bluuebunny/crossref_metadata_2025 huggingface dataset:
Anodic oxidation of InP using a citric-acid-based solution
Authors: Franz Gerhard
Published: July 2002

An electrolyte for anodic oxidation of InP is described which takes into account the extreme sensitivity of its native oxide to water. It is an aqueous solution of citric acid buffered to nearly neutral pH and highly diluted by glycerine or ethylene glycol which can produce smooth native oxide films on InP. The breakdown field is about 3.5×106 V/cm. Nearly no shrinkage even at temperatures up to 590 °C has been observed indicating that the oxide is very densely packed.
Substrate-affected instability in accumulation-mode InP metal-insulator-semiconductor field-effect transistor
Authors: Lee P. Z. , Chang H. L. , Meiners L. G.
Published: July 2002

The mechanism for drain current drift in accumulation-type InP metal-insulator-semiconductor field-effect transistor has in the past several years been attributed to oxide traps, interface states, and bulk traps. In this study we have found that deep levels in the semi-insulating InP substrate material can in some cases dominate the current drift of the accumulation-mode metal-insultor-semiconductor field-effect transistor. Iron, which is a deep-level acceptor, when present in large concentrations in semi-insulating InP substrate material, appears to provide poor transistor properties and a large long-term current drift.
Orthorhombic to tetragonal phase transition in Y1Ba2Cu3O7−x
Authors: Singh A. K. , Richards L. E. , Hoff H. A. , Letourneau V. , Pande C. S.
Published: July 2002

Quenching experiments were performed to study the orthorhombic to tetragonal phase transition in Y1Ba2Cu3O7−x. The quenched and unquenched specimens were characterized by x-ray diffraction and optical microscopy. The phase transition temperature was found to be dependent on the environment of the sealed specimens during quenching, and could be as high as 1173 K (900 °C). The phase transition is suggested to be of second order.
Electrical short-circuit current decay: Practical utility and variations of the method
Authors: Zondervan Albert , Verhoef Leendert , Lindholm Fredrik A. , Neugroschel A.
Published: July 2002

We review and extend the theory and experimental practice of the electrical short-circuit current decay (ESCCD) method for determining the effective back surface recombination velocity S and minority-carrier lifetime τ in p-n junction solar cells and diodes. The ratio of minority-carrier diffusion length to base thickness plays a key role in the transient ESCCD response which in general is an infinite sum of decaying exponentials. Their amplitudes and decay constants depend on this ratio. If this ratio is much less than unity, the response decays in proportion to (t/τ)−3/2 exp(−t/τ) for times that can be explored experimentally. If this ratio exceeds unity, a single mode of exponential decay predominates. For all intermediate cases a multimode fitting procedure yields S and τ. We present, with illustrative measurements of solar cells, three different ways to improve accuracy of the ESCCD method: (a) observing the amplitude and the decay constant for different injection levels, (b) altering the device under study by replacing the low-high junction (or back-surface-field region) by an ohmic contact, and (c) combining the observed decay constant with results of low- or high-frequency small-signal-admittance measurements.
High-frequency permeability in double-layered structure of amorphous Co-Ta-Zr films
Authors: Ochiai Y. , Hayakawa M. , Hayashi K. , Aso K.
Published: July 2002

The high-frequency permeability of amorphous Co-Ta-Zr films was studied and the frequency dependence was described in terms of the eddy-current-loss formula. For the double-layered structure intervened with SiO2 film, the degradation of the permeability became apparent with the decrease of SiO2 thickness.
The second-order spin-wave instability threshold in single-crystal yttrium-iron-garnet films under perpendicular pumping
Authors: Zhang Y. T. , Patton C. E. , Srinivasan G.
Published: July 2002

The second-order spin-wave instability threshold in yttrium-iron-garnet single-crystal thin films has been investigated under conditions of ferromagnetic resonance (FMR). The samples were (111) etched circular films of 500 μm diam and 5.1 μm thickness, grown on gadolinium gallium garnet substrates by liquid-phase epitaxy. The pulsed microwave power FMR absorption curves were measured by standard signal averaging techniques at 9.18 GHz and room temperature for three different perpendicular pumping configurations: (1) in-plane static field and out-of-plane microwave field, (2) mutually perpendicular in-plane static and microwave fields, and (3) out-of-plane static field and in-plane microwave field. The experimental results show that the upsweep and downsweep FMR curves for lower pulsed microwave powers at low duty cycle of 1% are identical, but there are foldover effects in the FMR profiles at higher powers. Theoretical expressions for the instability threshold for these three configurations were obtained by extending previous theories. The calculated thresholds are in good agreement with the experimental results for configurations (1) and (2). The results for configuration (3) indicate the presence of a true foldover effect, also consistent with instability theory.
An investigation of InxGa1−xAs/GaAs quantum wells grown by molecular-beam epitaxy
Authors: Jeong Jichai , Shahid M. A. , Lee J. C. , Schlesinger T. E. , Milnes A. G.
Published: July 2002

Photoluminescence (PL) and transmission electron microscopy have been used to study strained InxGa1−xAs/GaAs (x=0.24–0.28) quantum wells (QWs) grown by molecular-beam epitaxy. The three QWs grown without growth interruptions produce high intensity PL peaks of narrow full width at half-maximum (2.9 meV). On the other hand, the PL peaks in the QWs grown with 30-s interruptions are relatively broad, less symmetric, and show lower PL intensities, compared with the noninterrupted QWs. Our results show that high-quality strained InxGa1−xAs/GaAs QWs can be grown without growth interruptions.
Ellipsometric and Rutherford backscattering characterization of low-energy hydrogen-, helium-, neon-, and argon-bombarded silicon
Authors: Buckner J. L. , Vitkavage D. J. , Irene E. A.
Published: July 2002

