bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiple states in surface lattice constant behavior during the molecular beam epitaxial growth of ZnTe-ZnS strained layer superlattices
Authors: Karasawa Takeshi , Ohkawa Kazuhiro , Mitsuyu Tsuneo
Published: July 2002

ZnTe-ZnS short period (∼30 Å) strained layer superlattices were grown by molecular beam epitaxy and the growth process was observed in situ by using reflection high energy electron diffraction (RHEED). Surface lattice constant (a∥) behavior shows a transition from one state in which a∥ is equal to that of the substrate to the other in which a∥ depends on the depositing constituents. RHEED patterns show the same streaks for both states except the difference in streak separation. Transmission electron micrograph reveals that the resultant multilayer structures of the two states have the same quality. The experimental data may suggest a possible assumption that there exists multiple states for two-dimensional growth of a strained system with substantial lattice mismatch.
Electrical resistivity between 10 and 1000 K of ferromagnetic Co75Si25−xBx and Co100−x(Si0.6B0.4)x amorphous ribbons
Authors: Barquín L. Fernández , Fernández J. Rodríquez , Gómez Sal J. C. , Barandiarán J. M. , Vázquez M.
Published: July 2002

The study of the variation of the electrical resistivity ρ between 10 and 1000 K has been performed in the Co75Si25−xBx and Co100−x(Si0.6B0.4)x ferromagnetic amorphous series. A general analysis of the curves gives useful data about the main features of ρ in these materials: Curie temperatures Tc, temperatures of the minima Tmin, crystallization temperatures Tx, temperature coefficient of resistivity, and absolute resistivity. The correlations between these magnitudes have been discussed including direct comparison with the nonmagnetic Ni-Si-B similar compounds. An analysis of the structural and magnetic contributions to the resistivity is presented in the whole temperature range. The structural part is interpreted in the framework of the extended Ziman model and it is superposed on the magnetic term. A T2 magnetic contribution coming from the spin wave scattering is found at temperatures between Tmin and approximately 0.5 Tc. At higher temperatures, the magnetic part seems to be understood taking into account the mean field approximation. Saturation magnetization M(T) measurements over 300 K were carried out in order to get an experimental hint of the correlation between the magnetic ρ and M(T) with rather satisfactory results. Besides the general analysis we report the achievement of a progressive shift of Tmin in some compounds (in particular in Co70Si18B12) in which a tentative explanation might be based on phonon ineffectiveness arguments.
Niobium disilicide formation by rapid thermal processing: Resistivity-grain growth correlation and the role of native oxide
Authors: Horache E. , Fischer J. E. , Van der Spiegel J.
Published: July 2002

The formation of NbSi2 from Nb/Si(100) is studied using rf sputtering and rapid thermal processing. For a long sputter-etching time (10 min) of the Si substrate, NbSi2 is first formed at 720 °C. The lowest resistivity attained is 38 μΩ cm, one of the best for refractory metal silicides. The variation of the sheet resistance versus annealing temperature is correlated to grain growth. The grain size is deduced from the x-ray coherence length of the NbSi2(111) peak which sharpens and increases in intensity for T≳720 °C. For shorter sputter etching time (5 min), NbSi2 only forms above 895 °C. This is attributed to the native oxide at the Si interface. An estimated ternary phase diagram of Nb-Si-O shows that Nb and SiO2 coexist at this temperature. Unlike other refractory metal silicides, oxygen in the Nb film is expelled as the silicide is formed.
Low-temperature i
n s
i
t
u surface cleaning of oxide-patterned wafers by Ar/H2 plasma sputter
Authors: Yew Tri-Rung , Reif Rafael
Published: July 2002

This paper presents the investigation of low-temperature in situ surface cleaning of oxide-patterned wafers by an Ar/H2 plasma prior to the epitaxial growth on exposed silicon windows. Ar/H2 plasma sputter cleaning was carried out at 2.5 or 20-W rf power and a susceptor dc bias from 100 down to 0 V. Epitaxial layers were grown immediately after the in situ surface cleaning by ultralow-pressure chemical vapor deposition from SiH4/H2 in a high-vacuum system (base pressure, 10−7 Torr). Process temperatures were varied from 800 down to 500 °C. The epitaxial films were characterized by cross-sectional transmission electron microscopy, secondary-ion-mass spectroscopy, Nomarski optical microscopy, and ion channeling Rutherford backscattering spectroscopy. It was found that a highly structural epitaxial layer can be grown down to 600 °C and an epitaxial layer can be grown at 500 °C by utilizing the preepitaxial in situ Ar/H2 plasma sputter cleaning.
Magnetohydrodynamic liquid-metal flows in a rectangular channel with an axial magnetic field, a moving conducting wall and free surfaces
Authors: Talmage Gita , Walker John S. , Brown Samuel H. , Sondergaard Neal A. , Burt Patricia E.
Published: July 2002

Fully developed, viscous liquid-metal velocity profiles and induced magnetic field contours were studied for Hartmann numbers of M=2 and 10 and for different load currents for a particular rectangular channel configuration (two-dimensional Couette flow). The rectangular channel was assumed to have a homogeneous external (axial) magnetic field parallel to the moving, perfectly conducting top wall and the stationary, perfectly conducting bottom wall. The two stationary side walls were also perfect conductors. The small gap between the moving wall and each side wall was an insulating, free surface. The method of weighted residuals was used to obtain truncated series solutions for the variables of interest. The heavy load currents across the channel were obtained by simulating an external potential to the conducting moving wall. The load currents in each case were opposed by the induced electric field. Since there is no pressure gradient, the flow along the channel is driven by the viscous effects of the moving wall and the Lorentz body force and is retarded by the stationary walls. In the case where no load current is applied across the channel, the current circulates in the channel.

