bluuebunny/crossref_metadata_2025 huggingface dataset:
Fully nonlinear oscillatory convection in a rotating layer
Authors: Julien Keith , Knobloch Edgar
Published: July 2002

Two-dimensional overstable convection in a rotating layer is studied for large Taylor numbers. In this regime, the leading order nonlinearity arises from the distortion of the horizontally averaged temperature profile. Fully nonlinear solutions in the form of traveling and standing waves are obtained via an asymptotic expansion in the Taylor number. The formulation leads to a nonlinear eigenvalue problem for the vertical structure and frequency of each solution type and allows the computation of the Nusselt number and frequency as functions of the applied Rayleigh number.
Progress in Favré–Reynolds stress closures for compressible flows
Authors: Adumitroaie V. , Ristorcelli J. R. , Taulbee D. B.
Published: July 2002

A closure for the compressible portion of the pressure-strain covariance is developed. It is shown that, within the context of a pressure-strain closure assumption linear in the Reynolds stresses, an expression for the pressure-dilatation can be used to construct a representation for the pressure-strain. Additional closures for the unclosed terms in the Favré–Reynolds stress equations involving the mean acceleration are also constructed. The closures accommodate compressibility corrections depending on the magnitude of the turbulent Mach number, the mean density gradient, the mean pressure gradient, the mean dilatation, and, of course, the mean velocity gradients. The effects of the compressibility corrections on the Favré–Reynolds stresses are consistent with current DNS results. Using the compressible pressure-strain and mean acceleration closures in the Favré–Reynolds stress equations an algebraic closure for the Favré–Reynolds stresses is constructed. Noteworthy is the fact that, in the absence of mean velocity gradients, the mean density gradient produces Favré–Reynolds stresses in accelerating mean flows. Computations of the mixing layer using the compressible closures developed are described. Favré–Reynolds stress closure and two-equation algebraic models are compared to laboratory data for the mixing layer. Experimental data from diverse laboratories for the Favré–Reynolds stresses appears inconsistent and, as a consequence, comparison of the Reynolds stress predictions to the data is not conclusive. Reductions of the kinetic energy and the spread rate are consistent with the sizable decreases seen in these classes of flows.
Stability of coupled tearing and twisting modes in tokamaks
Authors: Fitzpatrick Richard
Published: July 2002

A dispersion relation is derived for resistive modes of arbitrary parity in a tokamak plasma. At low mode amplitude, tearing and twisting modes which have nonideal magnetohydrodynamical (MHD) behavior at only one rational surface at a time in the plasma are decoupled via sheared rotation and diamagnetic flows. At higher amplitude, more unstable ‘‘compound’’ modes develop which have nonideal behavior simultaneously at many surfaces. Such modes possess tearing parity layers at some of the nonideal surfaces, and twisting parity layers at others, but mixed parity layers are generally disallowed. At low mode number, ‘‘compound’’ modes are likely to have tearing parity layers at all of the nonideal surfaces in a very low-β plasma, but twisting parity layers become more probable as the plasma β is increased. At high mode number, unstable twisting modes which exceed a critical amplitude drive conventional magnetic island chains on alternate rational surfaces, to form an interlocking structure in which the O points and X points of neighboring chains line up.
The magnetic presheath boundary condition with E×B drifts
Authors: Hutchinson I. H.
Published: July 2002

It is demonstrated rigorously that the effects on a one-dimensional, collisionless, magnetic presheath with oblique magnetic field B of a uniform tangential electric field, causing a drift vD=E×B/B2, are equivalent to a transformation to a frame moving tangential to the surface. Therefore, in particular, the Chodura solution with parallel velocity v∥=cs (the sound speed) is transformed into a solution with v∥=cs+vD/tan α, where α is the field angle to the surface.
Another paradox involving the second law of thermodynamics
Authors: Sheehan D. P.
Published: July 2002

Recently a paradox has been posed that appears to challenge the second law of thermodynamics in a plasma blackbody environment [D. P. Sheehan, Phys. Plasmas 2, 1893 (1995)]. In this paper another, related paradox is posed in an unmagnetized Q plasma. Laboratory experiments simulating some necessary conditions for the paradoxical system corroborate theoretical predictions and fail to resolve the paradox in favor of the second law.
Self-consistent stability analysis of ablation fronts with small Froude numbers
Authors: Goncharov V. N. , Betti R. , McCrory R. L. , Verdon C. P.
Published: July 2002

The linear growth rate of the Rayleigh–Taylor instability is calculated for accelerated ablation fronts with small Froude numbers (Fr≪1). The derivation is carried out self-consistently by including the effects of finite thermal conductivity (κ∼Tν) and density gradient scale length (L). It is shown that long-wavelength modes with wave numbers kL0≪1 [L0=νν/(ν+1)ν+1 min(L)] have a growth rate γ≂√ATkg−βkVa, where Va is the ablation velocity, g is the acceleration, AT=1+O[(kL0)1/ν], and 1<β(ν)<2. Short-wavelength modes are stabilized by ablative convection, finite density gradient, and thermal smoothing. The growth rate is γ=√αg/L0+c20k4L20V2a−c0k2L0Va for 1≪kL0≪Fr−1/3, and γ=c1g/(Vak2L20)−c2kVa for the wave numbers near the cutoff kc. The parameters α and c0−2 mainly depend on the power index ν; and the cutoff kc of the unstable spectrum occurs for kcL0∼Fr−1/3≫1. Furthermore, an asymptotic formula reproducing the growth rate at small and large Froude numbers is derived and compared with numerical results.
Effect of rigid toroidal rotation on the stability of a tokamak plasma to tearing modes
Authors: Urquijo G. , Bhattacharyya S. N. , Sen A.
Published: July 2002

