bluuebunny/crossref_metadata_2025 huggingface dataset:
Short-circuit current of polycrystalline silicon solar cells with respect to grain size and grain-boundary recombination velocity
Authors: Dimitriadis C. A.
Published: July 2002

The influence of grain size and grain-boundary recombination velocity on the short-circuit current of polycrystalline silicon solar cells is investigated theoretically. Fit between theory and experiment for the variation of short-circuit current versus grain size allow us to determine the grain-boundary recombination velocity.
Modeling of dye-laser photon statistics
Authors: Marchesoni Fabio
Published: July 2002

We propose a model for dye lasers operating at resonance with a non-Gaussian fluctuating pump parameter. Analytical and numerical results are compared with recent experimental measurements on the intensity fluctuations of a dye laser and with previous theoretical predictions based on a fluctuating pump parameter of finite correlation time.
Photoelectron paramagnetic resonance studies of the dynamical parameters of shallow donor states in ZnS lattice (ZnS:Sc, ZnS:Al)
Authors: Godlewski M.
Published: July 2002

A new experimental approach is proposed for the determination of the dynamical parameters of shallow impurities such as activation energies, emission rates, capture cross section, and the radiative recombination rates. The intensity of the electron paramagnetic resonance signal of a deep center is used in order to monitor the kinetics of the charge transfer processes involving shallow impurities. The experimental results for aluminum- and scandium-doped ZnS:Cr are discussed.
Charge transfer and zero-temperature mobility in AlxGa1−xAs/GaAs (x<0.25) heterostructures
Authors: Thang Nguyen Toan , Fishman G. , Vinter B.
Published: July 2002

A self-consistent calculation of the electronic structure of an AlxGa1−xAs /GaAs heterostructure of finite thickness for x<0.25 can show an incomplete transfer of electrons from the doped AlGaAs to the GaAs. This makes the calculation of the low-temperature mobility more complicated than in conventional heterostructures or quantum wells. Suitable approximations for this case are discussed and corresponding results are presented. It is shown that while the low-temperature mobility is not too much influenced by the exact shape of the wave function when only intrasubband scattering plays a role, this mobility depends strongly on the detailed shapes of the electronic wave functions when intersubband scattering must be taken into account; this makes recent mobility calculations using variational wave functions questionable in the latter case.
Growth of crystalline zinc sulfide films on a (111)-oriented silicon by molecular-beam epitaxy
Authors: Yokoyama Meiso , Ohta Shin-ichi
Published: July 2002

The molecular-beam epitaxial growth of undoped ZnS layers on Si (111) is reported. Reflection high energy electron diffraction observations of grown films indicated that the optimum growth conditions necessary to obtain good crystallographic quality ZnS films exhibiting surface reconstruction are a substrate temperature of 300 °C and a molecular-beam flux ratio of 1. The layer growth rate depends on both substrate temperature and the molecular-beam flux ratio of Zn to S, JZn/JS. It was found that the growth rate became constant for JZn/JS ratios larger than 1. For the substrate temperatures larger than 400 °C the growth rate was found to decrease to nearly zero, abruptly.
Low-temperature grain growth of initially 〈100〉 textured polycrystalline silicon films amorphized by silicon ion implantation with normal incident angle
Authors: Egami Koji , Ogura Atsushi , Kimura Masakazu
Published: July 2002

〈100〉 textured polycrystalline silicon films deposited by low pressure chemical vapor deposition at 700 °C on SiO2/Si substrates have been amorphized by implantation with 100 keV 28Si+ ion at a dose of 2×1015/cm2 and thermally annealed at 550 °C for 168 h. In a 0.15-μm-thick film, the larger grain growth (1.5 μm) occurred, and the 〈100〉 oriented grains were found. This fact implies a possibility of the 〈100〉 oriented and large silicon grains formation by seed selection through ion channeling technique even if the 〈100〉 textured polycrystalline silicon film with relatively small channeling yields is utilized.
Defect structure and intermixing of ion-implanted AlxGa1−xAs/GaAs superlattices
Authors: Ralston J. , Wicks G. W. , Eastman L. F. , De Cooman B. C. , Carter C. B.
Published: July 2002

Cross-sectional transmission electron microscopy and Raman spectroscopy have been used to study the defect structure and intermixing of annealed ion-implanted Al0.3Ga0.7As/GaAs superlattices. The results show clearly that the amount and depth of superlattice layer intermixing depends on the ion mass. In superlattices that retain their structure after implantation and annealing, the distribution of defect clusters (primarily interstitial loops) is inhomogeneous; most defect clusters are nucleated in the GaAs layers. Examination of unannealed superlattice samples reveals that ion beam damage occurs preferentially in the GaAs layers.
Electron tunneling into Bi thin films under pressure
Authors: Zatet M. C. , Gunther Leon , Ratnam B. Asoka , Tedrow P. M.
Published: July 2002

We have studied the pressure dependence of the tunneling resistance of tunnel junctions between 300-nm-thick Bi films and 20-nm-thick films of Al deposited at room temperature. Native Al oxide formed by oxygen glow discharge provided the tunnel barrier. The resistance was measured as a function of voltage from 0 to about 1 V. Measurements were made from room temperature to below the superconducting transition temperature of the Al film. The pressure range covered was from 0 to about 8 kbar. The resistance decreases with increasing pressure in a way easily described by simple tunneling theory. In the resistance curves we observe pressure dependence of structure, which has in the past been associated with the pressure dependence of the Bi band structure.
Rigorous quantitative test of Biot–Savart–Lorentz forces
Authors: Moyssides P. G. , Pappas P. T.
Published: July 2002

