bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of deep centers in semi-insulating liquid-encapsulated Czochralski and vertical-gradient freeze GaAs
Authors: Fang Z-Q. , Look D. C.
Published: July 2002

Three-inch, semi-insulating (SI) GaAs, grown by the vertical gradient freeze (VGF) technique, has been studied by IR absorption, temperature-dependent dark current and Hall-effect, thermally stimulated current (TSC), and photoinduced current transient spectroscopy and has been compared with undoped, SI GaAs, both As-rich and Ga-rich, grown by the high-pressure liquid-encapsulated Czochralski method. The results clearly indicate that (1) the VGF GaAs contains less EL2, which suggests a less As-rich crystal stoichiometry; (2) in some VGF samples activation energies of 0.43 or 0.46 eV are deduced from temperature-dependent carrier concentration or resistivity measurements, respectively, and (3) VGF samples often show a thermal quenching behavior in the TSC peak T5. There is evidence to suggest that the 0.43 eV center is related to VAs, and T5 to VGa.
Three-dimensional ordering, spin excitations, and dilution effects in the quasi-1D ferromagnetic (DMeFc)(TCNE)
Authors: Narayan K. S. , Chi K. M. , Epstein A. J. , Miller Joel S.
Published: July 2002

The linear chain S =1/2 molecular ferromagnet decamethylferrocenium tetracyanoethanide [(DMeFc)(TCNE)] has been studied by frequency-dependent ac susceptibility experiments. χ′(T) and χ″(T) exhibit maxima in the temperature range of 4.8–4.9 K, which corresponds to the transition temperature to the three-dimensional (3D) ferromagnetic ground state. The 3D ordering is due to the presence of a finite interchain ferromagnetic interaction, as determined earlier by dc magnetic susceptibility and specific heat experiments. The results of ac susceptibility measurements below Tc are analyzed in terms of a Debye-like model to investigate the presence of gaps in the spin excitation spectrum of the system. Considerable changes are observed in the critical temperature on introducing spinless sites into the system. The transition temperature of the dilution series (DMeFc)x(DMeCo)1−x(TCNE), where (DMeCo)+=(decamethylcobaltocenium+) has spin S=0, decreases with increasing (1−x).
Control of heat transport in heat pipes by magnetic fields
Authors: Ueno S. , Iwaki S. , Tazume K. , Ara K.
Published: July 2002

We have observed that gas flow can be blocked or disturbed by magnetic fields. To explain this phenomenon, we developed a model called a ‘‘magnetic curtain’’ based on the paramagnetic properties of the oxygen molecule. In this paper, we applied this phenomenon to the control of heat transport in heat pipes. We used a heat pipe 20 mm in diameter and 500 mm in length packed with oxygen as a working fluid. We positioned this device vertically in an airgap 70-mm wide between the poles of electromagnet with 240 mm in diameter, in the direction perpendicular to the axis of the magnetic poles. The top side of the heat pipe was chilled with liquid nitrogen (77 K), and the lower side of the heat pipe was exposed to the room temperature (290 K). The efficiency of heat transport was measured by monitoring the change of the temperature at seven points inside and outside of the heat pipe in response to the step change of the top temperature from 290 to 77 K. When the middle part of the heat pipe was exposed to magnetic fields of 1.0 T with the gradient of 5–50 T/m, the heat transport was apparently blocked.
CuInSe2 for photovoltaic applications
Authors: Rockett A. , Birkmire R. W.
Published: July 2002

The properties and most successful methods for producing CuInSe2 films for solar-cell applications are reviewed and the production, analysis, and performance of photovoltaic devices based on CuInSe2 are discussed. The most successful methods for depositing thin CuInSe2 films for high-efficiency solar cells are three-source elemental evaporation and selenization of Cu/In layers in H2Se atmospheres. Devices based on CuInSe2 have achieved the highest conversion efficiencies for any nonepitaxial thin-film solar cell, 14.1% for a small cell and 10.4% (aperture efficiency) for a 3916-cm2 (4 sq. ft) device. Furthermore, high-efficiency devices have been produced by several groups and have shown no evidence of degradation of performance with time. The internal quantum efficiency is remarkably close to 100%, although various losses prevent making use of all of the generated carriers. The high performance results, in part, from the very-high-absorption coefficient of CuInSe2, which is of the order of 105 cm−1 for photons with energies slightly above 1 eV. Models of the operation of CuInSe2/CdS heterojunctions have begun to explain the processes limiting the device performance. The success of the models is based, in part, on the large amount of data which has accumulated on CuInSe2 in spite of the relatively short time it has been extensively studied.
Hydrogen diffusion and the catalysis of enhanced oxygen diffusion in silicon at temperatures below 500 °C
Authors: Newman R. C. , Tucker J. H. , Brown A. R. , McQuaid S. A.
Published: July 2002