The circulation is driven by the generator that is due to the axial variation of velocity in an axial magnetic field. The numerical results presented show that the radial gap and the free surface region represent electrical resistances in parallel between the perfectly conducting stationary wall and the perfectly conducting moving wall. The numerical results also show that the resistance of the radial gap increases as M2 while that of the free surface increases by M or M1/2. Thus, as M increases, the division of current shifts to the free surface region and the current density in the radial gap decreases as M−1. The theoretical magnetohydrodynamic model presented here was developed to provide numerical parameters to help in the design of liquid-metal current collectors. Numerical results were computed for one-dimensional Couette flow with no pressure gradient in an external, homogeneous axial magnetic field. One-dimensional Couette flow has no end effects, and thus the numerical results were compared with corresponding numerical results for the two-dimensional Couette flow case to determine end effects.
Dynamics of a high-current electron beam in an inverse high-power electron diode
Authors: Harper-Slaboszewicz V. J. , Poukey J. W. , Stygar W. A. , Lee J. R. , Fowler W. E.
Published: July 2002

The inverse triax diode is a low-impedance, high-power electron beam diode. A magnetically unbalanced electron flow in the outer gap, which results in an outward pinch, distinguishes this design. Particle code simulations show that this flow has two possible patterns, depending on the presence or absence of an anode plasma. A model for the beam dynamics based on anode plasma formation and incorporating the simulation results is developed. We compare the predictions of the model to experimental results, including time-resolved x-ray pinhole photographs obtained with a framing x-ray pinhole camera, and find reasonable agreement.
Magneto-optical memory media using BaTiON protective films
Authors: Maeno Yoshinori , Kobayashi Masanobu , Oishi Kayoko , Kawamura Kazutami
Published: July 2002

A new protective and enhancing film for magneto-optical memory media—BaTiON has been developed. The values of refractive index and extinction coefficient of the film were 2.75 and 0, respectively. Calculations give maximum Kerr rotation angles of 1.4 deg for three-layer-type media and more than 10 deg for reflective-layer-type media when such a film is used to enhance the rotation. The magneto-optical memory media using the film showed excellent recording characteristics.
Compressibilities and limiting internal pressures from the Tammann–Tait empirical equation of state
Authors: Perez A. , Dayantis J.
Published: July 2002

The Tammann–Tait empirical equation of state [Z. Phys. Chem. 17, 620 (1985)] is deduced from the thermodynamic equation of state, and compressibilities derived using the former equation are compared with those obtained using raw P,V,T, data for n-pentadecane. The agreement is in the range of 8%–15% and is not improved when the pressure is raised up to 3 100 bars.
Lattice dynamics of II-VI based diluted magnetic semiconductors
Authors: Talwar D. N. , Coleman Alan C. , Amirtharaj P. M.
Published: July 2002

The results of far infrared reflectivity and Raman scattering spectra reported recently in Hg1−xMnxTe samples with low composition of Mn impurities are analyzed theoretically. The Kramers–Kronig analysis in the spectral range (50–350 cm−1 ) is employed to obtain the proper energetic positions of the two optical phonons and a weak peak near ∼98 cm−1 (above the longitudinal acoustic-phonon band of HgTe). Simple schemes, based on the so called ‘‘oscillator fit’’ and modified random element isodisplacement models, are chosen with appropriate values of transition energies and strengths to reproduce the observed reflectivity spectra. A comprehensive calculation of the lattice dynamics in terms of semi-empirical Green’s function theory has provided convincing arguments that the feature near 98 cm−1 is a gap mode of Mn in HgTe.
Finite-element results of the slow compressional wave in a porous medium at ultrasonic frequencies
Authors: Teng Yu-chiung
Published: July 2002

Biot’s theory [J. Acoust. Soc. Am. 28, 168 (1956)] is investigated by the finite-element method at ultrasonic frequencies. The numerical results for an acoustic/poroelastic/acoustic system are presented by using the double-node layers technique of Teng and Kuo [Comput. Acoust. Int. Assoc. Mathe. Comput. Simul., 239 (1988)]. This work is motivated by the work of Plona [Appl. Phys. Lett. 36, 259 (1980], Johnson [Appl. Phys. Lett. 37, 1065 (1980)], and Johnson and Plona [J. Acoust. Soc. Am. 72, 556 (1982)], in which they have experimentally and analytically investigated the problem of wave propagation in a fluid/fluid-saturated-porous-solid/fluid system and fourth sound in a porous ‘‘superleak’’ saturated with superfluid helium. Given suitable physical parameters in the finite-element calculations, if the open-boundary conditions at the fluid/porous-solid interfaces are used, excellent agreement with Plona’s measurements has been obtained. The finite-element results with the sealed interfaces for the same model, showing a diminishing of the second type of compressional wave, also agree with the experimental work performed by Rasolofosaon [Appl. Phys. Lett. 52, 780 (1988)].
Comparative study of atomic ordering and alloy clustering in InGaP crystals grown by metalorganic vapor phase epitaxy, chloride-vapor phase epitaxy, and liquid phase epitaxy
Authors: Ueda O. , Hoshino M. , Takechi M. , Ozeki M. , Kato T. , Matsumoto T.
Published: July 2002

