra obtained from solid density plasmas produced by a high contrast (1010:1) subpicosecond laser pulse (0.5 μm) at 1018–1019 W/cm2. Stark broadening measurements of He-like and Li-like lines are used to infer the mean electron density at which emission takes place. The measurements indicate that there is an optimum condition to produce x-ray emission at solid density for a given isoelectronic sequence, and that the window of optimum conditions to obtain simultaneously the shortest and the brightest x-ray pulse at a given wavelength is relatively narrow. Lower intensity produces a short x-ray pulse but low brightness. The x-ray yield (and also the energy fraction in hot electrons) increases with the laser intensity, but above some laser intensity (1018 W/cm2 for Al) the plasma is overdriven: during the expansion, the plasma is still hot enough to emit, so that emission occurs at lower density and lasts much longer. Energy transport measurements indicate that approximately 6% of the laser energy is coupled to the target at 1018 W/cm2 (1% in thermal electrons with Te≊0.6 keV and 5% in suprathermal electrons with Th≊25 keV). At Iλ2=1018 W μm2/cm2 (no prepulse) around 1010 photons are emitted per laser shot, in 2π srd in cold Kα radiation (2–9 Å, depending on the target material) and up to 2×1011 photons are obtained in 2π srd with the unresolved transition array (UTA) emission from the Ta target.
A model of ultrashort laser pulse absorption in solid targets
Authors: Rozmus W. , Tikhonchuk V. T. , Cauble R.
Published: July 2002

A model for ultrashort laser pulse absorption and solid target heating has been developed. It combines a description of laser light absorption in the skin layer with a simple model of plasma heating. Heat wave propagation into the cold target material is the only loss mechanism balancing energy deposition due to absorption. An absorption coefficient is derived from the plasma conductivity and includes a description of physical processes responsible for collisional and collisionless skin layer absorption mechanisms. Comparison with recent femtosecond laser pulse interaction experiment data show good agreement over a wide range of pulse intensities. For laser intensities above 1016 W/cm2 plasma hydrodynamical expansion, which is neglected in our model contributes to a discrepancy between the calculated absorption and experimental data.
Eigenmode excitation of Alfvén ion cyclotron instability
Authors: Katsumata R. , Ichimura M. , Inutake M. , Hojo H. , Mase A. , Tamano T.
Published: July 2002

In the GAMMA 10 tandem mirror [M. Inutake et al., Phys. Rev. Lett. 55, 939 (1985)], plasmas with a high beta value (ratio of plasma pressure to magnetic pressure) are produced by using an ICRF (ion cyclotron range of frequency) heating. Magnetic field fluctuations identified as an Alfvén ion cyclotron (AIC) mode are excited with strong dependence on a perpendicular beta value and a temperature anisotropy T⊥/T∥ (a ratio between the temperatures perpendicular and parallel to the magnetic field line). Spatial structures and excitation conditions of the AIC mode are experimentally studied. AIC modes are spontaneously excited as axial eigenmodes, of which boundary is determined by the reflection point in anisotropic plasmas. The AIC mode in the GAMMA 10 is observed well below the theoretically predicted threshold.
A variational approach to parametric instabilities in inhomogeneous plasmas III: Two-plasmon decay
Authors: Afeyan Bedros B. , Williams Edward A.
Published: July 2002

The theory of the two-plasmon decay instability is recast in the form of a variational principle for the pump strength or intensity of the incident laser. This allows the calculation of growth rates, frequency shifts, and threshold conditions for two-plasmon decay modes that occur in integer power law density profiles, including the effects of oblique incidence of the laser and both S and P polarizations. The transition between parabolic profiles occurring at the peak of an exploding foil target and linear profiles on its flanks is treated as well.
Landau fluid models of collisionless magnetohydrodynamics
Authors: Snyder P. B. , Hammett G. W. , Dorland W.
Published: July 2002

A closed set of fluid moment equations including models of kinetic Landau damping is developed which describes the evolution of collisionless plasmas in the magnetohydrodynamic parameter regime. The model is fully electromagnetic and describes the dynamics of both compressional and shear Alfvén waves, as well as ion acoustic waves. The model allows for separate parallel and perpendicular pressures p∥ and p⊥, and, unlike previous models such as the Chew–Goldberger–Low theory, correctly predicts the instability threshold for the mirror instability. Both a simple 3+1 moment model and a more accurate 4+2 moment model are developed, and both could be useful for numerical simulations of astrophysical and fusion plasmas.
Hot electron production and heating by hot electrons in fast ignitor research
Authors: Key M. H. , Cable M. D. , Cowan T. E. , Estabrook K. G. , Hammel B. A. , Hatchett S. P. , Henry E. A. , Hinkel D. E. , Kilkenny J. D. , Koch J. A. , Kruer W. L. , Langdon A. B. , Lasinski B. F. , Lee R. W. , MacGowan B. J. , MacKinnon A. , Moody J. D. , Moran M. J. , Offenberger A. A. , Pennington D. M. , Perry M. D. , Phillips T. J. , Sangster T. C. , Singh M. S. , Stoyer M. A. , Tabak M. , Tietbohl G. L. , Tsukamoto M. , Wharton K. , Wilks S. C.
Published: July 2002