Ellipsometry and Rutherford backscattering/channeling were used to study silicon surfaces modified by low-energy hydrogen, helium, neon, and argon ion bombardment. Ellipsometry was found to be a very sensitive technique for characterization of these samples, able in some cases to simultaneously distinguish the ion identity, incident energy, and total dose experienced by the material. A comparison of the ellipsometric results for the different cases indicates qualitative differences in the physical modifications induced in the silicon surface region under bombardment by different ions. Comparison of the ellipsometric results with Rutherford backscattering/channeling data yielded estimates of the complex refractive index of the silicon layer modified by hydrogen and helium bombardment, showing a general decrease in the refractive index and an increase in the optical extinction coefficient upon bombardment. It was possible to explain these changes, at least qualitatively, by using the Bruggeman effective medium approximation to estimate the volume composition of this layer subject to certain simplifying assumptions. One result of this was the development of the exact solution for the three-component Bruggeman analysis; these equations are derived in the Appendix.
Instantaneous crystalline annihilation during normal grain growth in aluminum thin films
Authors: Thon A. , Brokman A.
Published: July 2002

The process of normal grain growth in unsupported thin aluminum film was studied in situ by heating the specimen during inspection in the transmission electron microscope. The growth mechanism was found to involve the instantaneous annihilation of a grain as a whole and its consumption by neighboring grains. This elementary process occurs in a time interval shorter than 0.04 s (the video camera time lag between two successive exposures), and it cannot be explained in terms of grain-boundary self-diffusion. Often the annihilation of a grain is followed by a cascade of similar events in its immediate neighborhood. It is possible that long-wave instabilities at the grain boundary grow through a critical stage in which the topological stability of the boundary is destroyed, yielding the spontaneous growth.
Electrical characteristics of hydrogen implanted silicon Schottky diodes having large difference in metal work function
Authors: Yapsir A. S. , Lu T.-M. , Hadizad P. , Corelli J. C. , Sugerman A. , Bakhru H.
Published: July 2002

Hydrogen ion implantation was carried out on Schottky diodes having large difference in metal work function, Ti/p-Si and PtSi/p-Si diodes. Current-voltage (I-V) measurements showed that, following ion implantation, Ti/p-Si diodes exhibited rectifying characteristics; in contrast, no significant rectifying behavior was observed in the PtSi/p-Si diodes. These results showed a dependence of the implantation effects upon metal overlayer work functions. Consequently, the observations did not seem to indicate the occurrence of Fermi level pinning due to a highly damaged near-surface region after ion implantation, as previously suggested. Capacitance-voltage (C-V) measurements revealed a decrease in the diode capacitances along with a significant reduction of acceptor concentration following the implantation. In general, the results suggest that ion implantation alters the electrical characteristic of the diodes mainly by creating defects in the semiconductor depletion region. All such defects act as recombination centers giving rise to a deviation of the electrical characteristics from the normal behavior. They do not play a role in producing a Fermi level pinning.
Influence of surfactants on a nonflowing dye laser
Authors: Moran M. B. , Marrs C. D.
Published: July 2002

The effect of surfactants on the performance of pulsed, laser-pumped, flowing dye lasers has been reported. The use of surfactants in a nonflowing dye cell permits remarkably improved performance in a laser that is much simpler and more compact. The characteristics of such a system are reported here. Solutions of the laser dye rhodamine 590 perchlorate in various solvents were studied. Up to 300% improvement in conversion efficiency was observed for solutions with surfactants. Operation of the laser with the ethylene glycol/sodium dodecyl sulfate solution demonstrated a consistent output of around 8.0 mJ at a repetition rate of 5 Hz. Preliminary results on the laser bandwidth, pulse width, energy stability, and conversion efficiency will be presented.
Very low-frequency hysteresis loops in ferroelectric liquid crystals: A new optical technique
Authors: Etxebarria J. , Jubindo M. A. Pérez , Ezcurra A. , Tello M. J.
Published: July 2002

A new optical technique for quantitative studies of switching processes in ferroelectric liquid crystals is reported. The molecular reorientational changes are determined directly as a function of the exciting electric field. By that means, information can be obtained which is similar and complementary to that derived from the polarization current measurements. The method is specially adapted for very low-frequency regimes (≤0.1 Hz). In contrast to the polarization technique, there are no spurious conductive and capacitive contributions. The features of the method are illustrated by studying the switching process of a 9-μm-thick sample of p-(n-decyloxybenzylidene)-p-amino-(2-methyl-buthyl) cinnamate (DOBAMBC) under a triangular wave of 0.03 Hz. The temperature dependence of the coercive fields of these low-frequency cycles is found to obey a power law at the chiral smectic C (Sm C*) phase. The frequency dependence of the coercive fields exhibits a null value at the zero-frequency limit in contrast to that of the solid-state ferroelectrics.
Composition, microstructure, and properties of crystalline molybdenum silicide thin films produced by annealing of amorphous Mo/Si multilayers
Authors: Loopstra O. B. , Sloof W. G. , de Keijser Th. H. , Mittemeijer E. J. , Radelaar S. , Kuiper A. E. T. , Wolters R. A. M.
Published: July 2002

