bluuebunny/crossref_metadata_2025 huggingface dataset:
The effects of ground-state dynamics on the emission spectra of electric-discharge-pumped XeCl lasers: A model for injection locking
Authors: Ohwa Mieko , Kushner Mark J.
Published: July 2002

The bandwidth of excimer lasers is typically 1–10 Å as a result of their transitions being multiline or bound-free. To obtain high power with narrow bandwidth injection locking is usually required. In this paper, we investigate the spectral characteristics of electric-discharge-pumped XeCl (B→X) lasers during injection locking and free-running operation. This study is performed using results from an electron kinetics and plasma chemistry model for Ne/Xe/HCl/H2 mixtures which includes multiline laser extraction. We find that the experimentally observed lasing spectrum cannot be explained if a thermal distribution is used for the vibrational levels of the X state. Therefore, the vibrational levels of the B, C, and X states are explicitly included in the model and the gain spectrum is computed using Franck–Condon factors. Results from the model indicate that bottlenecking occurs on the v′=0→v″=1 transition, while the dissociation rate for XeCl(X,v″=2) is faster than the removal rate for XeCl(X,v″=1). Injection locking characteristics are examined as a function of injection intensity and small-signal gain. Due to nonequilibrium dynamics in the ground state, locking efficiency does not necessarily increase with increasing small-signal gain.
Investigation of the SiO2/Si interface. II. Oxidation of an HF-cleaned Si(100) surface using photoemission spectroscopy with synchrotron radiation
Authors: Nakazawa M. , Nishioka Y. , Sekiyama H. , Kawase S.
Published: July 2002

The oxidation of a Si(100) surface cleaned using a HF solution and exposed to air, and the composition of the SiO2/Si interface are studied in situ by high resolution (ΔE<0.3 eV) photoemission spectroscopy, using synchrotron radiation. The results are compared with those of a Si(100) surface cleaned by repeated Ar ion sputtering and annealing. The presence of SiC and SiH bonding states at the SiO2/Si interface for the HF-cleaned Si restricts oxidation—the diffusion of oxygen atoms into the Si substrate. In the results, the proportions of Si2+ and Si3+ intermediary states at the interface increase and the interface broadens (0.85–1.0 nm), compared with the oxidation of the clean Si(100) surface.
Retardation of nucleation rate for grain size enhancement by deep silicon ion implantation of low-pressure chemical vapor deposited amorphous silicon films
Authors: Wu I.-W. , Chiang A. , Fuse M. , Öveçoglu L. , Huang T. Y.
Published: July 2002

The effects of silicon ion implantation on the crystallization kinetics and grain size of low-pressure chemical vapor deposited amorphous silicon on oxidized silicon substrate have been studied by x-ray diffraction and transmission electron microscopy. The most effective grain size enhancement was achieved by deep silicon ion implantation with the projected range located beyond the bottom interface to allow the maximum kinetic energy transfer at or near that interface. The grain size enhancement was due to a decrease of nucleation rate and an increase of the nucleation activation barrier from 3.9 to 4.9 eV for the Si+-implanted sample. The amorphous-to-crystalline grain growth activation barrier of 3.2 eV was not altered by Si+ implantation, but the growth rate was decreased. Retardation of nucleation and enhancement of grain size are attributable to the implant-recoiled oxygen. The average grain size increases from ∼0.2 to ∼2.0 μm by using 2×1015 cm−2 of Si+ implantation at 92 keV for 82-nm-thick films.
Hydrogen permeation into iron
Authors: Wampler W. R.
Published: July 2002

The permeation of deuterium (D) from the gas phase into solution in iron has been measured using a new method based on ion beam analysis. For bare metal surfaces the D uptake was observed to be limited by matrix diffusion through the bulk. The influence of chemisorbed oxygen on the D uptake rate was examined in detail. Submonolayer coverages of oxygen caused the D uptake to become surface-limited and reduced the D uptake rate by orders of magnitude. The temperature dependence of the surface-limited uptake rate suggests that a molecular precursor state may be involved in the D uptake for oxygen covered surfaces. The evidence indicates that chemisorbed oxygen reduces the D uptake and release rates by blocking sites where D can be chemisorbed on the surface.
Reflection high-energy electron diffraction electron-stimulated desorption from ZnSe(100)(2×1)-Se surfaces
Authors: Farrell H. H. , deMiguel J. L. , Tamargo M. C.
Published: July 2002

The electron-stimulated desorption (ESD) of Se from ZnSe(100)(2×1) surfaces prepared by molecular-beam epitaxy (MBE) and monitored with reflection high-energy electron diffraction is reported. Se atoms are removed from the growth surface according to a thermally activated ESD process. Consequently, this effect is most pronounced at higher temperatures and at lower growth rates. While ESD is commonly observed for ionic compounds, its significance for MBE growth of II-VI materials has not previously been discussed.
Introduction of defect levels in resistive-evaporated n-Si Schottky barrier diodes
Authors: Ohta E. , Kakishita K. , Lee H. Y. , Sato T. , Sakata M.
Published: July 2002

Defect levels in n-type Si Schottky barrier diodes made by resistive evaporation have been investigated by deep level transient spectroscopy. Three defect levels are observed at 0.16, 0.14, and 0.12 eV below the conduction band. The concentrations of the defect levels exponentially decrease into the substrate. The defects are introduced during etching process rather than evaporation process. The concentration of the defects increase with the thickness of the layer removed by etching before Schottky metal deposition, and decrease with the etching rate. This suggests that the defect levels are produced near the surface and are driven into the substrate during etching processes.
A magnetoresistive gradiometer for detection of perpendicularly recorded magnetic transitions
Authors: Gill H. S. , Hesterman V. W. , Tarnopolsky G. J. , Tran L. T. , Frank P. D. , Hamilton H.
Published: July 2002

