bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of device parameters on bistable semiconductor laser
Authors: Hori Yoshikazu , Sato Hisanao , Serizawa Hiroyuki , Kajiwara Takao
Published: July 2002

The effect of device parameters on static and dynamic properties of inhomogeneously current-injected bistable semiconductor lasers has been analyzed. It is shown that in addition to the fraction of current injection region in the cavity, the device parameters, such as dopant concentration in active layer, facet reflectivity, and cavity length, affect the hysteresis width and threshold current. The mechanism of transition between lasing and nonlasing states is discussed, in which a new interpretation is given about the bias dependence of switch-on delay time and the driving condition for switching off is clarified. The carrier increasing rates due to the bias current and dopant concentration in the active layer are dominant factors for the switching on and switching off, respectively.
Electron spin resonance studies of the temperature dependence of the ZnS visible photoluminescence
Authors: Cieplak M. Z. , Godlewski M.
Published: July 2002

A new time-resolved electron spin resonance experiment is presented. This experiment allows us to evaluate an efficiency of different nonradiative recombination mechanisms responsible for the strong temperature dependence of the ZnS:Al visible photoluminescence.
Quantitative abrasion resistance of optical coatings and surfaces
Authors: Ludwig Mark A. , Stoner Robert B.
Published: July 2002

A model for understanding the abrasion of a surface by falling abrasive is developed and tested experimentally. A quantitative measure of abrasion resistance, useful for characterizing optical surfaces and hard coatings, appears naturally in the theoretical model and experimental data. Numerical simulations reproduce both the model and the experimental data.
Experimental observation of current generation by asymmetrical heating of ions in a tokamak plasma
Authors: Gahl J. , Ishihara O. , Wong K. L. , Kristiansen M. , Hagler M.
Published: July 2002

The first experimental observation of current generation by asymmetrical heating of ions is reported. Ions were asymmetrically heated by a unidirectional fast Alfvén wave launched by a slow wave antenna inside a tokamak. Current generation was detected by measuring the asymmetry of the toroidal plasma current with probes at the top and bottom of the toroidal plasma column.
Scalar scattering characteristics of a periodic, impenetrable surface: Effect of surface modeling errors
Authors: Lakhtakia Akhlesh , Varadan Vijay K. , Varadan Vasundara V.
Published: July 2002

Use is made of the T-matrix method to examine the effect of surface profile modeling errors in studying the scalar scattering responses of impenetrable, periodic surfaces. It is shown that even small errors can alter the maximum surface slope significantly, thereby taxing the resources of numerical procedures and severely limiting their scopes of applicability. However, it is possible that the power diffraction coefficients are not very different when calculations are made with and without these errors. Possible implications for using such methods in order to understand the scattering behavior of fractal surfaces are discussed.
Disordering of AlAs-GaAs superlattices by Si and S implantation at different implant temperatures
Authors: Dobisz E. A. , Tell B. , Craighead H. G. , Tamargo M. C.
Published: July 2002

We have investigated by transmission electron microscopy the enhanced disordering of GaAs-AlAs superlattices due to Si and S implantation with subsquent annealing. The implants were performed at 77 K, room temperature, and 210 °C at a dose of 2.5×1014 cm−2 with energy of 100 keV. The greatest enhancement occurs, after annealing, for Si implants performed at 77 K. We find no enhancement due to S implants. The apparent damage due to implantation prior to annealing is strikingly less for superlattices compared with bulk GaAs.
Investigation of trapping states in a Nb-doped rutile by admittance spectroscopy
Authors: Kobayashi K. , Takata M. , Fujimura Y. , Okamoto S.
Published: July 2002

In order to obtain semiconductivity, rutile crystals have been doped with Nb by means of diffusion. The resulting Nb-doped rutile crystals have an electrical resistivity ≂80 Ω cm at room temperature. Impedance analysis of a Nb-doped TiO2-Au diode suggests that the measurement frequency must be lower than 10 kHz to detect the capacitance and conductance of the depletion layer. Thus, an admittance spectroscopic method is used to study traps in the diode of the Nb-doped TiO2-Au. Two trap levels, located at 0.24 and 0.37 eV below the bottom of the conduction band, have been detected by this method. The state densities and capture cross sections of these trap levels are also determined.
Excitation-energy dependence of electron lifetime in phosphorus-doped hydrogenated amorphous silicon
Authors: Oheda Hidetoshi
Published: July 2002

A simple method for evaluating the energy dependence of the lifetime of photocarriers in the steady state from the measurement of the ratio of steady state to the modulated photocurrents has been proposed. It was applied to phosphorus-doped hydrogenated amorphous silicon (a-Si:H), and the excitation-energy dependence of the lifetime for electrons was determined. The lifetime spectrum shows a break point at about 1.1 eV, below which the lifetime decreases with a decrease of the excitation energy, while it remains almost constant in the energy range higher than 1.1 eV. It has been concluded that there are two kinds of hole traps. One of them (X states) is located about 1.1 eV below the conduction-band edge and is characterized by slow recombination rate with electrons. This conclusion has been confirmed by the independent experiment on the dual-beam photocurrent. The other hole traps having large recombination rate with electrons are expected to be present at energies shallower than 0.7 eV from the conduction-band edge. In consequence of the different recombination rates with electrons among these hole traps, the recombination channel through X states becomes a dominant rate-limiting process in the steady-state photocurrent of phosphorus-doped a-Si:H.
Study of liquid-infiltrated Nb-Sn superconducting composite wire by specific-heat measurements
Authors: Hellman F. , Hong M. , Hull G. W. , Geballe T. H.
Published: July 2002