Amorphous Mo/Si multilayers were prepared by alternately sputtering Mo and Si onto silicon single-crystal substrates covered with SiO2 and onto substrates covered with polycrystalline Si. The multilayer thickness was about 200 nm and the composition modulation period was about 0.8 nm. The Mo/Si atomic ratio averaged over the multilayer was about 0.6. These specimens were isochronally annealed for 1 h at temperatures up to 1000 °C. In order to analyze annealing-induced variations in composition, microstructure, resistivity, and internal stresses, the specimens were investigated by x-ray diffractometry, Rutherford backscattering spectroscopy, and resistometry. Although the multilayer remained amorphous during annealing at temperatures below 350 °C, interdiffusion of Mo and Si occurred. Above 350 °C the layered structure disappeared and crystalline phases, viz., hexagonal MoSi2, Mo5Si3, and tetragonal MoSi2, appeared successively for increasing temperatures. According to the (equilibrium) phase diagram both hexagonal MoSi2 and crystalline Mo5Si3 were expected to occur simultaneously. It

appeared, however, that hexagonal MoSi2 formed first, probably because of difficult nucleation of crystalline Mo5Si3. The hexagonal MoSi2 nucleated homogeneously, whereas Mo5Si3 nucleated heterogeneously. In MoSix layers on SiO2 the Mo5Si3 grew at the outer surface and at the MoSix/substrate interface. In MoSix layers on polycrystalline Si the Mo5Si3 reacted with Si to form hexagonal MoSi2 at temperatures above 700 °C. Finally, the hexagonal MoSi2 phase transformed into tetragonal MoSi2. The resistivity of the MoSix layer decreased distinctly as soon as hexagonal MoSi2 was formed and an even larger decrease occurred when hexagonal MoSi2 transformed into tetragonal MoSi2. The latter resistivity decrease was accompanied by a considerable improvement of overall crystalline perfection of the MoSix layer. The lowest resistivity (58 μΩ cm) was obtained after annealing at 1000 °C. The internal stress in the MoSix layer can be explained by the difference in thermal contraction between the MoSix layer and the Si substrate. After annealing at 1000 °C the internal stress equaled about 2.0 GPa.
Peak shape analysis for ion mobility spectroscopy
Authors: Glasser M. L.
Published: July 2002

The factors determining arrival time line shapes in ion drift tube devices are discussed. An analysis is presented for the line shape due to diffusive drift and its modification due to various boundary conditions. The modification of the line shape due to ion neutralization by randomly placed impurities within the drift area is considered.
Hg content and thermal stability of the anodic sulfide films on Hg1−xCdxTe investigated by 30–40-MeV O5+ ion backscattering
Authors: Ippōshi T. , Takita K. , Murakami K. , Masuda K. , Kudo H. , Seki S.
Published: July 2002

The Hg content of anodic sulfide films on Hg1−xCdxTe (MCT) were investigated for as-grown and heat-treated films by using 30–40-MeV O5+ ion backscattering. Heat treatments were performed in a vacuum for 60 min at various temperatures up to 300 °C for the samples with x=0.20 and up to 350 °C for the samples with x=0.30 and 0.35. A significant Hg content of about 15 at. % of Cd was found in the as-grown anodic sulfide film on MCT samples with x=0.20, 0.30, and 0.35. After heat treatment above 260 °C for x=0.30 and 0.35 and above 210–240 °C for x=0.20, the Hg atoms were removed from the films, and Hg deficient layers were formed near the interface region of the MCT crystal. This suggests that the residual Hg in the anodic sulfide films introduced during the sulfidization process plays an important role toward the degradation of the passivation properties of the sulfide film on MCT.
Hydrocarbon dissociation on palladium studied with a hydrogen sensitive Pd-metal-oxide-semiconductor structure
Authors: Dannetun H. , Lundström I. , Petersson L.-G.
Published: July 2002

The polycrystalline Pd surface of a hydrogen sensitive palladium-silicon dioxide-silicon [Pd-MOS (metal-oxide-semiconductor)] structure has been exposed to small unsaturated hydrocarbons in the temperature range 300–500 K. Apart from the hydrogen response of the Pd-MOS structure also work function (ΔΦ) and electron energy-loss studies were performed. At 500 K the hydrocarbons dissociate completely upon adsorption and produce a surface with atomically adsorbed carbon. The Pd-MOS structure can be used to observe both the dehydrogenation of the hydrocarbon molecules and the process of carbon adsorbing on the palladium surface. The sticking coefficient at this temperature for all hydrocarbons is close to unity. Furthermore, the hydrogen sensitivity of the structure is not drastically reduced by the adsorbed carbon. If the hydrocarbon adsorption is performed at 300 K there is still, at least on the initially clean surface, a large dehydrogenation. The dissociation is, however, not at all complete and there are considerable amounts of hydrocarbon species adsorbed for each gas. The induced work function shifts due to the different hydrocarbons vary from −1.0 to −1.7 eV. The hydrogen sensitivity of the Pd-MOS structure is reduced for growing hydrocarbon coverages and disappears completely for work function shifts of −1.7 eV.
Electroluminescence from amorphous silicon carbide heterojunctions under reverse biased conditions
Authors: Alvarez F. , Fragnito H. L. , Chambouleyron I.
Published: July 2002

