bluuebunny/crossref_metadata_2025 huggingface dataset:
Anisotropic elasticity solutions for dislocation barriers at coherent twin boundaries in face-centered cubic metals
Authors: Blachon Dominique L. A. , Hartley Craig S.
Published: February 2003

The effect of elastic anisotropy on the stability of extended dislocation barriers at coherent twin boundaries in face-centered cubic metals has been determined. It is shown that the nature of the symmetry associated with the twin boundary is such that no image forces are developed on dislocations lying parallel to the boundary. It is found that the results are in qualitative agreement with earlier isotropic results.
Phase transitions in barium and bismuth under high pressure
Authors: Yoneda A. , Endo S.
Published: February 2003

The controversial phase transitions in barium and bismuth were studied with a manganin coil sensor. The transition in barium proposed at 80 kbars by Bastide etal. was confirmed at 95 kbars. For bismuth, the transition reported first by Bridgman around 45 kbars was confirmed at 40 kbars, but that around 65 kbars could not be detected. To make up the P-T diagram of barium, the confirmed transition and the so-called high-Ba transition were traced at elevated temperatures by the resistance anomaly of barium, and the melting points above 90 kbars were determined with a manganin ribbon sensor. The mechanism of the manganin sensor is discussed with regard to the volume change associated with a transition.
A model for diffusion of arsenic in degenerate silicon
Authors: Shrivastava Ritu , Marshak Alan H.
Published: February 2003

A model for arsenic diffusion in silicon is proposed based on Hu’s theory which takes into account the degeneracy of the mobile carriers, partial ionization of the impurity atoms, single acceptor level vacancies, and the internal electric field. For a constant source diffusion, the transport equation describing the As+-V− system can be separated. An efficient computer program based on a quasilinearization technique is written to obtain the impurity profiles from the processing data. It is shown that partial ionization significantly affects the diffusion process at high concentrations. The use of classical statistics yields an underestimate of the impurity concentration values. The computed profiles strongly depend on the values used for the intrinsic diffusion coefficient and vacancy energy. There is very good agreement between the vacancy-aided model and experimental results reported by Chiu and Ghosh using neutron activation analysis.
Galvanomagnetic properties of annealed InSb single crystals
Authors: Nagabhooshanam M. , Babu V. Hari
Published: February 2003

p-type InSb crystals have been obtained by annealing n-type InSb crystals at 350 °C in vacuum (10−5 Torr) for different durations. The dc Hall effect and conductivity studies have shown that the inversion temperature increases with increase in annealing time, whereas the Hall mobility decreases. The ratio of electron to hole mobility b is calculated from the log RH -vs-1/T curve and also from electron and hole concentrations. The ratio b is also calculated theoretically from electron and hole mobilities. The value b obtained from experiments is found to differ from the b calculated theoretically. This discrepancy has been attributed to the scattering of charge carriers by dislocations produced during annealing. Using the Dexter and Seitz mechanism [Phy. Rev. 86, 964 (1952)] the dislocation densities have been estimated in the annealed samples.
Room-temperature conductivity and the band structure of n-Ga1−xAlxAs
Authors: Temkin H. , Keramidas V. G.
Published: February 2003

Conductivity measurements on epitaxially grown silicon-doped n-Ga1−xAlxAs as a function of Al concentration x, for 0.10⩽x⩽0.65 are presented. Simple two-probe measurements were made possible by the development of a low-resistance Ohmic contact, with the contact resistance independent of x. A calculated three band (Γ, X, and L) conductivity of Ga1−xAlxAs as a function of x shows good agreement with the experimental results. The transition from a direct band-gap semiconductor to an indirect one occurs at xc =0.45 at 300 °K. The device performance, however, begins to be affected at much lower Al concentration.
Measurement of gain and absorption spectra in AlGaAs buried heterostructure lasers
Authors: Henry C. H. , Logan R. A. , Merritt F. R.
Published: February 2003

A new method for measuring absorption and gain spectra of lasers is presented. These spectra are deduced from measurements of spontaneous emission spectra at different laser currents supplemented by measurements of the laser line energy and the differential quantum efficiency. The spontaneous emission emerged from the side of the laser after traveling through a transparent cladding layer. At each current, the bias energy eV is determined. A simple theoretical model is used to convert eV to minority carrier density. The method is based on the application of general relations between the rates of spontaneous emission, stimulated emission, and optical absorption. A new general proof of these relations is presented. The gain versus carrier density relation at the laser line energy is measured for four samples having different active layer doping or Al composition. Gain increased superlinearly with carrier density in undoped and n-type samples and increased slightly sublinearly in a p-type sample. The losses at low carrier densities ranged from 100–200 cm−1. For one undoped sample, the changes in the absorption edge caused by the electron and hole densities increasing from 5×1016 to 1.1×1018 cm−3 were deduced by comparing the measured changes with a model calculation. It was found that the exponential broadening increased 20%, that the energy gap decreased 12–16 meV, and that the strength of optical absorption at low energies decreased by about a factor of 1.4.
Theory of defect-induced pulsations in semiconductor injection lasers
Authors: Henry C. H.
Published: February 2003