A magnetoresistive gradiometer to detect perpendicularly recorded transitions has been conceived. It utilizes two parallel magnetoresistive stripes with opposing sense/bias currents. The magnetoresistive elements mutually bias each other with the same polarity bias fields. The fields of a perpendicular transition centered between the two stripes increase the resistance of one stripe while decreasing that of the other, therefore providing maximum output signal using differential detection. The detector provides a Lorenztian-type readback waveform and rejection of common-mode noise. The experimental readback waveform exhibited a pulse width at half maximum of 0.7 μm for a head flying at 0.2 μm above the media surface.
The effect of metal surface passivation on the Au-InP interaction
Authors: Fatemi Navid S. , Weizer Victor G.
Published: July 2002

The effect of SiO2 encapsulation on reaction rates in the Au-InP system was studied. Scanning electron microscopy and x-ray photoelectron spectroscopy were used to investigate surface and/or interface morphologies and in-depth compositional profiles. It was found that the rate of dissolution of InP into Au and subsequent phase transformations are largely dependent on the condition of the free surface of the metalization. SiO2 capping of Au is reported for the first time to suppress the Au-InP reaction rate. The Au-InP interaction is shown to be quite similar to the Au-GaAs interaction despite differences in the behavior of the group-V elements.
Multifrequency surface acoustic wave investigations of metal film percolation
Authors: Hock R. , Wesner J.
Published: July 2002

Change of the sound velocity and the amplitude signal of surface acoustic waves (SAW) on LiNbO3 substrates has been measured as a function of frequency during the growth of metal films of Pb, Bi, and Au on the originally free-crystal surface. Simultaneously, we recorded the conductivity of the films. SAW propagation is strongly perturbed in the percolation region where the films become conducting and mechanically connected. Au films on LiNbO3 show a new and yet unreported behavior: sound velocity and attenuation stay nearly constant over a film thickness range of ≊10 nm and conductivity is finite but low. For comparison we measured the change of sound velocity and amplitude of a SAW on a nonpiezoelectric glass substrate during the growth of a Pb film. Sound velocity is found to vary nonlinearly for a film thickness ddc due to mass loading with increasing film thickness. No damping of the sound wave in the percolation region was observed. A new computerized ultrasonic system is described which made it possible to measure sound velocity and amplitude quasisimultaneously at up to three different frequencies.
Iron-related deep levels in n-type silicon
Authors: Kakishita K. , Kawakami K. , Suzuki S. , Ohta E. , Sakata M.
Published: July 2002

Deep levels in iron-doped n-type silicon have been investigated by deep-level transient spectroscopy (DLTS). Three deep levels of Ec−0.29 eV (E1), Ec−0.36 eV (E2), and Ec−0.48 eV (E3) were observed. The concentration of E1 and E2 levels increased during the storage at room temperature. The depth profile of the E3 level concentration indicates the out-diffusion and precipitation of the defects related to the E3 level. In addition, after annealing at 80 °C for 30 min, the E2 and E3 concentrations decreased and then recovered at room temperature. These results suggest that the defects related to these levels are mobile during quenching and storage at room temperature. The temperature dependence of the E3 level concentration shows a formation energy of about 2 eV, which is smaller than that of interstitial iron, and the E3 level concentration is two orders of magnitude lower than the concentration of interstitial iron. The origins of these levels are probably loosely associated iron-related complexes such as iron-acceptor pairs.
Arc pressure effect on the population of the Hg 63P levels
Authors: Karabourniotis D. , Couris S. , Drakakis E. , Damelincourt J. J.
Published: July 2002

Three mercury arcs at pressures 1.9, 2.9, and 5.2 bar have been studied spectroscopically. The determination of the population densities and of the deviations from Boltzmann’s law in the Hg 63P2,1,0 levels as a function of the arc pressure has been done from the ratio of the self-reversal to the line center minimum intensities, and the distance between the two side maxima of the optically thick 546.1, 435.8, and 404.7-nm lines, and the total intensity of the optically thin 577-nm line. The arcs were operated on ac (50 Hz) and the measurements have been made at 0.5 and 5 ms after the voltage-zero crossing. The analysis of the optically thick lines was based on a simplified model for the line self-absorption which is independent of the local thermodynamic equilibrium assumption. An attempt was also made to interpret qualitatively the obtained experimental results.
Damage of silicon in low-energy Ar discharge studied by photoinduced modulation absorption
Authors: Chen F. Y.
Published: July 2002

The damage of silicon processed by low-energy (70 eV) Ar discharge was investigated by the technique of photoinduced modulation absorption. It was found that low-energy Ar discharge causes damage that enhances the surface recombination velocity at the processed surface and reduces the carrier diffusion constant in the bulk. However, no significant change of the bulk carrier lifetime was found.
Low-temperature specific heat of (SN)x
Authors: Lou L. F.
Published: July 2002