We describe the results of the transmission electron microscope study of ordered and modulated structures in InGaP alloy semiconductors grown on (001) GaAs substrates by metalorganic vapor phase epitaxy, chloride-vapor phase epitaxy, and liquid phase epitaxy. Strong ordering of CuPt-type has been observed in InGaP grown by metalorganic vapor phase epitaxy at 630 °C, which is associated with an abnormality in the photoluminescence peak energy. CuPt-type ordered structures have also been observed in crystals grown by chloride-vapor phase epitaxy, but the degree of ordering is weaker and crystals grown at 576–740 °C exhibit normal photoluminescence peak energies. On the other hand, in crystals grown by liquid phase epitaxy, no ordered structure is found and the crystals exhibit normal photoluminescence peak energies. There is no dependence of modulated structures on the growth method since they are observed in all crystals. These results also lead us the previous conclusion by Kondow and co-workers that the ordered structures are not generated under thermal equilibrium conditions but rather by the diffusion and reconstruction of deposited atoms on the growth surface.
Analytical model for thin-film electroluminescent devices
Authors: Neyts K. A. , De Visschere P.
Published: July 2002

Up to now, models for the electrical behavior of thin-film electroluminescent devices have been proposed by several authors. These models usually account for electron tunneling, multiplication and recombination and involve considerable numerical calculations. In this paper we use a simplified but realistic tunnel characteristic, which makes it possible to calculate analytical steady-state solutions for a symmetrical device without space charge. Some interesting features of these solutions, like a waveform dependent threshold field and a double current-voltage characteristic will be discussed.
X-ray photoelectron spectroscopy analysis of Y-Ba-Cu-O surface barrier for superconducting junctions
Authors: Kominami Shin’ya , Tarutani Yoshinobu , Hirano Mikio
Published: July 2002

Fabrication of junctions with a Y-Ba-Cu-O/barrier/Y-Ba-Cu-O trilayered structure is attempted. The barrier layer is formed by CF4 plasma treatment. A nonlinear structure is observed in the current-voltage curve of the junction, but the Josephson current is not detected. The Y-Ba-Cu-O films before and after CF4 plasma treatment are investigated by x-ray photoelectron spectroscopy to clarify the junction’s structure. Compositional deviation is detected at the surface layer of the Y-Ba-Cu-O films. Of the CF4 plasma treatment effects, fluorination of yttrium and reduction of copper are observed.
Diffusion kinetics of Si in GaAs and related defect chemistry
Authors: Lee K. H. , Stevenson D. A. , Deal M. D.
Published: July 2002

The diffusion of Si in GaAs was investigated using diffusion sources from different tie triangle regions on the Si-Ga-As ternary phase diagram which provide constant chemical potentials for the three components under isothermal conditions. The Si profiles are measured with secondary ion mass spectrometry and differ significantly for the different sources. The Ga-Si-GaAs tie triangle source produces p-type Si doping with concentration independent diffusion coefficients, and a neutral As or Ga vacancy is proposed as the dominant mobile defect for these conditions. Arsenic-rich sources from two tie triangle regions and also a Si-GaAs tie line source produce Si donor diffusion with concentration-dependent diffusion behavior. The concentration-dependent diffusion coefficients of donor Si for As-rich source diffusion are related to the net ionized donor concentration showing three different regimes: intrinsic regime, intermediate regime, and saturation regime. Ga vacancies are proposed to be responsible for donor Si diffusion in GaAs: a V0Ga and/or V−Ga mechanism for the intrinsic regime; and a V−Ga related mechanism for the extrinsic and saturation regimes. The Si-GaAs tie line source resulted in two branch type profiles, intermediate between the As-rich and the Ga-rich source diffusion cases.
Growth temperature dependence of EL2 concentration in GaAs grown by metalorganic vapor-phase epitaxy using tertiarybutylarsine
Authors: Okabe T. , Kikkawa T. , Tanaka H. , Takikawa M. , Komeno J.
Published: July 2002

The EL2 concentration in GaAs grown by metalorganic vapor-phase epitaxy (MOVPE) using tertiarybutylarsine (tBAs) was measured by deep-level transient spectroscopy. EL2 concentration decreases monotonically with increasing growth temperature. Taking the origin of EL2 into consideration, we discuss the growth mechanisms of MOVPE using tBAs. The EL2 concentration is affected by the incorporation of excess As into the crystal, and, therefore, depends on the kind of reactant on the surface. We propose a model in which the reactant on the surface changes from As2H2 to As2 with increasing temperature. The temperature dependence of EL2 concentration is explained by our model where As2 dissociates into atomic As on the surface and As2H2 gives excess As in the crystal.
Nonlinear photoacoustic effect of semiconductors in dc electric field
Authors: Cheng Jian-chun , Zhang Shu-yi , Lu Yue-sheng
Published: July 2002

The nonlinear piezoelectric photoacoustic (PA) effect of silicon wafers in the applied dc electric field is studied experimentally and theoretically. The apparent nonlinear dependencies of PA amplitude and phase on the laser power are observed in experiments with different dc electric fields. The nonlinearity is explained theoretically by considering the nonlinear surface and bulk Auger recombinations. We present a ‘‘subsurface approximation’’ method to solve the nonlinear transport equation for photogenerated carriers in semi-infinite samples. A good agreement between the experimental results and theoretical predictions is obtained as the incident laser beam with and/or less than medium power.
Density sensitive line ratios for highly ionized atoms of the Cu i and Na i isoelectronic sequences
Authors: Feldman U. , Doschek G. A. , Seely J. F.
Published: July 2002

