bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface amorphization of Mylar(R) films with the excimer laser radiation above and below ablation threshold: Ellipsometric measurements
Authors: Lazare Sylvain , Benet Pascale
Published: July 2002

Ablation is the main phenomenon which occurs on a polymer surface when a pulse of ultraviolet radiation is absorbed. The front edge of the radiation pulse is absorbed by a volume which eventually vaporizes and the rest is partially blocked by the ablation plume of products and partially transmitted to the new surface left behind after ablation. Most of this transmitted energy is transformed into heat and raises the temperature of the surface sometimes above the melting point of the polymer. Due to the transient character of the irradiation which lasts 25 ns, a rapid cooling occurs. For semicrystalline polymers like poly(ethylene terephthalate) the surface is left in an amorphous state by this cooling. In this work the amorphous depth was measured by monochromatic ellipsometry as a function of the pulse energy. It is shown that amorphization has a threshold fluence (7 mJ/cm2 at 193 nm) which is lower than the ablation threshold (17 mJ/cm2). The ablation depth reaches a maximum of 850 Å at 193 nm when the ablation threshold is reached. Similarly the ablation depth measured at 248 nm is 1600 Å. The amorphization depths are proportional to the radiation penetration depths in the materials.
Monte Carlo simulation of keV electron transport in solid media
Authors: Öztürk N. , Williamson W.
Published: July 2002

Transport of 1–10 keV electrons in solid media is investigated by means of a single scattering Monte Carlo scheme. Interaction of the incident electron with the target is modeled using bound atom elastic scattering cross sections, together with inelastic collision cross sections and excitation functions, for the weakly bound outer electrons, obtained from dielectric theory with a model dielectric function. Inelastic collisions of the incident particle with the tightly bound inner shell electrons of the target are sampled using semiclassical ionization cross sections. Representative backscattering and transmission calculations are presented and compared with experimental data.
Resolution degradation of coaxial p-type germanium detectors due to hole trapping by point defects
Authors: Darken L. S. , Jellison G. E.
Published: July 2002

A quantitative relationship has been experimentally determined correlation the resolution degradation of p-type coaxial high-purity germanium detectors to the concentration of residual hole-trapping point defects. Detector diameters ranged from 48 to 65 mm, and the average electric-field strength was 1500 V/cm. The concept of a ‘‘standard level’’ is proposed, which originates in the similar capture kinetics of many commonly observed residual acceptors in high-purity germanium. A method for calculating the electric-field dependence of hole capture is presented and used to compare the data reported here with published modeling results parameterized by the mean-free-drift length. Good general agreement is found.
Reaction mechanism of electrochemical-vapor deposition of yttria-stabilized zirconia film
Authors: Sasaki Hirokazu , Yakawa Chiori , Otoshi Shoji , Suzuki Minoru , Ippommatsu Masamichi
Published: July 2002

The reaction mechanism for electrochemical-vapor deposition of yttria-stabilized zirconia was studied. Yttria-stabilized zirconia films were deposited on porous La(Sr)MnOx using the electrochemical-vapor-deposition process. The distribution of yttria concentration through the film was investigated by means of secondary-ion-mass spectroscopy and x-ray microanalysis and found to be nearly constant. The deposition rate was approximately proportional to the minus two-thirds power of the film thickness, the one-third power of the partial pressure of ZrCl4/YCl3 mixed gas, and the two-thirds power of the product of the reaction temperature and the electronic conductivity of yttria-stabilized zirconia film. These experimental results were explained by a model for electron transport through the YSZ film and reaction between the surface oxygen and the metal chloride on the chloride side of the film, both of which affect the deposition rate. If the film thickness is very small, the deposition rate is thought to be controlled by the surface reaction step. On the other hand, if large, the electron transport step is rate controlling.
Ion emission studies of pulsed laser evaporation of YBa2Cu3O7
Authors: Lunney James G. , Lawler Justin F. , Aratari Roberto
Published: July 2002

The plasma formed by the laser ablation of YBa2Cu3O7 has been studied by comparing the ion dose incident on the growing film with the deposition depth per pulse. The variation of the deposition depth and ion velocity with laser fluence was also measured and compared with a physical model of the ablation process.
Empirical determination of the electroabsorption coefficient in semiconductors
Authors: Galbraith I. , Ryvkin B.
Published: July 2002

On the basis of the integral formula of Rees relating the electroabsorption coefficient to the zero-field absorption coefficient, scaling rules for the electroabsorption coefficient are obtained. These rules allow the spectral and field dependence of the electroabsorption coefficient near the fundamental band edge to be obtained. They also allow the identification of trends, thus impacting on the choice of materials and design of optoelectronic devices.
Nonuniform precessional motion of the domain wall under weak fields in arbitrary directions
Authors: Chen Shoan Chung , Huang Huei Li
Published: July 2002

Comprehensive analysis of the influence of a weak in-plane field on the dynamics of a planar domain wall in a uniaxial ferromagnet with a small quality factor has been carried out. The peculiarities of the domain-wall movement in both subcritical Hz<Hw regimes and supercritical regimes of the domain-wall movement are analyzed. Numerical calculations for yttrium-iron-garnet-like material have been carried out. It is shown that the influence of the in-plane field which is parallel to the domain wall is more pronounced than the influence of the field which is normal to the domain wall for a given type of magnetic material considered.
Suppression of defect propagation in semiconductors by pseudomorphic layers
Authors: Chen Y. C. , Singh J. , Bhattacharya P. K.
Published: July 2002