The specific heat of (SN)x between 0.11 and 0.15 K was measured on a composite sample of many small (SN)x crystals. A smeared excess specific heat anomaly was obtained with its peak at the superconducting transition temperature (Tc =0.26 K, determined by the resistivity measurement4). The entropy related to the specific heat anomaly was comparable to that of a BCS superconductor with same Tc and normal-state specific heat. These results suggested that the superconductivity in (SN)x is likely a bulk effect. The anomaly-peak temperature was suppressed to 0.18 K in an applied magnetic field of 1 kG. A smeared Schottky magnetic anomaly was also induced, and persisted after the removal of applied field at 1 K. These results indicated coexistence of magnetic and superconducting ordering in (SN)x crystals.
Charge trapping in a layered organic photoconductor studied by photoacoustic and xerographic discharge measurements
Authors: Kanemitsu Yoshihiko , Imamura Shunji
Published: July 2002

The influence of charge trapping on photocarrier generation in a layered organic photoconductor consisting of a charge generation layer (CGL) and a charge transport layer was studied by means of photoacoustic and xerographic discharge techniques. The photocarrier generation efficiency in the CGL was derived by measuring the decrease in the photoacoustic (PA) signal when an electric field was applied to the sample. Prolonged light exposure under a high applied field increased the photocarrier generation efficiency and the negative xerographic residual potential. After the termination of the applied field, the PA signal reverted to the initial value very slowly. The recovery time of the PA signal after the termination of the applied field agreed well with the decay time of the xerographic residual potential. The increase in the photocarrier generation efficiency and the negative residual potential are due to the trapping of electrons in the CGL.
P-rich Si particles in separation by implanted oxygen structures revealed by low-temperature electron-spin resonance
Authors: Van Gorp G. , Stesmans A.
Published: July 2002

Low-temperature X- and K-band electron-spin-resonance measurements on separation by implanted oxygen structures formed by implanting oxygen to a dose ≊1.7×1018 cm−2 on [001] c-Si wafers—both n and p type [dopant concentration ≊(9–28)x1014 cm−3 ]—reveal the presence of a signal due to submetallic Si:P effectively doped to [P]≊2.0×1018 cm−3 . The signal is identified as originating from the polyhedron-shaped c-Si precipitates known to remain in the buried SiO2 layer near the bulkside Si/SiO2 interface, even after high-temperature annealing. The capstone in this identification stems from the faceted structure of these Si islands, which, combined with the concomitant misfit-induced and plane-index related strain, accounts for the anisotropic g and linewidth—not observed as such in bulk Si:P. This result indicates an impurity effect as contributing to the persistence of these Si microcrystallites upon annealing.
Heteroepitaxy of Si films on a Ge(100)-2×1 surface
Authors: Kawabata H. , Ueba H. , Tatsuyama C.
Published: July 2002

Heteroepitaxial growth of thin Si films on a Ge(100)-2×1 surface has been studied by means of low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and low-energy electron loss spectroscopy (LEELS). When the substrate temperature Ts was maintained at room temperature, the intensity of the Ge AES signals decreased with an increase in the Si deposition thickness dSi, in accordance with a layer-by-layer growth of the Si films. No ordered LEED pattern was observed upon Si deposition and the LEELS spectra changed to that observed for a sputtered Si, thereby revealing the growth of amorphous Si films at Ts=RT. At a higher temperature, Ts=500 °C, the long-lived Ge AES signals and the energy-loss features associated with the Ge surface states as well as the Ge 3d derived loss peak suggested the formation of small islands via the Volmer–Weber growth mode. The LEELS spectrum at dSi =30 Å became almost the same as that observed for a clean Si(100)-2×1 surface, as an indication of a single-crystalline growth of Si films on a Ge(100) surface.
Studies of majority-carrier traps in Zn-doped p-InP by thermally stimulated capacitance techniques
Authors: Singh A. , Anderson W. A.
Published: July 2002

High-barrier Yb/p-InP Schottky diodes were used to study majority-carrier traps in the Zn-doped p-InP single-crystal substrates by thermally stimulated capacitance (TSCAP) techniques. The TSCAP studies involved a forward bias VF=0.6 V, cooling to 90 K, bias switching to reverse bias VR=4.0 V, and then heating at a constant heating rate to 450 K. The junction capacitance was recorded as a function of temperature for various heating rates between 0.05 and 0.5 K/s, and corrected for temperature dependence of the diffusion voltage and the dielectric constant. The trapping parameters of the strong hole trap level were determined from the plots of dΔC/dT vs T at different heating rates, and values of Eh1=EV+0.59 eV and σp1 =3×10−21 cm2 were obtained for the activation energy and capture cross section, respectively, of the hole trap. From the TSCAP data at a constant heating rate and using the Eremin, Strokan, and Turebekov [Sov. Phys. Semicond. 15, 1010 (1981)] method, a hole trap with Eh1=EV+0.62 eV and σp1 =2×10−21 cm2 was also detected. From the amplitude of the steady-state positive capacitance step, a value of NTP =2.7×1014 cm−3 for the concentration of the hole trap level was estimated.
Time-resolved, photo-assisted electroluminescence in thin-film display panels
Authors: Pappalardo R. G. , Levinson M.
Published: July 2002

A new technique for the analysis of electroluminescent (EL) device physics is reported. Pulsed UV irradiation of thin-film electroluminescent (TFEL) display panels, when synchronous with one of the drive-voltage pulses, increases the EL intensity and enhances the polarization at the end of the EL pulse. The EL gain and the enhanced polarization relax jointly over times as long as 200 ms. A linear correlation is observed between EL-pulse intensity and the associated polarization changes. Interpulse UV irradiation decreases the existing polarization and lowers the intensity of the next EL pulse.
Selenization of metallic Cu-In thin films for CuInSe2 solar cells
Authors: Szot Jozef , Prinz Uwe
Published: July 2002