The stability of tearing modes in the presence of a rigid toroidal rotation of the plasma is examined. The effect of rotation is modeled by a centrifugal force, which in the cylindrical limit reduces to a uniform force transverse to the plasma column. The influence of this centrifugal force on the outer region matching data Δ, which provides a measure of the energy available for driving the tearing mode, is numerically investigated. It is found that the stability properties of the mode in the presence of the flow are sensitive to the equilibrium density profile.
Effect of technical noise on radiation linewidth in free-running gyrotron oscillators
Authors: Dumbrajs O. , Nusinovich G. S.
Published: July 2002

The theory describing the effect of fluctuations in technical parameters (voltages, beam current, external magnetic fields) on the linewidth of gyrotron radiation is presented. Results of the analysis of free-running gyrotron oscillators are given. The effect of technical fluctuations on the spectrum density of the frequency noise is considered and some estimates are compared with available experimental data.
Flux buildup in field reversed configurations using rotating magnetic fields
Authors: Hoffman Alan L.
Published: July 2002

Rotating magnetic field (RMF) current drive is a very attractive method for both increasing the flux and sustaining the current in field reversed configurations (FRC). It has been demonstrated in low temperature, low field rotamaks, and will now be applied to a new translation, confinement, and sustainment (TCS) experiment attached to the LSX/mod (Large s field-reversed configuration Experiment) facility [Hoffman et al. Fusion Technol. 23, 185 (1993)]. Previous RMF calculations have been concerned primarily with the plasma currents and particle orbits produced in one-dimensional cylinders with the rotating field strength of near equal magnitude to the confining axial field. Both fluid current and particle orbits are calculated here in the more interesting regime appropriate to TCS and reactors where the confinement field far exceeds the rotating field strength. New insight is gained into both the flux buildup requirements for two-dimensional equilibria and into the limits on ion rotation in this high confinement field regime.
A plasma window for transmission of particle beams and radiation from vacuum to atmosphere for various applications
Authors: Hershcovitch Ady
Published: July 2002

Many industrial and scientific processes like ion material modification, electron beam melting, and welding, as well as generation of synchrotron radiation are performed exclusively in vacuum nowadays, since electron guns, ion guns, their extractors, and accelerators must be kept at a reasonably high vacuum. Consequently, there are numerous limitations, among which are low production rates due to required pumping time, limits on the size of target objects, and degradation of particle beams and radiation through foils or differentially pumped sections. A novel apparatus, which utilized a short plasma arc, was successfully used to provide a vacuum-atmosphere interface as an alternative to differential pumping. Successful transmission of charged particle beams from a vacuum through the plasma to atmosphere was accomplished. Included in the article are a theoretical framework, experimental results, and possible applications for this novel interface.
Confinement and structure of electrostatically coupled dust clouds in a direct current plasma–sheath
Authors: Nunomura S. , Ohno N. , Takamura S.
Published: July 2002

Mechanisms for the confinement and the internal structure of an electrostatically coupled dust cloud formed in a dc glow discharge have been investigated from a comparative viewpoint between experimental observations and a simple model. Two kinds of dust clouds with different internal structures are clearly observed, depending on the dispersion of the size distribution of dust particles. The dust cloud can be trapped only in the plasma–sheath boundary area, corresponding to the potential minimum region determined by gravitational and electrostatic forces in the cathode sheath. No dust particles were found deep inside of the sheath, which is consistent with the analysis because the dust particles may be charged positively due to an extreme reduction of the electron density. The internal structure of the electrostatically coupled dust cloud was found to be arranged so that the total potential energy, including the repulsive Coulomb interaction among negative dust particles, may become minimal.
Beam tracing in inhomogeneous anisotropic plasmas
Authors: Pereverzev G. V.
Published: July 2002

An asymptotic method for solving the wave equation in the short-wavelength limit is presented. This method, called beam tracing, takes into account the wave properties, i.e., diffraction and interference. It reduces the full wave equation to a set of ordinary differential equations. In this respect, it differs from all other asymptotic techniques describing diffraction which end up with much more complicated partial differential equations. The resulting system of beam tracing equations is expressed in terms of the same Hamiltonian function as in geometric optics (ray tracing) and, similar to the ray tracing, allows powerful numerical solving algorithms. Thus the beam tracing combines the simplicity of ray tracing with a description of the wave phenomena, which are not included in the ray tracing. The beam tracing technique provides an efficient tool for calculation of wave fields in all problems where the short-wave approximation is applicable such as rf heating, current drive and plasma diagnostics with microwave beams.
Energetic proton production from relativistic laser interaction with high density plasmas
Authors: Krushelnick K. , Clark E. L. , Zepf M. , Davies J. R. , Beg F. N. , Machacek A. , Santala M. I. K. , Tatarakis M. , Watts I. , Norreys P. A. , Dangor A. E.
Published: July 2002

Energetic protons up to 30 MeV have been measured from high intensity laser interactions (⩽5×1019 W/cm2) with solid density plasmas. Up to 1012 protons (> 2 MeV) were observed at the rear of thin aluminum foil targets and measurements of their angular deflection were made. Similar energies were measured from ions produced from the front of the foils. Nuclear activation and track detector measurements suggest that the protons measured at the rear originate from the front surface of the target and are bent by large magnetic fields that exist in the plasma interior, which are likely generated by a laser-produced beam of fast electrons.
Resistance fluctuations in ohmic contacts due to discreteness of dopants
Authors: Boudville W. J. , McGill T. C.
Published: July 2002