The present paper describes an experiment performed at the National Technical University of Athens, comparing the theoretical Biot–Savart–Lorentz forces with the experimentally measured forces which arise on a part of a single circuit. The comparison is decisive and unique, as it is made for the first time after (1) the elimination of the singular or undetermined forces which inevitably arise in such experiments at the contacts of interacting parts, and (2) a complete systematic error elimination in the measurements themselves. The results, therefore, (a) for the first time treat noncontact forces, (b) are free of the ambiguities which have undermined previous experiments, and (c) indicate that the exerted forces are systematically smaller than the predicted Biot–Savart–Lorentz forces.
Chemical vapor deposition of hydrogenated amorphous silicon
Authors: Kurtz Sarah R. , Proscia James , Gordon Roy G.
Published: July 2002

Hydrogenated amorphous silicon films are made by atmospheric pressure chemical vapor deposition from polysilanes between 430 and 480 °C. The films have hole diffusion lengths up to 0.4 μm, as measured by the surface photovoltage technique. Oxygen impurities are shown to reduce the diffusion length. Stainless-steel and crystalline silicon substrates give slightly different results, implying that contamination is introduced by the substrates.
Study of electron traps in n-GaAs resulting from infrared rapid thermal annealing
Authors: Kuzuhara M. , Nozaki T.
Published: July 2002

Electron traps in n-GaAs resulting from infrared rapid thermal annealing (IRTA) have been studied by deep-level transient spectroscopy (DLTS). An electron trap with an activation energy of 0.20 eV from the conduction band, termed EN1, is introduced by IRTA above 800 °C. This trap formation is closely related to a rapid heating stage in an IRTA process. The EN1 concentration changes similarly to the concentration of the dominant midgap electron trap EL2 versus the variation of annealing temperature, annealing time, or encapsulating films. It is proposed that the IRTA-related EN1 trap is ascribed to defect complexes, including AsGa antisite defects, such as VAsAsGa.
Electron-spin resonance of NO2 trapped in SiO2 thin solid films
Authors: Schwartz Robert N. , Clark Marion D. , Chamulitrat Walee , Kevan Larry
Published: July 2002

Electron-spin-resonance spectroscopy has been used to detect the presence of NO2 in thin amorphous films of SiO2 grown by the plasma enhanced chemical vapor deposition technique. Temperature dependent spectra were observed over the range 4.2–165 K. Based on the experimental spectra and theoretical spectral simulations we found that in the temperature range of 12–87 K NO2 is undergoing axial-motional averaging about the axis in the molecular plane parallel to the O–O direction.
Be/BeO/Pb tunnel junctions with ion-beam-sputtered beryllium base electrodes
Authors: Okamoto Minoru , Takei Koji , Maeda Yasushi , Igarashi Masaru
Published: July 2002

Tunneling measurements were carried out to reveal superconducting properties of ion-beam-sputtered Be films with high Tc’s of 7 K. Be/BeO/Pb tunnel junctions with ion-beam-sputtered Be base electrodes were constructed for the first time. It was observed that values of 2Δ(0)/kTc were 3.1–3.5 for the Be films. These values suggest that ion-beam-sputtered Be films were weak coupling superconductors. It also turned out that BeO, the native oxide of the Be base electrodes, functioned as a good tunnel barrier with low leakage current.
Guided-wave electro-optic modulator in Ti:LiNbO3 at λ=2.6 μm
Authors: Eknoyan O. , Bulmer C. H. , Moeller R. P. , Burns W. K. , Levin K. H.
Published: July 2002

Guided-wave interferometric modulators at λ=2.6 μm, in Ti:LiNbO3, have been demonstrated. The design, fabrication, and performance of these modulators are presented. Extinction ratios as high as ∼30 dB with Vπ∼14 V for the extraordinary mode have been observed. No out-diffused modes were detected, likely as a result of the required diffusion conditions of high temperature and a long time.The devices are for use with state-of-the-art fluoride-glass fibers, whose transmission loss spectra currently reveal a minimum value near 2.55–2.6 μm.
Evidence of isovalent impurities in GaAs grown by molecular-beam epitaxy
Authors: Leroux M. , Neu G. , Contour J. P. , Massies J. , Vèrié C.
Published: July 2002

High-pressure, low-temperature photoluminescence spectra of Si-doped GaAs grown by molecular-beam epitaxy show well-defined features corresponding to nitrogen-bound exciton recombination, together with other isoelectronic center-bound excitonlike lines. Though N, when isolated, only influence weakly the GaAs electronic properties, we briefly discuss the consequences of its association with other impurities. It is suggested that complexes involving isovalent impurities may be responsible for part of the defect bound exciton luminescence, observed by several authors in molecular-beam-epitaxy–grown GaAs. The source of isovalent impurities is tentatively attributed to the high-temperature boron nitride crucibles.
Theory of photoluminescence in quantum wells in the presence of transverse electric field: Monte Carlo approach
Authors: Singh Jasprit
Published: July 2002