The results of specific-heat and inductive Tc measurements on reacted liquid-infiltrated superconducting composite wires with an overall composition of Nb-8 at. % Sn are presented. It is found that approximately 23 wt. % of the reacted wire is high Tc A15 phase, a result not expected from the accepted equilibrium phase diagram. The relatively sharp superconducting transition at 18 K is indicative of a uniform stoichiometric Nb-25 at. % Sn composition in the A15 phase. The large fraction of high Tc material in these wires is due to taking advantage of the rapid diffusion of Nb in liquid Sn. From a detailed analysis of the specific heat, comments on the reaction process are made. Implications for the equilibrium phase diagram are discussed.
Magnetostatic energy of magnetostatically coupled film edges
Authors: Nonaka Koutarou , Hirono Shigeru , Hatakeyama Iwao
Published: July 2002

This paper gives formulas for analyzing two curling regions which are magnetostatically coupled at film edges. Magnetostatic energy of coupled film edges having any given surface and volume charges can be calculated from the formulas. These formulas are expressed in terms of film width W, film thickness T1 and T2, saturation magnetization M1 and M2, curling length D1 and D2, and angle θ01 and θ02 between the magnetic moment and the film edge surface of the upper and under layers, respectively. Using these formulas, we have quantified the magnetization distribution in the coupled film edges and the decrease in energy caused by magnetostatic coupling and the conversion of surface charges into volume charges. The approximate formulas derived in the previous paper [J. Appl. Phys. 58, 1610 (1985)] are corrected in this paper.
Laser action from s
y
n-(methyl,methyl) bimane
Authors: Pavlopoulos Theodore G. , Boyer Joseph H. , Politzer I. R. , Lau Chun M.
Published: July 2002

Under the flashlamp excitation from an aqueous solution of syn-(methyl,methyl)bimane laser action was observed at 504 nm. The absorption, fluorescence, and triplet-triplet absorption spectra of this compound were also recorded. This compound showed good photochemical stability. The laser action properties of this new laser dye were compared with those of Coumarin 30.
1/ f  noise and number fluctuations
Authors: Clevers R. H. M.
Published: July 2002

In a semiconductor the density of carriers in each subband fluctuates owing to intraband transitions. We consider the spectral density for number fluctuations and for conductance fluctuations arising from such intraband transitions. It is shown that the spectral density for number fluctuations equals zero. If the mobility is the same in all subbands, the spectral density for conductance fluctuations equals zero. Otherwise the conductance fluctuations show a non-1/ f spectrum.
Magnetization distribution analysis in the film edge region under a homogeneous field
Authors: Hirono S. , Nonaka K. , Hatakeyama I.
Published: July 2002

We analyze the magnetization distribution in the edge region of a magnetic thin film when a homogeneous magnetic field is applied. The present theory can analyze the general curling state in which surface and volume charges coexist in the film edge region. In addition, the theory can quantitatively show each energy as the energy parameters vary. We also analyze the magnetic field distribution and magnetic-flux density distribution which are derived by the energy minimal magnetization distribution. The theory shows the good agreement with the experiment by the micro-Kerr method when film thickness is small.
Spectroscopic ellipsometry study of glow-discharge-deposited thin films of a-Ge:H
Authors: Blanco J. R. , McMarr P. J. , Vedam K. , Ross R. C.
Published: July 2002

Thin films of a-Ge:H with hydrogen contents ranging from 0 to 13 at. % prepared by the glow-discharge process have been studied by spectroscopic ellipsometry. The resulting ellipsometric parameters have been analyzed by using standard n-layer models, least-squares regression analysis, and the Bruggeman effective media approximation theory. The results of the analyses show that the atomic percentage of hydrogen, in the amorphous binary alloy of Ge and H, can be represented by a void volume fraction in an effective medium approximation. These results are compared with those of infrared absorption spectroscopy. A good correlation between the percentage void determined from ellipsometry and the H content measured in these a-Ge:H films is found.
A novel phased array acousto-optic Bragg cell
Authors: Chen T. S. , Yao S. K.
Published: July 2002

Asymmetry introduced to an otherwise planar phased array Bragg cell transducer design results in the elimination of one of two steering acoustic wave fronts. Therefore, all of the acoustic power is applied to the acousto-optic interaction process. In addition, a factor of 1.8 improvement in wide-band acousto-optic Bragg cell interaction efficiency is realized over the planar phased array design. The technique to establish the asymmetry was to use a periodic silver film as a quarter-wave step. This new technique is particularly suitable for the construction of wideband Bragg cells at microwave frequencies.
Mutual phase locking in series arrays of Josephson tunnel junctions at millimeter-wave frequencies
Authors: Lee G. S. , Schwarz S. E.
Published: July 2002

Mutual phase locking has been demonstrated in series arrays of two and four Josephson junctions at millimeter-wave frequencies. Experimental observations are in good agreement with theory reported earlier. This technique increases the output power available from a Josephson junction source. Available output power is expected to be proportional to the square of the number of junctions until the array impedance approaches the load impedance. The output frequency is voltage tunable over as much as an octave. Theory indicates that the technique can be extended to even larger arrays.
Wavelength selective infrared microscopy: A nondestructive and quick method for the investigation of buried structures in optoelectronic devices
Authors: Sartorius B. , Rosenzweig M.
Published: July 2002