The role of fluctuations in the potential due to randomly distributed dopants in the depletion layer of a metal-semiconductor junction is explored. To be specific, the case of n-GaAs is considered. Monte Carlo simulation techniques are used to calculate the potential in the junction. By using the WKB approximation and the two-band model, the small-signal resistance at zero bias is found to be lowered by up to half an order of magnitude from the result assuming a continuum distribution of dopant charge. The resistance is found to vary by an order of magnitude in the plane of the interface resulting in a very nonuniform distribution of the current.
Formation of p-type GaAs layers using Mg+ implantation and capless rapid thermal annealing
Authors: Masum Choudhury A. N. M. , Armiento C. A.
Published: July 2002

The enhanced overpressure proximity technique has been applied to the formation of p-GaAs layers using capless rapid thermal annealing of GaAs implanted with Mg+. Carrier concentrations in excess of 1×1019 cm−3 and excellent hole mobilities have been achieved without a dielectric encapsulant using this annealing method. Implants were performed at 200 or 320 keV with doses of 1×1014 cm−2 or 1×1015 cm−2. Hall measurements have yielded electrical activations as high as 86% and 38% for the low and high dose samples, respectively. Capacitance-voltage measurements on implanted samples indicate that this annealing technique can be used to control the doping profile for use in the fabrication of devices requiring p-n junctions.
ZnSe-ZnS strained-layer superlattice grown by low pressure metalorganic vapor phase epitaxy using methylalkyls
Authors: Yokogawa Toshiya , Ogura Mototsugu , Kajiwara Takao
Published: July 2002

Good quality ZnSe-ZnS strained-layer superlattice (SLS) has been successfully fabricated for the first time by low pressure metalorganic vapor phase epitaxy (MOVPE) using methylalkyls (dimethylzinc, dimethylselenide, and dimethylsulfide). The satellite peak observed by x-ray diffraction measurements and the periodic behavior of the atomic profiles by secondary ion mass spectrometry measurements confirm the formation of the SLS structure. From the photoluminescence measurements, the quantum size effect has been evidenced by the relationship between the ZnSe well-layer thickness and the peak energy shift of the light emission. Our results show that low pressure MOVPE using VI group alkyls can be quite useful for the growth of ZnSe-ZnS SLS.
p-type CdTe epilayers grown by photoassisted molecular beam epitaxy
Authors: Bicknell R. N. , Giles N. C. , Schetzina J. F.
Published: July 2002

We report the first successful substitutional doping of CdTe films with antimony. These p-type epilayers were prepared using a new technique, photoassisted molecular beam epitaxy, in which the substrate is illuminated during the film deposition process. Illumination was found to produce immediate and favorable changes in the electrical properties of the CdTe:Sb films such that highly activated p-type layers resulted. CdTe:Sb films grown under similar conditions, but in the absence of illumination, were found to be insulating.
High-power (cw) in-phase locked ‘‘Y’’ coupled laser arrays
Authors: Welch D. F. , Cross P. S. , Scifres D. R. , Streifer W. , Burnham R. D.
Published: July 2002

Buried heterostructure phased array lasers have been fabricated with ‘‘Y’’ coupling regions to produce in-phase locking. The far-field pattern corresponding to the in-phase emission of ten waveguides is stable under wide variations of operating conditions. Power outputs of up to 200 mW cw and 400 mW pulsed are obtained from a ten-element (50 μm aperture) array. By monitoring the far-field pattern under impulse excitation, the phase locking is shown to evolve in less than 300 ps.
High-resolution photovoltaic position sensing with Ti/Si superlattices
Authors: Willens R. H. , Levine B. F. , Bethea C. G. , Brasen D.
Published: July 2002

A detector to sense the position of a beam of light with a resolution of less than 100 Å has been fabricated with a Ti/Si amorphous superlattice on p-type Si. There are two regions of photovoltaic sensitivity, a low sensitivity region having a response of 1.6 mV/mm and a high sensitivity region having 1.5 mV/μm. This novel detector can sense the light spot position over large lateral dimensions, while the high central sensitivity region would permit servo driving to a null position with a high degree of precision. These characteristics also suggest the use of this device in a variety of other photonic transducers.
Growth of single-crystalline CoSi2 on (111) Si in solid phase epitaxy regime by a nonultrahigh vacuum method
Authors: Cheng H. C. , Wu I. C. , Chen L. J.
Published: July 2002

Single-crystal CoSi2 films have been grown in solid phase epitaxy regime under nonultrahigh vacuum conditions on (111) Si by electron gun deposition of Co thin films followed by rapid thermal annealing in Ar ambient. The single-crystal films were analyzed by transmission electron microscopy to share the (111) Si surface normal but are rotated 180° about that axis with respect to the substrate. The effect of gas ambient was found to be of critical importance in the growth of single-crystal CoSi2 on (111) Si. The present nonultrahigh vacuum treatments to grow single-crystal films on silicon shall greatly facilitate the fabrication of novel classes of high-speed and high-frequency devices employing buried silicide layers.
Spontaneously vitrifying crystalline alloys
Authors: von Allmen M. , Blatter A.
Published: July 2002