In an experimental study of the physics of fast ignition, the characteristics of the hot electron source at laser intensities up to 1020 W cm−2 have been measured and a diagnosis of the heating at depth by hot electrons has been initiated. Generation of hot electrons with more than 30% efficiency has been observed. Preliminary heating data suggest temperatures kT in the range 300–800 eV.
Modeling the spatial structure of the high latitude magnetic perturbations and the related current systems
Authors: Valdivia J. A. , Vassiliadis D. , Klimas A. , Sharma A. S.
Published: July 2002

Previous input–output analysis of the electrojet indices has been generalized to a spatio-temporal dynamical model of the high latitude magnetic perturbation (HLMP) by using the spatially dependent measurements that can be provided by a ground magnetometer array of latitudinal coverage. A technique that utilizes the daily rotation of the Earth as a longitudinal, or local time, sampling mechanism is used to construct a two-dimensional representation of the high latitude magnetic perturbations, both in magnetic latitude and local time, from the single latitudinal chain of magnetometers. Two-dimensional static, linear dynamical and nonlinear dynamical models for the evolution of the spatial structure of the HLMP are constructed by including a coupling to the solar wind as the energy input. The nonlinear spatial model of the HLMP produces better predictions than the linear one, reducing the average error from 65 to 50 nT for the Hx component. This can be taken as an indication that during intense activity, the HLMP and related current system evolves in a nonlinear fashion.
The density and clustering of magnetic nulls in stochastic magnetic fields
Authors: Albright B. J.
Published: July 2002

Many processes in astrophysical plasmas, such as magnetic reconnection and current sheet formation, are sensitive to the topology of the magnetic field. Magnetic nulls are special in a topological sense because they are connected to an infinite number of field lines. Complicated magnetic field geometries may have many nulls and many null–null lines. This work examines the statistical properties of zeros in a random divergence-free vector field model. An analytic expression for the density of nulls is obtained as a function of the dissipation and integral length scales of the random field and the exponent of the energy spectrum of the field. For a broad class of spectra which are similar to the spectra of turbulent cascades magnetic nulls form self-similar clusters. The fractal dimension of the set of nulls is computed as a function of the power law index of the random field. Complicated magnetic topologies may possess tangled webs of nulls and null–null lines. These webs of nulls may be the sites of current sheet formation and heating, and they may modify the properties of particle transport in turbulent plasma media.
Improved core fueling with high field side pellet injection in the DIII-D tokamak
Authors: Baylor L. R. , Jernigan T. C. , Combs S. K. , Houlberg W. A. , Murakami M. , Gohil P. , Burrell K. H. , Greenfield C. M. , Groebner R. J. , Hsieh C.-L. , La Haye R. J. , Parks P. B. , Staebler G. M. ,   DIII-D Team, Schmidt G. L. , Ernst D. R. , Synakowski E. J. , Porkolab M.
Published: July 2002

The capability to inject deuterium pellets from the magnetic high field side (HFS) has been added to the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)]. It is observed that pellets injected from the HFS lead to deeper mass deposition than identical pellets injected from the outside midplane, in spite of a factor of 4 lower pellet speed. HFS injected pellets have been used to generate peaked density profile plasmas [peaking factor (ne(0)/〈ne〉) in excess of 3] that develop internal transport barriers when centrally heated with neutral beam injection. The transport barriers are formed in conditions where Te∼Ti and q(0) is above unity. The peaked density profiles, characteristic of the internal transport barrier, persist for several energy confinement times. The pellets are also used to investigate transport barrier physics and modify plasma edge conditions. Transitions from L- to H-mode have been triggered by pellets, effectively lowering the H-mode threshold power by 2.4 MW. Pellets injected into H-mode plasmas are found to trigger edge localized modes (ELMs). ELMs triggered from the low field side (LFS) outside midplane injected pellets are of significantly longer duration than from HFS injected pellets.
Growth of In0.53Ga0.47As by liquid phase epitaxy over tungsten on structured InP substrates
Authors: Hancox J. E. , Houston P. A. , Hill G. , Chand N.
Published: July 2002

A first study involving lateral growth of In0.53Ga0.47As by liquid phase epitaxy over tungsten metal is being reported. Because of the rapid lateral nucleation process in the channels etched on (111) B InP substrates, seeding of the crystal through the metal layer is found unnecessary, enabling growth to occur over relatively large areas of continuous metal. The tungsten metal during growth was found to remain undissolved in the growth solution, and also acted as a mask for vertical growth when used on a plane InP substrate. The Schottky barrier characteristics between the tungsten and the top InGaAs layer indicate that this structure will be useful for metal base transistors.
Epitaxial Hg1−xCdxTe growth by low-temperature metalorganic chemical vapor deposition
Authors: Lu P.-Y. , Wang C.-H. , Williams L. M. , Chu S. N. G. , Stiles C. M.
Published: July 2002