The propagation of defects in semiconductor heterostructures has been studied both theoretically and experimentally. The simple model shows that defects originating from lattice-matched regions can be prevented from entering, or can be trapped by, a pseudomorphic layer, depending on the signs of the strain induced by the defect and the strain in the pseudomorphic layer. A pseudomorphic layer can therefore prevent the defect from propagating across in and entering the critical active region of a device. Experimentally, the photoluminescence intensities of Al0.4Ga0.6As/GaAs quantum wells with and without pseudomorphic In0.2Ga0.8As layers for prevention of defect propagation have been compared. GaAs substrates of high etch pit density were used to generate defects below the quantum well and silicon implantation was used to generate defects above it. The elevated temperatures during molecular-beam-epitaxial growth and postimplant rapid thermal annealing serve to assist in defect propagation in the respective regions of the heterostructure. The structures with pseudomorphic In0.2Ga0.8As layers consistently showed much higher quantum-well photoluminescence intensities than those without the pseudomorphic layers. These results indicate smaller defect densities in the quantum wells with pseudomorphic layers and strongly support the defect propagation model.
Creation of a new In-based material by laser irradiation of chalcopyrite-type ternary semiconductors
Authors: Tanino H. , Fujikake H. , Nakanishi H.
Published: July 2002

A new material mainly made of In has been created by laser irradiation of chalcopyrite-type ternary semiconductors containing In such as CuInSe2. The Raman spectra of the created material are always the same independent of the original compounds (CuInS2, CuInSe2, CuInTe2, and AgInSe2). The same spectra could not be produced by laser irradiation of CuGaSe2, AgGaSe2, In metal, or Cu-In alloys. The crystallization of a-Si:H was measured by laser irradiation in the same manner and it was found that CuInSe2 was more stable during laser irradiation than a-Si:H. Hence, CuInSe2 could be a promising candidate for solar cells.
Real-space transfer oscillations in coupled quantum wires
Authors: Utecht C. , Schöll E.
Published: July 2002

A model for nonlinear parallel transport in GaAs/n-AlxGa1−xAs quantum wires coupled via an external load circuit is developed. It takes into account the nonlinear dynamics of electric-field induced real-space electron transfer from GaAs to AlGaAs and delayed dielectric relaxation of the interface potential barrier. Quantum size effects are considered in the form of confining potentials. In the case of two symmetric quantum wires symmetric and asymmetric self-generated current oscillations of several hundred GHz are predicted. The coupling of two nonsymmetric wires yields quasi-periodic oscillations.
Background impurity profiles determined by tunneling spectroscopy
Authors: Reinacher N. , Demmerle W. , Smoliner J. , Gornik E. , Böhm G. , Weimann G.
Published: July 2002

Tunneling spectroscopy is used to determine the background impurity distribution in the GaAs buffer layer on GaAs-AlGaAs heterostructures. On a coupled two-dimensional system, consisting of an accumulation layer and an inversion layer separated by a thin AlGaAs barrier, resonant tunneling processes are used to determine the subband energies and the potential profiles in both two-dimensional channels. Comparing the measured peak positions in the resonant tunneling current with the results obtained from self-consistent calculations, the depth dependence of the residual charged impurities in the GaAs buffer is obtained over the first 1200 Å below the AlGaAs-GaAs interface. This information is a crucial sample parameter for all high-mobility two-dimensional electron systems and cannot be obtained from Hall measurements.
Photoluminescence and photoluminescence excitation studies on GaAs/Al0.25Ga0.75As asymmetric coupled double quantum well
Authors: Lee D. H. , Kim D. W. , Leem Y. A. , Oh J. C. , Park G. H. , Woo J. C. , Yoo K. H.
Published: July 2002

Photoluminescence (PL) and PL excitation (PLE) experiments on a GaAs/Al0.25Ga0.75As asymmetric coupled double quantum well are reported. In PLE, the seven peaks, four related to the heavy-hole coupled and the rest to the light-hole coupled excitonic states, are observed. The positions of seven peaks observed in PLE are in good agreement with the calculated results of multi-band envelope function approximation using the transfer matrix method. The result of the temperature-dependent PL above 100 K shows that, even though the wavefunctions are localized in different wells separated by 8 monolayer barrier, the heavy-hole coupled excitons in the two lowest levels are in thermal equilibrium. The observed activation energy is equal to the difference between the two levels.
Modification of polyimide surfaces using intense proton pulses
Authors: Feurer T. , Wahl S. , Langhoff H.
Published: July 2002

High intensity proton pulses of 50 ns length were used to modify polyimide surfaces. The deposited energy and power density were similar to the corresponding experiments with UV laser pulses. Due to the constant range of the protons a well-defined layer of about 1.5 μm is heated. The induced optical absorption, electrical conductivity, and the ablation were studied. The results are consistently explained by a thermal model.
Near-surface region characterization by extremely asymmetric Bragg reflection topography
Authors: Gao Dachao , Wilkins Stephen W. , Stevenson Andrew W. , Pain Geoff N.
Published: July 2002

Near-surface regions of Cd1−xMnxTe and Hg1−xCdxTe epilayers (down to tens of angstroms) on (001) GaAs substrates have been characterized by extremely asymmetric Bragg reflection topography (EABRT) with the laboratory x-ray source condition and a Lang camera, using x-ray grazing incidence angles less than the critical angle for total external reflection. The experimental topographs obtained in the present work illustrate the potential of the EABRT technique for nondestructive characterization of near-surface regions of crystals. The resolution of an image in EABRT is discussed in detail.
Rupture theory of thin power-law liquid film
Authors: Hwang Chi-Chuan , Chang Shang-Hwei
Published: July 2002