Certain metastable metallic crystals spontaneously vitrify upon low-temperature annealing, as recently demonstrated for the high-temperature solid solution of Cr and Ti. The driving force for the vitrification process can be accounted for by the concomitant decrease in lattice strain energy. Predictions for a number of binary phases are made and compared with preliminary experimental results. Spontaneous vitrification is found in the systems Co-Nb, Cr-Ti, Cu-Ti, Fe-Ti, Mn-Ti, and Nb-Ni.
Capacitance spectroscopy of Si-TaSi2 eutectic composite structures
Authors: Levinson M. , Ditchek B. M. , Yacobi B. G.
Published: July 2002

The Si matrix phase of directionally solidified Si-TaSi2 composite structures has been characterized by deep level capacitance transient spectroscopy, using the grown-in metal-semiconductor junctions. The Si is found to be of high quality. No electrically active Ta was detected with a minimum experimental sensitivity of ∼6×1011 cm−3. Some samples exhibited one of two defect states having electron emission activation energies of 0.36 and 0.65 eV. These states appear to be associated with dislocations.
Proposal for three-dimensional internal field mapping by cw electro-optic probing
Authors: Lo Y. H. , Wu M. C. , Zhu Z. H. , Wang S. Y. , Wang S.
Published: July 2002

The cw electro-optic probing technique is for the first time proposed to detect the three-dimensional internal field distribution in linear electro-optic material like GaAs. By changing the incident angles and positions of the probing beam, sufficient information of the electric field distribution is included in the phase retardation of the probing beam. If certain conditions on the probing beam are satisfied, a very simple linear relation between phase retardation and each field component can be found and the whole problem becomes not only mathematically solvable but experimentally feasible. Finally, a three-dimensional computer simulation is undertaken to illustrate the relation between field distribution and detected electro-optic signal.
Quantum confinement and strain effects in ZnSe-ZnSxSe1−x strained-layer superlattices
Authors: Mohammed K. , Olego D. J. , Newbury P. , Cammack D. A. , Dalby R. , Cornelissen H.
Published: July 2002

A photoluminescence study of ZnSe-ZnSxSe1−x strained-layer superlattices with x=0.19 grown by molecular beam epitaxy is presented. We observe clear shifts of the excitons to higher energies as the well widths are reduced. These shifts are interpreted in terms of quantum confinement effects using the envelope function approach and the strain-induced effects using the deformation potential theory. From our analysis we conclude that most of the band offsets between ZnSe-ZnSxSe1−x are taken up by the valence bands.
Si donor neutralization in high-purity GaAs
Authors: Pan N. , Lee B. , Bose S. S. , Kim M. H. , Hughes J. S. , Stillman G. E. , Arai Ken-ichi , Nashimoto Y.
Published: July 2002

The effects of hydrogen plasma exposure on the concentration of donors in high-purity lightly Si-doped molecular beam epitaxial GaAs have been investigated by photothermal ionization spectroscopy, low-temperature photoluminescence, capacitance-voltage, and Hall-effect measurements. Photothermal ionization measurements show that in addition to Si donors S and Ge donors are present in the original high-purity samples. After hydrogenation, the Si donor concentration is significantly reduced with a corresponding increase in mobility. Low-temperature photoluminescence also showed a decrease in the full width at half-maximum of the neutral donor bound exciton line indicating that the total impurity concentration is reduced. These results provide spectroscopic evidence to support the neutralization of Si donors confirming earlier results of the effects of hydrogen plasma exposure in GaAs.
Threshold for argon bubble growth in sputtered amorphous Nb3Ge
Authors: Pruymboom A. , Berghuis P. , Kes P. H. , Zandbergen H. W.
Published: July 2002

We have studied the influence of the bias potential on argon incorporation and bubble formation in sputtered thin films of a-Nb3Ge. Above 100 V bias bubbles are observed directly by transmission electron microscopy and indirectly by abrupt changes in the electronic properties. The influence of the sputter parameters on argon incorporation at 0 V bias is also investigated.
I
n s
i
t
u spectroscopic ellipsometry investigation of the nucleation of microcrystalline silicon
Authors: Drevillon B. , Godet C. , Kumar Satyendra
Published: July 2002

I n situ spectroscopic ellipsometry is used to reveal the structural changes that occur in the initial stages of the growth of microcrystalline silicon (μc-Si) deposited by glow discharge decomposition of a (SiH4,H2) mixture on silica substrates. In a first step, the real time measurements can be described by the following nucleation model: stable nuclei are created, with an average distance between them estimated to be ∼100 Å, followed by the growth of three-dimensional crystalline islands. In a second step an interfacial component composed of amorphous silicon and voids is produced as a consequence of the incomplete coalescence of the crystalline islands.
Single-lobed far-field pattern operation in a phased array with an integrated phase shifter
Authors: Matsumoto M. , Taneya M. , Matsui S. , Yano S. , Hijikata T.
Published: July 2002

A phased array with an integrated phase shifter which can convert a 180° phase mode into an in-phase mode was demonstrated. An Al2O3 facet coating with a different thickness on each array element was performed. It should act as the phase shifter. A stable single-lobed far-field pattern was obtained from the array with the phase shifter.
In-phase coupling between ridge guide lasers by introducing distributed saturable absorption regions in subordinate laser cavities
Authors: Zhu L. D. , Feak G. B. , Ballantyne J. M. , Wagner D. K. , Tihanyi Peter
Published: July 2002

Stable in-phase coupled supermode operation of a ridge waveguide laser array is achieved by introducing distributed saturable absorption regions in subordinate laser cavities. Diffraction-limited single-lobed emission beams were attained up to 27 mW per laser stripe, and threshold current for the array was kept near 10 mA per laser stripe.
Two-step rapid thermal annealing of Si-implanted InP:Fe
Authors: Rao Mulpuri V. , Thompson Phillip E.
Published: July 2002