We discuss extreme ultraviolet and x-ray spectral lines emitted by ions of the Cu i and Na i isoelectronic sequences and show that certain intensity ratios of these lines are sensitive to electron density in the range from about 1018 to 1022 cm−3. These lines therefore provide density diagnostics for high-temperature plasmas. We illustrate the density dependence for four ions of the Cu i sequence (Z=60, 71, 82, 92) and seven ions of the Na i sequence (Z=32, 42, 52, 62, 72, 82, 92). We also show that the dependence of the ratios on electron temperature is not strong, and demonstrate that opacity can be kept small by employing the spot spectroscopy technique.
Coupling-loss-arrested misaligned semiconductor laser arrays
Authors: Wang Zheng , Du Guotong , Gao Dingsan
Published: July 2002

Coupling-loss-arrested misaligned semiconductor laser arrays are designed and fabricated by liquid-phase epitaxy. In these devices, the losses in the normal misaligned arrays is collected by a gain-induced positive waveguide, and then the collected light couples with light in the adjacent waveguides evanescently, therefore avoiding the coupling loss and strengthening the coupling. The constructed co-cavity element should have better characteristics with respect to transverse-mode selection. A clean single-lobe far field as narrow as 3° and a relatively low threshold of 130 mA for a seven-element array are obtained.
Comments on ‘‘Measurements of minority-carrier diffusion length in n-CuInSe2 by electron-beam-induced current method’’ [J. Appl. Phys. 6
6, 5412 (1989)]
Authors: Luke Keung L.
Published: July 2002

The recent findings of Scheer, Wilhelm, and Lewerenz[J. Appl. Phys. 66, 5412 (1989)] regarding the application of the electron-beam-induced current technique in both the vertical and planar configurations to determine the minority-carrier diffusion length in low-diffusion-length material are compared to the results of an earlier analysis [J. Appl. Phys. 57, 1978 (1985)] of the same subject. The differences are briefly discussed.
Reply to ‘‘Comments on ‘Measurements of minority-carrier diffusion length in n-CuInSe2 by electron-beam-induced current method’ ’’ [J. Appl. Phys. 66, 5412 (1989)]
Authors: Scheer R. , Lewerenz H. J.
Published: July 2002

The application of the vertical electron-beam-induced current configuration for diffusion lengths in the submicron meter range is briefly discussed. Results of our experiments [J. Appl. Phys. 66, 5412 (1989)] are compared to earlier investigations by other authors.
Transport and magnetic properties of high-T
c YBa2Cu3O7−x films
Authors: Chung D. W. , Maartense I. , Peterson T. L. , Hemenger P. M.
Published: July 2002

Thin superconducting films of YBa2Cu3O7−x were deposited onto (100) SrTiO3 substrates at 750 °C in 100 and 200 mTorr of O2, by ArF excimer laser ablation. The as-deposited films were strongly oriented with the c axis perpendicular to the surface when they were cooled to room temperature in oxygen. The highest values of transport critical current density (Jc≳105 A/cm2 below 80 K) were observed in films cooled in flowing O2. We find that, in all films, Jc follows a power law (1−T/Tc)n with n≊2, near the critical temperature, Tc, when Tc is defined as the temperature at which Jc=0. It appears that this behavior is governed by the short coherence lengths in this high-Tc material, as suggested by G. Deutscher and K. A. Müller [Phys. Rev. Lett. 59, 1745 (1987)], and not by the specific nature of the large-scale structure of the films.
Enhancement of intrinsic photoluminescence due to lateral confinement in InP/InGaAs quantum wires and dots
Authors: Patillon J. N. , Gamonal R. , Iost M. , André J. P. , Soucail B. , Delalande C. , Voos M.
Published: July 2002

Low-temperature photoluminescence and photoluminescence excitation experiments have been performed on lattice-matched InGaAs/InP quantum wells, wires, and dots grown by metalorganic vapor-phase epitaxy and processed by electron-beam lithography. An enhancement of the intrinsic photoluminescence mechanism is found with decreasing dimensionality.
Anomalous Hall effect in polycrystalline HgTe
Authors: Nath Tirlok , Roy Savita , Saxena P. , Mathur P. C.
Published: July 2002

We report the anomalous Hall effect and nonuniformities introduced by aging in the bulk polycrystalline HgTe, which was grown in a predetermined profile, and measurements were taken in the temperature range of 82–350 K. It is found that anomalous behavior is caused by domain formation which is due to acceptor states and this domain formation effect gets diminished by annealing the sample in a mercury atmosphere.
Species dependence of passivation and reactivation of acceptors in hydrogenated GaAs
Authors: Szafranek I. , Stillman G. E.
Published: July 2002

Effects of passivation and light-induced reactivation of acceptors in high-purity hydrogenated GaAs are investigated with low-temperature photoluminescence. The effectiveness of both processes has been found to be strongly dependent on the chemical identity of acceptor species, thus allowing a qualitative assessment of the relative stability of different acceptor-hydrogen passivating complexes in p-type hydrogenated GaAs. Efficient neutralization of acceptors in high-purity n-type hydrogenated GaAs is also reported, in contradiction with results of recent studies on heavily doped materials where passivation of minority dopants was not observed. The implications of these experimental data on theoretical models of the [AV:acceptor passivation mechanism are discussed.
Characterization and modeling of silicon metal-oxide-semiconductor transistors at liquid-helium temperature: Influence of source-drain series resistances
Authors: Hafez I. M. , Balestra F. , Ghibaudo G.
Published: July 2002