The emission of visible radiation from reverse biased amorphous silicon carbide p-i-n junctions at room temperature was observed. The heterostructures were made by successively depositing boron-doped amorphous silicon carbide-intrinsic amorphous silicon carbide-phosphorous doped amorphous silicon on to indium-tin-oxide coated glass. The optical gap of the p, i, and n layers were 2.0, 2.25, and 1.7 eV, respectively. The reverse current producing the radiative emission is mainly due to a field-enhanced thermal injection mechanism. At low-current densities the total light emitted is proportional to the fifth power of the injected current. At higher injections, however, it becomes quadratic. These power law dependencies are interpreted in terms of electron recombination with trapped holes and band-to-band bimolecular recombination, respectively.
Magnetic properties of NdDyFeCoAlB alloys
Authors: Kim A. S.
Published: July 2002

The temperature stability of Nd-Fe-B alloy has been improved by the combined addition of Dy and Co and either Al, Ga, or Nb. However, additions of large amounts of Dy, Al, Ga, and Nb substantially reduce the Br from that of Nd-Fe-B, and thus reduce overall magnet performance. This study shows that properly combined additions of Dy, Co, and Al to pseudoternary (Nd,Dy)-(Fe,Co,Al)-B compounds improve both temperature stability and energy density. Hci and Br increase more than in the alloys modified with Dy, Co, or Al alone. The Hci of the alloys increases almost linearly with Dy content at a rate of about 6.8 kOe/at. % Dy, when the alloys contain approximately 5–6 at. % Co, and Al and Dy in a ratio of 1 to 1.2 Al/Dy. The temperature coefficients of Br and Hci, and the irreversible losses of (Nd,Dy)-(Fe,Co,Al)-B alloys are lower than those of the other alloys tested. When compared to Nd-Dy-Fe-Co-B alloy, the reduced consumption of Dy increases the energy products and reduces the material cost, without sacrificing temperature stability.
Introduction of spin disorder by exchange defects
Authors: Parker G. , Saslow W. M.
Published: July 2002

Individual negative bonds are introduced in an XY spin system on a square lattice with otherwise nearest-neighbor ferromagnetic interactions. Using a mean-field theory we have found better than 5% agreement between numerical calculations and a continuum theory for this discrete system. In addition, preliminary studies of the interaction of two negative bonds have been made. A continuum theory indicates a dipolelike interaction, some of whose features have been observed in the calculations. Our results are relevant to alloying-induced spin disorder, where defects which individually are not strong enough to disorder the host system can, through a long-range dipolar interaction, interact to produce noncollinearity in the spin system.
The magnetic properties of Sm-Ti-Fe and Nd-Ti-Fe hard and soft sputtered phases
Authors: Kamprath N. , Wickramasekara L. , Hegde H. , Liu N. C. , Jayanetti J. K. D. , Cadieu F. J.
Published: July 2002

A series of Sm-Ti-Fe and Nd-Ti-Fe film samples have been synthesized by rf diode sputtering for Fe-rich compositions. Samples have been directly crystallized onto heated substrates as well as first deposited amorphous and then subsequently crystallized. In the film plane magnetic fields have been applied during the deposition and during the crystallization to induce in-the-film-plane anisotropies into the films. A phase that contained only Sm, Ti, and Fe has been synthesized in film form that exhibited an in-plane intrinsic coercive force, iHc, of 31 kOe at room temperature and 58 kOe at 5 K. Tetragonal lattice parameters with a=8.391 Å and c=12.297 Å have been assigned to the high iHc phase by a fitting to 12 diffraction lines. The Nd-Ti-Fe and the Sm-Ti-Fe systems also exhibited a soft magnetic phase of the ThMn12-type at a nominal composition of Nd(TiFe11).
The mechanism of the high conduction state in the Ca2+Ge4+:YIG system
Authors: Yuan S. H. , Pardavi-Horváth M. , Wigen P. E. , De Gasperis P.
Published: July 2002

Semi-insulating epitaxial garnet films of p-type Ca2+Ge4:YIG can be excited to a high conduction state (HCS) under the effects of light and electric field. To clarify the mechanism of the HCS, epitaxial films of Ca2+:YIG, Ge4+:YIG, Ca or Ge excess Ca2+Ge4+:YIG have been investigated. dc I-V characteristics were measured in electric fields up to 105 V/cm, with and without light. Thermopower and deep level transient spectroscopy (DLTS) were measured between 140 and 300 K. At low electric field the conduction is ohmic. As the electric field is increased a square-law dependence is observed and at a critical field, on the order of 105 V/cm and whose value is sensitive to the frequency and intensity of the light, a negative resistance state is formed in Ca:YIG and CaGe:YIG (both p- and n-type) films, and in this region the sample suddenly transforms to the HCS. A very slow transformation to the HCS can also be observed at lower electric fields, on the order of 104 V/cm, by keeping the electric field constant and illuminating the sample with light on the order of 10 mW/cm2 intensity. Thermopower and DLTS data indicate that electrons located in compensated acceptor states are removed in the HCS. The presence of a sufficient number of compensated acceptors and oxygen vacancies serving as repulsive traps is a necessary condition for the formation of the HCS. The transition to this HCS is then proposed to be a process where electrons are transferred to the repulsive traps located below the conduction-band mobility edge. This trapping process lowers the Fermi level toward the valence band.
Spatial distribution of vacancy defects in GaP wafers
Authors: Domínguez-Adame F. , Piqueras J. , de Diego N. , Llopis J.
Published: July 2002