The Monte Carlo approach is used to study the quasibound electron and hole ground-state levels in a quantum well in the presence of a transverse electric field. A criteria is developed to ensure that the ground state is a true quasibound state. These techniques are applied to an Al0.3Ga0.7As/GaAs quantum well subjected to a high electric field perpendicular to the interfaces. Results on the electron and hole tunneling rates and their dependence on band-edge discontinuities are presented. The variation of the ground-state emission energy with the electric field is also presented.
Photoluminescence killer center in AlGaAs grown by molecular-beam epitaxy
Authors: Akimoto K. , Kamada M. , Taira K. , Arai M. , Watanabe N.
Published: July 2002

Origin of a nonradiative center in AlGaAs grown by molecular-beam epitaxy was investigated by secondary ion mass spectroscopy and deep-level transient spectroscopy, from the change of photoluminescence intensity with anneal treatment, and from its comparison with GaAs. Aluminum-oxygen complex is a most probable defect which acts as a nonradiative center in AlGaAs, and the oxygen would evaporate as Al2O from the surface, which would be a reason why the photoluminescence intensity increases under higher substrate temperature and lower V/III flux ratio. The electron-trap level at 0.76 eV from the conduction band would be the recombination center, and the photoluminescence intensity is inversely proportional to the trap concentration.
Theoretical study of the photovoltaic properties of polycrystalline silicon
Authors: Joshi D. P. , Srivastava R. S.
Published: July 2002

By considering the variation of grain-boundary space-charge potential barrier height with grain size and doping level, the dependence of polysilicon solar cell parameters on the grain size (d) and substrate resistivity have been theoretically investigated. A new relation is presented for the effective diffusion length of minority carriers in polysilicon which predicts that the effective diffusion length is approximately proportional to dr, where r varies from 0 to 1. Computations show that, as base resistivity decreases, the effect of the grain-boundary recombination process increases, and consequently the polysilicon cell parameters do not vary with resistivity in the same manner as has been observed for a single-crystal cell. Our theory predicts also the dominance of shunting effects of grain boundary at small grain sizes or low base resistivities. The available experimental data are found to be in good agreement with the predictions of the theory.
Photoconductivity in doped microcrystalline Si:H,Cl films
Authors: Augelli Vincenzo , Ligonzo Teresa , Murri Roberto , Schiavulli Luigi
Published: July 2002

Microcrystalline silicon films have been deposited by glow discharge in SiCl4-H2 mixture. We have studied the dependence of the photoconductivity on the nominal gas-phase doping. The behavior of the photoconductivity depends on the presence of chlorine, which, in turn, affects the deposition rate. These facts introduce several distinctive features in comparison with samples deposited from silane.
Studies on n-CdTe/p-CuInSe2 heterojunctions
Authors: Prasad J. J. B. , Rao D. Krishna , Sobhanadri J.
Published: July 2002

n-CdTe/p-CuInSe2 heterojunctions were fabricated by flash evaporating p-CuInSe2 on indium-doped CdTe single crystals. I-V characteristics and the photospectral response of the heterojunctions were studied. On illumination appreciable change in the I-V characteristics and photovoltaic effects were observered. A theoretical energy-band diagram for the heterojunction was constructed, and the theoretical and experimental barrier potentials were compared.
Barrier-height fixation in dc-sputtered Au-p silicon Schottky barriers
Authors: Straayer A. , Hellings G. J. A. , van Beek F. M. , van der Maesen F.
Published: July 2002

The sputter deposition of Au on p-silicon has been studied by means of forward and reverse current voltage characteristics. Barrier heights have been determined from Fowler plots and from activation energies. The observed increase of the barrier height with respect to evaporated contacts is mainly dependent on features of the discharge like the sputtering voltage, deposition time, gas composition, and pressure. It is for the most part independent of the semiconductor pretreatment before deposition or on the thickness of an insulating thin (<10 nm) layer. For low sputter voltages (<1 kV) there is an increase of the barrier height with increasing sputter voltage. Sputter voltages exceeding 1 kV result in a fixation of the barrier height at 0.60–0.65 eV. This fixation is due to the presence of sputter-induced traps in a thin surface layer of about 10 nm.
Study of CuInS2 grown by the traveling-heater method by electrolyte electroreflectance
Authors: Hsu T. M.
Published: July 2002

A study of the electrolyte electroreflectance spectra of CuInS2 grown by the traveling-heater method has been made. The energy gaps and broadening parameters were studied by varying the composition of the samples. Our results show that the energy gaps are in the range of 1.52 to 1.53 eV and have band-gap narrowing as the deviation from the stoichiometry increases, while the broadening parameters are in the range of 0.040 to 0.060 eV and found to be sensitive to the crystallization of the single crystal.
Band-structure dependence of impact ionization rate in GaAs
Authors: Kim K. , Kahen K. , Leburton J. P. , Hess K.
Published: July 2002

The band-structure dependence of the electron impact ionization rate in GaAs is studied by using local and nonlocal pseudopotential band structures and a Monte Carlo simulation code for the impact ionization rate α. We find that the difference in α for the two band structures reflects mainly the difference in the density of states.
Interaction of Ti with C- and SiC-contaminated Si surfaces
Authors: Taubenblatt Marc A. , Helms C. R.
Published: July 2002