An analysis of silicon metal-oxide-semiconductor (MOS) transistor operation at liquid-helium temperature is presented. More specifically, analytical models providing the drain current and transconductance characteristics in the linear and nonohmic regions are established in the presence of source-drain series resistances. These models, which rely on a specific mobility law for very low temperature, enable a good description of MOS transistor operation to be obtained. They permit the understanding and the prediction of the effects of source-drain series resistance both in the linear and nonlinear regions. Furthermore, they allow a suitable parameter extraction method to be developed for the liquid-helium temperature range. In addition, peculiarities of the drain voltage dependence of the mobility at low longitudinal electric field are also pointed out and empirically accounted for in the modeling of the output characteristics.
High-performance metal/SiO2/InSb capacitor fabricated by photoenhanced chemical vapor deposition
Authors: Sun Tai-Ping , Lee Si-Chen , Liu Kou-Chen , Pang Yen-Ming , Yang Sheng-Jenn
Published: July 2002

The high-performance AuCr/SiO2/InSb metal-oxide-semiconductor capacitor was fabricated successfully using photoenhanced chemical vapor deposition. The 1200-Å-thick SiO2 layer was deposited on the InSb substrate at a temperature below 200 °C. Their electrical and structural properties were analyzed by capacitance-voltage and Auger electron spectroscopy, respectively. The capacitance-voltage results show that the optimal growth temperature of SiO2 is 150 °C at which the flat-band voltage of the capacitor is close to ideal and the slow interface state density is less than 5 × 1010 cm−2. For SiO2 deposited at a lower temperature, although the flat-band voltage and interface state are poorer, the subsequent thermal annealing at 150 °C for 12 h improves both quantities to the level as the optimal condition. However, for SiO2 deposited at a higher temperature (190 °C), the flat-band voltage shifts to −4 V and the slow state density increases to 1.1 × 1011 cm−2. It is found from the Auger depth profile that whatever the deposition temperature was a Si-rich region followed by an oxygen-rich region was formed at the SiO2/InSb interface. These observations are shown to be consistent with the electrical characteristics of the capacitor.
Shallow junctions by out-diffusion from BF2 implanted polycrystalline silicon
Authors: Georgiou G. E. , Sheng T. T. , Kovalchick J. , Lynch W. T. , Malm D.
Published: July 2002

We describe reverse bias diode leakage and physical analysis (secondary ion mass spectroscopy, Rutherford backscattering and transmission electron microscopy) data from shallow p+/n junctions made by implanting various doses of BF2 into polycrystalline Si and out-diffusing at various temperature/time conditions, into the underlying (100) Si substrate. The polycrystalline Si is cobalt disilicided to provide the first level of metallization. Subsequent metallization consists of electroless plated Co followed by sputtered Al. The minimum process specifications giving good junction quality (reverse bias diode leakage current density ≤10 nA/cm2 at 10 V) are 5×1015 cm−2 BF2 outdiffused at 900 °C, 30 min with a junction depth 1200 Å below the polycrystalline Si. At these conditions, most of the BF2 (>90%) uniformly redistributes in the polycrystalline Si. There is a slight increase in B concentration towards the polycrystalline Si/Si interface which is characterized by a porous, <50-Å thin silicon oxide interface. The polycrystalline Si/Si interface is also characterized by a peaked fluorine concentration. The lower boron dose diffusing into the Si substrate may be used to explain the observation that these p+/n diodes are ∼10 times leakier than similar n+/p diodes made by outdiffusing As or P implanted from the polycrystalline Si diffusion source.
Chlorine-related neutral complex in screen-printed CdTe
Authors: Ka O. , Neu G.
Published: July 2002

Detailed low-temperature optical characterization of screen-printed CdTe is presented. Photoluminescence and excitation spectroscopy demonstrate the existence of a new defect center systematically found in all the deposited layers. A possible explanation is based on a local mode induced by the defect but the experimental data are also very similar to those presented by Monemar et al. [Phys. Rev. B 25, 7719 (1982)] for two complexes in GaP:Cu. including the characteristic orange luminescence (COL) center, and for an Ag-related complex in ZnTe:Ag. The growth process as well as the optical results lead to an identification of the defect with an isoelectronic complex involving Cl ([VCd 2ClTe]).
Trapping kinetics and metastability of the D
X center in AlGaAs
Authors: Mohapatra Y. N. , Kumar V.
Published: July 2002

Trapping characteristics of two peaks, named A and B, associated with the well-known DX center in molecular-beam epitaxial grown, silicon-doped AlxGa1−xAs (x=0.36) are studied by deep-level transient spectroscopy as function of filling pulse width. With increase in filling pulse duration, several interesting features are noted including interdependence of the two peaks apparently logarithmic increase in height, shift in the peak temperature of the low-temperature peak B, and sharp reduction in its width. These unusual features provide clues to the dynamics of carrier capture and emission at the defect. We propose a model to qualitatively explain these features.
Effect of NH3 plasma treatment of gate nitride on the performance of amorphous silicon thin-film transistors
Authors: Luan Shengwen , Neudeck Gerold W.
Published: July 2002