The relaxation of stress-induced dichroism of the 9-μm oxygen infrared absorption band has been investigated for Czochralski silicon annealed isothermally at various temperatures in the range 225–350 °C while the material was immersed in a hydrogen plasma. The in-diffusion of hydrogen atoms enhanced the rate of oxygen diffusion so that the dichroism was lost progressively from the external surfaces of samples. Comprehensive ancillary measurements demonstrated that the oxygen diffusion jumps were catalyzed by collisions with diffusing hydrogen atoms, rather than some other fast-diffusing species. The measurements allowed the hydrogen diffusion coefficient to be estimated as 1.7 × 102 exp( − 1.2 eV/kT) cm2 s−1 for the range of temperatures investigated. Increased rates of thermal donor formation were also found due to enhanced long-range oxygen diffusion. The new data are related to previous reports of enhanced oxygen diffusion jumps found in Czochralski silicon given post-growth heat treatments in hydrogen gas. It is implied that concentrations of hydrogen atoms as low as 108 cm−3 may significantly enhance oxygen diffusivity.
Diffusion marker experiments with rare-earth silicides: The case of lutetium silicide
Authors: Travlos A. , Aloupogiannis P. , Weber G. , Robaye G.
Published: July 2002

A marker study of the lutetium silicide prepared by vacuum furnace annealing of a Lu thin layer on Si substrate shows that Si atoms are the dominant diffusing species during the formation of LuSi2−x. Rutherford backscattering spectrometry is used to determine the position of the marker before and after the annealing. The silicide films are characterized by x-ray diffraction and scanning electron microscopy.
Augmentation of field uniformity and strength in spherical and cylindrical magnetic field sources
Authors: Leupold H. A. , Potenziani E.
Published: July 2002

High magnetic fields (≊20 kG) are realizable from spherical and cylindrical transverse field sources in relatively small structures (∼10 cm). In some applications where the working space is cylindrical and long compared to its diameter, these fields can be augmented by about 5 kOe without an increase in the outer dimensions of the original structures. In spherical sources, a similar procedure yields a field increase of approximately 3 kOe. A method is described whereby field distortions arising from access holes to the interiors of such magnet structures can be greatly reduced. Such options considerably enhance the range of applicability to millimeter/microwave and optical devices.
Differences in physical properties of hydrogenated and fluorinated amorphous silicon carbide prepared by reactive sputtering
Authors: Demichelis F. , Pirri C. F. , Tresso E. , Stapinski T.
Published: July 2002

The paper deals with structural, optical, and electrical properties of a-SiC:H and a-SiC:H,F films prepared by rf sputtering of a silicon target in Ar+H2+CH4 and Ar+H2+CF4 gas mixtures, respectively. The comparison of the physical properties of the two different sets of the samples has been considered and the influence of hydrogen and/or fluorine incorporation is examined and discussed.
Erbium doping in InGaAsP grown by liquid-phase epitaxy
Authors: Wu Meng-Chyi , Chen En-Hsing , Chin Tsung-Shune , Tu Yuan-Kuang
Published: July 2002

The Er-doped InGaAsP epitaxial layers lattice-matched to InP with wavelengths of 1.29 and 1.55 μm have been grown by liquid-phase epitaxy. When the Er amount doped in the InGaAsP growth solution is above 0.32 wt %, it will have a fairly rough surface morphology with many extensive deposits of erbium hydride and oxide. The lattice mismatch normal to the wafer surface between InGaAsP layer and InP substrate decreases linearly with the Er weight percent in the grown solution. From the wavelength-dispersive-x-ray-spectrometer analysis, we find the solid composition of the In1−xGaxAsyP1−y layer has been changed and may be due to the formation of microparticles of Er compounds, such as ErAs or ErP. This inference is also supported by photoluminescence (PL) measurements which show that the PL peak wavelength decreases with increasing Er wt %. The full width at half maximum of PL peak associated with the near band-gap transition has been effectively reduced and exhibits the narrowest value of 9.1 and 6.3 meV for the 1.29- and 1.55-μm-wavelength InGaAsP layers in the presence of Er. In addition, the carrier concentration of Er-doped InGaAsP layers are around 3–30×1014 cm−3 and is one to two orders of magnitude lower than those of undoped layers. These results can be attributed to the donor gettering by the rare-earth element of Er. The Er-related luminescence lines locate between 1.503 and 1.528 μm which differ from those previously reported at ∼1.54 μm and can only be observed for the 1.29-μm but not for the 1.55-μm-wavelength InGaAsP layers.
Ionization coefficients in selected gas mixtures of interest to particle detectors
Authors: Datskos P. G. , Carter J. G. , Christophorou L. G.
Published: July 2002