Cathodoluminescence scanning electron microscopy and positron annihilation techniques have been used to investigate the distribution of defects in GaP wafers. The results show the existence of a gradient of the concentration of vacancy-type defects along the wafer diameter, which causes inhomogeneity in the emission. Dislocation density and vacancy concentration profiles have been compared.
Role of impurities in zone melting recrystallization of 10 μm thick polycrystalline silicon films
Authors: Mertens P. W. , Wouters D. J. , Maes H. E. , De Veirman A. , Van Landuyt J.
Published: July 2002

Zone melting recrystallization (ZMR) of polycrystalline silicon on SiO2 can offer an interesting, i.e., cheaper, alternative to the dielectric isolation technology used for high-voltage integrated circuits or smart power devices. For that purpose crystalline Si layers of 10–15 μm thickness are needed. In this work a mercury-arc lamp stripheater was used to recrystallize 10 μm thick polycrystalline silicon films. In unseeded layers, grain boundaries and subgrain boundaries appeared. By applying seeding, single crystalline areas of at least 1 mm by 1 mm were obtained. In these layers stacking faults were revealed as being the major crystal defect. In ZMR oxygen, nitrogen, and carbon are the major impurities which are incorporated into the silicon either intentionally or unintentionally. Among these impurities, nitrogen and carbon are believed to play a crucial role in promoting the wetting of the insulator and cap layer by liquid silicon. In this paper the distribution and transport of oxygen and nitrogen during ZMR are studied. It is shown that nitrogen can cause dendritic growth and that oxygen is unlikely to do so.
Anisotropic plasma-chemical etching by an electron-beam-generated plasma
Authors: Verhey T. R. , Rocca J. J. , Boyer P. K.
Published: July 2002

Anisotropic etching of SiO2 has been achieved with a plasma generated by a broad-area low-energy (150–300 eV) electron beam in a He+CF4 atmosphere. Etch rates of up to 330 Å/min for SiO2 and 220 Å/min for Si were obtained. Etching occurred with good uniformity over the entire area exposed to the electron-beam-generated plasma. The fluxes of energetic charged particles to the sample surface are discussed in relation to their possible contribution to the etching process.
Laser heating and melting of thin films with time-dependent absorptance: An exact solution for time intervals less than or equal to the transit time
Authors: El-Adawi M. K. , Shalaby S. A.
Published: July 2002

Laser heating and melting is studied considering the laser-induced reflectivity variations R(τ). The study is made for time intervals less than or equal to the transit time using the Fourier series expansion technique together with the differential and integral forms of the heat diffusion equation. The equations obtained for the thickness of the molten layer Z(τ) and the rate of melting Z′(τ) are no longer quadratic. Computations for a thin silver film of thickness 5×10−5 m, subjected to constant laser irradiance of value q0=9×1010 W/m2 are carried out. Smaller threshold times required to initiate melting (i.e., damage) than those for the case of constant reflectivity are obtained. It is also found that melting occurs with nearly a constant rate.
Reactive synthesis of well-oriented zinc-oxide films by means of the facing targets sputtering method
Authors: Matsuoka Morito , Hoshi Yoichi , Naoe Masahiko
Published: July 2002

Well-oriented ZnO films are reactively synthesized by means of the facing targets sputtering (FTS) method. In this paper, the change in the crystallographic characteristics of ZnO films with respect to sputtering conditions are described in detail. Films obtained by means of the FTS method exhibit one of the best c-axis orientations reported to date. The following conditions are necessary for formation of well-oriented ZnO films with good surface smoothness: (1) High-energy particle bombardment on the film surface during deposition should be suppressed and (2) the sputtered particles landing on the substrate surface should have an appropriate energy level of several eV.
Phase transitions in Ru based thick-film (cermet) resistors
Authors: Morten B. , Prudenziati M. , Sacchi M. , Sirotti F.
Published: July 2002

Thick-film resistive inks have been prepared starting from powders obtained by precipitation of RuCl3 on two different lead-containing glasses. The structural and electrical properties of the films have been investigated after heat treatment at various temperatures. The evolution of the microstructure involves phase transformations from Pb-rich (Ru-deficient) pyrochlores to Ru pyrochlores and finally to RuO2. Together with these crystallographic features, the atomic absorption spectroscopy shows a gradual decrease of the Ru dissolved in the glass when the firing temperature increases. The conductivity of the samples decreases according to the transition from pyrochlore to dioxide. These results emphasize the role played by exchange reactions in the control of transport mechanisms in thick-film cermet resistors.
Metastable carrier concentration in GaAs/GaAlAs heterostructure under hydrostatic pressure
Authors: Suski T. , Litwin-Staszewska E. , Wiśniewski P. , Dmowski L. , Zhuang W. H. , Liang G. B. , Sun D. Z. , Zhen Y. P.
Published: July 2002

Different aspects of the metastable character of Si-related localized states in modulation-doped heterostructures of GaAs/GaAlAs have been studied. Hydrostatic pressure was used to change the two-dimensional electron-gas concentration at the active interface of the system. The performed studies give evidence that below a critical temperature of Tc=135 K for a given sample, at the same temperature and pressure conditions, an arbitrary carrier concentration in the quantum well can be obtained depending on the pressure at which the sample was cooled.
Molecular stream epitaxy and the role of the boundary layer in chemical vapor deposition
Authors: Katsuyama T. , Bedair S. M.
Published: July 2002