The nonlinear rupture problem of a thin power-law liquid film on a horizontal plane is studied. A nonlinear evolution equation is first derived for h(x,t), the film thickness, and then it is solved by numerical methods. The results reveal that the rupture time of the film decreases with decreasing the magnitude of the power-law exponent, n.
Theoretical analysis of gain saturation coefficients in InP-based strained-layer quantum-well lasers
Authors: Seki Shunji , Yamanaka Takayuki , Yokoyama Kiyoyuki , Sotirelis Paul , Hess Karl
Published: July 2002

The gain saturation coefficients of tensile-strained, lattice-matched, and compressive-strained InGaAs/InGaAsP quantum-well lasers (QWLs) are calculated from intrasubband relaxation times. The intrasubband relaxation times are in turn obtained within the random-phase approximation including carrier–carrier and carrier–polar-optical phonon interactions at room temperature. The effects of strain on the band structures are included by taking into account the strain-dependent coupling among heavy-hole, light-hole, and spin-orbit split-off subbands on the basis of the multiband effective-mass theory. It is demonstrated that the gain saturation coefficient in tensile-strained QWLs is less sensitive to the amount of strain than in compressive-strained QWLs where it markedly increases with strain.
Cathodoluminescence studies and finite element analysis of thermal stresses in GaAs/Si stripes
Authors: Lingunis E. H. , Haegel N. M. , Karam N. H.
Published: July 2002

Thermal stresses in selectively etched and selectively grown GaAs/Si (100) stripes of different width-to-thickness ratios are investigated by low-temperature cathodoluminescence (CL) spectroscopy and elastic finite element (FE) analysis. A qualitative description of the expected stress state based on FE results is followed by experimental stress measurement by low-temperature (10 K) CL spectroscopy. Precise determination of the heavy-hole (HH; mj=± 3/2) and light-hole (LH; mj=± 1/2) excitonic peak energies through deconvolution of the CL spectra allows for measurement of the longitudinal and transverse stress components (parallel and perpendicular to the long stripe dimension, respectively). The CL results show that the longitudinal stress remains fairly constant (tensile) as a function of position, whereas the transverse stress decreases monotonically with decreasing distance from stripe edges, assuming small negative (compressive) values in the immediate vicinity of the latter. No significant differences were found between selectively etched and selectively grown stripes. The experimental results are compared with finite element elastic calculations and discussed in view of the experimental and computational parameters.
Normal-incidence electroabsorption in Ga1−xAlxSb/AlSb L-valley quantum wells for 3–5 μm optical modulation
Authors: Xie H. , Wang W. I. , Meyer J. R. , Hoffman C. A. , Bartoli F. J.
Published: July 2002

Theoretical investigations are presented of the electric-field dependence of normal-incidence interconduction subband absorption in Ga1−xAlxSb/AlSb L-valley quantum wells. Under an applied electric field of 50 kV/cm, a blue shift of the absorption peak from 4.94 to 4.82 μm was found in a Ga0.7Al0.3Sb/AlSb structure with well width of 25 Å. The ability to absorb normally incident light and to achieve significant Stark shifts with bias makes the Ga1−xAlxSb/AlSb L-valley system an attractive choice for the 3–5 μm vertical optical modulators.
A metal:p-n-CdTe Schottky-barrier solar cell: Photoelectrochemical generation of a shallow p-type region in n-CdTe
Authors: Pugh J. Richard , Mao Duli , Zhang Ji-Guang , Heben Michael J. , Nelson Arthur J. , Frank Arthur J.
Published: July 2002

A simple method for producing a Au:p-n-CdTe Schottky barrier is described. The shallow p-n junction is formed by photoelectrochemical surface oxidization of n-CdTe. X-ray photoelectron spectroscopy, Auger electron spectroscopy depth profiling, and electron-beam-induced-current measurements provide important insight into the underlying causes of the formation of the p-type layer. Current-voltage and capacitance-voltage measurements show that the thin p-layer enhances the effective barrier height relative to that of a traditional Au:n-CdTe junction. These results account for the Au:p-n-CdTe cells exhibiting higher open-circuit photovoltages and higher photoconversion efficiencies than do Au:n-CdTe Schottky-barrier cells. From temperature dependence studies of the current-voltage characteristics, detailed information on the charge-transport mechanism of the junction was obtained. Photocurrent spectra of Au:p-n-CdTe as a function of temperature reveal that exciton excitation in CdTe contributes to the photocurrent.
Isothermal capacitance transient spectroscopy of grain-boundary interfacial states in Bi-doped SrTiO3 ceramics
Authors: Akita Chiyoshi , Fujimoto Masayuki , Ito Kenji , Shibagaki Shigeki , Okushi Hideyo , Haneda Hajime , Tanaka Junzo
Published: July 2002