A new approach for formation of photovoltaic CuInSe2 films by chalcogenization of Cu-In multilayers with a thin selenium layer and subsequent heat treatments is presented. Morphological, compositional, and structural properties of films along with aspects of various processing conditions are discussed. The possibility of obtaining perfectly homogeneous chalcopyrite ternary films was affected by composition deviations from stoichiometry, although films obtained in a modified two-stage heat treatment processing were of good structural and photovoltaic quality. Heterojunctions with (Zn, Cd)S as window material showed efficiencies better than 5%, mainly limited by low open-circuit voltage and poor fill factor. Short-circuit currents were comparable to CuInSe2-based cells fabricated by multiple-source evaporation.
Theory and design of semiconductor electron-wave interference filter/emitters
Authors: Glytsis E. N. , Gaylord T. K. , Brennan K. F.
Published: July 2002

A voltage-biased semiconductor superlattice structure is designed to operate simultaneously as a continuously voltage-tunable, electron interference filter and as an electron emitter. Using the analogies between electromagnetic waves and electron de Broglie waves, a systematic procedure for designing the quantum wells and barriers comprising the electron-wave filter/emitter superlattice is developed. A generalized procedure for analyzing the electron-current transmittance and reflectance spectral responses of these superlattice structures is then presented. A practical, continuously tunable filter/emitter consisting of multiple layers of Ga1−xAlxAs (compositional superlattice) is designed to emit nearly monoenergetic 0.20-eV electrons by appropriate selection of the layer compositions and thicknesses. The constraints required to have thicknesses that are integer multiples of the monolayer thickness and to avoid phonon scattering of electrons into the L band are included. The filter/emitter is shown to have a wide tunable energy range. A sensitivity analysis of the device characteristics in the presence of fabrication errors reveals a very stable device response. Such quantum electron-wave devices could serve as continuously tunable hot-electron emitters in ballistic transistors and in future guided electron-wave integrated circuits.
Heterogeneous silicon crystal growth on a single-crystal silicon wafer
Authors: Hide I. , Fujiya E. , Maeda Y. , Itoh S. , Tanabe S. , Usui T. , Akahane K.
Published: July 2002

Using a new process, a large grain polycrystalline silicon layer was grown directly from molten Si on a single-crystal silicon wafer at a rate 100 times faster than the conventional chemical vapor deposition process. A polycrystalline silicon layer was also produced on a single-crystal silicon wafer, which had an oxide layer and etched V grooves, through use of an additional ultrasonic wave effect in this process. A layer thickness of 100–600 μm and a grain size of 10 μm–3 mm were controllably obtained. After the growth of the polycrystalline layer, dislocation densities of 4×105 cm−2 for the single-crystal silicon substrate, and 2×106 cm−2 for the polycrystalline layer were obtained. Some devices were fabricated from the products of this new process, and the characteristics of these devices were investigated.
Passivation and generation of deep level defects in hydrogenated n-GaAs (Si)
Authors: Jalil A. , Heurtel A. , Marfaing Y. , Chevallier J.
Published: July 2002

Bulk n-type GaAs wafers (Si doped) have been exposed to a capacitively coupled rf hydrogen plasma at different power densities ranging from 0.01 to 0.2 W/cm2 at 260 °C. The electronic properties of these layers have been investigated by capacitance-voltage experiments and deep level transient spectroscopy. Besides the neutralization of the silicon donors by the in-diffused hydrogen atoms, we observe a modification of the deep level transient spectroscopy (DLTS) spectra after hydrogenation. For rf power densities lower than 0.1 W/cm2, the deep levels present in the region of the starting material explored by DLTS are passivated. The absence of electronic states associated with the silicon-hydrogen complexes in the neutralized donor region indicates that these complexes are either electrically inactive or deeply located in the energy band gap. For rf power densities higher than 0.1 W/cm2, two new deep electronic states appear at 0.41 and 0.55 eV below the conduction band. These levels are the signature of a large amount of defects in the near-surface region of n-GaAs (Si) after exposure to a rf hydrogen plasma at such power densities. Trapping of hydrogen on these defects is probably responsible for the accumulation of hydrogen in the near-surface region observed in the hydrogen diffusion profiles.
Microstructural and magnetization studies of sintered and melt-textured Y-Ba-Cu-O
Authors: Alford N. McN. , Button T. W. , Gough C. E. , Wellhofer F. , O’Connor D. A. , Colclough M. S. , Pollard R. J. , McCartney D. G.
Published: July 2002

For bulk applications, high-Tc superconductors generally require high critical current density, Jc. This paper reports two methods of producing high-Tc ceramic wires. The first is an extrusion and sintering route where Jc is routinely 600–1000 A cm−2. The second is by melt texturing or directional solidification where we have achieved in excess of 7000 A cm−2 by direct measurement at 77 K in zero field. However, the ease with which wire may be extruded and sintered is attractive and functioning devices have already been manufactured using this route. Fabrication of devices is facilitated by a unique processing route that has resulted in the strongest bulk ceramic yet reported (bend strength >200 MPa). The melt-texturing route and the problems associated with it are examined and compared with the extrusion and sintering route. The processing and the microstructures associated with the directionally solidified YBa2Cu3Ox will be examined in detail as will the resultant superconducting properties, in particular the magnetization.
Empirical model of breakdown in SF6: Corona-shielding effect
Authors: Novak J. P.
Published: July 2002