The interaction of Ti with C-contaminated Si surfaces has been studied using Auger electron spectroscopy, x-ray photoemission spectroscopy, and transmission electron microscopy. C contamination due to wet chemistry residues and thin SiC films has been investigated. Our results show that Ti reacts with exposed C to produce TiC upon deposition for both these forms of contamination. The C residues were found to neither impede the silicide reaction nor remain at the interface afterwards. However, SiC thin films (5 Å) prepared by annealing the Si surface in ethylene, blocked silicide formation, resulting in a highly nonuniform interface. The carbide phases formed before and after silicide formation agree with those predicted by a calculated Ti-Si-C ternary-phase diagram.
Fabrication methods for InGaAsP/GaAs visible laser structure with AlGaAs burying layers grown by liquid-phase epitaxy
Authors: Takahashi N. Shin-ichi , Fukushima Akira , Sasaki Tatsuya , Ishikawa Joji , Ninomiya Kazuhisa , Narui Hironobu , Kurita Shoichi
Published: July 2002

Liquid-phase-epitaxial (LPE) growth of AlGaAs layers has been used in fabricating InGaAsP buried heterostructure visible lasers on GaAs substrate. InGaAsP/InGaAsP double heterostructure wafers were grown on the p-type GaAs substrates by means of the melt-back method prior to the LPE growth for eliminating phosphorus contamination. An SiO2 film mask was deposited on the epitaxial wafer surface by the rf sputtering, and photoetched with stripes of 7–10 μm width in the 〈110〉 direction. After etching to the first p-InGaAsP cladding layer with a 3% Br-methanol solution, the second LPE growth of n-AlGaAs and p-GaAs layers was carried out. The InGaAsP active region is entirely surrounded by the InGaAsP cladding layers and the AlGaAs burying layer, therefore, it becomes possible to provide both lateral and vertical carrier and optical confinements. I-L characteristics were measured at room temperature under pulsed operation, but the lasing action was not obtained. The peak wavelength of the electroluminescence was 785 nm. The transverse mode behavior was analyzed by means of the effective refractive index approximation. And it seemed that this buried heterostructure is suitable for the transverse mode control of InGaAsP visible laser diodes.
A novel laser-addressed smectic liquid-crystal light valve
Authors: Nakamura Kenichi , Oda Yasuhiro , Sugimoto Mitsuhiro
Published: July 2002

Thermally induced optical storage and erasure of light scattering centers in liquid-crystal films with an electrochromic effect are studied. Films used consist of cyanobiphenyls doped with a small amount of electrolytic substance, thereby showing an electrochromic effect. The electrically induced coloration is found to be extremely effective for absorption of He-Ne laser power and therefore for heating of liquid-crystal films. Thermal writing and local erasure are successfully done with this effect.
Mass and energy dependence of implanted ion profiles in the AZ111 photoresist
Authors: Guimarães R. B. , Behar M. , Livi R. P. , de Souza J. P. , Zawislak F. C. , Fink D. , Biersack J. P.
Published: July 2002

Profiles of Bi, Xe, Sn, Kr, Ga, Fe, K, Ar, P, Na, and F implanted into the AZ111 photoresist are compared with recent theoretical predictions. With the exception of the noble gases and F, the experimental results are well fitted by the Biersack–Haggmark [Nucl. Instrum. Methods 174, 257 (1980)] Monte Carlo calculations. For the noble gases we obtain ranges up to a factor of 2 shorter than the above predictions. Fluor changes the profile as function of energy, being nearly Gaussian at 30 keV and distributing according to the calculated ionization at 70 keV.
Photoemission spectroscopy study of the Al/SiC interface
Authors: Porte L.
Published: July 2002

Aluminum layers of some nanometers thickness have been deposited onto α-SiC crystals and studied by x-ray and ultraviolet photoelectron spectroscopies as a function of annealing temperature. Annealing beyond 600 °C induces a complete disappearance of metallic Al on the crystal surface, penetration of Al into the bulk, and formation of aluminum carbide. Ultraviolet photoemission spectra recorded after annealing at 360 °C could be explained by a beginning of interfacial reaction. However, there is no clear experimental evidence that reaction occurs at such a low temperature.
A characterization model for constant current stressed voltage-time characteristics of thin thermal oxides grown on silicon substrates
Authors: Chen Chiou-Feng , Wu Ching-Yuan
Published: July 2002

The constant-current-stressed voltage-time (V-t) characteristics of the thin SiO2 films thermally grown on the silicon substrate has been analyzed by using a theoretical model which includes the effects of dynamic trapping (i.e., electron trapping and detrapping), positive charge generation, weak spots, and robust area. The experimental methods have been developed to extract the physical parameters concerned with electron trapping and detrapping as well as positive charge generation. The time-dependent dielectric breakdown of the intrinsic thin SiO2 films under a constant current stress can be predicted through a criterion which assumes that the positive ions generated from impact ionization are aggregated near the interface between SiO2 and Si within the weak spots. Computer simulations using the proposed model indicate that the life of the intrinsic thin SiO2 film can be elongated if the trapping effect is less severe, the trapped electron centroid is closer to the anode electrode, the generated positive ions have a smaller recombination capture cross section, and the weak spots have a larger area ratio with respect to the total area. Besides, experiments have been performed to observe the effects of electron trapping and positive charge generation. Furthermore, the physical parameters of the poly-Si and Al-gate thin SiO2 films have been obtained under different constant current densities and the theoretical simulations have been performed. Good agreement between the experimental data and the theoretical simulations suggests that the proposed model can be used as a computer-aided-design (CAD) tool to predict the life of the intrinsic thin SiO2 films.
Preparation of highly photosensitive hydrogenated amorphous Si-C alloys from a glow-discharge plasma
Authors: Matsuda A. , Yamaoka T. , Wolff S. , Koyama M. , Imanishi Y. , Kataoka H. , Matsuura H. , Tanaka K.
Published: July 2002