We report the first low-temperature metalorganic chemical vapor deposition of Hg1−xCdxTe using a thermal precracking technique. The precracking technique enables one to grow epitaxial Hg1−xCdxTe on CdTe substrates at temperatures as low as 225 °C. The growth rate is 1–2 μm/h. The film is epitaxial and has good morphology. The Hg1−xCdxTe epilayer also shows infrared transmission with a sharp cut-off edge. The Hg0.7Cd0.3Te material is n type and has a room-temperature mobility of 12 200 cm2/V s with carrier concentration of 2.7×1017 cm−3 and 77 K mobility of 27 000 cm2/V s with carrier concentration of 1.0×1017 cm−3. This low-temperature precracking technique offers the feasibility of fabricating structures with sharp heterojunctions for Hg1−xCdxTe compounds by metalorganic chemical vapor deposition.
Dislocation filtering in semiconductor superlattices with lattice-matched and lattice-mismatched layer materials
Authors: Gourley P. L. , Drummond T. J. , Doyle B. L.
Published: July 2002

We investigate the ability of semiconductor superlattices to filter or block threading dislocations by growing and studying structural properties of superlattices composed of alternating layers (∼100 Å each) of InxGa1−xAs and InyAl1−yAs. These superlattices were grown with x=y corresponding to lattice-matched compositions such that the layers have minimal strain, and x≠y corresponding to lattice-mismatched compositions such that the layers have large coherent strains. By correlating the number of dislocations observed in optical images of the superlattices, with the amount of layer strain determined by x-ray double diffraction analysis, we investigate the effect of strain on the filtering ability. We find that both types of superlattices are effective in filtering dislocations.
Effect of hydrogen plasma treatment on transparent conducting oxides
Authors: Major S. , Kumar Satyendra , Bhatnagar M. , Chopra K. L.
Published: July 2002

The effect of hydrogen plasma treatment on indium tin oxide (ITO), fluorine-doped tin oxide (FTO), and indium-doped zinc oxide (IZO) films has been studied. X-ray photoelectron spectroscopy analysis shows that ITO and FTO surfaces get reduced to yield elemental indium and tin, respectively. Annealing of the plasma treated films in air leads to re-oxidation of the reduced surface and the electro-optical properties are recovered. In contrast, IZO films are not reduced by plasma treatment and show no changes in the electrical and optical properties. The surface of plasma treated IZO films shows a higher binding energy O(1s) peak probably due to OH or OH...O species which appear to form a protective layer against plasma degradation.
Improved quality Si-on-Si3N4 structures by ion beam synthesis and lamp annealing
Authors: Reeson K. J. , Hemment P. L. F. , Meekison C. D. , Booker G. R. , Kilner J. A. , Chater R. J. , Davis J. R. , Celler G. K.
Published: July 2002

Silicon wafers were implanted with 200 keV 14N+ ions to a dose of 0.95×1018 14N+ cm−2 at a temperature of 520 °C. These wafers were then annealed at 1405 °C for 30 min, a temperature significantly higher than that normally used (1200 °C) for annealing buried nitride, silicon-on-insulator (SOI) structures. Annealing leads to the formation of a well defined layer of essentially single-crystal Si3N4 containing a few low angle grain boundaries. The Si/Si3N4 interfaces are abrupt, the lower one being almost planar while the upper one shows some irregularities due to fingerlike protrusions of Si3N4 and has an associated region of defective silicon. The silicon overlay is single crystal with no resolvable defects making the wafers good candidates for SOI substrates.
Design of low velocity-spread cusp guns for axis encircling beams
Authors: Lawson W.
Published: July 2002

The design of a novel electron gun suitable for intense beam cyclotron resonance devices is introduced here. An annular Pierce-type gun is used in conjunction with an unbalanced nonadiabatic field reversal and an adiabatic compression region to produce an axis-encircling beam. This beam is ideally suited for interaction with electromagnetic waves that have strong on-axis electric fields (e.g., the TE011 mode). Low velocity spreads are achieved by utilizing the beam self-fields in the compression region and by focusing in the Pierce gun.
Laser photoablation processes in organosilane thin films
Authors: Marinero E. E. , Miller R. D.
Published: July 2002

We report on the excimer laser-induced photoablation of some organosilane polymers utilizing quartz microbalance techniques to monitor the nature of the ablation phenomenon. A fluence threshold for the ablation process is identified beyond which the material removal rate depends nonlinearly on the adsorbed laser fluence. Below this threshold, photo-oxidation of the polymer is observed as evidenced by mass uptake of the film. Our results suggest that photoablation of the polysilanes studied is a result of a combination of thermal and photochemical processes.
Electron mobility in hydrogenated amorphous silicon under single and double injection
Authors: Silver M. , Winborne G. , Adler D. , Cannella V.
Published: July 2002

A recent suggestion that the band mobility of electrons in hydrogenated amorphous silicon (a-Si:H) is larger under high-level double-injection than under single-injection conditions because of the neutralization of charged defect states in the former case is tested by studying the transit time of carriers under both conditions. It is found that the drift mobility at 320 K in a device allowing the injection only of electrons is approximately 1 cm2/V s, consistent with the results of many earlier investigations. On contrast, the 320 K drift mobility in a device in which double injection of both electrons and holes occurs is estimated to be about 15 cm2/V s, more than an order of magnitude larger. We conclude that the band mobility of electrons in a-Si:H is indeed considerably larger in the presence of high-level double injection than under single-injection conditions.
Low-temperature photoluminescence from InGaAs/InP quantum wires and boxes
Authors: Temkin H. , Dolan G. J. , Panish M. B. , Chu S. N. G.
Published: July 2002