The size of defects necessary to cause pulsations, in otherwise ideal semiconductor injection lasers, is calculated for two defect models: a nonradiative region and a number of nonradiative surfaces. The point of instability for pulsations is found by solving the linearized rate equations describing small oscillations about the steady state and determining the length of the nonradiative region or the number of surfaces for which damped oscillations change to growing oscillations. The validity of this method is verified by computer calculations of large amplitude pulsations in a particular case. An oscillating light intensity induces an oscillating component of gain. Part of the oscillating gain is in phase with the light intensity in the absorbing region, causing growth, and is directly out of phase in the amplifying region, causing damping. The laser pulsates if the in-phase gain in the absorbing region is dominant. This component of gain is enhanced by a short nonradiative lifetime. This mechanism applies over a broad range of parameters with optimum values of about 0.06–0.10 nsec for the nonradiative lifetime and 1–2 mW for the laser power. The requirement for pulsations found in earlier studies of divided contact lasers, that the gain versus carrier density relation g(n) be nonlinear with dg/dn greater in the absorbing region than in the amplifying region, is not required for pulsations if the relaxation time is short. However, increased dg/dn in the absorbing region greatly enhances the ability of a small defect to produce pulsations. For g(n) increasing linearity with n, a defect at least 11 μ long is needed to cause pulsations, whereas for dg/dn twice as great in the absorbing region as in the amplifying region, a defect only 4 μ long can cause pulsations. The possibility of increased dg/dn and absorption in the nonradiative region due to local heating is discussed. For optimum lifetime and surface recombination velocity, each nonradiative surface is approximately equivalent to a nonradiative region about 1/2 μ in length. Accordingly, two nonradiative cleaved surfaces are insufficient to be the sole cause of pulsations.
Studies of (GaAl)As injection lasers operating with an optical fiber resonator
Authors: Figueroa Luis , Lau Kam Y. , Yen Huan W. , Yariv Amnon
Published: February 2003

The characteristics of an optical fiber external resonator in conjunction with (GaAl)As stripe geometry lasers are described. We have observed a 6–10% reduction in the threshold current and have obtained 150 ps pulses at gigahertz repetition rates. The fiber resonator has also been used to quench self-pulsations in a (GaAl)As injection laser. In order to explain many of our results we have used a model that uses the conventional semiconductor rate equations modified by the addition of saturable electron traps and the effects of the external cavity. Our results predict many of the self-locking effects observed in injection lasers operating in an external cavity. Furthermore, the degree of self-locking will be a strong function of the external cavity length and the density of saturable absorbers.
Coherent cancellation of background in four-wave mixing spectroscopy
Authors: Yacoby Y. , Fitzgibbon R. , Lax B.
Published: February 2003

A technique for the cancellation of background contribution to four-wave mixing is proposed and demonstrated. The technique consists of the destructive interference of the background parametric waves produced by two samples that differ only in one or more properties of interest. This cancellation technique is applicable even when the background itself contains resonances in the frequency range of interest. Cancellation factors of 500 and higher were achieved using a double cell for liquid specimens. This technique is demonstrated using phenol water solution. It is shown that with full background the 1004-cm−1 phenol line can hardly be observed at 1% phenol concentration whereas the same line is easily observed when the background is cancelled even at 0.1% phenol concentration. This technique can also be used to extract the real and imaginary parts of the nonlinear susceptibility without the use of the Kramers-Kronig relations. We have performed this calculation in the case of 5% phenol solution in water.
A backscattering formula for acoustic transducers
Authors: Atalar Abdullah
Published: February 2003

A backscattering formula for a single transducer geometry is derived. It expresses the output voltage of the transducer in terms of the angular spectra of scalar and vector acoustic potentials on a plane. The formulation is suitable for acoustic problems involving wide angular spectrum beams. The derived formula gives a simple expression for the problem of a circular transducer facing a plane reflector. The output voltage of a transducer receiving the backscattered waves from an arbitrary size spherical flaw is also presented.
An analysis of transverse modes in acoustic surface wave resonators
Authors: Sinha B. K. , Tiersten H. F.
Published: February 2003

A system of approximate surface wave equations employed in an earlier treatment of the reflection of straight-crested surface waves by arrays of reflecting strips is extended to the case of variable-crested surface waves. Although the basic straight-crested surface wave velocities are determined as in the previous treatment, in the present case a reduction in straight-crested surface wave velocity in the unplated region due to the adjacent plated regions, which is essential for the existence of the guided transverse modes, is determined by means of a perturbation procedure. The attendant depth dependence for each region is employed in the variational principle as in the earlier treatment, but now the variable cresting relation for the isotropic substrate is incorporated in the description. The resulting equations are applied in the determination of both the transverse modes in each region and the transmission line representation of each mode. The transverse wave numbers in a given mode are taken to be the same in the plated and unplated regions in order that the interior edge conditions be satisfied pointwise. The system of parallel transmission lines is applied in the analysis of the reflection of variable-crested surface waves by uniformly spaced arrays. The response to a rectangular input of a particular reflecting array consisting of aluminum reflecting strips on ST-cut quartz is calculated and compared with measurements.
A general analytic technique for nonlinear dynamic transport processes during laser annealing
Authors: Kim Dae M. , Shah Rajiv R. , Crosthwait D. Lloyd
Published: February 2003