The preparation conditions for the deposition of hydrogenated amorphous silicon-carbon alloys (a-SiC:H) from a glow-discharge plasma have been systematically scanned by changing the starting-gas materials as well as the starting gas to hydrogen dilution ratio. A highly photosensitive alloy showing a photoconductivity to dark conductivity ratio of 107 at a band gap of 2.0 eV was prepared under optimized conditions.
Photoconductivity parameters in lithium niobate
Authors: Gerson Robert , Kirchhoff J. F. , Halliburton L. E. , Bryan D. A.
Published: July 2002

Measurements on a variety of doped (magnesium and/or iron) and undoped lithium niobate crystals in the oxidized state demonstrate an Arrhenius dependence of dark conductivity on reciprocal temperature between 460 and 590 K. All of the crystals had roughly the same conductivity and activation energy (1.21 eV) over the temperature range, implying that all have about the same free-carrier concentration and mobility. The enhanced photoconductivity of magnesium-doped lithium niobate is attributed to a greatly reduced trapping cross section of Fe3+ for electrons, the smaller cross section being due to a changed substitutional site for Fe3+. The Fe3+ trapping cross section is calculated from photoconductivity data to be of order 10−18 m2 in undoped lithium niobate. This implies a photoelectron lifetime of order 6×10−11 s in a relatively pure (2-ppm Fe) oxidized crystal.
Selective optical compensation effect of two new near-band-edge emissions in simultaneously acceptor (Zn+) and donor (Se+) ion-implanted GaAs
Authors: Makita Yunosuke , Nomura Toshio , Kudo Kazuhiro , Irie Katsuhiro , Ohnishi Nobukazu , Takeuchi Yoshinori , Tanaka Hideki , Tanoue Hisao , Mitsuhashi Yoshinobu
Published: July 2002

Newly discovered Zn-associated emissions in GaAs, ‘‘g’’ and [g-g], were found to be completely suppressed by the simultaneous presence of Zn and Se atoms. This selective optical compensation (SOC) effect observed when acceptor (Zn) and donor (Se) atoms exist in combination was established by simultaneously implanting Zn+ and Se+ ions into almost carbon-free ultrapure GaAs made by molecular-beam epitaxy. It is suggested that the failure to observe ‘‘g’’ and [g-g] emissions in acceptor-incorporated GaAs prepared by conventional epitaxial methods may be ascribed to this SOC effect, in which donor atoms were unintentionally introduced into the epitaxial layer.
Effect of dislocations in metal-insulator-semiconductor solar cells
Authors: Divigalpitiya W. M. Ranjith , Morrison S. Roy
Published: July 2002

The I–V characteristics are measured for a series of metal-insulator-semiconductor cells of Al–SiO2–pSi structure with dislocation loops penetrating different depths into the semiconductor surface. All cell parameters except reverse saturation photocurrent are observed to be degraded with increasing dislocation length. The reverse saturation photocurrent is independent of the extent of damage in the samples. The experimental results are explained in terms of a mathematical model based on hopping conduction of captured carriers along dislocations. The current along a dislocation is shown to vary, to the first approximation, as exp(qV0/2kT), contrary to the general expectation that such a current is linear in the voltage V0. To our knowledge, this is the first time that conduction along dislocations has been observed at room temperature.
Incorporation of erbium in GaAs by liquid-phase epitaxy
Authors: Bantien F. , Bauser E. , Weber J.
Published: July 2002

The incorporation of the lanthanide element erbium in GaAs during growth by liquid-phase epitaxy is investigated by low-temperature photoluminescence measurements. After an anneal of the epitaxial layers at 850 °C, a characteristic Er-associated optical transition appears at a wavelength of ∼1.55 μm, however, no erbium-related photoluminescence signal is found in the as-grown GaAs:Er layers. The Zeeman splitting of the new photoluminescence lines reveals a cubic symmetry of the optically active Er complex. Successive mechanical polishing and annealing of the layers provides evidence for the incorporation of Er within the layer as an optically inactive Er complex, which is activated only at the surface by thermal annealing.
Transient conductivity studies in tellurium thin films
Authors: Pamler W. , Marinero E. E.
Published: July 2002

Laser-induced phase transformations in Te thin films have been studied utilizing time-resolved conductivity measurements. The dynamics of melting, recrystallization, and the onset of amorphization as a function of laser fluence have been investigated. Results are presented for melt duration, depth, and velocities (melt in and regrowth) with ns-time resolution. The necessary conditions for glass formation directly from the melt in Te are also determined. This necessitates complete melt through to the substrate interface and requires no first-order transition. Heat-flow calculations indicate large undercooling in the dynamics of recrystallization and that the material response to the excimer laser radiation is purely thermal.
Reversible structural changes in discharge-produced amorphous silicon
Authors: Hong C. S. , Hwang H. L.
Published: July 2002