InGaAs/InP quantum well layers grown by gas source molecular beam epitaxy have been used to fabricate quantum wires and boxes with transverse dimensions as small as ∼300 Å. These artificial structures exhibit intense low-temperature photoluminescence and show exciton shifts of 8–14 meV expected of low dimensional confinement. Low surface recombination velocity characteristic of InP and its alloys should allow luminescence studies of features as small as ∼30 Å under moderate excitation intensities.
Slow relaxation and electric field quenching of persistent conductivity in GaAs metal-semiconductor field-effect transistors with different buffer layer structures
Authors: Liou Jenn-Chorng , Lau Kei May
Published: July 2002

Slow relaxation in photoconductivity and high transverse field effects have been investigated in GaAs metal-semiconductor field-effect transistors with undoped GaAs buffers and AlGaAs/GaAs superlattice buffers. Persistent photoconductivity (PPC) has been observed in both types of devices at 77 K. Complete electric field quenching of the PPC is possible in devices with a GaAs buffer. A high electric field resulted in more profound effects on the channel conductance of the superlattice buffered devices. The barrier established by the superlattice precludes complete elimination of the PPC and thermal quenching is necessary.
Raman scattering studies of ion beam induced mixing at the amorphous germanium/crystalline silicon interface
Authors: Kshirsagar S. T. , Rajarshi S. V. , Dusane R. O. , Vaidya Jayashri , Bhide V. G.
Published: July 2002

Thin layers of amorphous germanium vacuum deposited onto a 〈111〉 surface of crystalline silicon were irradiated with a Kr+ ion beam to produce an amorphous Si-Ge alloy at the interface. Raman scattering measurements were performed on these films both before and after the ion irradiation. The vanishing of the strong Si-Si lattice mode near 521 cm−1 and an appearance of the localized Si-Ge vibrational mode near 375 cm−1 in the Raman spectra of ion-irradiated films are correlated to the formation of an amorphous alloy of probable composition of Si0.2Ge0.8 at the interface.
Room-temperature continuous operation of p-n AlxGa1−xAs-GaAs quantum well heterostructure lasers grown on Si
Authors: Deppe D. G. , Holonyak N. , Nam D. W. , Hsieh K. C. , Jackson G. S. , Matyi R. J. , Shichijo H. , Epler J. E. , Chung H. F.
Published: July 2002

We describe the construction and room-temperature (300 K) continuous (cw) operation of p-n diode AlxGa1−xAs-GaAs quantum well heterostructure (QWH) lasers grown on Si substrates. The QWH crystal is grown in two stages, the first part by molecular beam epitaxy (MBE) and the single-well quantum well active region by metalorganic chemical vapor deposition (MOCVD). Simple gain-guided stripe configuration lasers fabricated on the MBE MOCVD QWH wafer operate cw at 300 K and have pulsed thresholds as low as 1.8×103 A/cm2.
Relation between surface potential and pH
Authors: Williams Richard , Labib Mohamed E.
Published: July 2002

Applications involving the semiconductor-electrolyte interface require a good understanding of charge carrier transport at the interface and the related concept of Fermi level in an electrolyte. The meaning of electrolyte Fermi level is currently an active research question. As an experimental approach to the problem, we have developed a convenient technique, using a Kelvin probe. Using this, we can measure the surface potential without making contact to the solution. An important question is how the surface potential is related to the solution composition. We find that surface potential depends on the pH of the solution in a well-defined way. From our data, we can estimate the absolute emf of the hydrogen electrode. The result agrees well with published values, determined by other means.
Thermoelastic surface deformation—time evolution
Authors: Tankovsky N. S. , Mitev A. P. , Kebedjiev A. G.
Published: July 2002

A method is reported, which allows us to measure the dynamics of the surface thermoelastic deformations. We have obtained the time evolution of amplitudes of surface deformations induced by absorption of a laser beam in Plexiglas samples of different geometry. A qualitative discussion of the obtained results is made.
Segmented-mirror phased-array lasers
Authors: De Silvestri S. , Laporta P. , Magni V. , Svelto O.
Published: July 2002

A scheme for phase-locked laser arrays in both one- and two-dimensional configurations is discussed. The scheme can be applied to any laser and its validity has been proved for the case of a pulsed neodimium laser.
Self-consistent analysis of gain saturation in channeled-substrate-planar double-heterojunction lasers
Authors: Butler Jerome K. , Evans Gary A.
Published: July 2002