We present an approximate analytic technique capable of describing the dynamics of nonlinear heat and mass diffusion. The technique is based on using adiabatic approximation in the Green’s-function formulation and is illustrated for the case of heat transport during pulsed and cw laser annealing of Si. In particular, the heating efficiency is discussed explicitly as a function of pulse intensity for a fixed pulse energy.
Coupling of electron-beam energy to an expanding thick-shelled target
Authors: Sweeney M. A.
Published: February 2003

The effect of spherical expansion on energy coupling to the pusher region of an ablatively driven net-energy-gain electron-beam target is discussed. The effect is evaluated numerically by using the density distribution in the coronal layers, obtained from hydrodynamic calculations, in a spherical-geometry Monte Carlo transport code. Much of the incident energy is absorbed in the low-density blowoff or is backscattered. Net energy gain targets will therefore require higher powers, and the optimum shell thickness may be less than predicted by previous calculations, which used deposition profiles for unexpanded material. Nevertheless, energy requirements are slightly lowered due to a decrease in bremsstrahlung heating of the pusher with target expansion.
Temperature-fluctuation noise of thin films supported by a substrate
Authors: van Vliet K. M. , van der Ziel A. , Schmidt R. R.
Published: February 2003

A computation is given of the fluctuations in average temperature of an isolated thin film on a substrate, the noise being due to two causes: (i) fluctuations in blackbody radiation absorbed and emitted by the front surface; (ii) thermal diffusion in the sample and the substrate. The surface source results in a large 1/f range, the level of which decreases with increasing heat conductivity of the substrate; the noise goes over into a 1/f2 spectrum at high frequencies. The noise due to the volume source results in a 1/f1/2 spectrum, going over into a 1/f3/2 spectrum at higher frequencies; the noise also decreases with increasing heat conductivity of the substrate. The integrated total noise is of the order kT20/C . Under most circumstances the spectrum due to the volume source dominates.
Enhanced neutral-beam divergence due to imperfect magnetic shielding
Authors: Conrad J. R.
Published: February 2003

A previous calculation of neutral-beam divergence due to imperfect magnetic shielding of the gas-cell neutralizer is generalized to include the case in which the intrinsic magnetic-field–free divergence of the beam is finite.
Simulation of the influence of bonding materials on electromagnetic wave propagation in laminated composites
Authors: Nayfeh Adnan H.
Published: February 2003

Two model analyses are constructed in order to determine the influence of bonding materials on the propagation of electromagnetic waves in otherwise bilaminated composites. The geometric arrangement of the composite with the bond is treated as a special type of a trilaminated composite in which each of its major constituents is sandwiched between two bonding layers. In the first model, a recently developed continuum mixture theory of electromagnetic wave propagation in bilaminated composites is extended to treat the trilaminated composite. Here, details of the propagation process in the major components and also in the bonding layers are derived. In the second model, the entire effect of the bonds is treated as a modifier to interfacial continuity conditions. In this model the details of the propagation process in the bonding material are ignored. It is found that the results of both models correlate well with each other and also with some exact solutions for a rather wide range of frequencies.
Electron emission from depletion layers of silicon p-n junctions
Authors: van Gorkom G. G. P. , Hoeberechts A. M. E.
Published: February 2003

Measurements of the energy distribution of electrons emitted in vacuum by very shallow silicon p-n junctions are described. It has been found that diodes with the junction perpendicular to the surface show a relatively narrow peak and a broad band, while diodes with the junction parallel to the surface only give a narrow peak (half-width 0.50 eV). The broad band is ascribed to electrons emitted from the depletion layer of the junction, and the narrow peak is attributed to electrons emitted from the neutral n layer.
Interfacial layer theory of the Schottky barrier diodes
Authors: Wu Ching-Yuan
Published: February 2003

The interfacial layer theory considering the surface fixed charge and the voltage drop across the interfacial layer is developed for the Schottky barrier diodes fabricated on the n-type semiconductor substrate. It is shown that the positive surface fixed charge will reduce the barrier height and then increases the reverse current; the voltage drop across the interfacial layer will increase the ideality factor of the forward biased I-V characteristic and the voltage dependence of the reverse-biased I-V characteristic, aside from the effects of the image force lowering; the fluctuations of the experimental data deduced from the fabricated Schottky barrier diodes with different fabricating conditions are mainly due to the variations of the interfacial-layer properties such as the interfacial-layer thickness, the interface states, the surface fixed charges.
Dipolar orientation and hysteresis in polyvinylidene fluoride
Authors: Date M. , Furukawa T. , Fukada E.
Published: February 2003

Dielectric hysteresis of stretched polyvinylidene fluoride films under a sinusoidal electric field of a period of 300 sec with an amplitude of 240 MV/m is observed by the aid of a minicomputer. It is found that the coercive field is about 50 MV/m and the remanent polarization is about 65 mC/m2. The dipolar polarization initially present in the sample is determined from the shape of the hysteresis loop for the first cycle. If the poled film is annealed at 100 °C for 1 h, the hysteresis loop becomes distorted for the first cycle, but returns to the normal shape after two or three cycles. The linear relationship between the residual dipolar polarization and the piezoelectric stress constant is determined.
Reflectance modulation by a vibrating circular membrane of piezoresistive semiconductor
Authors: Lal M. N. , Das B. L.
Published: February 2003