This work studies the reversible, structural changes of undoped hydrogenated amorphous silicon films under prolonged illumination and thermal annealing. Experimental results from infrared spectroscopy showed that the strength of the stretch modes of SiH and SiH2 decrease more slowly in the initial stage and then more rapidly at about 1018 cm−3 spin density during prolonged illumination periods. On the other hand, the strength can be restored to its original value after a certain period of thermal annealing at 250 °C. These results are correlated with those obtained from electron paramagnetic resonance and photoconductivity measurements, in which the rate equations were analyzed to reveal the origin of recombinations responsible for the weak Si–Si bond breaking. An explanation is proposed in this study to illustrate the light-induced bond breaking and its repair.
High coercive force and large remanent moment magnetic films with special anisotropies (invited)
Authors: Cadieu F. J.
Published: July 2002

Special sputtering methods have been used to synthesize magnetic films that exhibit high intrinsic coercive forces iHc, large remanent moments, and special anisotropies. By special anisotropies we mean that the easy direction of magnetization in various films can be made to be either in or out of the film plane or in a particular direction within the film plane. To achieve high coercive forces in the films it has been necessary to synthesize the films from high iHc rare-earth transition metal systems such as SmCo5, Nd2Fe14B, and several new compounds in the Sm-Ti-Fe system. Films have been synthesized with different crystal textures by varying the sputtering parameters. The magnetic properties observed have been found to be strongly dependent on the film texture. Several possible film scale geometries for electronic applications have been considered.
Experimental determination of the shift of the Preisach distribution with magnetization
Authors: Salling C. , Schultz S.
Published: July 2002

The remanent magnetization Mr(H−) of the particulate recording media is measured as a function of the applied dc field, −H−, starting from selected states of initial remanence, Mri. The curves of [Mr(H−)−Mri] for Mri≠0 are shifted with respect to the Mri=0 curve along the H− axis by an amount ΔHp− . In general, ΔHp− is an increasing function of Mri and the particle demagnetizing factor. We take the measured ΔHp− to be related to the average value of the interaction field for the sample. The existence of a nonzero ΔHp− supports the idea that systems of ferromagnetic particles can be modeled using a ‘‘moving Preisach distribution.’’
Isotropic vector Preisach model of hysteresis
Authors: Mayergoyz I. D. , Friedman G.
Published: July 2002

The isotropic vector Preisach model of hysteresis is briefly described and the problem of fitting experimental data by this model is posed. An integral equation is derived which allows for the determination of Preisach’s function from experimentally measured ‘‘first-order transition curves.’’ An analytical technique for the solution of this integral equation is discussed.
Defect-state generation in Czochralski-grown (100) silicon rapidly annealed with incoherent light
Authors: Barbier D. , Remram M. , Joly J. F. , Laugier A.
Published: July 2002

Defect-state generation in Czochralski-grown (100) silicon after rapid thermal annealing has been studied. Deep-level transient spectroscopy experiments have been carried out using Schottky barriers made on n- or p-type as-grown wafers after irradiation with a commercially available incoherent light annealing device. Neither electrical degradation nor electron-trap generation appeared in the case of n-type silicon wafers annealed for 5 s. On the other hand, the junction degradation together with the generation of three hole-trap levels H1(0.45 eV), H2(0.29 eV), and H3(0.3 eV) have been observed in boron-doped silicon using a short duration (5 s) plateau temperature between 850 and 1050 °C. Peak concentrations ranging from 1013 to 1014 cm−3 were measured after annealing at 1000 °C for the three hole traps. By increasing the plateau duration up to 20 s hole traps were no longer detected in boron-doped Czochralski-grown silicon. Moreover H2(0.29 eV) is stable at room temperature whereas both H1(0.45 eV) and H3(0.3 eV) decayed in unbiased samples after several weeks. A comparison of the trap properties with those of already known defect states suggested that residual 3D metal traces (Fe, V, Cr) might be responsible for all the observed defect states. In addition the intrinsic defects generated during the temperature plateau are likely to play a significant role in the final defect-state concentration after rapid thermal annealing.
Etching on polar (111) surfaces of CdTe crystals studied with Auger electron spectroscopy
Authors: Lu Y.-C. , Stahle C. M. , Feigelson R. S. , Morimoto J.
Published: July 2002

Various reducing and oxidizing etches were applied to the polar (111)Cd and (111)Te surfaces of CdTe crystals. The induced surface layers were studied with Auger electron spectroscopy, and the chemical reactions involved were discussed. A dithionite etch left both (111) Cd and (111)Te surfaces Cd rich. The sulfur in the etch solution appeared to replace Te in the near surface. A hydrazine etch left the Cd to Te ratio about one to one on the surfaces. A large oxygen peak was observed to increase as the etching time and temperature increased, indicating that the etch was not reducing. Hydrogen heat treatment left the surface stoichiometric, free of contamination and crystalline. Hydrogen heat treatment was the best method we have tried to retain the stoichiometry of the (111)CdTe surfaces. The surfaces treated with oxidizing EAg-1 solution were Te rich, and the strong correlation between the relative concentration of Te and Ag suggested a reaction between Te and Ag. The Te(NOO)/Te(MNN) ratio on (111)Te surfaces was always significantly higher than that on (111)Cd surfaces after hydrogen heat treatment or sputter cleaning consistent with the crystallographic polarity we reported previously.
Electro-optic effect in semiconductor superlattices
Authors: Chang Yia-Chung , Schulman J. N. , Efron U.
Published: July 2002