It is shown that an isothermal capacitance transient spectroscopy (ICTS) technique is applicable to evaluate the interfacial state of SrTiO3 ceramics. ICTS signals were observed for Bi-doped and undoped SrTiO3 ceramics, and ascribed to interfacial states of grain boundaries. The interfacial states were located at Ei=0.7 eV below the conduction band for the Bi-doped samples and at Ei=0.5 eV for the undoped sample. This result indicates that the dopant bismuth caused deeper interfacial states in energy. The semiquantitative simulation of the ICTS signals suggests that the interfacial density of states of the SrTiO3-Bi2O3 system is more broad compared with other electronic ceramics such as ZnO-Bi2O3 and SiC-BeO systems.
Time-resolved energy transfer and absorption bleaching measurements in CuCl microcrystallites
Authors: Faller P. , Netiksis V. , Grun J. B. , Hönerlage B.
Published: July 2002

By degenerate pump and test measurements, we determine the coherence time and the lifetime of excitons in CuCl quantum dots. We show the importance of the induced recombination of coherent exciton states, excited in microcrystallites by two-photon absorption.
Surface segregation effects of In in GaAs
Authors: Dosanjh S. S. , Zhang X. M. , Sansom D. , Harris J. J. , Fahy M. R. , Joyce B. A. , Clegg J. B.
Published: July 2002

Photoluminescence (PL), secondary-ion mass spectroscopy (SIMS), and cross-sectional transmission electron microscopy (TEM) measurements have been performed to assess surface segregation of In in GaAs during molecular-beam epitaxial growth of InAs monolayers between GaAs layers. The InAs growth temperature at which In segregation is detectable depends on the characterization technique used; using PL it is above 420 °C, but from TEM and SIMS it is 420 and 340 °C, respectively. These results highlight the need for complementary information to provide a better understanding of the segregation phenomenon. SIMS data show that the total amount of In segregating and the extent of its distribution both increase with InAs deposition temperature.
Surfactant-mediated growth of germanium on silicon (001) with submonolayer coverage of Sb and Te
Authors: Osten H. J. , Klatt J. , Lippert G. , Bugiel E. , Higuchi S.
Published: July 2002

Surfactant-mediated growth of germanium on silicon (001) with submonolayer coverages of antimony and tellurium, respectively, was investigated with reflection high-energy electron diffraction and transmission electron microscopy. Approximately 0.2 monolayer of antimony is needed for a complete suppression of islanding for the growth at 450 °C. For growth at a lower temperature (270 °C), only approximately 10% of a monolayer antimony or tellurium is needed in order to obtain smooth epitaxial germanium layers. No differences could be detected between tellurium and antimony in the behavior as a surfactant. The performed surfactant-mediated growth experiments can be understood as the kinetic suppression of islanding due to a reduction in surface diffusion of germanium adatoms.
Real-time spectroellipsometry investigation of the interaction of silane with a Pd thin film: Formation of palladium silicides
Authors: Yakovlev V. , Drévillon B. , Layadi N. , Roca i Cabarrocas P.
Published: July 2002

We present the application of spectroscopic phase modulated ellipsometry to the study of both ultrafast and slow processes of the interaction of silane (SiH4) with thin films of palladium. Changes of the optical properties of thin films exposed to different SiH4 fluxes are monitored by in situ single wavelength ellipsometry in the case of high fluxes which lead to ultrafast processes and by in situ spectroscopic ellipsometry at low fluxes and slow kinetics. The study of the interaction of SiH4 with Pd at 250 °C reveals the complicated character of the process which depends on the flux of silane and leads to the formation of palladium disilicide, palladium hydrides, and an intrinsic porosity. A qualitative model of the process is proposed. The initial stage of the reaction at high fluxes of SiH4 is dominated by a grain boundary diffusion of SiH4 inside the Pd film, followed by the catalytic decomposition of SiH4 and a strong process of an intrinsic formation of porosity. This fast process (duration of 10 ms) proceeds through the formation of a metastable Pd-rich phase. The appearance of the intrinsic porosity enhances the diffusion of SiH4 inside the Pd film, which results in a drastic acceleration of the silicide formation. At low SiH4 fluxes the characteristic time of the reaction increases up to some tens of minutes and proceeds through the formation of both silicide and palladium hydride.
Temperature measurements of a neon Z-pinch plasma
Authors: Welch B. L. , Young F. C. , Griem H. R.
Published: July 2002

A neon Z-pinch plasma, appropriate for sodium/neon photopumping experiments, is studied in detail using temporally, spatially, and spectrally resolved measurements of Ne VII, Ne VIII, and Ne IX emissions. The neon is imploded with a 1 μs rise time, 150–180 kA peak current pulse. Two successive implosions are identified. The first implosion produces a 1-mm-diam plasma with an electron density of 9×1019 cm−3 and a temperature of 200 eV. The second implosion produces a larger diameter (3.5 mm), less dense (7×1018 cm−3) plasma with a temperature of 100 eV. A 70% Ne IX ground-state population at the second implosion is deduced from the measurements.
Fission-fragment excitation of the high-pressure atomic neon laser at 703.2 and 724.5 nm
Authors: Hebner G. A.
Published: July 2002

The results of a parametric investigation of the high-pressure fission-fragment excited atomic neon laser operating on the 703.2-nm (3p[1/2]1→3s[3/2]20) and 724.5-nm (3p[1/2]1→3s[3/2]10) transitions in He/Ne/Ar and He/Ne/Kr gas mixtures are reported. The highest measured power efficiency was 0.12% using a 1550-Torr He/Ne/Kr (17/75/8) gas mixture at a pump power of 1 kW/cm3. The power efficiency and the ratio of the 703.2- to the 724.5-nm laser output as a function of total pressure, He/Ne ratio, and percent of Ar or Kr will be discussed.
Photocarrier mobility in processable polyaniline
Authors: Annapoorni S. , Sundaresan N. S. , Pandey S. S. , Malhotra B. D.
Published: July 2002