Molecular stream epitaxy (MSE) is a new growth technique that modifies the nature of the metalorganic chemical vapor deposition (MOCVD) process to take advantage of molecular-beam epitaxy (MBE) growth concepts, and was used for the growth of InGaAs, GaAsP, and InGaAs/GaAsP strained-layer superlattices (SLSs). In this technique, the growth proceeds by rotating the substrate to cut into streams of reactant gases and thus eliminates gas-flow transients and provides a method to mechanically shear off the gaseous boundary layer above the substrate between successive exposures. In the growth of InGaAs and GaAsP, growth rate enhancement and compositional changes were observed in the faster rotation regime. These phenomena were attributed to the effective reduction of the diffusion boundary layer above the substrate. In the growth of InGaAs/GaAsP SLSs the individual layer thickness of these SLSs was controlled precisely down to 8 Å by simply changing the exposure time to the stream of reactant gases. The optical properties of these SLSs were comparable to those obtained for equivalent superlattices by gas source MBE.
A simple new method to grow crystalline metallic thin films on amorphous substrates
Authors: Romeo N.
Published: July 2002

A new method, called concentration gradient thin-film crystallization, suitable to grow crystalline metallic thin films on amorphous substrates, has been developed. The method consists of the simple deposition of two metallic layers one after each other on an amorphous substrate kept at a given temperature. Both the right concentrations of the two elements and the right substrate temperature depend on the phase diagram of the considered alloy.
A nonlinear analysis of the kinetics of reversible structural relaxation in Co-Fe based metallic glasses
Authors: Komatsu T. , Iwasaki K. , Sato S. , Matusita K.
Published: July 2002

The kinetics of reversible resistivity changes during structural relaxation in various Co-Fe based metallic glasses was examined using a nonlinear kinetic form Ψ=exp[−(t/τm)n]. It was found that the data excellently fit the nonlinear kinetic form. The compositional dependence of the kinetic parameters (distribution parameter n, activation energy Ea, and preexponential factor τ0) were obtained, and the microscopic mechanism of atomic rearrangements during the relaxation is discussed.
Spatial distribution of defects in GaAs:Te wafers studied by cathodoluminescence
Authors: Méndez B. , Piqueras J. , Domínguez-Adame F. , de Diego N.
Published: July 2002

Cathodoluminescence (CL) scanning electron microscopy and positron annihilation techniques have been used to investigate the distribution of defects in GaAs:Te wafers. Dislocation density and near-band-edge CL profiles along the wafer have different shapes. Positron lifetime measurements do not show spatial changes of vacancy concentration in the wafers, but a higher vacancy concentration has been detected in the Te-doped samples relative to SI samples. Results are discussed in terms of vacancies and impurity vacancy complexes.
Dependence of silver distributions in electron-beam-exposed regions on dosage as well as on the thicknesses of dry-sensitized layers and chalcogenide glass films
Authors: Liang Yong-Cheng , Tada Kunio
Published: July 2002

When a chalcogenide glass film of composition As10Ge22.5Se67.5 is sensitized with evaporated silver selenide and is exposed to an electron beam, it is suggested that, as is the case for photodoping, silver will migrate from the unexposed region into the exposed one. This results in different silver distributions in the exposed regions. The distribution has been found, for the first time, to depend on various factors other than dosage, namely, the thicknesses of sensitized layers and glass films, and the size of the exposed region. Moreover, the form of the distribution is affected by the thickness of the sensitized layer but not that of the glass film, while it is not the thickness of the sensitized layer but that of the glass film which has an effect on the rate of change of silver concentration at the periphery or at the center versus dosage. By considering the amount of silver selenide remaining on the top of the exposed region, and by further assuming that silver diffusivity in the doped region is small when its concentration is low and that it will increase as the concentration is sufficiently large, one may be able to qualitatively explain the dependence of the distribution on the thickness of the sensitized layer.
Evidence for amorphous multilayered silicon obtained by deposition under modulated pressure of hydrogen
Authors: Vergnat M. , George B. , Bruson A. , Marchal G. , Mangin Ph. , Demai J. J.
Published: July 2002

A new method of fabrication of layered structure of silicon is presented. The silicon was evaporated continuously under a modulated pressure of hydrogen. A contrast was dense and less dense silicon layers is evidenced by low-angle x-ray scattering and cross-sectional electron microscopy.
Heteroepitaxial growth of ZnSe on (111) Si by low-pressure metalorganic chemical vapor deposition
Authors: Lee M. K. , Chang J. H. , Yeh M. Y. , Lin Y. F.
Published: July 2002

ZnSe epitaxial layers were successfully grown on (111) Si substrates by low-pressure metalorganic chemical vapor deposition. It is not necessary that the reactant inlet tubes project to near the substrates. From x-ray and scanning electron microscopy examinations, single-crystalline ZnSe epilayers with mirrorlike surfaces can be obtained. The carrier concentration profile shows that the carrier distribution in the epilayer is very uniform. The electron mobility of the epilayer at room temperature is 280 cm2 /V s. The efficient 77-K photoluminescence indicates that the ZnSe epilayers are of good quality.
Effect of neutron irradiation on responsivity of p-i-n photodetectors
Authors: Gedam Subhash G. , Banerjee Pranab K. , Mitra Shashanka S.
Published: July 2002

Neutron irradiation induced degradation in the responsivity of Si and Ge p-i-n photodetectors has been studied. The responsivity of an irradiated photodetector normalized to its preirradiation responsivity was found to have a spectral dependence in the case of the Si photodetector. In the case of the Ge photodetector, the relative responsivity was found to be independent of wavelength in the most part of the spectrum covered in the experiment.
Experimental technique for the determination of surface acoustic wave grating impedance and velocity perturbations
Authors: Hunt W. D. , Hunsinger B. J.
Published: July 2002