A self-consistent model for semiconductor lasers [using the channeled-substrate-planar (CSP) double-heterojunction (DH) laser as an example] which does not assume constant optical power along the laser axis is developed. This approach allows for the analysis of high-power lasers with low facet reflectivities which produce nonuniform photon densities along the propagation direction. Analytical equations for the modal gain coefficient, the threshold current density, and the radiated power for a specific CSP laser structure are obtained.
Continuous room-temperature operation of a 759-nm GaAlAs distributed feedback laser
Authors: Takigawa S. , Kume M. , Hamada K. , Tateoka K. , Naitoh H. , Yoshikawa N. , Yamamoto A. , Shimizu H. , Itoh K.
Published: July 2002

The first continuous wave (cw) operation at room temperature of a GaAlAs short-wavelength distributed feedback (DFB) laser is reported. The cw operation at a wavelength of 759 nm was realized by use of the buried twin-ridge substrate (BTRS) structure which has an excellent current confinement efficiency in the active region. The hybrid liquid phase epitaxy and the metalorganic chemical vapor deposition growth technology were used for the fabrication of short-wavelength GaAlAs DFB BTRS lasers.
Polarizable capacitance versus voltage characteristics for metal, oxide, and silicon capacitors passivated by various oxide glasses
Authors: Kobayashi Keiji
Published: July 2002

It was found experimentally that polarizable capacitance versus voltage (C-V) characteristics for metal-oxide-silicon (MOS) capacitors, passivated by various oxide glasses, depend on molar polarizability for passivation glasses. Experimental data showed C-V curve shifts toward higher voltage were evidently caused by polarizable ions in glasses. The possibility for making a material choice in semiconductor device passivation was discussed, using the Poisson equation for the glass-passivated MOS capacitors.
Detection of pulsed ultrasound on nonspecular surfaces by optical holography
Authors: Aharoni A. , Tur M. , Jassby K. M.
Published: July 2002

A real-time holographic technique is described for the detection of ultrasound pulses on unpolished surfaces of common engineering materials. Results obtained on a rough aluminum surface offer a detection resolution limit of 0.1 Å.
Evidence of electron induced interfacial defects in electron-gun-deposited insulator InP structures
Authors: Choujaa A. , Kumar S. N. , Blanchet R. , Viktorovitch P.
Published: July 2002

Using the photoluminescence and capacitance-voltage measurements, it has been shown that low-energy electron beam evaporation of Al2O3 on n-type InP induces defects in the interfacial region of the InP-Al2O3 structure. These defects seem to be located as fixed charge traps in the insulator as well as confined within a few hundreds of angstroms of the InP in the interfacial region. By introducing a metallic grid in the path of the evaporating dielectic flux, the substrate was effectively protected from the electron bombardment which resulted in a major improvement of the final metal-insulator-semiconductor device characteristics.
Effect of slow cooling rates on the superconducting characteristics of YBa2Cu3O7−x
Authors: Gopalakrishnan I. K. , Yakhmi J. V. , Vaidya M. A. , Iyer R. M.
Published: July 2002

We describe an oxygen annealing procedure to obtain bulk YBa2Cu3O7−x samples with zero electrical resistance states at 105 K, a narrow transition width of ∼1 K, and Jc values in excess of 200 A cm−2 at 77 K. It is suggested that enhanced superconducting characteristics result from incorporating very slow cooling rates (0.1 K/min) during oxygen annealing which possibly maximizes the occupancy of 0, 1/2, 0 oxygen sites and leads to a near-perfect ordering of vacancies at 1/2, 0, 0 sites in the orthorhombic unit cell of YBa2Cu3O7−x.
Bistability in two-mode semiconductor lasers via gain saturation
Authors: Tang C. L. , Schremer A. , Fujita T.
Published: July 2002

The conditions required to achieve bistability in two-mode semiconductor lasers via the nonlinearity associated with gain saturation are discussed. The laser can be switched between the bistable states through coherent or incoherent optical control. Wavelength bistability in such a laser is demonstrated experimentally.
High power, high efficient neodymium:yttrium aluminum garnet laser end pumped by a laser diode array
Authors: Berger Josef , Welch David F. , Scifres Don R. , Streifer William , Cross Peter S.
Published: July 2002

We report the highest electrical to optical conversion efficiency, 10.8%, at 415 mW cw, 1.06 μm, from a neodymium:yttrium aluminum garnet end pumped by a monolithic, 200-μm-wide laser diode array. The highest cw output powers up to 465 mW are achieved. The beam profile is TEM00 at all power levels.
High-efficiency Al0.3Ga0.7As solar cells grown by molecular beam epitaxy
Authors: Amano Chikara , Sugiura Hideo , Ando Koshi , Yamaguchi Masafumi , Saletes Anne
Published: July 2002

This letter reports the growth of high-efficiency Al0.3Ga0.7As solar cells by molecular beam epitaxy. As the growth temperature increases from 650 to 750 °C, the concentration of midgap electron traps in the active layers decreases from 4×1015 to less than 3×1013 cm−3 and the hole diffusion length in the layers improves from 2.0 to 2.6 μm. For cells grown at 750 °C, an efficiency of 14.6% (AM1.5, 100 mW/cm2 for an active area) is obtained.
Narrow linewidth 1.5 μm semiconductor laser with a resonant optical reflector
Authors: Olsson N. A. , Henry C. H. , Kazarinov R. F. , Lee H. J. , Johnson B. H. , Orlowsky K. J.
Published: July 2002