Photoconductivity experiments using steady illumination with visible light have been carried out with emeraldine base to estimate the mobility of the photoexcited charge carrier. The results are compared with the earlier transient photoconductivity measurements. The low value for mobility of 3.5×10−5 cm2/V s obtained is ascribed to bipolaron formation. Photoelectrochemical measurements of charge decay with emeraldine salt electrode are also reported and compared with the above values.
Self-consistent calculation of intervalley deformation potentials in GaAs and Ge
Authors: Krishnamurthy Srinivasan , Cardona Manuel
Published: July 2002

We use the ab initio tight-binding method with ad-hoc site diagonal potentials to calculate electronic and structural properties of semiconductors. By distorting the lattice to simulate L or X phonons, intervalley deformation potentials, D, for electron and hole transfer in GaAs and Ge are obtained self-consistently. In most cases, self-consistency increases the value of D by only about 10%. The values obtained, however, are larger than those from fitted tight-binding or empirical pseudopotential methods and in good agreement with recent experiments.
Preparation of copper indium diselenide by selenization of copper indium oxide
Authors: Weng Shixing , Cocivera Michael
Published: July 2002

A process is reported for preparation of thin films of copper indium diselenide (CIS). This process involves two steps: (a) formation of Cu2In2O5 by spray pyrolysis and (b) reaction of Cu2In2O5 with selenium vapor to form CIS. The purity of the CIS prepared by this method can approach that of the material prepared by vacuum deposition methods because highly purified water and nitrate salts can be used in the spray pyrolysis step, and the purity of the selenium used in the second step can be identical to that used in any of the vacuum processes. This two-step process appears to have general applicability; we have been able to prepare a variety of sulfides and tellurides in addition to selenides. The advantage of this process is that any metal ion added to the spray solution is incorporated in the oxide and remains in the selenide after the selenization. Comparison of the Cu/In ratios of the selenide films with those of the precursor oxide films shows that there was a slight decrease in the copper content when the oxide was converted to the selenide. The consistency of the composition of the films prepared at 400 °C is comparable to that of films prepared by the other methods such as thermal processing of elemental layers and reactive sputtering of Cu and In with selenium vapor. Auger composition studies indicated that selenium substitution occurred stepwise. The x-ray-diffraction data for CIS were consistent with a chalcopyrite phase. The data for the resistivity and Hall-effect measurements at room temperature indicated a marked dependence of the resistivity and the hole density on the Cu/In atomic ratio. When this ratio was around 1.45, the resistivity had low values around 30 Ω cm, and the hole density was in the 1017 cm−3 range. A direct band gap of 0.95 eV was determined from the optical-absorption spectrum of this material.
Alloy composition dependence of defect energy levels in GaxIn1−xP/InP:Fe and GaxIn1−xP/InP:S (x≤0.24)
Authors: Zhao Y.-G. , Brebner J. L. , Masut R. A. , Zhao G. , Bensaada A. , Wan J. Z.
Published: July 2002

The defect energy levels in metalorganic chemical vapor deposition (MOCVD) grown GaxIn1−xP/InP:Fe and GaxIn1−xP/InP:S epilayers (x≤0.24) have been studied by photoluminescence (PL) and photoconductivity (PC) measurements. To understand the origin of the observed deep levels, we have determined the temperature dependence of the intensity and half-width of the dominant deep-level PL peaks. We find that (1) the dominant deep-level peaks of the samples grown on the same substrate are related to the epilayer composition, and move to higher energies with increasing gallium content; (2) the dominant deep-level peaks of the samples with the same epilayer composition grown on different substrates are different. They are attributed to the impurity in the substrate diffusing into the epilayer during MOCVD growth, forming an impurity-vacancy complex. The following tentative assignments are proposed: the dominant deep-level peaks in GaxIn1−xP/InP:Fe and GaxIn1−xP/InP:S are attributed to the emission of a (V)P-(Fe)III complex and a (V)III-(S)P complex, respectively. Comparing the deep level with the near-band-edge emission we show that (1) all deep levels are independent of the band edge as x is varied; (2) the composition dependences of the deep levels associated with such complexes depend on the site occupied by the impurity atom.
Effects of oxygen partial pressure and substrate temperature on the in situ growth of the Ba1−xRbxBiO3 films by laser ablation
Authors: Chen Yung-Fu , Lin Wen-Tai , Pan Fu-Min
Published: July 2002

Effects of oxygen partial pressure and substrate temperature as well as the Rb content in the target on the in situ growth of Ba1−xRbxBiO3 (BRBO) films prepared by laser ablation are studied. The optimal target composition for growing the superconducting films in the present study is Ba:Rb:Bi=0.6:0.8:1.0. Oxygen partial pressure plays an important role in controlling the doping of Rb into the BRBO phase and hence the growth of the superconducting films. For the Ba0.6Rb0.8BiO3 target the superconducting films can be grown at 410–485 °C in 1–50 mTorr of O2 and the optimal pressure is about 20 mTorr, under which Rb is readily doped into the BRBO phase. Meanwhile the best film with Tc (onset) of 27.5 K and Tc (zero) of 25 K is grown at 475 °C in 20 mTorr of O2. The (100) preferred orientation is present in most of the superconducting films, while the (110) orientation is dominant in the films grown in 30–40 mTorr of O2 at 430–450 °C which are about 100 °C higher than those reported previously. For the superconducting films thicker than 0.6 μm the cracking is commonly observed and the lower the growth temperature the greater the cracking. The degradation of the Tc of the BRBO film on exposure to air (moisture) can be attributed to the surface contamination which may also be one of the causes for the semiconductive behavior of electrical resistivity in the normal state.
Re-evaporation effects and optical properties of molecular-beam-epitaxial AlGaAs/GaAs/AlGaAs wells
Authors: Wood Colin E. C. , Tabatabaei Saeyed A. , Sheldon Peter
Published: July 2002