Rapid thermal annealing has been used to electrically activate Si-implanted InP:Fe. A two-step annealing cycle in which the short (5 s) high-temperature step is followed by a relatively long (25–60 s) 100 °C lower temperature step gave higher activation and carrier mobility than the corresponding short high-temperature or long low-temperature single step annealing cycle. A good surface morphology was achieved by using InP proximity anneal if the maximum annealing temperature is limited to 900 °C for not more than 5 s. The maximum mobilities and activations obtained for 200 keV/5×1013 cm−2 and 150 keV/1×1013 cm−2 Si+ implants were 1740 and 2260 cm2/V s and 88 and 98%, respectively. The position of the peak carrier concentration in the depth profile closely matched that of the Lindhard–Scharff–Schiott prediction.
Resonance Raman scattering in CdTe-ZnTe superlattices
Authors: Menéndez J. , Pinczuk A. , Valladares J. P. , Feldman R. D. , Austin R. F.
Published: July 2002

We present a resonance Raman study of strain and excitons in CdTe-ZnTe superlattices. We obtain the strain configuration of the samples from the strain-induced shifts in the Raman frequencies of confined longitudinal optical phonons. We find that CdTe-ZnTe superlattices are not always in a free-standing configuration, as previously suggested. For individual layer thicknesses of the order of 20–30 Å, our superlattices can be grown lattice matched with their Cd0.1Zn0.9Te substrates. In resonance with the fundamental gap of the superlattice, we observe an enhancement of the Raman cross section not only for CdTe phonons but also (in the samples with the thinnest layers) for phonons confined in ZnTe. This behavior can be understood in terms of a small valence-band offset.
Use of multilayer targets to inject trace elements into laser-produced plasma
Authors: Zigler A. , Kolbe J. , Lee R. W.
Published: July 2002

The use of multilayer target with predrilled holes to inject trace elements into laser-produced plasma is presented. The tracer plasma obtained shows a smaller source size and reduced opacity compared to a plasma target. The preparation and alignment of the proposed target are extremely simple.
Channeling study of structural effects at the Al(111)/Si(111) interface formed by ionized cluster beam deposition
Authors: Jin H.-S. , Yapsir A. S. , Lu T.-M. , Gibson W. M. , Yamada I. , Takagi T.
Published: July 2002

Epitaxial Al(111)/Si(111) films grown by the ionized cluster beam technique have been studied using the high-energy He+ channeling technique. No observable strain has been detected between the Si substrate and the Al layer despite their large (∼25%) lattice mismatch. Displaced Al atoms have been observed in the Al film, which increases with the depth and reaches 30% near the Al/Si interface. A large step increase of dechanneling occurs at the Al/Si interface which might be accounted for by the existence of ‘‘semicoherent’’ interface in which four Al planes are matched to three Si planes.
Resonant tunneling spectroscopy of hot minority electrons injected in gallium arsenide quantum wells
Authors: Capasso Federico , Sen Susanta , Cho Alfred Y. , Hutchinson Albert L.
Published: July 2002

We have employed a new electron spectroscopy technique based on resonant tunneling to study hot minority-electron transport in GaAs quantum wells, following ballistic injection. Direct information on the momentum and energy distribution perpendicular to the heterointerfaces is obtained from the measured resonant tunneling current without requiring derivative techniques. For injection energies of ≂0.2 eV, strong energy and momentum relaxation occurs over distances≲250 Å making impossible the observation of minority-electron ballistic transport in heavily doped (>1018 cm−3) GaAs. The energy distribution is found to be strongly non-Maxwellian; from our data we can infer electron scattering times ≤10−14 which are consistent with recent evidence of strong electron-hole scattering in GaAs quantum wells.
Dependence of the conduction in In0.53Ga0.47As-InP double-barrier tunneling structures on the mesa-etching process
Authors: Vuong T. H. H. , Tsui D. C. , Tsang W. T.
Published: July 2002

Measurements of the current-voltage curves of several In0.53Ga0.47As-InP double-barrier tunneling structures are presented as a function of the etching process used. It is shown that the large nontunneling leakage current previously observed in devices etched with the HBr:H3PO4:K2Cr2O7 solution is caused by conduction at the etched edges of the mesas. This leakage current is significantly reduced by the selective etching of the InGaAs from InP and the peak-to-valley ratio is thereby increased to a maximum value of 3.1 at 4.2 K. The resonance voltage values are symmetrical about zero bias in contrast to results obtained from similar structures of the AlGaAs-GaAs and HgTe-HgCdTe systems, and are in good agreement with theory for the more pronounced of the two resonances observed in these devices.
Effect of rapid thermal annealing for the compositional disordering of Si-implanted AlGaAs/GaAs superlattices
Authors: Kobayashi Junji , Fukunaga Toshiaki , Ishida Koichi , Nakashima Hisao , Flood Jane D. , Bahir Gad , Merz James L.
Published: July 2002

We have investigated the effect of rapid thermal annealing (RTA) for the compositional disordering of Si-implanted AlGaAs/GaAs superlattices (SL) in comparison with that of furnace annealing (FA). By using RTA (970 °C, 10 s), the implantation damage can be eliminated without disordering the SL, while the disordering occurs when FA (850 °C, 30 min) is used. Secondary ion mass spectrometry analyses show that the difference between RTA and FA is due to the extent of Si diffusion into the AlGaAs/GaAs SL.
Tunneling transfer field-effect transistor: A negative transconductance device
Authors: Vinter B. , Tardella A.
Published: July 2002