In this paper we present an optical method to control the geometry of buried layers in optoelectronic heterostructures. The technique uses an optical microscope equipped for infrared applications and relies on the fact that the different layers of the multilayer structure have different band gaps. Accordingly transmission/absorption, reflectance, and photoluminescence of the inidividual layers exhibit their characteristic near-band-gap spectral variations at different wavelengths. By appropriate selection of the wavelength range used for image formation, any layer of interest can be made visible. As an example we investigated a mushroom-type InGaAsP/InP 1500-nm laser structure with subsequent mass transport. Both technological steps, the formation of the mushroom by underetching, and the regrowth by mass transport represent critical processes in the fabrication of these index-guided lasers. Our results show clearly that the successful accomplishment of the process can be controlled by images of the selected buried layer. Contrast and resolution of the pictures are sufficient to show any irregularity in etching or regrowth. The main advantage of the method is that it offers the possibility of investigating whole wafers without sample preparation and in a nondestructive way, which is in marked contrast to observation with a scanning electron microscope, where only profiles along cleaved facets can be inspected.
Partially oxidized amorphous silicon as the tunneling barrier for Josephson devices
Authors: Celaschi Sergio
Published: July 2002

Superconducting Nb(polycrystalline)/Pb tunnel junctions were fabricated by electron-beam deposition. Partially oxidized amorphous silicon (a-Si) is used as the tunneling barrier. A thin layer of Al (10 Å) passivates the Nb surface against the formation of conductive Nb suboxides. A detailed study of the behavior of oxidized a-Si as the tunneling barrier is reported. The insulator is shaped as a double height barrier to account for the partially oxidized nature of the a-Si deposited layer. Average barrier heights are inferred to be 15±5 meV and 1.2± 0.2 eV for the a-Si and SiOX layers, respectively. Increasing the deposited a-Si thickness, one observes a systematic degradation of the Nb/Pb superconducting tunnel characteristics, which correlates with deviations from the metal-insulator-metal tunneling theory. These anomalies are associated with the intrinsic properties of the unoxidized fraction of the a-Si layer. From the technological point of view, our results indicate that such oxidized semiconducting barriers can yield high-quality Josephson junctions. The high Vm products (30±10 mV) together with the low values of the specific capacitances (2.0±0.5 μF/cm2) guarantee favorable properties for fast device applications.
Profiling of inhomogeneous carrier transport properties with the influence of temperature in silicon-on-insulator films formed by oxygen implantation
Authors: Cristoloveanu S. , Lee J. H. , Pumfrey J. , Davis J. R. , Arrowsmith R. P. , Hemment P. L. F.
Published: July 2002

The nonhomogeneous distribution of the carrier transport properties in silicon on insulator thin films synthesized by oxygen implantation are determined using gate-controlled p-type Hall devices. The conductivity, Hall effect, and capacitance were measured between 77 and 300 K as a function of the gate voltage and then differentiated to obtain depth profiles. The hole mobility is high and nearly constant in the top 100 nm of the film but drops rapidly in the region containing implantation-induced defects. The very good quality of the top layer, similar to that of bulk Si, is confirmed by the temperature behavior of both the mobility and the ionized impurity concentration at various depths in the film. Acoustic phonon scattering is found to prevail above 120 K and Coulombian scattering below. A difference between the profile of the total number of holes and that of the mobile holes is observed at low temperatures and explained in terms of long-range potential fluctuations.
Development of low-energy oxygen ion beams for surface studies
Authors: Walther S. R. , Leung K. N. , Kunkel W. B.
Published: July 2002

A small microwave ion source has been constructed to generate low-energy (5–10 eV) oxygen beams. The source is fabricated from a quartz tube and is enclosed by a microwave cavity. The source is operated without an external extraction voltage. Positive ions effuse from the source with energies equal to the plasma potential. The source has been operated in a cw mode producing an atomic oxygen ion fluence >1×1014 cm−2 s−1 with energies as low as 5.5 eV. The ‘‘self-extracted’’ ion beam can be used to simulate the oxygen environment encountered in low earth orbits.
Comment on ‘‘Misfit stress in InGaAs/InP heteroepitaxial structures grown by vapor-phase epitaxy’’ [J. Appl. Phys. 57, 249 (1985)]
Authors: Noyan I. C. , Segmüller Armin
Published: July 2002

The proper elastic equations for an epitaxial bilayer system are presented, amending an earlier paper published by other authors in this journal. The stress profile normal to the surface and the radius of curvature are given as functions of the epitaxial mismatch.
Magnetocentrifugal separation of particulates: Theory and principles of operation
Authors: Zimmels Yoram
Published: July 2002

The theory and principles of operation of the new magnetocentrifugal separation are formulated. Magnetic and centrifugal g numbers for monodisperse and polydisperse particulates are defined. It is shown that the magnitude of electromagnetic and centrifugal forces can be matched in the full scale of centrifugal fields available to date. Magnetocentrifugal separation can be applied to separation of particulates down to colloidal and molecular sizes, and using a stationary fluid, it is independent of particle size, being controlled by density and magnetization of particles and fluid. Magnetic field configurations, different cases related to magnetization and density distributions of particulates, and specific modes of operations are discussed. Finally, diffusion controlled systems and potential applications of the new technology are considered.
Dislocation effects on carrier concentration for molecular-beam-epitaxially grown GaAs
Authors: Shinohara Masanori , Hyuga Fumiaki , Watanabe Kazuo , Imamura Yoshihiro
Published: July 2002