In this paper it has been shown that a large reflectance modulation of light may be obtained with the help of a piezoresistive semiconducting circular membrane under forced vibrations due to sound waves. The membrane is fitted to the base of a Helmholtz resonator so that it responds even to weak sound waves incident at the mouth of the resonator. Numerical calculations show that the relative change in reflectivity for Ge as well as GaSb in the infrared region is so large that this method of light intensity modulation may be used fruitfully for communication purposes.
Laser annealing of low-fluence ion-implanted silicon
Authors: Prussin S. , von der Ohe W.
Published: February 2003

Ruby laser pulses of 1.5–2.5 J cm−2 were shown to be effective in dissolving defect nuclei in {100} and {111} silicon surfaces implanted with 1014–1015 B cm−2 and (1–5)×1014 P cm−2. No melting and only partial electrical activation appear to occur. A sequential moderate thermal anneal, 10 min at 1000 °C, results in full electrical activation. A {111} silicon surface, made amorphous by an ion implantation of 5×1014 P cm−2 was electrically activated and completely cleared of defect nuclei without apparent melting by preceding the laser anneal by a two-step thermal anneal (30 min at 550 °C, 10 min at 1000 °C). The mechanism of pulse laser annealing of nonamorphous ion-implanted surfaces is discussed.
Thermionic emission properties of a single-crystal LaB6 cathode
Authors: Futamoto M. , Nakazawa M. , Usami K. , Hosoki S. , Kawabe U.
Published: February 2003

A new type of LaB6 cathode has been developed. It consists of a 〈001〉 oriented LaB6 single-crystal tip and a glassy carbon filament. The influence of gas pressure on the thermionic emission properties are investigated for O2, H2O, CH4, and H2. Evaporation rates and surface composition of the LaB6 cathode are also examined. Thermionic emission current decreased in all gases examined here, depending on cathode temperature and gas pressure. In O2 and H2O gas atmosphere, the cathode surface composition appears to change to La2O3 as gas pressure is increased. The evaporation rate of the LaB6 single crystals is represented by equation V=4×1014 exp [−(570×103/RT)] μm/h, for the temperature range between 1800 and 2200 K.
An improved empirical formula for the electric field near the surface of field emitters
Authors: Gipson G. S.
Published: February 2003

A combination of numerical and analytical techniques is used to develop an improved empirical formula for the electric field near the surface of field emitters. The new relationship is shown to account accurately for the shank variation and the dependence of the field upon polar angle. Also discussed is the suitability of empirical formulas for ion trajectory calculations.
Determination of the proportional contents of ingredients in InxAl1−xP, InxGa1−xP, and AlxGa1−xP by radioactive source x-ray fluoroscopy
Authors: Miller D. , Shreter U. , Weil R. , Maor D. , Rosner B. , Pratt B.
Published: February 2003

Curves are presented for the determination of the proportional contents of ingredients in InxAl1−xP, InxGa1−xP, and AlxGa1−xP from the relative intensity of x-ray fluorescence of In, P, and Al in these materials. The curves apply for the case where fluorescence is induced in the ternary compounds by the 5.9-keV x rays from an 55Fe radioactive source. Each curve has to be calibrated at one point with pure InP or AlP to normalize the system for detector efficiency and for inaccuracies in the cross sections used in the calculations. The accuracy of the results depend on x. Assuming inaccuracies of ±10% in all the coefficients used, the worst deviation in x is ±0.04 at x=0.50. Experimental verification is presented for the case of InxGa1−xP .
An induced back surface field solar cell employing a negative barrier metal-insulator-semiconductor contact
Authors: Tarr N. G. , Pulfrey D. L. , Iles P. A.
Published: February 2003

A simple theory of current flow in negative barrier metal-insulator-semiconductor (MIS) junctions is developed. The properties of negative barrier MIS contacts are found to be closely related to those of positive barrier MIS junctions in which the semiconductor surface is strongly inverted. It is shown that by an appropriate choice of barrier metal work function and insulator thickness it should be possible to produce a negative barrier MIS contact which does not impede the flow of majority carriers, but which acts as a surface of low effective recombination velocity for minority carriers. It is demonstrated experimentally that such minority-carrier reflecting negative barrier contacts can provide an enhancement in solar cell open circuit voltage equal to that obtained with a diffused back surface field. This is the first report of an induced back surface field solar cell.
Microwave energy compression using a high-intensity electron beam switch
Authors: Birx D. L. , Scalapino D. J.
Published: February 2003

Stored microwave energy has been released using a high-intensity electron beam switch. Experiments using this switch have produced energy compression at room temperature and pulses as short as several nanoseconds. Here we discuss the experimental results and the underlying theory.
Charge measurements on individual particles exiting laboratory precipitators with positive and negative corona at various temperatures
Authors: McDonald Jack R. , Anderson Marlin H. , Mosley Ronald B. , Sparks Leslie E.
Published: February 2003