A compact narrow linewidth semiconductor laser is described. An emission linewidth of 135 kHz at 5 mW of output power is obtained from a 1.5-μm semiconductor laser butt coupled to an external resonant optical reflector (ROR). The ROR, made with dielectric waveguides on silicon substrate, has transmission and reflection bandwidths as narrow as 0.35 Å.
Nature of the self-limiting effect in the low-pressure chemical vapor deposition of tungsten
Authors: Lifshitz N.
Published: July 2002

We propose a mechanism for the self-limiting effect which occurs in the low-pressure chemical vapor deposition of tungsten. When W is deposited by silicon reduction of tungsten hexafluoride WF6, the deposition suddenly ceases at an early stage. No such effect is observed in the deposition of Mo using analogous chemistry. We believe the self-limiting effect is due to the formation of nonvolatile lower fluorides of tungsten. Our hypothesis is supported by secondary ion mass spectroscopy studies which indicate the presence of fluorine (≊3%) in W films, whereas in Mo films the concentration of fluorine is an order of magnitude lower.
Low-temperature electron transport in a one-side modulation-doped Al0.33Ga0.67As/GaAs/Al0.33Ga0.67As single quantum well structure
Authors: Cho N. M. , Ogale S. B. , Madhukar A.
Published: July 2002

The contributions of the remote ionized impurity scattering, alloy disorder scattering, and scattering due to band-edge discontinuity fluctuation to the low-temperature electron mobility in one-side modulation-doped Al0.33 Ga0.67 As/GaAs/Al0.33Ga0.67As single square quantum well structures are theoretically investigated via the memory function approach. The carrier wave functions and potential distributions used are obtained self-consistently. Dependence of mobility on quantum well width and spacer layer thickness shows that mobilities of the order of 106 cm2 /V s can be achieved in such structures.
Very low threshold planar buried heterostructure InGaAsP/InP laser diodes prepared by three-stage metalorganic chemical vapor deposition
Authors: Ishiguro H. , Kawabata T. , Koike S.
Published: July 2002

Low threshold InGaAsP/InP lasers with planar buried heterostructure were grown entirely by low-pressure metalorganic chemical vapor deposition (MOCVD). The threshold current Ith=10 mA and the differential quantum efficiency ηd =60%, which are comparable to lasers grown by liquid phase epitaxy, were obtained. Most lasers randomly selected from one wafer have threshold currents of Ith=10–25 mA, because of high thickness uniformity of MOCVD growth. Stable fundamental transverse mode operation was also obtained up to an output power of 40 mW/facet, due to controlling the active layer width less than 2 μm.
GaAlAs laser diodes with metalorganic chemical vapor deposition grown ZnSe layer for injection blocking and optical confinement
Authors: Iwano H. , Tsunekawa Y. , Shimada M. , Takamura T. , Seki T. , Ohshima H.
Published: July 2002

A transverse mode stabilized GaAlAs laser diode which includes a ZnSe layer for the waveguide has been developed. The double heterostructure of the GaAlAs laser is formed by low-pressure metalorganic chemical vapor deposition (MOCVD), and a ZnSe layer is grown by adduct-source MOCVD in order to block the injection current and change the real refractive index in the lateral direction. The fundamental transverse mode oscillation of more than 15 mW is obtained with a low threshold current of 28 mA and a high quantum efficiency of 76%. An output power as high as 25 mW is achieved.
Dramatic enhancement in the gain of a GaAs/AlGaAs heterostructure bipolar transistor by surface chemical passivation
Authors: Sandroff C. J. , Nottenburg R. N. , Bischoff J.-C. , Bhat R.
Published: July 2002

With a simple chemical treatment we have passivated nonradiative recombination centers at the periphery of a GaAs/AlGaAs heterostructure bipolar transistor, resulting in a 60-fold increase in the current gain of the device at low collector currents. This large enhancement in gain was achieved by spin coating thin films of Na2S9H2O onto the devices after their fabrication. We briefly discuss the passivation mechanism and the implications for other III-V optoelectronic devices.
Grain growth in arsenic-implanted polycrystalline Si
Authors: Zheng L. R. , Hung L. S. , Mayer J. W.
Published: July 2002

Transmission electron microscopy and Rutherford backscattering were used with polycrystalline Si films implanted at 100 keV with 3×1016 arsenic ions/cm2. During annealing, grain growth occurred first in the implanted portion, then arsenic diffused into the unimplanted poly-Si, and finally grain growth occurred in this region. We believe that arsenic in the implanted region accumulates on grain boundaries during grain growth and subsequently diffuses along grain boundaries into the unimplanted region where grain growth occurs when arsenic can diffuse into the interior of the polycrystalline Si grains.
Anomalous behavior of reverse leakage currents in liquid phase epitaxial HgCdTe photodiodes with 10 MeV electron irradiations
Authors: Stapp R. S. , Feller D. G. , Johnson L. R. , Westmark C. I. , Bajaj J. , Vural K. , Newman P. R. , Blazejewski E. R.
Published: July 2002