A double channel field-effect structure is proposed in which the resonant tunneling between states in either part of the channel is employed to control the parallel transport in the channel. Realistic calculations of the conductance in this structure show that one can use it to design a negative transconductance device or as a velocity field transistor with much improved mobility modulation.
Observation of resonant tunneling through GaAs quantum well states confined by AlAs X-point barriers
Authors: Bonnefoi A. R. , McGill T. C. , Burnham R. D. , Anderson G. B.
Published: July 2002

Experimental evidence of resonant tunneling via quasistationary states confined by AlAs X-point potential energy barriers is reported in GaAs/AlAs double barrier heterostructures grown in the [100] direction. The quantum well energy levels giving rise to the negative differential resistances observed in the current-voltage characteristics are identified by calculating the energy-band diagrams of the structures. These resonant energy levels correspond to states confined in the GaAs well not only by the AlAs Γ-point potential energy barriers but also by the AlAs X-point barriers. The quasibound X states are associated with the large longitudinal effective mass in AlAs corresponding to the direction perpendicular to the heterojunction interfaces.
Multikilowatt compact axial flow CO2 laser
Authors: Harry J. E. , Evans D. R.
Published: July 2002

A high power, compact axial flow CO2 laser is described with a power output of 3.5 kW and a discharge length of 0.6 m using an unfolded cavity. The high power per unit length is achieved by the use of multiple electrodes with gas injection through porous anodes. Discharge currents of more than 2 A and cavity diameters up to 150 mm have been used with 12 anodes without the glow to arc transition occurring. An electrical to optical conversion efficiency of 23% has been achieved. The results indicate the effect of the current density and degree of turbulence in the transition regions of the discharges adjacent to the anodes in offsetting the glow to arc transition.
Highly stable indium alloyed TbFe amorphous films for magneto-optic memory
Authors: Iijima Tetsuo
Published: July 2002

Indium alloyed TbFe amorphous films for use as a magneto-optic memory are proposed and studied. These TbFeIn films show strong resistance to corrosion and oxidation. Indium is effective in suppressing oxygen diffusion into the films. An oxygen diffusion coefficient of 5×10−25 m2/s is calculated for TbFeIn films incubated at room temperature. Activation energy is 1.3 eV. This value is over 1.5 times larger than that of TbFe films, where the value is obtained with ellipsometry measurements by R. Allen and G. A. N. Connell [J. Appl. Phys. 53, 2353 (1982)].
Relaxation of stresses in CdTe layers grown by molecular beam epitaxy
Authors: Fontaine C. , Gailliard J. P. , Magli S. , Million A. , Piaguet J.
Published: July 2002

X-ray diffraction has been used to study CdTe layers grown by molecular beam epitaxy on Cd0.96Zn0.04Te or InSb substrates with either (111) or (001) orientation. The layers are elastically strained up to a critical thickness, above which misfit dislocations are generated. Our experimental determinations of the critical thickness and the relaxation of the stress while increasing the layer thickness are different from predictions of the existing models. We present a discussion of relaxation based on the determination of the minimum energy state of the layer for a given thickness. We show that above the critical thickness, the layer relaxes so that the product of the stress by the thickness remains constant. This constant has been experimentally determined for both (111) and (001) orientation.
Mechanism of compensation in heavily silicon-doped gallium arsenide grown by molecular beam epitaxy
Authors: Maguire J. , Murray R. , Newman R. C. , Beall R. B. , Harris J. J.
Published: July 2002

Silicon-doped GaAs grown by molecular beam epitaxy has been characterized by Hall measurements, infrared local vibrational mode (LVM) absorption, secondary ion and laser source mass spectroscopy. Highly doped samples with [Si]∼3×1019 cm−3 show only a low carrier concentration of 8×1017 cm−3. LVM spectroscopy shows that SiGa donors are compensated predominantly by [Si-X] complexes, where X has been assigned previously to a gallium vacancy (VGa). Other compensating impurities are not present in the layers at significant concentrations.
Resonant Zener tunneling of electrons between valence-band and conduction-band quantum wells
Authors: Allam Jeremy , Beltram Fabio , Capasso Federico , Cho Alfred Y.
Published: July 2002

We report the observation of resonant tunneling effects at high applied fields in the reverse-bias current-voltage characteristic of multiple quantum well p-i-n diodes. The Al0.48In0.52As/Ga0.47In0.53As structure (grown by molecular beam epitaxy with 35 periods of 139 Å barriers and 139 Å wells) shows two steps in the dark current. These are associated with Zener tunneling of electrons across the band gap from the lowest subband in the valence-band quantum wells to the first and second subbands of adjacent conduction-band wells.
Optical time-of-flight measurement of carrier diffusion and trapping in an InGaAs/InP heterostructure
Authors: Westland D. J. , Mihailovic D. , Ryan J. F. , Scott M. D.
Published: July 2002

We have measured the diffusion and trapping of photoexcited hot carriers in an InGaAs/InP heterostructure using an optical time-of-fight technique with picosecond time resolution. The ambipolar diffusivity is found to decrease by an order of magnitude between 4 K and room temperature, and the efficiency of trapping of carriers into the well increases rapidly in the same temperature range. A mean trapping time of 4 ps is measured for a 50 Å well.
Temperature-dependent damage production in ion-implanted strained-layer superlattices
Authors: Myers D. R. , Arnold G. W. , Dawson L. R. , Biefeld R. M. , Hills C. R. , Doyle B. L.
Published: July 2002