The values of charge on individual particles exiting three different laboratory precipitators have been measured in an experimental apparatus containing a Millikan cell. Measurements were obtained for dioctylphthalate (DOP) droplets and fly ash particles at temperatures from 23 to 343 °C. At comparable voltages and currents for positive and negative coronas, the data show that the ratio of the values of negative-to-positive charge for radii in the range 0.6–1.3 μm increases from about 1 to 2 as the temperature increases from 37 to 343 °C. The predictions of a mathematical model of electrostatic precipitation which employs an ionic charging theory show good agreement with all the positive charging data, but show good agreement with the negative charging data only at temperatures below 37 °C. The differences in the measurements and the model predictions are consistent with the postulation of free electron charging at elevated temperatures in negative corona.
Grain boundary etching in InP
Authors: Hershenson Larry , Zanio Ken
Published: February 2003

Grain boundaries in bulk polycrystalline InP wafers are preferentially attacked by a 5 HCl:3 HNO3:4 HF etch. Canyons with depths greater than 10 μm and widths approximately 1 μm are the most common form of attack. Although the etch has no effect on simple twin boundaries, preferential attack occurs at interfaces formed by multiple twinning events.
Neutron transmutation doping of silicon. I. Electrical parameters versus fluence
Authors: Meese J. M.
Published: February 2003

Thermal-neutron transmutation doping of silicon produces phosphorus donors by the nuclear reaction 30Si(n,γ)31Si →31P+β−. Nearly exact compensation of residual impurities in float-zone silicon is possible with careful monitoring of the neutron fluence. To achieve this goal, an understanding of the dependence on neutron fluence of the various room-temperature semiconductor electrical parameters is required. An analysis of the fluence dependence of resistivity, Hall coefficient, mobility, and carrier concentration is presented.
Calibration of foil-like manganin gauges in planar shock wave experiments
Authors: Rosenberg Z. , Yaziv D. , Partom Y.
Published: February 2003

Commercial manganin gauges were calibrated in a series of plane shock wave experiments. The calibration curve obtained is linear in the 0–1.5-GPa range and curves for higher stresses (1.5–18.1 GPa). The linear portion is attributed to the elastic behavior of the gauge. This was confirmed by experiments which included rarefactions from free surfaces. The onset of hysteresis was found to be at 1.5 GPa. The experiments demonstrated that the gauge’s response does not depend on the target material in which the gauge is embedded. Also the thickness of the insulating layer which surrounds the gauge does not have any influence on its relative resistance changes.
Phase formation in the AuCu-Al thin film bilayer system
Authors: Campisano S. U. , Costanzo E. , Cristofolini R.
Published: February 2003

Phase formation in the AuCu-Al thin-film system has been studied by nuclear backscatering of energetic ions and by x-ray diffraction techniques. At temperatures between 150° and 220 °C Au2Al or Al2Cu are formed initially from Au-rich or Cu-rich solid solutiions, respectively. The growth kinetics are slower than in the corresponding bilayers of Al-Cu or Al-Au while the sequence of compound formation is unchanged.
Microwave helicon resonances in n-InSb spheres
Authors: Dixon Joseph R. , Furdyna Jacek K.
Published: February 2003

Microwave resonances in n-type InSb spheres placed in a magnetic field are studied experimentally and analyzed in light of the recently developed theory of Ford and Werner for the interaction of electromagnetic waves with a gyrotropic sphere. The Ford-Werner theory is a generalization of the Mie theory to the case of gyrotropic media. The present study constitutes an experimental check on the Ford-Werner theory, demonstrating that the theory is capable of fitting microwave resonance spectra remarkably well. Magnetic and electric dimensional resonances and plasma-shifted cyclotron resonance of gyrotropic semiconductor spheres are examined for their usefulness as accurate diagnostic measures of various material parameters, such as carrier concentration, the static dielectric constant, and carrier mobility. Special attention is given to establishing the limits of the accuracy of this method. For example, the static dielectric constant of the InSb lattice is found to be 16.8±0.2 from this set of measurements. Good theoretical fits are obtained for the resonance positions and shapes, but not for all of the resonance amplitudes. The discrepancy is attributed to an insufficiently accurate representation of the carrier system resulting from the use of the Drude free-electron model in the present analysis.
Properties of p+-n+ AlGaAs diodes
Authors: Bedair S. M.
Published: February 2003

AlxGa1−xAs p+-n+ diodes have been studied in the direct band-gap range. Tunnel diodes were achieved in alloys with band gaps up to about 1.85 eV. For these devices the I-V characteristics show a second hump, which is believed to be due to tunneling from the conduction band on the n side of the junction to an impurity band on the p side of the junction. The location of this band was found to be independent of the band gap. In alloys with band gaps in the range 1.85–1.95 eV, backward diodes were obtained.
Anomalous behavior in the radiation pattern of piezoelectric transducers induced by parasitic Lamb wave generation
Authors: Delannoy B. , Bruneel C. , Haine F. , Torguet R.
Published: February 2003