We have measured and report the total gas-number-density normalized effective ionization coefficient, ᾱ/N, as a function of the density-reduced electric field, E/N for Ar, CO2, CF4, the binary gas mixtures CF4:Ar (20:80), CO2:Ar(20:80), CO2:CH4(20:80) and for the ternary gas mixtures CO2:CF4:Ar (10:10:80) and H2O:CF4:Ar(2:18:80). We also report the limiting value, (E/N)lim of the above gaseous systems. A comparison of our results on the unitary gases shows good agreement with previous measurements. The results on the ternary mixtures show that the addition of CO2 or H2O to the binary gas mixture CF4:Ar lowers the electron energies and increases ᾱ/N(E/N).
Excitonic line broadening in bulk grown Cd1−xZnxTe
Authors: Oettinger K. , Hofmann D. M. , Efros Al. L. , Meyer B. K. , Salk M. , Benz K. W.
Published: July 2002

Cd1−xZnxTe crystals grown by the traveling heater method have been investigated by low-temperature photoluminescence. The excitonic energy gap as a function of the alloy composition was determined over the complete range of x=0 to x=1. The composition dependent broadening of the neutral acceptor bound exciton (A 0X) line was determined. Theoretical calculations, where the A 0X exciton is treated within the pseudodonor model and the conduction/valence band offset between CdTe and ZnTe is taken into account, give close agreement with the experiment for x≤0.77. Evidence for clustering of Zn atoms is found for x≥0.77.
Phase transformations in nitrogen-implanted α-iron
Authors: Kopcewicz Michal/ , Jagielski Jacek , Turos Andrzej , Williamson D. L.
Published: July 2002

A systematic study of nitride-phase formation in iron implanted with nitrogen was performed by conversion electron Mössbauer spectroscopy (CEMS). The samples of α-iron were implanted at room temperature with 100 keV N+2 ions whose mean range in the iron target was about 55 nm. The implanted dose varied from 5×1016 to 6×1017 N atoms/cm2. After implantation each sample was isothermally annealed in vacuum for 1 h at temperatures from 150 to 500 °C in 50 °C steps. The CEMS measurements allowed identification of the iron nitride phases formed by implantation and after annealing. At low doses (up to 1.5×1017 N atoms/cm2), the nitrogen-containing α′-martensite and/or α″-Fe16N2 phases appear. For intermediate doses (2×1017–2.7×1017 N atoms/cm2) ε-Fe3N is formed additionally. For doses higher than 3×1017 N atoms/cm2 the dominant phase is ε-Fe2N. In the course of annealing, ε-Fe2N decomposes to ε-Fe3N and γ′-Fe4N and finally disappears at about 300–350 °C. At 500 °C only the Zeeman sextet of α-Fe remains in the spectra. Considerable nitrogen release as detected by nuclear reaction analysis accompanied the phase evolution during annealing. These measurements lead to a new phase diagram for the implanted FeN system.
Oxidation kinetics of thin and ultrathin cobalt films
Authors: Smardz L. , Köbler U. , Zinn W.
Published: July 2002

We have prepared polycrystalline Co films on epitaxially oxidized Si(111) surfaces and studied their oxidation kinetics under atmospheric conditions using the fact that metallic cobalt is a ferromagnet but CoO is an antiferromagnet and therefore practically nonmagnetic. As a consequence, oxidation is associated with a loss in magnetism. Results show that all samples with an initial thickness of di ≳ 5 nm oxidize practically instantaneously, whereby a constant amount of 2.5 nm of metal is transformed into oxide. For di < 5 nm the time constant for oxidation increases considerably and follows an approximately linear dependence with decreasing film thickness, reaching an extrapolated value of τ=190 days for di → 0. This increasing time constant let all samples with di < 2.5 nm appear ferromagnetic within the course of this study due to a nonoxidized metallic rest. Auger electron spectroscopy analyses revealed that the main oxidation product is in fact CoO, especially near to the metal interface, but that other compounds are also likely to be formed summing up to a total thickness of 6 nm including adsorbates. A second point of interest was the unidirectional magnetic anisotropy which the oxide imposes to the metal due to an exchange interaction at the interface. This anisotropy shows a sharp onset at a CoO thickness as small as ∼0.25 nm from which an anisotropy constant of ∼4.5×106 J/m3 can be estimated for ultrathin CoO layers.
The effects of density fluctuations in organic coatings
Authors: Fishman R. S. , Kurtze D. A. , Bierwagen G. P.
Published: July 2002