Dislocation effects on carrier concentration for Si-doped and Si-implanted molecular-beam-epitaxially (MBE) grown GaAs layers are investigated by small area (40×40 μm2) Hall measurements. It is found that there is no correlation of carrier concentration with dislocation density and distance from a dislocation to a Hall device. The photoluminescence 1.51-eV bound exiton peak and the 1.49-eV carbon acceptor peak intensity variations are small across a wafer. Moreover, there are no variations in high-resolution photoluminescence intensity and in electron-beam-induced current image between positions close to and far from a dislocation. These results indicate that carrier concentration is not affected by dislocations in MBE-grown epilayers because of the absence of a denuded zone around the dislocation. Acceptors and/or point defects are depleted in liquid-encapsulated Czochralski-grown GaAs, whereas this does not take place during the MBE growth processes.
Characterization of GaAs self-aligned refractory-gate metal-semiconductor field-effect transistor (MESFET) integrated circuits
Authors: Magerlein J. H. , Webb D. J. , Callegari A. , Feder J. D. , Fryxell T. , Guthrie H. C. , Hoh Peter D. , Mitchell J. W. , Pomerene A. T. S. , Scontras S. , Spiers Guy D. , Greiner J. H.
Published: July 2002

GaAs metal-semiconductor field-effect transistors (MESFETs) and other integrated-circuit elements were characterized by including extensive process test sites on wafers with digital logic and memory circuits. A self-aligned, refractory-gate enhancement/depletion (E/D) process was employed which included 47SiF+ channel and source/drain implants, capless arsenic overpressure furnace annealing, WSi0.11 gate metal with in situ sputter cleaning, Ni-Au-Ge ohmic contacts, Si3N4 or SiO2 insulation, and Ni-Au wiring. On-water threshold voltage standard deviations as low as 31 mV for 1-μm E-FETs and 49 mV for 1-μm D-FETs were measured using 51-mm standard semi-insulating liquid-encapsulated Czochralski GaAs substrates. Threshold voltage control from wafer to wafer was of order 100 mV. Schottky diode barrier height was about 0.73 eV with an ideality of 1.2, although small self-aligned Schottky gates often showed excess conduction believed to occur at the gate edges. FET square-law coefficient, subthreshold leakage, gate capacitance, backgating, contact resistance, and wiring and insulation characteristics were also measured and found satisfactory. Fully functional 1-μm gate E/D MESFET circuits including a 4×4 bit multiplier, a 4×4 crosspoint switch, a 448-bit static RAM, and an integrated photodiode amplifier were demonstrated.
Polycrystalline n-SrTiO3 as an electrode for the photoelectrochromic switching of Prussian blue films
Authors: Ziegler John P. , Lesniewski E. Ken , Hemminger John C.
Published: July 2002

We have developed methods for the preparation of polycrystalline n-SrTiO3 electrodes which show low dark currents and reasonable efficiencies for photoelectrochromic switching of Prussian blue films. Electrochemical methods were used to characterize the polycrystalline electrodes and the Prussian blue films. The Prussian blue→Prussian white charge-transfer reaction occurs via a state within the SrTiO3 band gap, located at ∼−0.68 V (versus saturated calomel electrode), the same as that measured on single-crystal n-SrTiO3 electrodes. Good image contrast and stability are demonstrated with these polycrystalline electrodes.
Bonding of silicon to silicon by solid-phase epitaxy
Authors: Bhagat Jayant K. , Hicks David B.
Published: July 2002

Using concepts of solid-phase epitaxy, a sealed and structurally sound bond between two silicon wafers has been achieved with aluminum, platinum silicide, or germanium as the transport medium. Only in the case of aluminum did microprobe analysis show an interface clear of the bonding medium. The bond quality was tested by bonding wafers of different crystal orientation and then intentionally cleaving and fracturing the bonded wafers. A clean fracture was obtained without the wafers falling apart. Leak test of sealed cavities suggests that a hermetically sealed enclosure can be achieved with this technique.
Iron-oxygen–based perpendicular magnetic thin films
Authors: Mizoguchi T. , Akutsu N. , Akimitsu M.
Published: July 2002

Nonstoichiometric FexO1−x and FexMyO1−x−y films, where M is either a nonmagnetic element, e.g., Si, or a magnetic element, e.g., Co, were prepared by sputter deposition. They showed increasing ferromagnetic magnetization with decreasing oxygen concentration below 1−x−y<0.5, and strong perpendicular magnetic anisotropy which overwhelmed the shape anisotropy of the thin ferromagnetic films in certain composition ranges. The magnetization of perpendicular magnetic films attained more than 500 emu/cm3 with an anisotropy energy of 2×106 erg/cm3. Ferromagnetic amorphous metallic phases precipitated between columnar structure of nonmagnetic oxide phase were considered to be responsible for the ferromagnetism of these films. The perpendicular anisotropy was also interpreted by the internal shape effect arising from fine elongated ferromagnetic phases distributed in a nonmagnetic phase with their long axis perpendicular to the film plane. They had an appropriate coercivity for the perpendicular magnetic recording media with a high resistance against wear and corrosion and a low friction constant.
Dark current transients in SbI3-doped HgI2 crystals
Authors: Nissenbaum J. , Schieber M. , Burshtein Z.
Published: July 2002