Changes of index of refraction of semiconductor superlattices due to electric field are studied theoretically. A parabolic band effective-mass approximation is used for the conduction, heavy-hole, and light-hole bands. Excitonic effects are considered for wide barrier superlattices (or multiple quantum wells) and are found to substantially enhance the electro-optic effect near the onset of the excitonic absorption.
Spontaneous vitrification in Cr-Ti bulk alloys
Authors: Blatter A. , von Allmen M. , Baltzer N.
Published: July 2002

We describe a new process that enables the formation of amorphous Cr40Ti60 cubelets with dimensions in the millimeter range by a sequence of standard metallurgical procedures. Vitrification occurs spontaneously during low-temperature furnace annealing. The resulting amorphous material contains small-grained crystalline inclusions. Mechanically, the process results in a marked increase of the microhardness and a decrease of the elastic modulus of the material.
Phase equilibria and liquid-phase-epitaxy growth of PbSnSeTe lattice-matched to PbSe
Authors: McCann Patrick J. , Fuchs Jacob , Feit Ze’ev , Fonstad Clifton G.
Published: July 2002

The phase equilibria data necessary for growing solid compounds of Pb1−xsSnxsSe1−ys Teys lattice matched to PbSe from melts consisting of (Pb1−xLSnxL)1−z (Se1−yLTeyL)z are presented. Liquidus data for values of xL from 0% to 40% and yL from 0% to 40% for temperatures between 450 and 540 °C are also presented. The influence of tellurium on the liquidus temperature is shown to be negligible at least for yL less than 40%. A crossover in the liquid-solid tie lines of tin, xs vs xL, for layers grown at 650 and 450 °C is observed at xL equal to 14%. The liquid-solid tie-line data for tellurium, ys vs yL, show a low segregation coefficient relative to selenium for yL less than 40%, thus explaining tellurium’s limited influence on the liquidus temperature. The lattice-matching conditions for xL =5%, 10%, and 20% are yL =16.4%, 25%, and 33.5%, respectively. A significant lattice-pulling effect is observed for the 5% tin case and is expected for the 10% and 20% tin cases. This effect, along with the low relative segregation coefficient for tellurium, makes it possible to easily grow lattice-matched layers of PbSnSeTe on PbSe by liquid phase epitaxy.
Image charge focusing of relativistic electron beams
Authors: Humphries S. , Ekdahl Carl B.
Published: July 2002

Experimental results are reported on the transport of a relativistic electron beam by image charge effects. The transport system consisted of a cylindrical metal tube periodically interrupted by transverse conducting grids with high transparency. Partial cancellation of the beam electric fields increased the space-charge-limited current level, allowing propagation in a magnetically self-pinched mode. A 400-keV, 4-kA beam traveled 30 cm in high vacuum through 10 focusing foils. Capture of the beam was almost 100% efficient; beam emittance was not severely degraded during capture and transport. The radius of the self-contained beam was 1.4 cm; the beam position was centered by the image current in the transport tube to within 1 mm. The favorable results imply that image charge focusing could be considered for transport in high-current linear induction accelerators.
Low-temperature properties and phototransport in silicon-on-insulator films synthesized by oxygen implantation
Authors: Papaioannou George , Cristoloveanu Sorin , Hemment Peter
Published: July 2002

Silicon-on-insulator material formed by oxygen implantation (SIMOX) is analyzed by comparing conductivity and Hall-effect measurements performed at low temperature, under darkness, illumination, and substrate biasing. The quality of SIMOX films annealed at high temperatures above 1300 °C is found to be greatly enhanced in comparison with that obtained after conventional annealing at 1150–1200 °C. The analysis is fulfilled by discussing the carrier mobility and lifetime behavior, impurity ionization, doping compensation, film contamination, and scattering mechanisms. Hopping conduction is found to prevail below 60 K.
Low-noise metal medium for high-density longitudinal recording
Authors: Christner J. A. , Ranjan R. , Peterson R. L. , Lee J. I.
Published: July 2002

A low-noise medium that shows potential for future high-density longitudinal magnetic recording applications has been prepared and studied. The disk consists of a CoCr-based ternary alloy and a few percent of a third transition metal sputter deposited on a Cr underlayer. The media noise power is low and nearly frequency independent up to 80 kfci, in sharp contrast to the noise power spectra typical of metal films. Because of the exceptionally low media noise, we have obtained signal-to-noise ratios (SNR) greater than 35 dB up to 30 kfci on media having a 70% amplitude density (D70) of 20 kfci. Other characteristics of the media include overwrite better than −35 dB, saturation magnetization of 500 emu/cm3, and coercivity of 1300 Oe. The grain diameter, coercivity, and D70 depend strongly upon the Cr underlayer thickness. The data suggest that the low-noise results from reduced intergranular exchange coupling.
Crystal quality investigation of InGaAs/InP and InGaAlAs/InP single heterostructures grown by molecular-beam epitaxy
Authors: Ferrari C. , Franzosi P. , Gastaldi L. , Taiariol F.
Published: July 2002

X-ray double-crystal diffractometry has been used to assess the crystal quality of InGaAs/InP single heterostructures grown by molecular-beam epitaxy. Experiments performed on step etched samples have indeed shown that the width of the epilayer Bragg peak as a function of the epilayer thickness is in good agreement with the theoretical predictions for perfect crystals. Finally, preliminary observations of InGaAlAs/InP heterostructures have shown very narrow Bragg peaks and this demonstrates the good crystal quality of the quaternary layers.
Dielectric measurements of selected ceramic materials at 245 GHz
Authors: Dutta J. M. , Jones C. R.
Published: July 2002