In order to improve ultrasonic image quality, transducers, similar to those currently used in nondestructive testing and medical imaging applications, have been studied extensively. Attention has been given to single isolated transducers, for which anomalous radiation patterns have been obtained, and to transducers integrated in an array structure, where additional problems occur due to coupling effects between nearest neighbors. An experimental study of these phenomena has made it possible in both cases to find the origin of the perturbations with respect to the theoretical situations which occur in the radiation pattern. Solutions for increasing these perturbations are also suggested.
Studies of the hot-electron population in an electron beam stabilized mirror-confined plasma
Authors: Gerassimenko M. , Petrasso R. , Klinkowstein R. E.
Published: February 2003

X-ray and diamagnetic loop measurements following electron beam injection into a hot ion plasma trapped in a minimum-B mirror system are reported. The hot electrons, believed to be responsible for the novel stabilization of the plasma by electron beam injection, are found to have a temperature kT∼2–3 keV, and a density of about 1% of the plasma’s at the midplane. Axially, the hot electrons are more widely distributed than the trapped ions.
Resonant tunneling spectroscopy in Schottky diodes
Authors: Calleja E. , Piqueras J.
Published: February 2003

A new method to detect deep centers close to the interface in metal-semiconductor contacts is reported. The presence of humps in the logIF- VF characteristics attributed to resonant tunneling contributions to the total forward current is investigated via the slope changes in the logIF- VF plots. Although the relation between the voltage VFm at which the minimum of d2 logIF/ dV2F occurs, and the energy position of the levels causing the resonant tunneling current is not easy to calculate, this new method represents a powerful means to detect traps lying near the interface.
Photoluminescence of nitrogen (N)-implanted and N-free In0.30Ga0.70P grown by liquid phase epitaxy
Authors: Fujimoto Akira , Makita Yunosuke , Nojiri Hidetoshi , Kanayama Toshihiko , Tsurushima Toshio , Shimada Jun-ichi
Published: February 2003

Photoluminescence (PL) studies were performed at 2 K for nitrogen (N)-implanted and N-free In0.30Ga0.70P crystals, which were grown by a step-cooling liquid-phase-epitaxial method. For the N-implanted In0.30Ga0.70P, an isoelectronic trap was found to be formed at annealing temperature over 600 °C. The binding energy of the excitons bound to the above traps was determined to be 92 meV from the temperature dependence of the PL spectra.
Thermodynamic energy conversion efficiencies
Authors: Landsberg P. T. , Tonge G.
Published: February 2003

Much recent work on thermodynamic energy conversion efficiencies is here presented ab initio and from a unified point of view. New considerations are offered and previous work is analyzed in light of the unified presentation. The energy conversion processes discussed include, for example, the conversion into light in a laser or light-emitting diode and the direct or indirect conversion of solar radiation into work. The thermodynamic limiting efficiencies of these various processes are derived by applying simple balance equations to a generalized energy convertor. The new work includes the distinction between temperatures based on fluxes and temperatures ∂U/∂S based on standard thermodynamics, etc., and their application in the correct context. Also the use of standard entropy formulas is justified without relying on thermodynamic equilibrium and the results are then applied to nonequilibrium situations in energy conversion.
High-frequency diffraction of 2-D scatterers by an incident anisotropic cylindrical wave
Authors: Hongo Kohei , Nakajima Eiji
Published: February 2003

A simple formula is derived for estimating the asymptotic solution for two-dimensional diffraction when a cylindrical obstacle is illuminated by an anisotropic cylindrical wave. The result is applied to derive the asymptotic diffracted field by a half-plane, by a wedge, or by a circular cylinder. The solution for a half-plane has been derived by other methods and both results are found to agree. The numerical calculations of the asymptotic solutions for the diffracted field by a slit and by a circular cylinder are carried out for the case when the obstacle is illuminated by an isotropic cylindrical wave. These numerical results are then compared with the exact solutions. It is found that the asymptotic series solutions provide precise results for estimating a diffracted field.
Parametric study of an optically pumped far infrared oscillator
Authors: Siegrist M. R. , Green M. R. , Morgan P. D. , Kjelberg I. , Watterson R. L.
Published: February 2003

We derive an equation to predict the output of an optically pumped far infrared oscillator as function of pump pulse and resonator parameters. Results of a parametric study are presented and a comparison is made with experimental results from a D2O laser at 66 μm.
Spectral output from a premixed chain reaction cw HF laser
Authors: Stanton Alan C. , Bien Fritz
Published: February 2003

Spectral measurements of the output from a purely chemical chain reaction cw HF laser are reported. The laser is a subsonic H2-F2 flame, with supersonic premixing and spatially uniform initiation by a stationary normal shock. Initial chemical production of fluorine atoms is by the bimolecular reaction of F2 with NO. Spectral measurements of the laser output near the initiating shock indicate lasing transitions in the P branches of the v=3 → v=2, v=2 → v=1, and v=1 → v=0 HF bands. Further downstream, the upper vibrational levels are strongly deactivated, and lasing occurs only in the v=1 → v=0 band. Laser emission in the v=2 → v=1 band reappears at reduced NO flow rates, suggesting efficient deactivation of HF (v) by NO, possibly through multiquantum V-V exchange. An approximate rate of 5×10−13±0.5 cm3/sec for deactivation of HF (v=2) by NO is inferred.
Lasing characteristics of GaInAsP/InP narrow planar stripe lasers
Authors: Oe Kunishige , Ando Seigo , Sugiyama Koichi
Published: February 2003