It is usually assumed that the pigment and polymer concentrations are homogeneously distributed in an organic coating. This would imply that voids only appear when the pigment volume concentration (PVC) p exceeds the critical pigment volume concentration (CPVC) pc. However, a great deal of experimental work suggests that voids actually appear even below the CPVC. In this article, we present a phenomenological theory for the effects of density fluctuations on the formation of voids both below and above the CPVC. If the distribution of the local PVC p(x) is Gaussian, then our theory contains two phenomenological parameters: a coarseness parameter Cp which is proportional to the width of the Gaussian distribution, and the diameter d0 of the smallest densely packed cluster of pigment particles. When Cp=0, the homogeneous model of void formation is recovered; but for any nonzero coarseness, voids will appear even below the CPVC. In agreement with earlier work, we find that optical measurements will underestimate pc. While bulk properties like the void density depend only on the coarseness parameter Cp, microscopic properties like the distribution of void diameters dv(x) in the coating also depend on the diameter d0. Above the void percolation threshold pv of an organic coating, chains of voids span the sample. If the coarseness parameter of the Gaussian model is larger than about 0.2, then pv will drop below pc. As in our earlier work, we find that the peak in the mass density overestimates the CPVC. By formulating a simple theory for the Young’s modulus of the coating, we show that the Young’s modulus also peaks above pc for any nonzero Cp, in agreement with recent experiments.
Evaluation of the minority carrier diffusion length and edge surface-recombination velocity in GaAs p/n solar cells
Authors: Hakimzadeh Roshanak , Möller Hans J. , Bailey Sheila G.
Published: July 2002

The hole minority carrier diffusion length (Lp) and the edge surface-recombination velocity (Vs) were measured as a function of distance (x) from the p-n junction in GaAs p/n concentrator solar cells. The measured Vs values were used in a theoretical expression for the normalized electron beam-induced current. A fit of the experimental data was used to determine Lp. Lp measured in irradiated cells showed a marked reduction as compared to the unirradiated cells. Our results were compared to results obtained in previous studies that did not account for Vs.
Ultrahigh vacuum study of indium oxide GaAs(110) interfaces
Authors: Golan A. , Shapira Yoram , Eizenberg M.
Published: July 2002

Indium oxide/n-GaAs(110) interfaces fabricated by means of reactive evaporation of indium in the presence of oxygen onto ultrahigh vacuum cleaved GaAs(110) have been studied by means of Auger electron spectroscopy and electron energy loss spectroscopy. The results show that the growth of the indium oxide layers at room temperature under a wide range of oxygen pressures followed the Stransky–Krastanov model. In all cases the presence of In clusters at the interface was observed, and at the high-pressure regime (∼ 1 × 10−4 Torr) some oxidation of the GaAs surface was noted as well. These results can be correlated to our earlier report [J. Appl. Phys. 69, 1494 (1991)] on the performance of diodes produced under high vacuum conditions.
Scattering by finite wires
Authors: Waterman P. C. , Pedersen J. C.
Published: July 2002

For a conducting wire of finite length illuminated by an incident electromagnetic wave, induced surface current is represented as the sum of a driven term and resonant traveling waves, for which free-space propagation behavior is slightly modified by a perturbation m. Requiring current to vanish at the ends of the wire, both m and the resulting amplitude are obtained for normal incidence by applying Galerkin’s method to the resulting trial function. In the Rayleigh limit cross sections are expressed analytically. For wires up to one-half wavelength long, we find equivalence with Tai’s variational results [J. Appl. Phys. 23, 909 (1952)]. Beyond this point, the driven term goes over to the infinite cylinder current, as wire length increases. At the same time, for highly conducting wires one finds an explicit formula for m, in which ‖m−1‖≪1; for moderate conductivity, m reduces to the attenuated propagation behavior found by Sommerfeld [J. A. Stratton, Electromagnetic Theory (McGraw-Hill, New York, 1941), pp. 524ff] for infinite-length wires.
Rapid thermally processed ferroelectric Bi4Ti3O12 thin films
Authors: Joshi P. C. , Krupanidhi S. B. , Mansingh Abhai
Published: July 2002