The effect of NH3 plasma treatment of the hydrogenated amorphous silicon nitride (a-SiNx:H) gate insulator on the performance of hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) has been studied for different deposition conditions of the gate nitride. The TFT subthreshold slope and threshold voltage decrease with increasing rf power of gate nitride deposition. When increasing the rf power from 25 to 100 W, an increase in field-effect mobility, from 0.29 to 0.37 cm2/V s, is obtained. The NH3 plasma treatment causes a general increase in subthreshold slope and threshold voltage. It also degrades the field-effect mobility as large as 40%. However, the desirable effect of the plasma treatment is that the resulting devices have a higher stability exhibited by a 25% reduction of hysteresis width of transfer characteristics and by their higher resistance to prolonged positive gate field application. Based only on the electrical measurements, an exact model of the plasma interaction with the a-SiNx:H could not be developed. However, it is postulated that both radiation damage and nitridation/amination can occur.
Thermal evolution from a precursor to the Y-Ba-Cu-O superconductor: X-ray absorption spectroscopy study and application to thick-film technology
Authors: Sacchi Maurizio , Sirotti Fausto , Prudenziati Maria
Published: July 2002

The local structure around copper and yttrium atoms in a Y-Ba-Cu-O precursor prepared by spray pyrolysis is investigated by means of x-ray absorption spectroscopy. Near-edge and extended x-ray absorption fine structure analysis, together with powder diffraction measurements, give detailed information about structure and morphology of the precursor, as well as a clear picture of its thermal evolution towards the superconducting phase. Thick films prepared starting from this precursor are characterized. Their excellent electrical properties exemplify possible applications of this material.
Magnetic field and temperature dependence of flux creep in oriented grained and single-crystalline YBa2Cu3Ox
Authors: Keller C. , Küpfer H. , Gurevich A. , Meier-Hirmer R. , Wolf T. , Flükiger R. , Selvamanickam V. , Salama K.
Published: July 2002

Thermally activated flux creep of oriented grained and single-crystalline YBa2Cu3Ox was studied in fields up to 12 T and at temperatures ranging between 4 and 90 K. In fixed fields the activation energy U0 of both samples was found to increase with temperature, pass through some maximum and drop to the order of kBT around the irreversibility line. While at constant temperature U0 of the oriented grained sample showed a monotonous decrease with field; in the case of the single crystal it was found to follow a characteristic minimum-maximum structure paralleled by the previously observed field dependence of the shielding current. This clearly demonstrates the influence of the coupling properties, i.e., bulk behavior of the oriented grained sample and granularity of the single crystal, on relaxation. Therefore, models exclusively based either on a pinning or on a junction approach alone could not describe our experimental findings. A more appropriate explanation is based on the properties of the defect structure. Depending on field and temperature, defective regions are driven into the normal state whereby additional pinning centers are created which in turn give rise to increasing activation energies. The connectivity of the sample then depends on size and density of these defects.
I
n s
i
t
u small-angle x-ray scattering from coal during fluid extraction
Authors: Nemmers Scott , Horne David K. , Bale Harold D.
Published: July 2002

I n situ small-angle scattering measurements were made on a subbituminous coal during various stages of fluid extraction with tetrahydrofuran. The experiments not only showed the changes in the porosity due to fluid exposure, but also the pore filling characteristics of the fluid needed for extraction. Specifically, the experiments showed that the extensive micropore structure formed during fluid exposure at temperatures and pressures in the range of 380 °C and 4.5 MPa played a key role in the interaction of the fluid and coal matrix needed for a substantial extraction yield. Two distinct types of fluid penetration into the pore system were in evidence. One process involved the filling of the macropore structure. This process was observed at low temperature (120 °C) and high pressure, and did not cause appreciable swelling of the structure, but proved to be a reversible process when the fluid pressure was reduced. In contrast, the filling of the micropore system was accompanied by micropore dilation, which was irreversible at low temperatures.
Defect microstructure in laser-assisted modulation molecular-beam epitaxy GaAs on (100) silicon
Authors: Christou A. , Stoemenos J. , Flevaris N. , Komninou Ph. , Georgakilas A.
Published: July 2002

Two-dimensional growth of GaAs on (100) silicon has been achieved by combining laser-assisted growth and modulation molecular-beam epitaxy techniques. The misfit dislocations were shown to form a regular cross-grid with satellite reflections characteristic of a two-dimensional homoepitaxial growth as also revealed by the perfection of the moiré patterns of the GaAs/Si interface. The few antiphase domains generated at the interface were observed to annihilate very fast. The top surface of GaAs was free of antiphase domains. Planar defects such as stacking faults and microtwins are also eliminated.
In situ study of film stresses in metal silicides using absorption-edge-contour mapping
Authors: White G. E. , Chen Haydn
Published: July 2002

The stresses present in palladium- and nickel-silicide thin films during deposition and subsequent annealing processes have been monitored using the absorption-edge–contour mapping technique employing synchrotron radiation. A miniature fabrication chamber has been constructed for this purpose. The magnitude and the sense of the film stresses vary with the deposition condition and the annealing process. Film relaxation occurs during annealing so that a state of no stress can be reached at annealing temperature. The origins of fllm stresses as well as the changes of stress magnitudes are discussed.
Tungsten metallization for stable and self-aligned InP-based laser devices
Authors: Katz A. , Pearton S. J. , Geva M.
Published: July 2002