The lasing characteristics of the GaInAsP/InP narrow planar stripe lasers which were prepared by using InP epilayers as Zn-diffusion masks in order to reduce the introduction of defects during the fabrication procedures were investigated. The narrow (?7 μm) stripe lasers showed good mode characteristics to operate in a fundamental-transverse mode up to the output power of more than 20 mW per facet and in a single longitudinal mode in the power region. The threshold current was found to increase significantly and shifts of the lasing output towards shorter wavelength occurred as the stripe width was reduced. Remarkably wide near-field patterns along the junction plane were obtained and far-field patterns were found to be characterized by twin peaks in the narrow stripe lasers.
Pulsed discharge N2/SF6 laser with cw x radiation as a preionization source
Authors: Arai Tsunenori , Obara Minoru , Fujioka Tomoo
Published: February 2003

A cw x-ray generator was used as a preionizer for a pulsed-discharge uv N2/SF6 laser. We revealed experimentally that cw x radiation was effective for preionization of a N2 laser discharge. We observed that the N2 laser energy increased linearly with increasing initial electron number density generated by a cw x-ray preionizer when the electron number density was below 6×107 cm−3 and the input energy loading was kept at 35 J/l. In the case of x-ray illumination, the N2 laser energy increased by a factor of 12 over that of pure N2 gas when SF6 was added.
Intracavity second-harmonic generation in a synchronously mode-locked cw dye laser
Authors: Yamashita Mikio , Sibbett Wilson , Welford Dave , Bradley Daniel J.
Published: February 2003

An internally frequency-doubled and synchronously mode-locked dye laser has been operated. The average power ∼0.13 mW of the second-harmonic wave with a pulse duration of ∼3 ps has been generated from a thin ADP crystal under pumping by the average power ∼800 mW of a mode-locked Ar ion laser. The effect of intracavity second-harmonic generation on the pulse duration of the fundamental wave is discussed.
Laser pulse amplification through exchange of energy with an electron beam via nonlinear radiation pressure effects
Authors: Mavaddat R. , Ghatak A. K.
Published: February 2003

The transfer of energy between electrons and an electromagnetic field via nonlinear radiation pressure effects is discussed. It is shown that a net transfer of energy from electrons to the interacting field is possible if the field intensity changes with time while its relative spatial distribution is maintained. Ignoring the space-charge effects an expression is derived for the gain of an amplifying system, based on this concept.
Eddy current compensation in toroidal deflection yokes
Authors: Pfeiffer H. C. , Sturans M. A.
Published: February 2003

A toroidal yoke for an electron-beam lithography system is compensated for deflection placement errors that normally result from eddy currents generated within the coil windings, as well as driver current settling time and inductive or capacitive coupling within the yoke. Compensation is achieved through the addition of passive conductive material along the outer periphery of the yoke. Both theoretical and experimental results are presented. Agreement is shown to be very good in a specific E-beam lithography system.
Nonlinear effects in heat-pulse experiments
Authors: Phillips W. A.
Published: February 2003

The nonlinear diffusion equation has been solved numerically to examine the effects of the temperature dependences of the heat capacity and the thermal conductivity on the variation of temperature with time in heat-pulse experiments. A range of dependences, simulating amorphous and crystalline insulators at low temperatures, and a range of temperature throws up to 25% have been used in the calculations. It is found that the use of the ordinary diffusion equation may introduce errors of up to 10% for throws of 10%. The effects are particularly noticeable if the thermometer is relatively close to the heater, and resemble those observed in recent low-temperature experiments.
Electromagnetic radiation from line sources embedded in a uniaxial dielectric or plasma half-space backed by a medium of finite conductivity
Authors: Mukherjee P. K. , Mann D. S.
Published: February 2003

This paper treats the problem of electromagnetic radiation from the electric and magnetic line sources embedded in a uniaxially anisotropic dielectric or plasma half-space backed by a finitely conducting medium. The anisotropy of the uniaxial medium is taken along the x direction and the line source is aligned parallel with the z axis. For the envisaged geometry, E and H modes are independently excited by a magnetic and an electric line source, respectively. Expressions for the far-zone radiation field and the radiation pattern are obtained via the saddle-point technique of integration. It is noted that the radiation from an electric line source remains unaffected by the anisotropy of the medium and possesses only a radial component of the Poynting vector. In contrast, the radiation from a magnetic line source not only depends on the anisotropy of the medium but has, in addition to the radial component, a circumferential component of the Poynting vector indicating deviation of the resultant energy flow from the radial direction. Numerical results for the radiation pattern and also for the angle of deviation of the power flow from the radial direction, for the magnetic line source, are presented for a wide range of parameters characterizing the anisotropy of the uniaxial medium, the location of the line source, electron-plasma density, and the conductivity of the half-space backing the uniaxial medium. It is revealed that in the case of a uniaxial plasma or dielectric backed by a perfect conductor, the radiation has a finite strength of unity both in directions ϑ=0 and ϑ=π, in contrast to the case of a medium backed by a finitely conducting medium.
Brillouin and dielectric sidescatter of 10-μm light by a plasma
Authors: Herbst Mark J. , Clayton Christopher E. , Chen Francis F.
Published: February 2003