The transient characteristics of the dark current have been measured in SbI3-doped HgI2 single crystals as a function of voltage and temperature for different dopant concentrations. The doping by Sb3+ was found to introduce a hole trapping level 0.5-eV deep, with a density which was of the same order of magnitude as the SbI3 content. The room-temperature effective hole mobility was 5×10−8 cm2/V s for 1.5 wt.% dopant content, as compared to about 2×10−6 cm2/V s for 0.1 wt.% dopant content. Previous results obtained with undoped crystals showed an effective mobility of 5×10−7 cm2/V s, but the trap depth was different, 0.7 eV, and the concentration was much lower, only of the order of 1015 cm−3.
Determination of terrace size and edge roughness in vicinal Si{100} surfaces by surface-sensitive diffraction
Authors: Saloner D. , Martin J. A. , Tringides M. C. , Savage D. E. , Aumann C. E. , Lagally M. G.
Published: July 2002

The capabilities of high-resolution surface-sensitive electron diffraction to determine quantitatively the terrace size, terrace size distribution, and terrace-edge roughness are explored and illustrated with measurements on a vicinal near-{100} Si surface. It is shown that terrace edge roughness can be determined with the appropriate measurement. To explain measurements on the Si surface, shadowing, terrace-edge distortion, double-height steps, unequal areas of adjoining terraces, and multiple scattering are considered. The influence of the instrument response on measurement precision is discussed.
Analysis of crystal field and exchange interactions in Nd2Fe14B
Authors: Parker F. T.
Published: July 2002

The spin-reorientation parameters in Nd2Fe14B are used to obtain the rare-earth crystal field and exchange interactions. By expressing the anisotropy energies K1 and K2 in terms of the rare-earth crystal field interaction parameters B0n 〈00n〉, the canting angle is found in terms of the ratio B04 〈004〉/B02 〈002〉 . From the experimental canting angle at 4.2 K, B04/B02 =−0.013. The temperature dependence of the 〈00n〉 yields the rare-earth–transition-metal exchange interaction, μB He=323 K, at the spin-reorientation temperature, 133 K. Room-temperature anisotropy data are used to individually determine B02 and B04: B02 =−1.93 K, and B04 =0.025 K. The values of K1 and K2 deduced from these results are in good agreement with experimental values at 4.2 K and room temperature.
Current-voltage characteristic of pulsed space-charge-limited currents in GaAs
Authors: Gildenblat Gennady Sh. , Rao Ashwin R.
Published: July 2002

We introduce a general parametric form of the current-voltage characteristic of space-charge-limited currents (SCLC) in a trap-free material with nonlinear velocity-field (v-F) dependence. An exact solution is obtained for two important v-F models describing the gradual transition from the Mott–Gurney law to the regime of drift-velocity saturation. In particular, we discuss the effect of negative differential mobility on the current-voltage characteristic of SCLC in the high-field region. The theory shows a good agreement with experimental data for low-temperature pulsed SCLC in GaAs.
Observation of single-mode oscillation in gain-guided GaAlAs laser array
Authors: Wang S. C. , Leung K. M. , Gacusan L. Z.
Published: July 2002

A single-longitudinal-mode oscillation has been observed for the gain-guided GaAlAs laser arrays under controlled conditions. These multiple-element laser arrays were operated under continuous-wave conditions with controllable temperatures and currents. We have observed single-longitudinal-mode operation at near threshold and above threshold for operating temperatures of 10–37 °C. A mode intensity ratio of over 50:1 was observed with fairly stable output. In addition, a single-lobed far-field pattern under single-mode oscillation was also observed.
Reply to ‘‘Comments on ‘Direct experimental determination of voltage across high-low junctions’ ’’ [J. Appl. Phys. 5
9, 285 (1985)]
Authors: Daud T. , Lindholm F. A.
Published: July 2002

Bellone, Caruso, and Vitale [J. Appl. Phys. 61,▪▪▪▪(1987)] dispute our assumption of an ohmic contact formed by the metal-semiconductor junctions to the low-doped region of a back-surface-field solar cell. Attention is drawn to the mechanism that can lead to an ohmic contact in our experiment. Experimental evidence cited in our paper and additional test data presented here show that the assumption of an ohmic contact is indeed valid. It is pointed out that our work has mainly focused on the alteration of the solar-cell structure only slightly to experimentally assess an aspect of the solar-cell theory. The overlapping part of the two studies were done independently.
Interstitial interactions: Aluminum-boron, aluminum-gallium, and boron-gallium pull effect
Authors: Aronowitz S.
Published: July 2002

Quantum chemical calculations on a model silicon lattice where combinations of interstitial p-type dopant species (aluminum-boron, aluminum-gallium, and boron-gallium) interact predict that all combinations will exhibit a pull effect. Diffusion of either member of a set will be retarded; the boron-gallium pair will exhibit the greatest attraction between p-type dopant pairs. There predictions are confirmed experimentally. Moreover, unanticipated enhanced electrical activity, greatly exceeding the additive, also is observed.
The use of amorphous-crystalline silicon heterojunctions for the application to an imaging device
Authors: Mimura Hidenori , Hatanaka Yoshinori
Published: July 2002