An empirical relationship for the breakdown voltage in a nonuniform field in SF6 is derived with the help of a correlation of experimental data for a rod-plane geometry. The model is based on the hypothesis that the corona shielding radius and the critical corona length are related by a simple formula. In the first approximation this formula depends on the rod radius and the critical corona length at critical pressure; for small gap lengths a correction term, dependent on the gap length, is suggested.
Titanium silicide synthesis as an effect of cw CO2-laser irradiation
Authors: Ursu I. , Craciun V. , Mihailescu I. N. , Ivanov E. , Nicolescu G. , Plostinaru D. , Corici A. , Craciunoiu F.
Published: July 2002

The synthesis of TiSi2 was obtained by continuous wave CO2-laser scanning of a two-layer structure of polycrystalline silicon and titanium on a silicon base. The characterization studies were performed by Rutherford backscattering, scanning electron microscopy, and four-point probe measurements. It was shown that the silicon cap layer prevents the oxidation of the titanium film and couples better the infrared laser radiation to the base due to its lower reflectivity, thus profitably enhancing processing efficiency.
The shielding effectiveness of yttrium barium cuprate superconductors
Authors: Russell G. J. , Taylor K. N. R.
Published: July 2002

Measurements of the shielding effectiveness of yttrium barium cuprate have shown that at low signal amplitudes the insertion loss is significant over a wide frequency range. The performance, however, is extremely sensitive to the signal amplitude and to the presence of local static fields. The major contribution to the shielding arises from reflection at the sample surfaces due to the impedance mismatch. An absorption component also exists which is associated with energy loss processes involving the breaking of weak-link intergranular contacts which allow flux to move into and through the material. These effects are closely related to the nonlinear magnetic properties of these superconductors which also lead to the appearance of a rich harmonic content in the transmitted waveform. While these effects are not encouraging for the use of these materials as shields, the suggestion is made that they could form the basis of a new class of frequency upconverters and mixers for high-frequency communication.
Microstructure studies of epitaxial YBa2Cu3O7–δ films
Authors: Li D. X. , Wang X. K. , Li D. Q. , Chang R. P. H. , Ketterson J. B.
Published: July 2002

Thin films of YBaCuO were prepared as a superlattice of three constituents on SrTiO3 (100) substrates from three electron guns using a dedicated, computer-controlled evaporator. The results indicate that the as-deposited thin films grow as a superlattice of the three constituents, with a mixture of amorphous and polycrystalline regions. After annealing, however, the multilayer films are converted to the homogeneous superconducting phase; the morphology, studied with transmission electron microscopy, consisted of an array of orthogonal interconnecting rectangular bars. The better films had Tc(R=0)=90 K and Jc=2.9×106 A/cm2 at 4.2 K. The selected area electron diffraction pattern, and the high-resolution electron microscopy images show that the interconnecting bars are single crystals of the 1-2-3 phase. During annealing, the growth rate along the a and b directions is faster than along the c direction. For the films with the a axis oriented perpendicular to the substrate, the grains nucleated directly on the (100) surface of the SrTiO3 and grow through to the film surface. The grain boundary of two interconnecting rectangular crystals (bars) is abrupt at the atomic level over most of the boundary. The superconducting films and the substrates have a well-defined epitaxial relationship; the b and c axes are parallel to the in-plane 〈001〉 substrate axes for the a-axis oriented films. Depending on the film preparation conditions, the c-axis can also be perpendicular to the substrate plane. The morphology of samples with poorer superconducting performance consists of somewhat randomly oriented crystal bars of the 1-2-3 phase.
Temperature measurements in a vapor axial deposition flame by spontaneous Raman spectroscopy
Authors: Allendorf M. D. , Bautista J. R. , Potkay E.
Published: July 2002

Spontaneous Raman spectra of oxygen and nitrogen have been used to determine temperatures in flames produced by a vapor axial deposition (VAD) burner, both with and without silicon tetrachloride added to form silica particles. VAD flames in the absence of silicon tetrachloride contain steep temperature gradients in both the axial and radial directions. The addition of silicon tetrachloride produces substantial changes in flame structure, as characterized by the movement of an axial thermal front to a location higher in the flame. This indicates that the effects of silicon tetrachloride upon flame properties cannot be neglected in computational models designed to predict silica deposition rates. These results also show that spontaneous Raman scattering measurements are feasible in silica-laden VAD flames and can yield insight into the structure of such flames. Because of the presence of large thermal gradients, the high spatial resolution obtained in these measurements (0.6 mm of the laser beam was imaged) represents the minimum required to obtain accurate measurements of temperature and species concentrations in these complex diffusion flames.
Structural, optical, and electrical properties of Pb1−xYbxTe films (0<x<0.25)
Authors: Das S. K. , Suryanarayanan R.
Published: July 2002

We present the structural, optical, and electrical properties of Pb1−xYbxTe films (0<x<0.25) obtained by coevaporation onto Vycor, NaCl, and BaF2 substrates. They crystallize in the NaCl-type structure. The lattice parameter decreases slowly as x increases, not obeying the Vegard’s law. Our data seem to indicate the stability of Yb2+ for 0<x<0.25. The optical band gap increases linearly with x. The resistivity of the films (n type) increases slowly whereas the mobility (135 cm2/V s for x=0.008) decreases faster as x increases.
Epitaxially oriented YBa2Cu3O7−x thin films on 〈100〉 MgO prepared by metallo-organic decomposition
Authors: Hung L. S. , Lee S. T. , Braunstein G. H. , Agostinelli J. A.
Published: July 2002