Sidescatter of CO2 laser light from underdense, laser-heated plasmas in H2 and He is observed at ϑ=90°. Spectrum, exponentiation, isotropy, and polarization measurements are used to deconvolve two separate mechanisms: (1) Doppler-shifted reflections from moving dielectric discontinuities created in the laser-ionization process, and (2) Stimulated Brillouin scattering seeded by these reflections. The dielectric sidescatter is unpolarized and azimuthally symmetric, similar to the diffuse component of scattering in solid-target experiments. The Brillouin sidescatter saturates at a low level corresponding to an ion wave amplitude of 0.1–1.0%, consistent with previous data on the saturation of backscatter.
rf study of the cathode sheath in a Penning discharge
Authors: Guharay K. , Basu J.
Published: February 2003

The cathode sheath in a cold-cathode Penning discharge operating in the high-pressure mode has been investigated by using an rf impedance method. The effect of the presheath lying between the sheath and the plasma has been taken into consideration in deriving the sheath parameters from the impedance of the discharge, measured at two frequencies, under various discharge conditions. The sheath thickness and the dc incremental resistance of the sheath are found to decrease with the discharge current (the static magnetic field being held fixed), while these parameters decrease first, and then remain almost unchanged, if the magnetic field is increased (the discharge current being kept constant).
A new technique for observing the amorphous to crystalline transformation in thin surface layers on silicon wafers
Authors: Drosd B. , Washburn J.
Published: February 2003

Thin amorphous (α) films of silicon created by ion implantation have been studied in situ while undergoing the amorphous to crystalline transformation in the electron microscope. The specimens were prepared in such a manner that the amorphous/crystalline interface was viewed edge on and its advance during annealing was readily observed over distances of several microns. Growth rates and activation energies were measured. The active role that defects play during the regrowth process was also studied. An additional advantage of the technique was that in a single specimen different segments of the recrystallization front advanced along several different growth directions simultaneously, hence the effect of regrowth direction on the interface migration rate and defect formation was graphically displayed in a single specimen.
A comparison of ’’normal’’ lasers and lasers exhibiting light jumps
Authors: Campbell J. C. , Abbott S. M. , Dentai A. G.
Published: February 2003

We have done a comparative examination of two sets of lasers, one set exhibiting a light jump and unusually low pulsation frequencies and another set of ’’normal’’ lasers which do not show these phenomena. Our characterization involved measurements of the near field and far field, the emission spectrum versus current, and the pulsation frequency versus current. These measurements did not reveal any major differences between the two types of lasers except that the pulsation frequencies tend to be lower when light jumps are present. In addition, the laser facets were stained with a dilute A/B etch and inspected with a scanning electron microscope. This showed that the distinction between the two types of lasers may be the position of the tail of the proton bombardment with respect to the active layer.
Visible-spectrum multiple-quantum-well In1−x′Gax′P1−z′Asz′- In1−xGaxP1−zAsz (x≳x′, z≳z′) heterostructure lasers
Authors: Chin R. , Holonyak N. , Vojak B. A.
Published: February 2003

Data are presented showing that high quality visible-spectrum multiple- quantum-well In1−x′Gax′P1−z′Asz′- In1−x Gax P1−z Asz (x≳x′, z≳z′) heterostructures can be grown on GaAs1−yPy (y∼0.30) substrates by a mechanized computer-controlled liquid phase epitaxial process. Undoped visible-spectrum (6600–6000 Å) heterostructures with as many as 12 uniform coupled quantum wells (Lz∼160 Å) have been grown and have been examined (77 and 300 K) via photopumping. Phonon participation in the recombination process is dominant in these quaternary quantum-well heterostructures and lowers the recombination energy by as much as 2?ωLO (InGaPAs)∼68 meV below the lowest (n=1, n′=1′) confined-particle transitions.
Ion implantation of sulfur in Cr-doped InP at room temperature
Authors: Kasahara J. , Gibbons J. F. , Magee T. J. , Peng J.
Published: February 2003

A double-layer encapsulant of phosphorous glass (PSG)/Si3N4 is shown to be useful for postimplantation annealing of sulfur-implanted InP up to 900 °C without surface deterioration. Under high-dose implantation and high-temperature annealing conditions, however, a highly conductive layer is formed near the surface of the InP. A highly compensated or p region is also produced in the deeper part of the implanted layer. The existence of both thermally-induced and damage-induced conductivity must be taken into account to estimate the electrical activity of implanted species from sheet carrier concentration. An estimated real electrical activity of sulfur implanted into InP at room temperature has been established by subtracting damage-induced carrier concentration obtained from argon implantation data. A maximum electrical activity of 68% was obtained on a sample implanted to a dose of 1×1014 S+/cm2 and annealed at 900 °C for 20 min.