Experiments on p-type hydrogenated amorphous silicon (a-Si:H)/n-type crystalline silicon (c-Si) heterojunctions were performed to determine the suitability of their application to an imaging device. Optoelectrical properties such as current voltage (I-V), capacitance voltage (C-V), and spectral photoresponses were measured in the a-Si:H/c-Si heterojunctions prepared with or without a mesh used to keep the glow-discharge plasma away from the c-Si substrate. The C-V characteristics revealed that there was something (probably interface defect states) obstructing the spread of the depletion layer in c-Si at the interface of a-Si:H and c-Si when c-Si was exposed in the glow-discharge plasma during the deposition of a-Si:H; the C-V characteristics also revealed that the origin of the interface defect states was considered to be due to the damage of c-Si caused by the positive-ion bombardment from the plasma at the initial stage of the deposition of a-Si:H. In a-Si:H/c-Si junctions with few interface defect states, the spectral photoresponses and I-V characteristics showed a wide photoresponse, good photocurrent characteristics, and a low dark current in the reverse bias. A new Si target without a diode array was demonstrated to be of high quality for the application of this heterojunction to an imaging device.
Anisotropic transport in modulation-doped quantum-well structures
Authors: Radulescu D. C. , Wicks G. W. , Schaff W. J. , Calawa A. R. , Eastman L. F.
Published: July 2002

Anisotropic electron transport has been observed in GaAs modulation-doped quantum wells grown by molecular-beam epitaxy on a thick (001) Al0.3Ga0.7As buffer grown at 620 °C. The low-field electron mobility at 77 K in the [110] direction is a factor of 2 larger than the mobility in the [1̄10] direction for a 90-Å quantum well. Thicker quantum wells (150, 200, and 300 Å) show progressively less anisotropy, which vanishes for a 300-Å quantum well. The degree of anisotropy is also reduced or eliminated by suspending growth of the Al0.3Ga0.7As for a period of 300 s prior to growing the GaAs quantum well. Growing the Al0.3Ga0.7As buffer at higher temperatures (680 °C) also reduces the degree of anisotropy. Higher two-dimensional electron gas sheet densities result in less anisotropy. The anisotropy is eliminated by replacing the thick Al0.3Ga0.7As buffer with a periodic multilayer structure comprising 15 Å of GaAs and 200 Å of Al0.3Ga0.7As. The degree of anisotropy is related to the thickness and growth parameters of the Al0.3Ga0.7As layer grown just prior to the growth of the GaAs quantum well.
Observation of radiative surface states on InP
Authors: Kim T. S. , Lester S. D. , Streetman B. G.
Published: July 2002

We have observed radiative surface recombination centers on InP by low-temperature photoluminescence. The luminescence band is observed only after etched or annealed surfaces are treated with hydrofluoric acid (HF), and is not found after rinsing in deionized water. These observations and x-ray photoemission studies of the treated surfaces indicate that the recombination centers are related to the near-surface stoichiometry or to the composition of native oxide layers. The peak energy of the transition has been studied as a function of excitation power and is found to increase from 1.392 eV at low power densities to 1.404 eV and higher power densities.
Cohesion energy in anisotropic particles aqueous slurries
Authors: Fripiat J. J. , Setton R.
Published: July 2002

A method of calculating the cohesive energy of clay-rich slurries is presented. It is based on an empirical law relating the distribution of distances within the aggregates to the proportion of surfaces at these distances. The result of the calculation shows that the cohesive energy is the product of two functions, F and S: the former is itself a product of the Hamaker constant, the cube of the total surface of the clay and the square of the clay/liquid ratio, whereas the latter depends only on two parameters: the fraction of platelets in closest approach, and the distance of closest approach. The calculations have been extended to predict the influence of porosity on the cohesion energy of some rocks.
High-field electron-drift velocity and temperature in gallium phosphide
Authors: Arora Vijay K. , Mui David S. L. , Morkoç Hadis
Published: July 2002

The drift velocity and electron temperature in gallium phosphide as a function of electric field are studied and modeled with a constant mean-free path. Comparisons between theory and recently reported experimental results are made. An interpretation of the high-field transport parameters in terms of those of ohmic transport is given.
Preparation of microcrystalline Si1−xCx thin films
Authors: Fujii Yoshihisa , Hatano Akitsugu , Suzuki Akira , Yoshida Masaru , Nakajima Shigeo
Published: July 2002

Si1−xCx (x∼0.5) films have been prepared by glow discharge decomposition of SiH4, CH4, and H2 gas mixtures. Their structural properties are examined by infrared absorption and reflection electron diffraction. It is found that the film structure depends on the ratio of source gas to hydrogen gas [(SiH4+CH4)/H2], and microcrystalline films can be obtained even at a low temperature of 350 °C when the source gas ratio is less than 0.004.
Effect of nonuniform carrier distribution on channel mobility measurement in metal/SiO2/Si field effect transistors
Authors: Li Jia , Ma T.-P.
Published: July 2002

The apparent channel mobility of a metal/SiO2/Si field-effect transistor as determined from the current-voltage measurement may yield a significantly underestimated value if proper care is not taken to restrict the applied source-drain voltage. Unlike the well-known velocity saturation effect, the effect to be discussed is due to the nonuniform distribution of carriers along the channel, and therefore is independent of the channel length, but is a function of the ratio of the source-drain voltage to the thermal voltage kT/e. It is more pronounced for devices with thinner gate oxide in the low carrier-concentration regime.
Pulsed DF and DF-CO2 laser performance
Authors: Dreiling T. D.
Published: July 2002