Elemental materials that condense on surfaces near effusion cells can be reevaporated toward substrates when heated by radiation from effusion furnaces. There they accumulate as unwanted impurities at interfaces and distribute throughout epitaxial films during growth. This effect is greatly increased when shutters are closed. Re-evaporated aluminum is shown to degrade minority-carrier properties of Al0.3Ga0.7As/GaAs double heterostructures. Modified temperature schedules and hardware to reduce re-evaporation effects are suggested.
Influence of mismatch on the defects in relaxed epitaxial InGaAs/GaAs(100) films grown by molecular beam epitaxy
Authors: Westwood D. I. , Woolf D. A. , Vilà A. , Cornet A. , Morante J. R.
Published: July 2002

Thick (∼3 μm) films of InxGa1−xAs grown on GaAs(100) substrates, across the whole composition range, have been examined by transmission electron microscopy and double-crystal x-ray diffraction. The results were compared with the observed growth mode of the material determined by in situ reflection high-energy electron diffraction in the molecular beam epitaxy growth system. The quality of the material degraded noticeably for compositions up to x∼0.5 associated with an increased density of dislocations and stacking faults. In contrast, improvements in quality as x approached 1.0 were correlated with the introduction of an increasingly more regular array of edge dislocations.
Electromigration-induced failure and reliability of metallizations in integrated circuits
Authors: Itskovich I. F. , Sorbello R. S.
Published: July 2002

It is shown that electromigration-induced open-circuit failures of completely passivated polycrystalline metallizations in integrated circuits under normal operating conditions can be controlled by lattice diffusion rather than grain-boundary diffusion. This is due to the bottleneck effect associated with low lattice diffusivity, which drastically reduces the flux of matter leaving the grain-boundary network during void growth. The estimated typical failure times are orders of magnitude larger than those predicted by models that completely neglect lattice diffusion.
Selective excitation of GeF and GeF2 in glow discharges of GeF4
Authors: Yagi Shigeru , Ohta Tsuyoshi , Saito Kazuhito , Obi Kinich
Published: July 2002

Intense ultraviolet emission bands around 340 nm were measured in microwave (MW) and rf glow discharges of GeF4. The bands are due to excited GeF2 and identical with the 340 nm bands in the rf discharges of GeH4-CF4-H2 mixtures which were published earlier. The emitting species drastically changed from GeF in matched MW discharges to GeF2 in rf discharges by way of an intermediate case in mismatched MW discharges. Selective excitation of GeF in MW plasma and GeF2 in rf plasma is discussed on the basis of a difference in electron energy between both plasmas and the energy is estimated in each case.
Dependence of window effects on Al content of a window layer in high-power AlGaAs window structure lasers with window grown on facets
Authors: Matsumoto M. , Sasaki K. , Kondo M. , Ishizumi T. , Takeoka T. , Yamamoto S.
Published: July 2002

In high-power AlGaAs window structure lasers with a window grown on facets (WGF) structure, dependence of window effects on Al content of the window layer is examined. When the Al content of the window layer is more than that of the cladding layer, the window effects are found. But, in other cases, the window effects do not occur. A calculation of a carrier leakage from the active layer to the window layer is performed. From the result, we deduce that the reduction of the window effects is caused by the carrier leakage. In the WGF laser with the confirmed window effects, a maximum output power of 350 mW is achieved and highly reliable operation under 100 mW at 50 °C beyond 10000 h is attained.
Time-resolved electric-field measurements in 30 kHz hydrogen discharges by optical emission Stark spectroscopy
Authors: Booth Jean-Paul , Derouard Jacques , Fadlallah Majida , Sadeghi Nader
Published: July 2002

The temporal behavior of the cathode sheath in 30 kHz 0.4–1 Torr H2 discharges has been investigated by optical emission spectroscopy. Analysis of the Stark splitting of plasma-induced H Balmer delta emission was used to measure the electric field with spatial and temporal resolution in the instantaneous cathode sheath. The location of the plasma/sheath boundary was determined from the position of the maximum of the H2 d 3Πu→a 3Σg+ (0,0) Q1 emission at 622.5 nm. Both methods showed that the sheath width increases as the cathode voltage becomes more negative, whereas the width remains constant as the applied voltage drops off. Analysis of the electric-field profile provided information on the time evolution of the ion density close to the electrode during the cathode half-cycle, in agreement with recent numerical calculations. At the beginning of the anodic half-cycle an intense flash of plasma-induced emission was observed, localized within 3 mm from the electrode.
Structural and optical band-gap properties of the amorphous semiconducting Si1−xBx alloy
Authors: Carlsson J. R. A. , Li X.-H. , Gong S. F. , Hentzell H. T. G.
Published: July 2002