We have characterized damage production in both (InGa)As/GaAs and Ga(AsP)/GaP strained-layer superlattices (SLS’s) for fluences sufficient to induce compositional disordering at three different implant temperatures. Dramatically different implant temperatures are required to produce similar defect distributions between the two SLS systems. Implants at lower temperatures [80 K for the (InGa)As/GaAs system, 300 K and below for the Ga(AsP)/GaP system] exhibit amorphous zones at depths consistent with the predictions of ion range codes; while implants at elevated temperatures [25 °C in (InGa)As/GaAs, 400 °C in the Ga(AsP)/GaP system] exhibit greatly reduced damage levels characterized mainly by extended defects.
Fracture toughness measurements of YBa2Cu3Ox single crystals
Authors: Cook Robert F. , Dinger Timothy R. , Clarke David R.
Published: July 2002

We report fracture toughness measurements on single crystals of YBa2Cu3Ox, the phase responsible for superconductivity above liquid-nitrogen temperatures. Indentation crack length measurements on the (010) orthorhombic crystal growth faces revealed the (100) and (001) planes as preferred fracture planes. The toughness of these planes is Kc=1.1±0.3 MPa m1/2, and the hardness H=8.7±2.4 GPa. The observed growth of both radial and lateral cracks in ambient air suggests that these crystals are susceptible to moisture-enhanced nonequilibrium crack propagation.
Highly nondegenerate four-wave mixing in semiconductor lasers due to spectral hole burning
Authors: Agrawal Govind P.
Published: July 2002

Spectral hole burning in semiconductor lasers manifests as a nonlinear suppression of the mode gain by a few percent. In the presence of a probe wave, the same mechanism can lead to highly nondegenerate four-wave mixing (NDFWM) by creating the dynamic gain and index gratings at the beat frequency of the pump and probe waves. Since the grating efficiency is governed by the intraband relaxation time (typically <1 ps), significant NDFWM can occur even for a pump-probe detuning ∼100 GHz. We present the results for the conjugate reflectivity and the probe transmittivity when an InGaAsP laser is used as a traveling-wave amplifier.
Ion-beam-induced epitaxy and interfacial segregation of Au in amorphous silicon
Authors: Elliman R. G. , Jacobson D. C. , Linnros J. , Poate J. M.
Published: July 2002

The segregation and diffusion of Au are examined during ion-beam-induced solid phase epitaxial crystallization of Au-implanted amorphous silicon layers. Epitaxy was induced at temperatures as low as 220 °C by irradiation with 1.5 MeV Ar ions. At these temperatures Au is segregated to form a narrow layer at the moving crystal/amorphous interface. The size of the segregated layer depends on the velocity of the interface compared to the Au diffusivity in amorphous Si. The growth rate for ion-beam-induced epitaxy is found to be independent of Au concentration and near-complete epitaxial crystallization of the amorphous layers can be achieved, even for Au concentrations ∼2 at. %.
Two distinct interface trap peaks in radiation-damaged metal/SiO2/Si structures
Authors: da Silva Eronides F. , Nishioka Yasushiro , Ma T.-P.
Published: July 2002

Two distinct peaks in the interface trap distribution on (100) Si, one above and the other below the Si midgap energy, have been observed in a wide selection of metal/SiO2/Si capacitors after they are exposed to ionizing radiation. The samples tested cover a wide range of gate electrode materials (Al, polycrystalline Si, Mo, and TiSi2) and oxidation environments [dry O2, steam, dry O2+TCA (trichloroethane), and dry O2+HCl at various temperatures]. Among all the samples tested, the peak above midgap (∼Ev+0.75 eV) appeared immediately after irradiation, and for most samples the peak below midgap (∼Ev+0.35 eV) only appeared at long times (up to a few months) after irradiation. The evolution of the two peaks as a function of time has been found to depend strongly on the gate electrode, oxidation environment, sample storage temperature, and gate bias during storage. Detailed studies of these two peaks should lead to a better understanding of the defect formation process at the SiO2/Si interface.
Lasing wavelength of an asymmetric double quantum well laser diode
Authors: Tokuda Yasunori , Matsui Teruhito , Fujiwara Kenzo , Tsukada Noriaki , Nakayama Takashi
Published: July 2002

It is demonstrated that in an asymmetric coupled GaAs double quantum well structure, we are able to choose a lasing wavelength out of at least four quantum state transitions by cavity loss control. The assignments of the observed lasing transitions are determined by photoluminescence measurement for the laser wafer, as well as by calculations using an isolated potential well model. We propose that one can realize wide-range wavelength tuning and multistep wavelength switching functions by modifying the two-dimensional density of states.
Possibility of optical bistability due to resonant intersubband excitation in stepped modulation-doped quantum wells
Authors: Newson D. J. , Kurobe A.
Published: July 2002

We propose the use of a novel doped, stepped semiconductor quantum well structure as an optical nonlinear element. The large nonlinearity results from the change of many-body effects on resonant excitation of electrons from the ground to the first excited subband. Self-consistent calculations showed that the intersubband energy separation can be increased by up to 7 meV on intense illumination, compared to 1 meV for a conventional, square quantum well. We estimate that optical switching at powers below 1 W are feasible in an optimized structure, with switching times of about 1 ps.
One-dimensional GaAs wires fabricated by focused ion beam implantation
Authors: Hiramoto Toshiro , Hirakawa Kazuhiko , Iye Yasuhiro , Ikoma Toshiaki
Published: July 2002