Superconducting thin films of YBa2Cu3O7−x were prepared by metallo-organic decomposition. Both ion channeling and x-ray diffraction measurements showed that the oxide films grown on 〈100〉 MgO are epitaxially oriented in structure. The minimum yield of metal components varied from 0.58 to 0.32 in channeling measurements with the analyzing beam at energies ranging from 4.5 to 1.0 MeV. All x-ray diffraction lines corresponded to the (00l) reflections of the superconducting phase. The film exhibited complete superconductivity at 79–80 K with a transition width of 2.5 K.
Optical power limiting and bistability in polymer-dispersed liquid-crystal films with linear feedback
Authors: Kim J. Y. , Palffy-Muhoray P.
Published: July 2002

Polymer-dispersed liquid-crystal films are composite materials consisting of a liquid crystal dispersed in the form of micron-sized droplets in a polymer binder. External fields may be used to control the alignment of the liquid crystal in the inclusions. If the refractive indices of the polymer and the liquid crystal are appropriately matched, the film may be switched from an opaque scattering state to a clear transparent state by externally applied fields. We have studied the behavior of polymer-dispersed liquid-crystal films in feedback systems where the applied voltage depends on the intensity of light transmitted by the film. Linear feedback of the photodetector voltage gives rise to an optical transmittance which is a nonlinear function of incident power. This results in optical power limiting behavior in the case of negative feedback, and in optical bistability when the feedback is positive.
Optical studies of Ce-doped Gd2SiO5 single crystals
Authors: Sekita M. , Miyazawa Y. , Akahane T. , Chiba T.
Published: July 2002

Absorption, emission, and excitation spectra of Ce-doped Gd2 SiO5 have been measured. The emission spectrum is decomposed into two Gaussian bands corresponding to the transitions from Ce3+ 5d 2 T2 to two 4f levels of 2 F7/2 and 2 F5/2 . It is found that the energy difference between ground 2 F5/2 and 2 F7/2 levels varies from 2004 to 1326 cm−1 with increasing Ce concentration from 0.2% to 1%. Concentration quenching is weak in Ce-doped Gd2 SiO5 compared with that in the laser and fluorescent materials. The energy-level structure is determined for Ce3+ in Gd2 SiO5 based on the analyses of the optical spectra. The spectral characteristics indicate that the Ce-doped Gd2 SiO5 crystal is suitable for the application to the scintillation detector.
Laser chemical vapor deposition of Ti from TiBr4
Authors: Chou W. B. , Azer M. N. , Mazumder J.
Published: July 2002

Titanium metal has been deposited on a stainless-steel substrate by decomposing TiBr4 with a 1.4-kW cw TEM00 CO2 laser. Both the film thickness and deposition rate of the films have been studied as a function of partial vapor pressure of TiBr4, irradiation time, and chamber temperature. The observed deposition rate (190 μm/h) was two orders of magnitude greater than the deposition rate calculated for the production of pure titanium films using chemical vapor deposition. In addition, the films have been analyzed by Auger electron spectroscopy, scanning electron microscopy, and stylus profilometry, and these results show that the coatings are relatively pure (90%) and uniform.
CO2 laser-generated acoustic wave in aluminum
Authors: Wang M. R. , Meng H. C.
Published: July 2002

The CO2 laser, is for the first time, used as a light source to generate acoustic waves (P, R, and S waves) in an Al sample. The relationship between the acoustic wave amplitude and the incident laser energy is investigated. The spectra of the resonance P and S waves in the Al sample for the frequency range between 1 and 10 MHz are presented. The value of the amplitude ratio between the generated P and S waves is 2.0–3.0.
Evaluation of the trap concentration in highly doped semiconductors from low-frequency noise spectra
Authors: Kugler S.
Published: July 2002

Low-frequency noise measurements were carried out in AlGaAs/GaAs heterostructures. At temperatures between 100 and 300 K the spectra showed superpositions of a 1/f spectrum and two generation-recombination (g-r) noise contributions. From the amplitude of the 1/f spectrum Hooge parameters at room temperatures between 1.2 and 2×10−5 were obtained. A model for calculating the trap concentration in these highly doped semiconductors is proposed. This model assumes the location of the g-r noise within the surface depletion region. The activation energies of the two traps were evaluated to 0.43 and 0.37 eV with corresponding capture cross sections of 2×10−13 and 5×10−14 cm2, respectively. The trap concentrations were evaluated to 2×1017 and 3×1017 cm−3, respectively.
Effect of polymer matrix on a reversible light-induced change in charge acceptance and retention of molecularly doped polymers
Authors: Kanemitsu Yoshihiko , Imanishi Dai , Imamura Shunji
Published: July 2002

We have studied the effects of a polymer matrix on charge acceptance and retention of polymers doped with hole-transport molecules in order to understand the nature of traps in molecularly doped polymers (MDPs). Prolonged illumination decreases charge acceptance and retention of MDPs. A light-induced change in charge acceptance depends on the kind of polymer binder. A remarkable change is observed in acidic polymer binders or basic polymer binders exhibiting broad absorption spectra. In MDPs manifesting a remarkable light-induced change, the transient photocurrent pulse shape becomes dispersive after prolonged light exposure. The experimental results show that the shallow charge emission centers increase during light exposure. These shallow charge emission centers are metastable states formed by charge transfer between the transport molecule and the polymer matrix during light exposure.
Impurity optical absorption of SbSeI:Ni single crystals
Authors: Kim Wha-Tek , Kim Yong-Geun , Kim Hyung-Gon , Youn Hong-Suk , Lee Soo-Il , Kwun Sook-Il
Published: July 2002