A comprehensive set of pulsed DF and DF-CO2 laser performance measurements is presented as a function of gas mixture composition (F2, O2, D2, diluent, and CO2), laser threshold gain, and reaction initiation strength. All the data were collected on a 47-l device using flash photodissociation of F2 to initiate the D2/F2 chain reaction. For helium buffered mixtures, maximum DF laser energy was found to occur at the highest pressures investigated (760 Torr), where the least amount of O2 is required for stabilization of the D2-F2 mixture prior to initiation. The addition of N2 or NF3 is deleterious to DF laser performance. However, at low partial pressures (∼100 Torr) the performance of N2 or NF3 diluted mixtures is comparable to that of He mixtures, suggesting that N2 or NF3 may be acceptable alternatives to He diluent in some laser system designs. The maximum DF-CO2 transfer laser energy was found to be 40% higher than the corresponding DF laser energy for comparable gas mixtures without any CO2. As with DF, the DF-CO2 laser energy was found to scale with the pump rate parameter, PF2(F/F2)1/2, provided the partial pressure of CO2 was adjusted to maintain a constant ratio of PCO2/(PF2(F/F2)1/2)2. The presence of NF3 caused a strong decline in DF-CO2 laser output, which is believed to be due to the ν1, symmetric stretch absorption band of NF3 at 10.3 μm.
Enhancement of electrical conductivity of poly( p-phenylene) and polynaphthylene films by heat treatment
Authors: Yoshino Katsumi , Ueno Hideki , Uesugi Fumito , Satoh Masaharu
Published: July 2002

Electrical conductivity of poly(p-phenylene) and polynaphthylene films increases by many orders of magnitude by the heat treatment at temperatures between 400 and 1000 °C, which is interpreted in terms of the carbonization. A linear temperature dependence of thermoelectric power also supports this interpretation.
Collection of electron-beam-generated carriers in the presence of a grain boundary or an epitaxial interface
Authors: Paz O. , Borrego J. M.
Published: July 2002

A new technique is presented for determining the transport properties of minority carriers (the diffusion length and recombination velocity) generated when polycrystalline grains, with a grain size smaller than the diffusion length, are irradiated by an electron beam. An analogous case that can be handled using this technique is the determination of the recombination velocity at the interface between an epitaxial layer and a heavily doped substrate with a very short lifetime. For 1–2-μm grains in a polycrystalline GaAs solar cell, we found that the diffusion lengths can equal bulk-diffusion lengths observed in single-crystal material, but high recombination levels prevail at the grain boundaries, the recombination velocity there may reach 2×106 cm s−1 and is inversely proportional to the grain size.
Anode plasma ionization due to sheath heating in magnetically insulated ion diodes
Authors: Slutz Stephen A.
Published: July 2002

We show that anode plasma sheath heating can cause undesirable in situ ionization of the anode plasma in magnetically insulated ion diodes. We find that extremely high electron energies will occur in the anode plasma sheath due to an increasing magnetic field at the anode surface during the diode pulse. These high-energy electrons can collisionally ionize the plasma ions to an unwanted ionization state. Multiply ionized anode plasma ions represent a beam contaminant that may cause undesired preheat in inertial confinement fusion (ICF) capsules. The fraction of unwanted higher ionization states increases with anode plasma density. Therefore, this effect places an upper limit on the anode plasma density that can be used in an ICF application. As an example, we estimate the fraction of Li++ generated by sheath heating in the PBFA-II Applied-B ion diode as a function of the initial Li+ anode plasma density and obtain an upper limit for a lithium anode plasma density of approximately 1×1016 cm−3. At anode plasma densities of 1×1016 cm−3 or less there will be substantial motion of the ion emitting surface during the diode pulse. We discuss the advantages and disadvantages of this plasma motion.
Helium scattering study of the growth mechanism and phase transitions of Pb overlayers on Cu(100)
Authors: Sánchez A. , Ibañez J. , Miranda R. , Ferrer S.
Published: July 2002

We present the first results of thermal energy He scattering by an heteroepitaxial system, namely Pb on Cu(100). The intensity of the specularly reflected He beam as a function of the coverage of Pb is sensitive to disordered adsorption, to the ordering of the overlayer, and to three-dimensional cluster growth. Quantitative information, such as the number of random vacancies in the as-deposited monolayer, can be obtained. The large differences in the cross sections for diffuse scattering between Pb adatoms on the Cu terraces and on the steps have been used to determine the heat of two-dimensional vaporization of Pb atoms from step to terrace sites.
Modification of dopant profiles due to surface and interface interactions: Applications to semiconductor materials
Authors: Jagannadham K. , Narayan J.
Published: July 2002