We have developed a novel, simple technique for fabrication of one-dimensional GaAs wires by utilizing only a focused ion beam (FIB) technology. The FIB implantation forms high-resistive regions which confine an n+ channel into a very narrow conductive wire. The minimum width of the GaAs wire fabricated by the present technology is 20 nm. Magnetoconductance of the wires shows a behavior of one-dimensional localization and a conductance fluctuation due to a quantum interference effect. This is the first observation of the quantum interference effect in GaAs wires fabricated only by FIB implantation. Measured magnetoconductances are compared with the existing theories.
Self Bragg matched beam steering using the double color pumped photorefractive oscillator
Authors: Fischer Baruch , Sternklar Shmuel
Published: July 2002

A new method for steering light beams with automatic (self-aligning) Bragg matching is presented. This device enables, in principle, a large beam deflection range which is not limited by the Bragg condition. It is based on a double color pumped photorefractive oscillator. Two input beams of different colors induce and pump a dynamic four-wave mixing process in a photorefractive BaTiO3 crystal in which two other beams and a common grating are self-generated. Steering is achieved by wavelength tuning of one of the pump beams. A deflection range of about 1.7°, with an efficiency ranging from 50 to 90%, is measured for a wavelength difference Δλ of ±30 nm for the two pumps (using argon ion laser lines). A deflection of 4.7° with an efficiency of 10% is seen for Δλ=144.8 nm (corresponding to pumps at 488 and 632.8 nm).
Efficient operation of a chemically pumped oxygen iodine laser utilizing dilute hydrogen peroxide
Authors: Yoshida S. , Fujii H. , Sawano T. , Endo M. , Fujioka T.
Published: July 2002

A chemically pumped oxygen iodine laser system has been operated employing 35 wt. % H2O2 rather than commonly used 90 wt. % H2O2. Laser power as high as 40 W has been extracted. The maimum overall efficiency of 20.7%, which is almost 25% higher than the previously reported best data, has been achieved.
Optically tuned, all-semiconductor optical interference filter
Authors: Gourley P. L. , Biefeld R. M. , Johnson P. B.
Published: July 2002

Optical tuning of an epitaxial, all-semiconductor optical interference filter is reported. The filter is a high reflector composed of alternating, strained layers of GaP (360 Å) and GaAs0.2P0.8 (360 Å) grown by metalorganic chemical vapor deposition. With low optical power, these reflectors exhibit reflectances up to 90% at 510 nm over a 10-nm bandwidth. With absorbed optical pulses of energy density 3 mJ/cm2, this high-reflectance zone can be blue shifted by 20 Å. As a result, very large changes in reflectance can be produced. The effect is interpreted as a plasma-induced refractive index depression in a semiconductor superlattice. Furthermore, the layer strain enhances the optically induced index change of the high reflector compared to that in bulk materials.
Spectral evolution in an electron beam pumped XeF laser
Authors: Harris D. G. , Burde D. H. , Malins R. J. , Tillotson J. H.
Published: July 2002

A spectral sweep in the 353-nm band of an electron beam pumped XeF laser has been investigated. The time-integrated lasing spectra broaden as the pulse length, electron beam pump rate, and intracavity flux are increased. Several possible explanations are discussed.
XeF laser at a high electron beam pump rate
Authors: Mandl A. , Litzenberger L.
Published: July 2002

A significant increase of the XeF laser efficiency has been observed in an electron beam pumped device. Mixtures of NF3, Xe, and Ne at 300 K and a density of 3 amagat were pumped at a rate of 300 kW/cm3 with a 500-ns pulse. This deposited 150 J/l into the laser cavity. Measurements were made for various mixtures and output couplings. The highest intrinsic laser efficiency (defined as the ratio of laser output energy to e-beam energy deposited into the gas) observed was 4.7%.
X-ray study of a ferroelectric twin in poly(vinylidene fluoride)
Authors: Takahashi N.
Published: July 2002

A possibility for ferroelectric twinning of 60° domains existing in the phase-I crystallite of poly(vinylidene fluoride) has been examined by the use of an x-ray diffraction method. Interdomain interference causes anomalous splitting of the calculated diffraction peaks. Anomalous changes in the profiles are observed for the crystallites in a film under electric fields up to 120 MV/m, and can be explained in terms of the twin structure.
Thermal donor formation in silicon: A new kinetic model based on self-interstitial aggregation
Authors: Mathiot D.
Published: July 2002

A new kinetic model is presented for the formation of thermal donors near 450 °C in oxygen-rich silicon. This model is based on the aggregation of the self-interstitials generated by the early stage of oxygen precipitation. Good agreement is obtained with published experimental kinetics, and the model is able to account for several other observations, such as the influence of carbon.
Structural and photoluminescent properties of GaInAs quantum wells with InP barriers grown by organometallic vapor phase epitaxy
Authors: Carey K. W. , Hull R. , Fouquet J. E. , Kellert F. G. , Trott G. R.
Published: July 2002

Ga0.47In.53As/InP quantum well structures grown by atmospheric pressure organometallic vapor phase epitaxy are characterized by high-resolution transmission electron microscopy (HRTEM) and 4 K photoluminescence (PL). Microdensitometer analysis of the HRTEM images shows GaInAs wells as narrow as 10 Å with slightly asymmetric interface widths. The InP to GaInAs transitions occur within 200 monolayers while the GaInAs to InP transitions are 3–5 monolayers wide, probably due to As carryover. 4 K PL shows half-widths below 9 meV for quantization shifts up to 140 meV. PL peak shifts as large as 395 meV for the narrowest quantum wells are observed compared to bulk Ga0.47In0.53As.