Single crystals of SbSeI:Ni were grown by the Bridgman technique. The impurity optical absorption spectra of these single crystals were investigated at room temperature. We observed impurity optical absorption peaks at 4334, 7763, 8857, 8952, and 11 587 cm−1 due to nickel impurity. These impurity optical absorption peaks are assigned to the electronic transitions from the ground state 3T1(3F) to the excited states 3T2(3F), 3A2(3F), 1T2(1D), 1E(1D), and 3T1(3P) of Ni2+ ions sited at Td symmetry of the SbSeI host lattice.
The electrical noise of carbon fibers
Authors: Dillon R. O. , Kirby Roger D. , Spain I. L.
Published: July 2002

The low-frequency excess electrical noise has been measured on carbon fibers with a wide range of crystalline perfection and corresponding electrical and mechanical properties. Fibers include those prepared from ex-PAN and ex-pitch polymers, and a catalytic-chemical vapor deposited filament. The extensional (Young’s) moduli of these fibers varied from about 220 to 890 GPa (35–130 Msi), while the electrical resistivities varied from about 19 to 1 μΩ m. The low-frequency electrical noise of each fiber was found to be proportional to I2 and to vary as 1/f α, where f is the frequency and α is about 1.15. The most striking feature of the results was the strong dependence of the normalized noise power on the degree of crystalline perfection.
Electrical characterization of gallium planar-doped ZnSe grown by molecular-beam epitaxy
Authors: Shibli S. M. , Tamargo M. C. , De Miguel J. L. , Skromme B. J. , Nahory R. E. , Farrell H. H.
Published: July 2002

We report electrical characterization of a series of ZnSe samples which are planar doped by a new approach to doping involving periodic deposition of sheets of Ga on Zn- or Se-rich surfaces. For samples planar doped on Zn-rich surfaces, the mobility could be described by ionized-impurity scattering and polar optical-phonon scattering mechanisms, while planar-doped samples on Se-rich surfaces and uniformly doped samples require additional scattering mechanisms to describe their mobilities. The latter two cases give higher mobilities than the first, a result which is in conflict with the fact that the latter have higher total ionized-impurity concentrations and compensation. These results of higher mobilities along with higher total ionized-impurity concentrations are interpreted as evidence of donor-acceptor pair formation.
Changes in soft magnetic properties of Fe multilayered films due to lattice mismatches between Fe and intermediate layers
Authors: Nakatani R. , Kobayashi T.
Published: July 2002

Fe multilayered films with various intermediate layers are formed. Their magnetic properties and film structures are examined to understand the mechanism originating soft magnetic properties. The soft magnetic properties change with the lattice mismatches between Fe and intermediate layers, showing low coercive force and high relative permeability at lattice mismatches from 0.4 to 1.2%. It is thought that the lattice mismatches above 0.4% decrease Fe crystallite size and improve soft magnetic properties. Although Fe crystallite size is small at the lattice mismatches above 1.2%, the soft magnetic properties are poor. This is because the large lattice mismatch increases internal stress and magnetic anisotropy energy. This report indicates that the good soft magnetic properties are obtained when both Fe crystallite size and internal stress are small.
Characterization of n-type regions in GaAs formed by silicon fluoride molecular ion implantations
Authors: Gray M. L. , Parsey J. M. , Ahrens R. E. , Pearton S. J. , Short K. T. , Sargent L. , Blakemore J. S.
Published: July 2002

Implantations of silicon and silicon fluoride ions into semi-insulating GaAs wafers were performed to compare and evaluate the quality of the n-type layers that were produced. The use of SiFx (x=1,2,3) molecular ion implantations creates n-type active regions and n+ ohmic contact layers employing a higher implant energy than that needed to achieve a similar projected range for silicon ions. The higher energy allows the implanter to operate with a more stable and reproducible ion beam for shallow implant applications. Variables affecting the net electrically active ion distributions, such as the ion beam incidence angle, and the use of furnace or rapid thermal annealing cycles for implantation activation are addressed. Capacitance-voltage profiles were obtained for the n-type regions, and the free carrier distributions for the n+ implantations were obtained by polaron electrolytic profiling. The implanted regions were characterized by Hall-effect measurements, cathodoluminescence, and secondary ion mass spectroscopy.
Spectroscopic studies of the influence of oxygen partial pressure on the incorporation of residual silicon impurities in vapor-phase epitaxial gallium arsenide
Authors: Lee B. , Arai K. , Skromme B. J. , Bose S. S. , Roth T. J. , Aguilar J. A. , Lepkowski T. R. , Tien N. C. , Stillman G. E.
Published: July 2002

The incorporation of residual shallow impurity species, in particular Si, in both chloride and hydride vapor-phase epitaxial GaAs layers grown with oxygen intentionally injected into the source zone has been studied. Photothermal ionization spectroscopy and photoluminescence show that both the Si donor and acceptor concentrations are significantly reduced by the oxygen. The observed reduction of carrier concentration and the increase in Hall mobility with increasing oxygen partial pressure are mainly due to the reduction of Si impurity concentration. Although oxygen can form deep levels as indicated by the 1.4889-eV bound-exciton line in photoluminescence, the main effect of oxygen injection is to improve the material purity by suppression of the incorporation of residual Si.
Temperature dependence of reactive ion etching of GaAs with CCl2F2:O2
Authors: Pearton S. J. , Emerson A. B. , Chakrabarti U. K. , Lane E. , Jones K. S. , Short K. T. , White Alice E. , Fullowan T. R.
Published: July 2002