We have observed an anomalous behavior of reverse-bias leakage current in Hg1−xCdxTe n+-on-p photodiodes at 77 K as a function of total 10 MeV electron dose. For ZnS/SiO2 passivated planar configurations of photodiodes with 0.25<x<0.5, the leakage current increases superlinearly with increasing total dose greater than 10 krad, saturates at doses between 100 and 200 krad, followed by a dramatic recovery that is sometimes complete to near-preradiation values. For x≂0.2, very little or no recovery is observed. The effects of 60CO gamma irradiation are nearly identical.
Applications of polymer electrets for pollution studies
Authors: Pillai P. K. C. , Khurana Paramdeep
Published: July 2002

The analysis and identification of the pollutants sticking onto the surfaces of electrets prepared from polymethylmethacrylate and polytetrafluoroethylene have been done by scanning electron microscopic, mass spectrometric, and near infrared spectrophotometric techniques. Electret samples exposed to atmospheres containing carbon tetrachloride, xylene, and acetone at their saturation vapor densities, individually, and in mixed atmospheric conditions of carbon tetrachloride and acetone have shown characteristic spectra of these pollutants. Scanning electron microscopic studies of the exposed electret samples have also shown corresponding structural changes. These studies have clearly indicated that electrets are efficient devices for collecting, detecting, and even controlling various types of pollutants.
Sublinear current response in high-efficiency, high-resistivity silicon solar cells: Theory and experiment
Authors: Green Martin A. , Zhao Jianhua , King David L.
Published: July 2002

Improvements in the efficiency of high-resistivity silicon concentrator solar cells with conventional top and rear contacts are reported. These improvements have been obtained despite a substantially sublinear increase in cell short-circuit current with increasing solar concentration. The theory of operation of cells of this type under short circuit is outlined. This theory accurately describes the observed current sublinearity and indicates how it can be eliminated.
Microwave phase stability of directly modulated semiconductor injection lasers
Authors: Lau K. Y.
Published: July 2002

The microwave phase stability of directly modulated high-speed semiconductor lasers was studied. It was shown that optical feedback had a serious effect on microwave phase stability of the modulated signal and must be reduced to below −40 dB for satisfactory phase performance.
Multiple quantum well AlGaAs/GaAs field-effect transistor structures for power applications
Authors: Daembkes Heinrich , Weimann Günter
Published: July 2002

Room-temperature properties of modulation-doped AlGaAs/GaAs field-effect transistor structures with three quantum wells are investigated. For channel spacings of 31 nm and doping levels of about 1.4×1012 cm−2 per barrier layer the individual channels are continuously controllable. For a spacing of 50 nm and doping excess of 2×1012 cm−2 it is shown that the channels remain under velocity saturation but conduction sets on at markedly different gate voltages and so the channels are controlled consecutively. Because of very high current density of up to 500 mA/mm, high transconductance, low source resistance, and output conductance close to zero, the multiple quantum well field-effect transistors are excellent candidates for power devices in the millimeter wave range.
Lattice location of heavily doped As atoms in Si films grown by partially ionized molecular beam epitaxy
Authors: Sugiyama Tetsuya , Itoh Tadatsugu
Published: July 2002

Lattice location of heavily doped As atoms in Si epitaxial films grown by partially ionized molecular beam epitaxy was investigated. It was revealed from carrier concentration measurements and Rutherford backscattering studies that the electrical activity was smaller than the fraction of substitutional As atoms below a substrate temperature of 800 °C. It may be due to the presence of inactive substitutional As atoms located in slightly displaced sites from the lattice. Activation energies of 1.76 and 0.84 eV were obtained for electrical activity and for a fraction of substitutional As atoms, respectively.
Resonance absorption of radiation field by an intense relativistic electron beam in inverse cyclotron maser geometry
Authors: Kawasaki Sunao , Kamada Kei-ichi , Masuzaki Masaru , Takuma Hiroshi
Published: July 2002

Attenuation of the radiation field by an intense, mildly relativistic electron beam moving in a longitudinal magnetic field was studied experimentally in the frequency range of x-band microwaves. Nearly complete absorption of the radiation externally injected along the beam was found to be near a particular value of the axial guide magnetic field. The interaction mechanism is identified as the coupling between the waveguide modes and the beam cyclotron wave propagating backwards. It is concluded that the absorption should be the inverse process of the electron cyclotron maser by a dense relativistic electron beam.
Transverse effects and slowing down in the switching dynamics of induced absorption optical bistability
Authors: Wegener M. , Klingshirn C. , Daunois A. , Bigot J.-Y. , Eddeqaqi N. Cherkaoui , Grun J.-B.
Published: July 2002

The switching dynamics of photothermal-induced absorption optical bistability is studied in CdS. The bistable element being held near its switching threshold is switched by a pulse of an excimer laser, which can be regarded as δ shaped in time with respect to the thermal relaxation time of the sample. The dynamics of the switching process is influenced by the transverse relaxation of the temperature in the sample. Under appropriate conditions either a slowing down or a fast switching is observed.
Electronic structures of strained-layer superlattices (Si)2n/(Si1−xGex)2n (100) with n=1–10
Authors: Shen Dingli , Zhang Kaiming , Xie Xide
Published: July 2002