In this paper several new methods are presented whereby successive laser probe scans can be used to measure the reflection coefficient and velocity perturbation for a grating structure on a surface acoustic wave substrate. These techniques can be used to evaluate the perturbations presented by any overlay material arranged in a grating structure. This includes etched grooves, evaporated metals, and deposited dielectrics. The methods utilize the results presented previously [J. Appl. Phys. 60, 3532 (1986)] which indicate that the propagation of a beam profile can be very accurately predicted if a carefully measured slowness surface is used in conjunction with the angular spectrum of the plane-waves diffraction theory.
Surface states and the temperature dependence of microindentation damage in silicon
Authors: Danyluk Steven , Lee Soo-Wohn
Published: July 2002

The interrelationship between mechanical and electronic properties of crystalline semiconductors has been explored through indentation of doped single-crystal silicon. The indentations were etched and the damage that extended beyond the immediate contact zone has been measured as a function of isothermal temperature of the silicon during the indentation. The damage zone exhibited a maximum at 150 °C. The surface properties of the silicon have been modeled with a finite, fixed number of surface states which possess an energy within the band gap. The spatial extent (Debye length) of the space-charge region has been calculated as a function of temperature, doping level, surface state energy, and density. The temperature variation of the Debye length is similar to that of the experimentally measured damage zone size when the indentation load was 0.49 N; both range in the 10−6 m and exhibit a maximum with temperature. The model implies that the deformation mode of silicon may be additionally influenced by external applied voltages, suitable doping, and/or surface preparation.
A study of the fast permeability relaxation in amorphous ferromagnets
Authors: Allia P. , Beatrice C. , Vinai F. , Mazzetti P
Published: July 2002

The strong relaxation of the ac magnetic permeability, observed in amorphous ferromagnets at very short times after demagnetization, is studied under different experimental conditions. The behavior of the fast permeability relaxation with temperature, applied stress, and driving field frequency clearly shows that this effect has a predominant dissipative character, very different from the diffusive permeability aftereffect, ascribed instead to activated processes of directional ordering. Optical measurements of domain wall motion at the sample surface suggest that the dissipative relaxation of the permeability is to be ascribed to a progressive reduction in the number of the domain walls participating in the magnetization process.
Electron-beam evaporated phosphosilicate glass encapsulant for post-implant annealing of GaAs
Authors: Singh S. , Baiocchi F. , Butherus A. D. , Grodkiewicz W. H. , Schwartz B. , Van Uitert L. G. , Yesis L. , Zydzik G. J.
Published: July 2002

Electron-beam deposited films of phosphosilicate (PSG) have been investigated as dielectrics for the encapsulation of Si-implanted GaAs for the purpose of post-implant annealing. The processing parameters that were optimized included the thickness of PSG film, the substrate temperature, and the annealing time and temperature. PSG films deposited at temperatures ≥300 °C showed no signs of deterioration up to temperatures in excess of 900 °C for 30-min anneals carried out in a forming gas and/or nitrogen ambient. Depth profiles in excellent agreement with the Lindhard–Scharff–Schiott curves were obtained with 1000-Å-thick films when annealed at 850 °C for 30 min. The diffusion coefficient of implanted silicon was found to be an order of magnitude smaller for the PSG films than that for the conventional plasma assisted chemical vapor deposited SiO2 films at 850 °C.
Optimum growth condition of single-crystalline undoped ZnS grown by the molecular-beam-epitaxial method using a H2S gas source
Authors: Kaneda Shigeo , Shimoguchi Takefumi , Takahashi Hironobu , Motoyama Shin-ici , Kano Fumihisa , Yokoyama Meiso , Satou Shuji
Published: July 2002

Crystal characterization by photoluminescence and x-ray diffraction has been performed to find out the optimum growth condition of ZnS grown by the gas-source molecular-beam-epitaxial (MBE) method. In this crystal growth, important parameters are the cracking temperature of H2S gas (Tcr), the film thickness (d), both molecular-beam flux intensities (JZn and JΣS or inlet H2S gas pressure Pin), and substrate temperature (Tsub). A single crystal having a fairly high quality, whose half width of x-ray diffraction FWHM is about 0.119° (the reference value of the GaAs substrate used is 0.093°), is obtained under the growth conditions Pin=1.4×10−5 Torr (corresponding flux intensity JΣS=7×1015 cm−2 s−1), JZn/JΣS=1, and Tsub=325 °C in the case of Tcr=780 °C and d≂1 μm.
Surface segregation and preferential sputtering of bismuth in rf-magnetron-sputtered iron-garnet films
Authors: Krumme J.-P. , Otterloo A. F. , Zalm P. C. , Pertruzzello J.
Published: July 2002

Auger electron spectroscopy, x-ray photoelectron spectroscopy, and secondary-ion mass spectrometry have been used to elucidate the role of surface segregation and preferential sputtering of bismuth in rf-magnetron-sputtered bismuth–iron-garnet films. It turns out that bismuth is enriched by a factor of up to 2.4, as compared to the bulk content, within the first 1–1.5 nm beneath the advancing film surface during growth. Furthermore, Ar+-ion bombardment at projectile energies as low as 50 eV gives rise to a rather complete depletion of bismuth in the garnet surface. As neither surface segregation nor preferential sputtering of bismuth can be observed in as-polished single-crystalline Bi12SiO20 used as our reference, we conclude that the bond strength between bismuth and oxygen is weaker than that of the other garnet constituents. This is confirmed by comparing the calculated sputter yield of the element oxide. Thus, bismuth-rich crystallographically perfect epitaxial iron-garnet films can only be grown by sputtering if the growing film is protected against energetic particle bombardment.
A modeling of diamond film growth
Authors: Chen Inan
Published: July 2002