Tungsten thin films on n-InP layers have been investigated for potential use as a refractory ohmic contact for self-aligned In-based etched mesa buried heterostructure laser devices. The W films were rf sputter deposited onto InP substrates, S doped in the range of 1×1018–1×1019 cm−3. The deposition parameters were optimized to produce films with the lowest possible induced stress, minimum argon content, and best morphology for as-deposited wafers and after undergoing reactive-ion etching and high-temperature thermal cycles (700 °C), which are required for the self-aligned technology. These parameters were obtained for films that were rf sputter deposited at a discharge power of 240 W and under argon pressure of about 10 mTorr. A thermal expansion coefficient of 5.84×10−6 C−1 and a biaxial elastic modulus of 0.97×1012 Pa were measured for the films. The electrical behavior of the W films sputtered onto n-InP was studied by means of I-V and contact resistance measurements, which revealed a linear ohmic contact as-deposited, while sputtered onto n-InP substrates, S doped to the level of 5×1018 cm−3 or higher. Rapid thermal processing at elevated temperatures improved the ohmic contact quality and decreased the specific contact resistance values to a minimum of 3.5×10−6 Ω cm2 as a result of heating the W/InP (S doped 1×1019 cm−3) at 600 °C.
Laser-plasma generation of currents along a conductive target
Authors: Kabashin A. V. , Konov V. I. , Nikitin P. I. , Prokhorov A. M. , Konjević N. , Vikor L.
Published: July 2002

Large electric currents have been observed along conductive targets on which plasma was initiated by means of spatially modulated radiation. Two successive pulses of TEA CO2laser with intensities I≤109 W/cm2 were used in the experiments. The most effective generation of the currents was observed during the second laser pulse delayed for 4 μs, when an asymmetric plasma ‘‘grating’’ was produced on the target. Two different mechanisms for generating such currents in a closed circuit have been established. One of them results from a dipole moment of plasma, while the other is due to the processes at plasma-surface interface. To obtain correct measurements of the voltage induced by a laser plasma, a fiber optical modulator of light has been used for the first time.
Monte Carlo simulation of photoelectron emission from a gold specimen
Authors: Takeuchi Koichi , Murata Kenji
Published: July 2002

A Monte Carlo model is proposed for calculating the photoelectron intensity taking into account the elastic scattering of photoelectrons in gold, by applying Mott cross sections. Angular distributions and depth distributions of emitted electrons from the gold surface are calculated. The results are discussed both for the new model and the conventional model. The discrepancy in angular distribution between the two models increases proportionally with the asymmetry parameter and the inelastic mean free path. Also it is found that photoelectrons are originated at nearby shallower layers with the Monte Carlo model due to elastic scattering than that with a conventional one. Monte Carlo calculations have also been done with the screened Rutherford cross section for elastic scattering. The results of the intensities and the average production depth of photo and Auger electrons are discussed in comparison with the new Monte Carlo results.
Study of subboundary generation in silicon-on-insulator films recrystallized by a pseudoline electron beam
Authors: Horita Susumu , Fukao Kazuichi , Ishiwara Hiroshi
Published: July 2002

We investigated subboundary generation in silicon-on-insulator (SOI) structures which have square-shaped SOI regions and surrounding seed stripes. The SOI films were melted using a pseudoline electron beam, which was produced by oscillating a spot beam faster than the thermal response time of the substrate, and recrystallized through laterally seeded epitaxial growth from the seed stripes. It was found that a molten zone with a concave trailing edge was not effective to form a subboundary-free SOI region wider than several tens of micrometers, since the curved liquid-solid (L-S) interface easily generated subboundaries along 〈100〉 directions. It was also found that the temperature fluctuation due to the oscillation of the spot beam was not directly related to subboundary generation, although it produced some crystalline defects in the films. Concerning the size of SOI patterns, a two-dimensional array of small SOI patterns, each of which is surrounded by seed stripes, was found much more effective to increase the total subboundary-free area than that of larger SOI patterns. From these results, an optimum oscillation waveform was synthesized by combining the triangular and sinusoidal waveforms, so that the trailing edge of the molten zone became straight. Then, in order to minimize generation of {111} facets at the L-S interface which is known to be the origin of subboundaries, the pseudoline beam was swept in the 〈110〉 direction as a whole. As a result, a 150-μm-square SOI region or 5×7 array of 50-μm-square SOI regions was recrystallized by a single sweep without generation of subboundaries.
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i incorporation of ballistic and heating effects in a four-moment approach to the Boltzmann equation
Authors: Portengen T. , Boots H. M. J. , Schuurmans M. F. H.
Published: July 2002

A new four-moment method for the approximate solution of the Boltzmann equation is considered. It is based on a systematic expansion of the distribution function in Hermite polynomials that accounts a priori for ballistic and heating effects. The closure relation for the fourth moment, the ‘‘quadratic energy density,’’ is tested using numerically exact solutions of the coupled Boltzmann–Poisson equations for the n+nn+ diode in the constant relaxation time approximation. It is shown that the present expansion converges faster than expansions that do not account a priori for heating and drift of the electrons. The quality of the expansion is also discussed in relation to the value of the relaxation time.
Measurement of sodium density and the Na 514-nm transition probability in a high-pressure sodium arc
Authors: Benson T. P. , Bhattacharya A. K.
Published: July 2002