The etch rate of GaAs during reactive ion etching (RIE) in a CCl2F2:O2 discharge (4 mTorr, 0.56 W cm−2) shows a strong temperature dependence, increasing from ∼500 Å min−1 at 50 °C to 2800 Å min−1 at 400 °C. Arrhenius plots of the etch rate show two activation energies (0.17 eV from 50 to 150 °C and 0.11 eV from 150 to 400 °C). There is no significant plasma power density dependence of the etch rate at elevated temperatures (≥100 °C) in contrast to the strong dependence at 50 °C. The surface morphology undergoes smooth-to-rough-to-smooth-to-rough transitions at ∼150, 250, and 400 °C, respectively, although TiPtAu Schottky diodes exhibit near-ideal behavior on GaAs etched at 150 °C. The As-to-Ga ratio in the first 100 Å from the surface increases with increasing RIE temperature, with chloride residues absent above 150 °C. Fluorocarbon residues were present on all samples, but were limited to the first 10–15 Å. As determined by x-ray photoelectron spectroscopy, fluorine was present almost exclusively as metallic gallium fluorides, while oxygen was present as both Ga and As oxides. Ion channeling detected lattice disorder to depths of ∼200 Å for etch temperatures from 50 to 250 °C, while there was less damage for etching at 400 °C. No new RIE-induced deep levels were observed by capacitance transient spectroscopy in any of our samples, although the concentration of the midgap donor EL2 increased with increasing temperature during the RIE process.
Rapid thermal diffusion of Zn into n-type GaAs0.6P0.4 from Zn-doped oxide films
Authors: Usami Akira , Tokuda Yutaka , Shiraki Hiroyuki , Ueda Hiroyuki , Wada Takao , Kan Hirobumi , Murakami Tadayoshi
Published: July 2002

Rapid thermal diffusion (RTD) of Zn into n-type GaAs0.6 P0.4 from Zn-doped oxide films using tungsten halogen lamps was successfully used to fabricate p+n junctions. RTD was performed in the temperature range 910–1080 °C for 9 s, and the heating rates were varied in the range 10–83 °C/s. The RTD of Zn was also carried out from (Zn,Ga)- and (Zn,P)-doped oxide films to study the diffusion mechanism. The Zn diffusion by RTD occurs through an interstitial-substitutional diffusion mechanism similar to the conventional furnace processing. However, the RTD of Zn was enhanced with the heating rate, especially at 83 °C/s. This was ascribed to the stress field induced in the heating stage. Electrical characteristics of fabricated diodes are presented.
Structural characterization of molecular-beam epitaxially grown Zn1−x MnxSe on GaAs(001) substrates
Authors: Qadri S. B. , Samarth N. , Furdyna J. K.
Published: July 2002

Epitaxially grown single-crystal films of Zn1−xMnxSe have been characterized by x-ray diffraction techniques. Their dislocation densities have been estimated from double-crystal rocking-curve measurements. Values of the unit cell parameters normal and parallel to the substrate surface, as determined from (004) and (444) reflections, indicate that the films have some degree of tetragonal distortion for higher Mn compositions.
Substrate temperature lowering in GaAs selective epitaxial growth by molecular-beam epitaxy
Authors: Okamoto A. , Ohata K.
Published: July 2002

GaAs selective epitaxial growth by molecular-beam epitaxy (MBE) was studied as a function of substrate temperature. Selectivity was observed at as low as 600 °C with 1×10−5 Torr As pressure and a 0.04 μm/h growth rate. The heterogeneous nucleation theory gives a good explanation for the selectivity dependence on substrate temperature. Selective epitaxial growth by MBE is promising for device applications which require thin localized epilayers.
The role of traps in the restoration of faded holographic images in Bi12SiO20
Authors: Attard Alfred E.
Published: July 2002

Faded holographic images stored in Bi12SiO20 can be restored to levels suitable for signal processing by means of applied light and electric fields. The process is relatively insensitive to the wavelength of the restoring radiation. A single beam incident at any angle will restore the image. A model has been developed that satisfactorily accounts for all the observed features of the phenomena. The model assumes differential depopulation of very long-lived electron and hole traps. Finally, we suggest a procedure that may permit useful storage of holographic images for long intervals of time, without resorting to the restoration process.
Effects of post-deposition argon implantation on the memory properties of plasma-deposited silicon nitride films
Authors: Shams Q. A. , Brown W. D.
Published: July 2002

Post-deposition ion implantation has been used to introduce argon into plasma-enhanced chemically vapor deposited silicon nitride films in an attempt to influence the transfer, trapping, and emission of charge during write/erase exercising of the metal-silicon nitride-silicon oxide-silicon structure. Argon was implanted into the SiH4 -NH3 -N2 deposited films at energies ranging from 25 to 75 keV, current densities ranging from 0.1 to 75 μA/cm2 and fluences ranging from 1×1012 to 1×1016 ions/cm2. Physical properties of the films were studied by ellipsometry and infrared spectroscopy, while high frequency capacitance-voltage (C-V) curves were used to obtain programming, retention, and endurance characteristics.