Thin amorphous Si1−xBx films, with x0 ranging from 0 to 0.5, were coevaporated onto preoxidized (100) Si wafers and quartz substrates, by using a dual-electron-gun high-vacuum system. In order to study how the structural and optical properties depended on concentration and annealing temperature, heat treatments of the films were carried out at temperatures from 400 up to 1000 °C. The films were characterized by means of transmission electron microscopy, Auger electron spectroscopy, and spectrophotometry. It is shown that: (i) An amorphous Si1−xBx alloy can exist up to very high temperatures (≥1000 °C), when x is larger than ∼0.4; (ii) at 400 °C the optical band gap of an amorphous Si1−xBx alloy has the maximum value (1.59 eV) for x0=0.02 and then decreases to lower values for higher concentrations (e.g., 1.18 eV for x0=0.3); (iii) the measured optical band gap of amorphous Si1−xBx increases gradually with increasing annealing temperature up to 700–900 °C, and then increases rapidly when annealed at a higher temperature by about 0.5 eV. These changes can be associated with microstructural alterations. The stable amorphous Si1−xBx alloy with x0=0.3 has, for instance, a measured band gap of 1.23 and 1.74 eV after annealing at 800 and 900 °C, respectively. The relationship between the microstructure and the band gap of the films is discussed.
Dynamics of laser-induced periodic surface structures in excimer laser ablation of polymers
Authors: Dyer P. E. , Farley R. J.
Published: July 2002

In situ microscopy and optical diffraction studies of ripple structures produced on excimer laser ablated polymers are reported, allowing their development rate to be estimated and motion to be observed. The formation of these ‘‘anomalous’’ ripple structures (grating vector perpendicular to the polarized laser electric field direction) is analyzed within the framework of a model describing interference between the transmitted and diffracted beams at the surface. Experimental observations are consistent with theory if substantial modification of the (effective) optical constants of the polymer occurs under ablation conditions. A model describing the ripple dynamics under multipulse irradiation is reported and compared with the experimental findings.
Subsidiary absorption spin wave instability processes in yttrium iron garnet thin films, critical modes, and the ‘‘kink’’ effect
Authors: Wiese G. , Kabos P. , Patton C. E.
Published: July 2002

Butterfly curves of the subsidiary absorption spin wave instability threshold microwave field amplitude versus static field have been measured at 10 GHz on a 12.8-μm-thick single crystal yttrium iron garnet film for two field configurations, one with the static magnetic field in plane and the microwave field out of plane (IP case) and the other with the static field normal to the film plane and the microwave field in plane (PI case). The results for the IP case are similar to earlier results which show a ‘‘kink’’ in the butterfly curve accompanied by a jump of the critical mode wave number k at the kink field. For the PI case, however, there is no observed kink effect. The different butterfly curves for the IP and PI cases are explained on the basis of a new theory for thin films which takes into account the discrete standing wave modes in the film. For the IP case, the theory yields critical modes with wave vectors in the film plane and the kink effect as before. For the PI case, the critical modes have wave vector k components perpendicular to the film plane, the minimum threshold critical modes are modified significantly, and the theory yields smooth butterfly curves with no kink. Quantitative fits to the data were obtained, based on a single trial function for the k-dependent spin wave linewidth.
Origin of perpendicular magnetic anisotropy of Ni-polyethylene coevaporated films
Authors: Maro Tsuyoshi , Kitakami Osamu
Published: July 2002

The origin of the large perpendicular magnetic anisotropy (0.5–1×10−6 erg/cm3) of Ni-polyethelene coevaporated films has been studied. It is indicated that the anisotropy can be very well explained by uniaxial anisotropy induced by the large tensile stress (1–3×1010 dyn/cm2) through the inverse magnetostrictive effect. Other factors, such as magnetocrystalline or shape anisotropy, produce little effect on the perpendicular anisotropy of the films.
Magnetic and magneto-optical properties of multilayers Fe-Si/Pd
Authors: Zhou Shi-Ming , Liu Yi-Hua , Chen Liang-Yao , Su Yi , Qian You-Hua , Xie Xi-De
Published: July 2002

The magnetic and magneto-optical properties of Fe-Si/Pd multilayers prepared by rf sputtering were studied. For Fe-Si/Pd multilayers with a fixed Fe-Si layer thickness dm of 15 Å and the Pd layer thickness dp increasing from 10.8 to 18 Å, the saturation magnetization Ms and the Kerr rotation θk decrease sharply and reach a minimum. With dp further increasing, the multilayers increase. Ms is almost constant and θk decreases slightly when dp≳36 Å. For Fe-Si/Pd (54 Å) multilayers the room temperature Ms decreases and θk increases, respectively, with increasing dm. This is caused by the spin-polarization effect of Pd atoms near the interfaces.
Gas phase chemistry in a direct current plasma jet diamond reactor
Authors: Reeve S. W. , Weimer W. A. , Cerio F. M.
Published: July 2002

Reaction products contained in the exhaust gas of a dc plasma jet reactor system were detected using mass spectrometry. The major reaction products formed from a feed gas mixture of 96% H2, 3% CH4, and 1% O2 injected into an argon plasma jet were CH4, C2H2, C2H6, CO, and H2O. The products formed without O2 in the reactor feed were CH4, C2H2, and C2H6. Addition of O2 to the reactor gas feed increased the diamond deposition rate by ∼30% with no degradation in quality. A chemical kinetics model for flames was adapted to this reactor and accurately predicted the major reaction products formed for a reactor feed without O2, indicating the gas phase chemistry may be described by a reaction set developed for hydrocarbon combustion and the chemistry is thermally driven. When compared to experimental results, the model predicts: (1) a maximum temperature in the gas of 3000 K, (2) only 1.2% of the H2 in the reactor feed is dissociated, and (3) CH3 is the primary diamond growth precursor.
Influence of convection on solidification of binary solutions cooling from below
Authors: Chen Falin , Yang Tsung L. , Lu Jay W.
Published: July 2002