Spatially resolved arc temperatures and sodium density measurements are presented for two high-pressure sodium arcs. Absolute intensities of the optically thick 818/819-nm lines were used to determine the arc temperature while the radial profile of the optically thin 514-nm line was Abel inverted to determine the Na atomic density. Agreement with an independent measurement of the Na density obtained by controlling pressure of sodium in the lamp with a tin bath consistently required a value for the Na 514-nm transition probability 2–3 times smaller than the literature value (A=0.011×108 s−1 ) of Wiese, Smith, and Miles [Atomic Transition Probabilities, NSRDS-NBS 4 (NBS, Washington, DC, 1971), Vol. II], obtained from quantum mechanical calculations. The results of three separate experiments indicate that the value should be modified to A=0.0040×108 s−1 with a standard deviation of ±21%. A more detailed error analysis including systematic error would indicate an accuracy to within ±33%.
Tracer diffusion of 110Ag in YBa2Cu3O7−δ
Authors: Chen Nan , Rothman S. J. , Routbort J. L.
Published: July 2002

Tracer diffusion of 110Ag in YBa2Cu3O7−δ has been measured in the temperature range 800–950 °C using serial sectioning. The polycrystalline samples were made either from a powder containing about 0.2% Zr prepared by a conventional technique, or from a purer powder that had been calcined in low-pressure oxygen. Concentration profiles indicate both a volume and a fast diffusivity path contribution to diffusion. The activation energies were 227±3 and 249±17 kJ/mole for samples made from powder calcined in low-pressure oxygen and conventional powder, respectively. Diffusion was slower in the samples made from the purer powder.
Thermally induced optical bistability in ZnSe epilayers grown by molecular-beam epitaxy
Authors: Kudlek G. , Hollandt J. , Presser N. , Gutowski J. , Durbin S. M. , Menke D. R. , Kobayashi M. , Gunshor R. L.
Published: July 2002

For the first time, ZnSe epitaxial layers grown by molecular-beam epitaxy are shown to exhibit large contrast, low power, and extremely long-term stable thermally induced absorptive optical bistability. It is observed over a wide temperature range between 169 K and RT, with a strongly variable loop width and a switch-back adjustable to be less than 50% of the respective switch-down value. Critical slowing down as well as switch-down times are studied in dependence of the excess over the switch-down intensity values.
The relationship between the pyrolysis of trimethylgallium in the gas phase and that on the surface
Authors: Hoshino Masataka
Published: July 2002

Trimethylgallium (TMGa) heterogeneously decomposes predominantly at a lower partial pressure than 3×10−3 atm in the presence of GaAs. As the TMGa partial pressure becomes larger, more TMGa decomposes in the gas phase than on the surface. The decomposition mechanism using the Langmuir adsorption isotherm is explained; the TMGa adsorbs on the surface obeying the Langmuir adsorption isotherm and TMGa decomposes on the surface as well as in the gas phase. From this decomposition mechanism the TMGa decomposition rate constant in H2 without the surface catalysis is evaluated as ln kg(s−1) =38.8–57.6 (kcal/mol)/RT.
Secondary ion mass spectroscopic investigation of GaInAsP/InP laser structures made by metalorganic vapor phase epitaxy regrowth
Authors: Harde P. , Fidorra F. , Venghaus H.
Published: July 2002

Buried ridge structure GaInAsP/InP lasers with stripes parallel to 〈011〉 and 〈01̄1〉 directions (designated type A and B, respectively) were fabricated by MOVPE regrowth. Type A lasers exhibit considerably lower threshold current, higher maximum output power, and higher yield than type-B devices. Secondary ion mass spectroscopy depth profiles taken with high spatial resolution using the checkerboard matrix gate technique reveal elemental distributions as expected for type-A lasers, but the following unexpected results were observed for type B structures: A considerable amount of phosphorus is found in the GaInAs above the laser stripes, which is correlated with a reduced gallium concentration and a higher proportion of indium. Zinc, diffused into the GaInAs to make ohmic contacts, has a reduced concentration above the laser stripes, but occasionally exhibits exceptionally high concentrations with strong localization. The sputter rate in a region extending up to 15 μm on both sides of the laser stripe is significantly enhanced after zinc diffusion into the top GaInAs layer of type B structures. The observed anomalies are attributed to reduced crystalline perfection of the InP regrown above 〈01̄1〉 oriented laser stripes. The lower crystallinity favors efficient phosphorus outdiffusion from the InP during growth of the GaInAs and it also enhances zinc diffusion. The experiments emphasize the need to optimize the growth parameters for MOVPE regrowth above 〈011〉 and 〈01̄1〉 oriented structures separately.
Transient signals induced by laser irradiation of negative ions in hollow electrode discharges of Cl2 and HCl in N2
Authors: Han J. C. , Suto Masako , Lee J. C. , Petrović Z. Lj.
Published: July 2002

A technique for sampling negative ions in hollow-cathode and hollow-anode discharges of strongly electronegative gases is presented. The negative ions were mass analyzed to be Cl−, Cl−2, and Cl−3 for the discharge of Cl2/N2 mixture and Cl− for HCl/N2. The dependence of negative ion intensity on gas pressure and discharge voltage was investigated. Photodetachment of negative ions was used to induce photoelectron transient signals that probe ion concentrations. The transient signal indicates that negative ions originate in discharge, but not in the mass-analyzer region. Time dependence of the negative ion signal induced by laser irradiation was measured by a quadrupole mass analyzer and used to study the kinetics of charged particles responsible for the transport of laser-induced perturbation. The observed negative ion transient signal is a useful means for studying negative ion kinetics in plasma.