Polycrystalline Bi4Ti3O12 thin films having perovskite structure were successfully produced on platinum coated silicon substrates by the sol-gel technique. Crack-free and crystalline films of 5000 Å thickness were fabricated by spinning and post-deposition rapid thermal annealing treatment at 500 °C for 20 s. The films exhibited good structural, dielectric, and ferroelectric properties. The measured dielectric constant and loss factor at a frequency of 100 kHz were 180 and 0.014 and remanent polarization and coercive field were 5.4 μC/cm2 and 135 kV/cm, respectively. The films showed good switching endurance under bipolar stressing at least up to 1010 cycles.
Negative nonlinear absorption effects in erbium-yttrium aluminum garnets
Authors: Maeda Yoshinobu
Published: July 2002

Negative nonlinear absorption, which causes the transmission to decrease as the laser intensity increases, was observed in a 16 at. % Er:YAG crystal using a laser diode operating at 787 and 784 nm. This effect for 787 nm was strong because 787 nm was the center of an absorption peak that is related to the excited-state absorption from 4I13/2 to 2H11/2. It is suggested that these phenomena take place because the absorption cross section from 4I13/2 to 2H11/2 is larger than that from 4I15/2 to 4I9/2 using a double-absorption model.
Laser induced oxygen adsorption and intensity degradation of porous Si
Authors: Zheng X. L. , Chen H. C. , Wang W.
Published: July 2002

For light-emitting porous Si there has been a severe problem with instability and degradation in the light emission. We performed in situ photoluminescence measurements to monitor the degradation process under ambient atmosphere of different gases and in ultrahigh-vacuum environment. We found that laser induced oxygen adsorption is the major cause for the light emission degradation, while the laser heating effect can be excluded. We also found the degraded intensity can be partially recovered by reducing the surface oxygen concentration.
Swept frequency permeameters for measuring the complex, off-diagonal permeability tensor components of anisotropic, thin magnetic films
Authors: Grimes Craig A. , Prodan John V.
Published: July 2002

To better understand wave propagation through magnetic media we have measured the high-frequency off-diagonal permeability tensor components of magnetic thin films using a thin-film permeameter. Although the off-diagonal components are commonly considered to be of negligible value, for some materials they are substantial, of a magnitude comparable to that of the diagonal terms. Since the out-of-plane off-diagonal coupling terms are primarily imaginary below resonance, and real above, they may introduce unexpected phase errors into the read/write process of magnetic recording and bulk material measurements and are therefore worthy of attention. The permeameters used to measured the off-diagonal terms are based upon the design of C. A. Grimes, P. L. Trouilloid, and R. M. Walser [IEEE Trans. Magn. MAG-24, 603 (1988)], which measure diagonal terms, but with different pickup coil and sample seat geometries. For z normal to the film, and with x and y defining, respectively, the hard and easy magnetization axes of the basal plane we measure μxy and μxz. A microwave scattering parameter test set is used to measure the scattering parameters of the jig from which the complex permeability is determined. The permeameters reported on here operate over the frequency range of approximately 10–600 MHz, and have a low level permeance detection limit of about 1 μm. Measurements of cosputtered amorphous Co55Zr45 thin films show that the out-of-plane permeability coupling term μxz is a significant fraction of the basal plane hard axis permeability.
Effects of rapid recurrent annealing on structure and magneto-optical properties of garnet films
Authors: Zhang S. J. , Guo X. Y. , Zhang F. P. , Xu C. L. , Shi F. L. , Zhang H. W. , Zhong Z. Y. , Guo B. J.
Published: July 2002

A new method to improve the morphology and the microstructure of sputtered bismuth-substituted garnet films for optical storage is discussed. The method employs a high ramp up rate and recurrent annealing as well as quenching in an air environment, which results in smaller grain size, smoother surface, and less void volume in the garnet films than that from a conventional oven annealing. We have discovered that samples prepared with a more recurrent annealing only appeared as a single garnet phase, and the samples with a less recurrent annealing appeared as a garnet phase as well as DyFeO3 phase. We observed the microstructure of the annealed films with scanning electron microscopy (SEM). By applying the new method, the as-deposited films had been successfully crystallized to the (BiDy)3(FeGa)5O12 garnet phase with the grain size of about 300–400 Å. They exhibited excellent magneto-optical properties with a high coercive force about 1300 Oe and an effective Kerr angle of 1.5°. The crystallization process of as-deposited amorphous films as well as the structure, composition, and magnetic and magneto-optical properties of the crystallized garnet films were examined.
Improvement of FMR linewidth in Bi-substituted lutetium iron garnet thin films for the MSW-optical-mode interaction
Authors: Silliman S. D. , Gualtieri D. M. , Stancil D. D.
Published: July 2002