The directional solidification of aqueous ammonium chloride solutions has been considered by theoretical and experimental approaches to investigate the influence of convection on solidification. By comparing the growth of crystal from experiments in which convective flows occur and that from theoretical analysis in which no convection is considered, the effect on solidification due to each individual convective flow, such as the double-diffusive salt-finger convection above the melt/mush interface, the buoyant flow in the mushy layer, the plume flow issued directly from the interior of the mush into the bulk melt, and the mushy-layer mode circulation induced by the subcritical instability and so on, is identified. It is found, in general, that the salt-finger convection and mushy-layer mode circulation inhibit the growth of the dendritic mushy zone and the plume flow enhances the growth of eutectic solid layer while suppresses the mushy layer. The buoyant flow effect is virtually negligible.
Measurement of the electronic transfer process in nitride film on a silicon substrate via photoconductance decay
Authors: Zhong L. , Tsuya H. , Shimura F.
Published: July 2002

A temperature-controlled laser-microwave photoconductance lifetime measurement technique combined with ultraviolet irradiation is used to investigate the electronic transfer process at charge trapping sites, the K centers, in low pressure chemical vapor deposited nitride film on a silicon substrate in the temperature range 300–500 K. A relationship between the lifetime and the space charge in the dielectric film is discussed in order to correlate the lifetime data with electronic transfer process on K centers. An isothermal transfer process is then found following a stretched exponential function of annealing time with a temperature-independent stretched factor around 0.14 and a time constant characteristic of activation energy around 0.81 eV.
Superlattice excitons and optical absorption
Authors: Young P. M. , Ehrenreich H. , Hui P. M. , Johnson N. F.
Published: July 2002

A formalism based on the superlattice crystal coordinate representation, which is valid for arbitrary well and barrier widths, is developed and applied to the Wannier exciton problem. A simple model for the electron-hole Coulomb interaction within the independent subband approximation permits nonvariational calculation of exciton binding energies, oscillator strengths, and optical absorption of both bound and continuum exciton states. The effects of growth axis directed electric and magnetic fields are emphasized. Numerical results for GaAs/ Ga1−xAlxAs and In1−xGaxAs/GaAs exciton binding energies and oscillator strengths as functions of well width, barrier width, and electric and magnetic field strengths show excellent agreement with experiment.
Theory of the electron fracture mode in solids
Authors: Cherepanov Genady P. , Borzykh Andrew A.
Published: July 2002

The theoretical model serving to explain and describe the phenomenon of the electron fracture mode (EFM) discovered experimentally nearly 20 years ago is advanced. EFM is characterized by the brittle cleavage of common plastic crystals proceeding with supersonic velocities independently of initial cracks when subjected to high-intensity electron beams. Using the invariant Γ integral of an electromagnetic deformable medium, it is proven that two electrons moving faster than the phase speed of light attract one another, as distinct from the common Coulomb’s law. Self-packing of such relativistic electron beams is studied using a periodic chain model. It is suggested that during irradiation of a solid by a high-intensity electron beam, some electron clusters are formed, which act as wedges cutting the crystalline specimen. The dynamic problem of supersonic cutting by a thin wedge is studied, and the drag is calculated. The length of the resulting crack is computed. The theoretical results are confirmed by available experimental data.
The structural homogeneity of boron carbide thin films fabricated using plasma-enhanced chemical vapor deposition from B5H9+CH4
Authors: Lee Sunwoo , Mazurowski J. , O’Brien W. L. , Dong Q. Y. , Jia J. J. , Callcott T. A. , Tan Yexin , Miyano K. E. , Ederer D. L. , Mueller D. R. , Dowben P. A.
Published: July 2002

Boron carbide thin films of several B/C ratios have been deposited on Si(111) using plasma-enhanced chemical vapor deposition from nido-pentaborane(9) (B5H9) and methane (CH4). X-ray diffraction studies of boron carbide thin films on Si(111) exhibited characteristic microcrystalline diffraction lines. Soft x-ray emission spectroscopy was used to verify that the local electronic structure and composition of each sample corresponded to a homogeneous solid solution boron carbide phase.
Evaluation of silicon-on-insulator substrates using photoconductive frequency resolved spectroscopy
Authors: Lourenço M. A. , Homewood K. P. , Hemment P. L. F.
Published: July 2002

We describe here the application of photoconductive frequency resolved spectroscopy to determine excess carrier lifetime distributions and carrier kinetics in SIMOX (separation by implanting oxygen) material. In order to evaluate the influence of the implant and anneal processes on the quality of the silicon overlayer we have also analyzed unprocessed bulk silicon, high temperature annealed bulk silicon and as-implanted SIMOX material. Our photoconductive frequency resolved spectroscopy results reveal that the SIMOX layers have a higher density of defects than standard device quality silicon substrates. Characteristic parameters of the dominant traps in these materials have been obtained from Arrhenius plots of the lifetime distributions. The defects found in these SIMOX layers are shown to be formed during the high temperature anneal stage of the material production.