The kinetics of segregation of dopant solute atoms in the presence of free surfaces and interfaces are analyzed by solving the diffusion equation with a drift term. The drift term includes the configurational interaction energy associated with an oversize or an undersize atom near a coherent interface when the continuity conditions are satisfied. Both an analytical solution and a numerical procedure are provided to solve the problem by eigenfunction expansion method. A new procedure for evaluating the eigenvalues to include higher-order terms is given. It is further established that an attractive force due to either a soft second phase or a free surface gives rise to a minimum in the concentration profile near the interface while a hard second phase results in a monotonically increasing concentration. The position of the minimum in the concentration profile in the presence of a soft second phase or the slope of the concentration profile in the presence of a hard second phase provides a measure of the strength of the defect and the interaction-energy term which can be compared with experimental observations. In particular, we have considered changes in the dopant profiles in silicon under the influence of the free surface, in silicon with silicon dioxide, gallium arsenide, germanium, magnesium oxide and in germanium with silicon, all deposited as a second phase, respectively.
Thermal stability of thin-film amorphous W-Ru, W-Re, and Ta-Ir alloys
Authors: Denier van der Gon A. W. , Barbour J. C. , de Reus R. , Saris F. W.
Published: July 2002

The crystallization behavior of self-supporting thin-film amorphous W-Ru, W-Re, and Ta-Ir alloys has been studied with transmission electron microscopy. Crystallization temperatures have been observed which are much lower than the temperatures predicted by a semiempirical model: the highest observed temperatures are 775 °C for W-Ru and W-Re alloys, and 900 °C for the Ta-Ir alloys. All three systems show maximum thermal stability at a composition expected using enthalpy considerations.
Electrical and metallurgical characteristics of PtxSi1−x/n-GaAs contacts
Authors: Budhani R. C. , Bunshah R. F. , Bardin T. T. , Pronko J. G.
Published: July 2002

Forward current–voltage characteristics of carrier transport at PtxSi1−x/n-GaAs interfaces have been measured in the as-deposited state and after annealing at 500 °C for 4 h. The single phase alloy Pt0.5Si0.5 shows Schottky diode characteristics with the barrier height (φb) 0.70 eV and the ideality factor (η) 1.17. Rutherford backscattering of He4 ions and Auger depth profiles for Pt, Si, Ga, and As reveal that the Pt0.5Si0.5/n-GaAs interface remains metallurgically inert even after the heat treatment. The observed metallurgical nonreactivity is reflected in the diode characteristics of the annealed samples which show negligible changes in φb and η. The silicon rich PtxSi1−x (x<0.5) alloy compositions show near-Ohmic transport in the as-deposited and annealed states. These films are also metallurgically inert on annealing.
Bismuth-doped tin telluride
Authors: Tamor M. A. , Holloway H. , Ager R. M. , Gierczak C. A. , Carter R. O.
Published: July 2002

By optimizing the growth conditions and doping with Bi, we have produced epitaxial layers of SnTe with hole concentration as low as 2.6×1018 cm−3. This is more than an order of magnitude less than the smallest carrier concentration reported for undoped bulk crystals (even with heat treatment to reduce the metal vacancy concentration). The hole mobility is found to depend somewhat on the Bi content. Measurements of the refractive index of low carrier concentration SnTe show very little dispersion for wavelengths up to 30 μm.
Integrated optical bent waveguide with grown 45° mirror by selective liquid-phase epitaxy of GaAs
Authors: Kim Sang Bae , Kwon Young Se
Published: July 2002

An integrated optical bent waveguide with as-grown 45° mirror is fabricated using nearly atomically smooth facets only. These facets are grown by single-step selective liquid-phase epitaxy of GaAs. The mirror orientation is automatically adjusted to the optimum angles since the waveguide on {100} substrate uses only the as-grown {111} and {100} crystal planes as waveguide walls and 45° mirrors. The technique for the mirror location control is described taking into consideration the growth rate anisotropy.
The determination of diffusion length and surface barrier width from surface photovoltage measurements in CdSe and amorphous Si films
Authors: Moore A. R. , Lin Hong-sheng
Published: July 2002

Surface photovoltage data on CdSe films measured by Storr and Haneman have been analyzed with a formula originally intended to apply to amorphous silicon. The minority-carrier diffusion length and surface barrier width obtained are comparable to the results of Storr and Haneman using a different formula directly applicable to CdSe. It is shown also that a-Si:H analysis is generally suitable for deriving thin-film surface parameters.
The variably spaced superlattice electroluminescent display: A new high efficiency electroluminescence scheme
Authors: Brennan K. F. , Summers C. J.
Published: July 2002

We present a new, highly efficient dc electroluminescent display. A variably spaced superlattice scheme is suggested herein which can produce high-energy injection of electrons into a ZnSe:Mn active layer in which impact excitation of the Mn centers can occur. The device is predicted to operate at an applied external bias an order of magnitude less than the best dc electroluminescent device to date. The device is predicted to have comparable brightness, since it operates in the saturation regime. The improved efficiency stems from avoiding significant energy loss to phonons. The electrons sequentially tunnel through a multilayer stack under bias and emerge into the active layer at an energy equal to the conduction-band bending. The injection energy is chosen to coincide with the impact excitation energy of the Mn centers. Different device designs are presented and their performance is predicted.
The temperature dependence of the optical dispersion parameters in Hg0.795Cd0.205Te
Authors: Toyoda T. , Hanba S.
Published: July 2002

In Hg0.795Cd0.205Te, the optical dispersion parameters (single-oscillator energy E0 and dispersion energy Ed) were analyzed in the temperature range from 100 to 300 K using the data by Finkman and Nemirovsky [J. Appl. Phys. 50, 4356 (1979)]. E0 and Ed exhibit large temperature dependence in Hg0.795Cd0.205Te. The signs of dE0/dT and dEd/dT are positive and absolute values of them are +1.67×10−3 eV/K and +17.4×10−3 eV/K, respectively.