A double-beam interferometer which incorporates quasioptical components developed in this laboratory has been used to measure near millimeter-wave dielectric properties of a variety of ceramic materials. We report here the results obtained on samples of various standard and advanced ceramics including alumina, silicon nitride, beryllia, and boron nitride. Results are compared with the data obtained by other researchers on similar samples.
Characterization of deep levels in Bi12GeO20 by photoinduced current transient spectroscopy
Authors: Benjelloun N. , Tapiero M. , Zielinger J. P. , Launay J. C. , Marsaud F.
Published: July 2002

A systematic investigation of deep levels in undoped and doped (Fe, Fe/V, excess of Bi) single crystals of Bi12 GeO20 (BGO) has been performed by photoinduced current transient spectroscopy. A list of traps in the energy range 0.1–1.0 eV with their thermal characteristics and their concentrations has been drawn up. Ten different levels have been detected, a few of them subdividing probably into substructures. In all probability, these trap species are present simultaneously in all the crystals but their concentrations differ considerably (typically from less than 1012 up to 5×1015 cm−3 ) so that dominant levels emerge. Variations in the number, nature, and concentration of the dominant centers were observed from preparation to preparation even for undoped BGO. This makes it difficult to draw reliable conclusions concerning the effect of doping, though some of the observed changes are probably directly related to Fe or Fe/V doping. This study of BGO also enabled us to test the experimental tool that we have worked out and progressively refined.
Thermal response of a laser-irradiated metal slab
Authors: Bartholomeusz Brian Josef
Published: July 2002

The analytical solution of temperature profiles in complex laser-heated structures is only possible for a few simple cases. This is partly due to the nature of heat-source terms that preclude the use of conventional series-type solutions. In this study we utilize a Laplace-transform method in conjunction with Fourier integrals to obtain solutions for the temperature profiles in a laser-irradiated rare-earth–transition-metal slab. The results provide a convenient qualitative tool to study the thermal response of laser-irradiated solids.
Ion implantation into gallium arsenide
Authors: Anholt R. , Balasingam P. , Chou S. Y. , Sigmon T. W. , Deal M.
Published: July 2002

Secondary-ion-mass-spectrometry studies of the implantation profiles of 20- to 400-keV Si, Se, and Be ions into GaAs are reported. The measured profiles are fit with Pearson-IV distributions whose moments are fit to functions of the ion energy to obtain simple, widely applicable analytical formulas. Also, profiles are measured for varying wafer tilt and rotation angles to the ion beam, and for varying dislocation densities and doses. For implantation through dielectric caps, the profiles in the GaAs can be simulated using shifted, bare-wafer Pearson-IV distributions for Be, or mixtures of shifted Pearson-IV and Gaussians for Si and Se. Also, knock-on distributions of Si and O atoms resulting from implanting through SiO2 caps were measured.
Stray capacitance effect in superconducting quantum interferometers
Authors: Leoni R. , Carelli P. , Foglietti V.
Published: July 2002

The experimental results obtained with low noise dc superconducting quantum interference devices (dc-SQUIDs) are sometimes not well understood. In particular, when the critical current is high, very irregular voltage versus flux characteristics can be measured. On the other hand, when the critical current is low, the characteristics follow perfectly the resistively shunted junction model. We have studied the dynamics of a dc-SQUID in the presence of stray capacitance and shunting resistors imbalance. The equations describing a circuit model for this physical system are integrated numerically and the results are compared with voltage versus flux characteristics obtained from fabricated devices. We find that the theoretical analysis accounts very well for previously misunderstood experimental features of the dc-SQUID. This model can give more physical sense to the various regimes of behavior of the dc-SQUID giving more insight into the experimental results.
Radiation-enhanced diffusion in Ni/Zr diffusion couples
Authors: Ding Fu-rong , Averback R. S. , Hahn H.
Published: July 2002

Radiation-enhanced diffusion and ion-beam mixing in Ni/Zr diffusion couples were investigated. The Kirkendall geometry was employed for this experiment to determine the radiation-enhanced diffusivities of both Ni and Zr in the amorphous (a-) NiZr interdiffusion zone. W, Au, and Hf were employed as markers. The activation enthalpy for radiation-enhanced interdiffusion was determined to be ≊0.4 eV, and Ni was found to be the faster moving species. The dose-rate dependence of the interdiffusion coefficient in the a-NiZr was typical of that of crystalline materials and suggests a point-defect-like diffusion mechanism in irradiated metallic glasses.
The annealing behavior of light-induced defects in a-Si:H
Authors: Qiu Changhua , Li Wei , Han Daxing , Pankove Jacques
Published: July 2002

An a-Si:H sample was soaked by AM1 light at 300 K (state B1) and 100 K (state B2), respectively. An annealing activation energy of 1.2 eV was found for the metastable subband-gap absorption. However, for the recovery of the mobility-lifetime product, μτ, an activation energy of 0.9 eV was found for both states B1 and B2. The capture cross section of the recombination centers was estimated. It is suggested that the degradation in the μτ product is due to the creation of new recombination centers near the dark Fermi level with at least an eight times larger capture cross section than that of neutral dangling bonds.