The growth of diamond films from mixtures of methane and hydrogen has been investigated by mathematical modeling. The gas-phase reactions of H radicals with methane are treated by solving the rate equations, while the surface reactions are studied by Monte Carlo simulation. The results provide a quantitative interpretation of the observations, such as the need for a large number of H radicals per hydrocarbon gas molecule, and the insensitivity to the chemical nature of the precursor gas.
Doping effects of 3D metal on single-phase YBa2Cu3O7−δ
Authors: He Z. H. , Chen Z. Y. , Xia J. S. , Pan G. Q. , Qian Y. T. , Zhang Q. R.
Published: July 2002

The measurements of x-ray diffraction, the temperature dependence of the dc resistance and the ac susceptibility have been performed for the single-phase 3D-metal doping systems YBa2 Cu3−x Mx Oy (M=Fe, Co, and Ni; x=0.025, 0.05, 0.075, 0.10, 0.25, and 0.50 for Ni and Co and 0.05, 0.075, 0.10, 0.15, and 0.20 for Fe). With an increase of impurity content, two structural transitions were observed for the Co and Fe dopants but only one for the Ni dopant. The resistivity in the normal state changes from metallic to semiconductinglike behavior and the depression of Tc is linear with the impurity concentration (x) when x<0.10. A weak Curie–Weiss type paramagnetism, which is enhanced with impurity content, exists in the samples studied. Incorporating other work on oxygen defects, we suggest that a change of oxygen content induced by doping was the dominant effect on superconductivity in these samples.
Properties of cobalt in FZ and CZ silicon studied by Mössbauer spectroscopy
Authors: Utzig J.
Published: July 2002

Mössbauer effect investigations were performed on the Co system in n- and p-type silicon [floating zone (FZ) and Czochralski (CZ)]. The samples were saturated with Co-57 between 1080 and 1100 °C and quenched and annealed isochronically up to 600 °C and isothermally for times up to 22 h. In n-type material, a transformation of a quadrupole doublet into a single line with increasing annealing temperature is observed, independent of the P and O concentrations. In p-type samples, three quadrupole doublets are found after quenching, which are attributed to different CoB pairs following an interpretation given by Bergholz [Physica, 116B, 312 (1983)]. These quadrupole doublets transform during annealing at first into the quadrupole doublet and then into the single line found in n-type silicon. This transformation is interpreted as the decomposition of the CoB pairs followed by the precipitation of the interstitial Co. The transformation observed in n-type Si is interpreted as a morphological change of the CoSi2 precipitate.
Phase locking and stability properties for two coupled semiconductor lasers
Authors: Tsacoyeanes James G.
Published: July 2002

In this paper, a theoretical investigation of the locking of two weakly coupled semiconductor lasers is presented. The analysis begins with a set of rate equations for the electric fields and carrier densities inside each laser diode cavity. From these, the dynamic stability of the solutions as a function of the detuning between the lasers and the linewidth enhancement factor of each laser is determined. It is seen that when the linewidth enhancement factor is the same for both lasers, the entire locking bandwidth is dynamically stable. When the linewidth enhancement factor is different for the two lasers, asymmetric locking occurs, and only a portion of the locking bandwidth is dynamically stable.
Electron and hole dynamics in amorphous silicon
Authors: Werner A. , Kunst M.
Published: July 2002

Charge carrier dynamics in doped and undoped hydrogenated amorphous silicon (a-Si:H) films is studied by contactless time-resolved photoconductivity measurements. Subband-gap and above band-gap excitation are used to generate excess mobile charge carriers. In undoped a-Si:H the electron decay at charge carrier concentrations larger than 1016 cm−3 is mainly due to an electron-hole recombination which is controlled by hole dispersion. n doping introduces hole traps which increase the effective electron lifetime drastically as they quench this electron-hole recombination channel. At high n-doping levels the electron decay becomes faster due to an increase of the concentration of recombination centers upon doping. In lightly doped p-type samples the transient photoconductivity reflects the interaction of mobile holes with states in the valence-band tail. In heavily doped p- and n-type films the majority carriers decay by a second-order recombination process with trapped minority charge carriers. The transport parameters deduced agree with time-of-flight data.
Two-stage parametric amplification in N-(4-nitrophenyl)-L-prolinol crystals: Application to subpicosecond time resolution of parametric emission
Authors: Ledoux I. , Zyss J. , Migus A. , Hulin D. , Antonetti A.
Published: July 2002

Huge gain values (>107) are evidenced in parametric amplification of infrared subpicosecond pulses using two successive organic N-(4-nitrophenyl)-L-prolinol crystals acting as parametric amplifiers. Temporal analysis of parametric emission in the first crystal is performed in the second one. Application to the detection of long-wavelength pulses (>1.6 μm) is demonstrated with a high temporal resolution.
On the field effect in polycrystalline CdSe thin-film transistors
Authors: Van Calster A. , Vanfleteren J. , De Rycke I. , De Baets J.
Published: July 2002

Based on the grain barrier model of Levinson an expression of the off-current Ioff of a thin-film transistor is derived.The dependence of Ioff on the donor concentration ND and the semiconductor thickness ds is discussed and compared to experimental data. It is shown that NDds has to be smaller than the grain-boundary trap concentration in order to obtain enhancement thin-film transistors completely turned off at VG=0.