The empirical tight-binding method is used to calculate the electronic structures of type II strained-layer semiconductor superlattices (Si)2n /(Si1−x Gex )2n (100) with n=1–10. The effects of lattice-constant variation on nearest neighbor interactions have been taken into account. The energy gaps and positions of the conduction-band minimum are obtained for various number of layers. The effects of band folding and band discontinuity on the gap of Si/Ge are analyzed. The 2DEG (two-dimensional electron gas) localized in the Si layer can be explained in terms of the change of ΔEc because of structural strain. The strained band agrees quite well with electroreflectance experiment and other calculations. Studies on interface states are also presented.
Flux penetration profiles in powdered DyBa2Cu3O7
Authors: Daeumling M. , Seuntjens J. , Larbalestier D. C.
Published: July 2002

Flux penetration measurements on powdered specimens of DyBa2Cu3O7 have been performed by using Campbell’s [J. Phys., C 2, 1492 (1969)] method at 4.2 K in magnetic fields up to 7 T. There are three principal results of the measurements. The first is that although there is a small region of surface current, there is indeed a linear bulk flux profile. Thus there is a uniform bulk current flowing through the sample, and the Bean model is appropriate for these compounds. The second result is that the magnetic moment is independent of particle size (over the range 3–12 μm), even when the powders are single crystals. This implies that the currents are subdivided on a scale finer than the grain size. The third result is that Jc (4.2 K, 1–7 T) is very high, reaching 107 A/cm2.
Improvements in corrosion resistance of Tb-Fe thin films
Authors: Kobayashi M. , Maeno Y. , Oishi K. , Kawamura K.
Published: July 2002

Electrochemical corrosion of Tb-Fe films was studied by immersion in a NaCl solution. The corrosion resistance was improved by adding Al, Cr, Hf, Mo, and/or Ti to Tb-Fe. The improvement mechanism, which was studied by transmittance change measuring, microscopic observation, and electron probe microanalysis, is the concentration of the additive metals and formation of passive states by the metals.
Nanosecond laser amplification via degenerate multiwave mixing in silicon
Authors: Khoo I. C. , Normandin R.
Published: July 2002

We present the results of a detailed study of degenerate multiwave mixing mediated nanosecond 1.06 μm pulse amplification in silicon, taking into account higher order diffracted beams, self-phase modulation, pump depletions, intensity-dependent absorption losses, electron-hole plasma attenuation, and other geometrical optical parameters. Excellent agreements between theory and experiment are obtained.
Dye laser frequency locking to the hyperfine structure (3S1/2, F=2−3P1/2, F=2) of sodium D1 line by using polarization spectroscopy
Authors: Kim Jung Bog , Kong Hong Jin , Lee Sang Soo
Published: July 2002

The frequency of a single-mode dye laser is locked to a hyperfine structure of the sodium D1 line without modulating the laser frequency. The frequency locking method uses the error signal from a dispersion curve generated from the polarization spectroscopic output. The servo loop provides a frequency fluctuation less than ±0.3 MHz for more than 30 min.
Real-time technique for the characterization of tunable single-frequency lasers
Authors: Strzelecki E. M. , Cohen D. A. , Corzine S. W. , Karin J. R. , Coldren L. A.
Published: July 2002

An all-fiber Mach–Zehnder interferometric system has been developed for characterization of tunable semiconductor lasers. The tuning rate, range, and linearity of directly frequency-modulated lasers as well as laser linewidth are measured using the same system. To investigate the features of the system and demonstrate its usefulness, 1.3 μm coupled-cavity lasers, tunable with constant amplitude, were characterized. The effects of optical feedback on laser parameters have also been investigated.
Effects of Na2S and (NH4)2S edge passivation treatments on the dark current-voltage characteristics of GaAs p
n diodes
Authors: Carpenter M. S. , Melloch M. R. , Lundstrom M. S. , Tobin S. P.
Published: July 2002

We have investigated the dark current-voltage characteristics of GaAs pn homojunctions whose surfaces have been passivated with Na2S and (NH4)2S chemical treatments. Reductions in 2kT perimeter recombination currents by a factor of 3.2 were obtained for the two treatments. A shunt leakage, observed at low forward bias for the Na2S treated devices, is virtually eliminated with the (NH4)2S treatment. It is also shown that even the high quality, large area (0.25 cm2) pn diodes used in this study are dominated by 2kT edge currents before passivation.
Strain relaxation in low lattice mismatch epitaxy of CdTe/Cd0.97Zn0.03Te (001) by channeling
Authors: Chami A. C. , Ligeon E. , Danielou R. , Fontenille J. , Lentz G. , Magnea N. , Mariette H.
Published: July 2002

A measurement of the misfit dislocation density at the CdTe(001)/Cd0.97Zn0.03Te (001) interface has been obtained by channeling. This method allows an accurate determination of the critical thickness (390 nm) and appears sensitive for misfit dislocation density determination in systems with lattice mismatch as low as Δa/a≂3×10−4. The formation energy of misfit dislocations is estimated to be about 10−8 J/m.