Thin films of bismuth-substituted lutetium iron garnet (BiLuIG) for the magnetostatic wave (MSW)-optical-mode interaction can be grown by liquid-phase epitaxy from the standard PbO-based melt system developed for yttrium iron garnet (YIG). The addition of MgO to the melt to counteract the effect of lea on the ferromagnetic resonance (FMR) linewidth is investigated. BiLuIG thin films were grown on paramagnetic gadolinium gallium garnet substrates with varying amounts of MgO added. The ferromagnetic resonance linewidth, optical waveguide absorption, and MSW passband were measured. The addition of magnesium reduced the FMR linewidth from an average of 3 Oe down to under 1 Oe, with little effect on other parameters.
A method of separating the giant magnetoresistance and the anisotropic magnetoresistance in multilayers
Authors: Miller B. H. , Chen E. Youjun , Dahlberg E. Dan
Published: July 2002

In studies of the giant magnetoresistance (GMR) of ferromagnetic/nonmagnetic/ferromagnetic sandwich films, both the anisotropic magnetoresistance (AMR) and the GMR change with the angle between the magnetizations of the individual layers when the current direction is fixed. A technique is presented that separates the two phenomena and shows explicitly the angular dependence of the GMR. The technique relies on layered films in which the magnetization of one or more layers is held fixed by an exchange biasing field and the magnetization of another layer is rotated by an applied field. The separation of the two magnetoresistance contributions takes advantage of the fact that the GMR has a cosine angular dependence and the AMR of the rotated layer has a cosine squared angular dependence. The results indicate the GMR can be isolated from the AMR using only data containing contributions from both.
Effect of pressure on the growth of crystallites of low-pressure chemical-vapor-deposited polycrystalline silicon films and the effective electron mobility under high normal field in thin-film transistors
Authors: Dimitriadis C. A. , Stoemenos J. , Coxon P. A. , Friligkos S. , Antonopoulos J. , Economou N. A.
Published: July 2002

The morphology of polycrystalline films grown by low-pressure chemical-vapor deposition (LPCVD) is investigated by transmission electron microscopy (TEM) as a function of the film thickness, the deposition pressure, and the level of contamination. An orientation filtering mechanism, due to the growth-velocity competition in the early stage of growth, is responsible for the preferred orientation of the films. The size of the crystallites, the surface roughness, and the type of the structural defects are investigated by combined cross-sectional and plane-view TEM analysis. In polycrystalline silicon thin-film transistors (TFTs), the influence of surface roughness scattering on the mobility is investigated by measuring the effective electron mobility under high effective normal field at 295 and 77 K. Although the surface curvature is increased when the deposition pressure is decreased, the surface roughness scattering is constant in the deposition pressure range from 40 to 0.5 mTorr. By decreasing the deposition pressure from 40 to 10 mTorr, although the grain size increases, the TFT performance degrades due to the following factors: (a) the increase of the grain-boundary trap density which is related to the change of the mode of growth at 10 mTorr; and (b) the increase of impurity contamination in the environment of the LPCVD system with constant silane flow rate at all pressures. At a deposition pressure of 0.5 mTorr the TFT performance is improved indicating that the grain size is the prevailing key factor.
Low dislocation density GaAs on Si heteroepitaxy with atomic hydrogen irradiation for optoelectronic integration
Authors: Okada Yoshitaka , Shimomura Hirofumi , Kawabe Mitsuo
Published: July 2002

Basic experimental results obtained for the low-temperature molecular beam epitaxy with atomic hydrogen have been presented. GaAs films grown at different substrate temperatures have exhibited different values of dislocation densities and the average dislocation density as low as 3×104 cm−2 has been successfully obtained for the films grown at a low-temperature of 330 °C with atomic hydrogen irradiation. These are among the lowest dislocation values reported to date. The surface cleaning effects and reconstruction of vicinal Si(100) surfaces during the atomic hydrogen irradiation, and also the electrical properties of epitaxial films have been investigated and analyzed. Physics behind the drastic dislocation density reduction has been investigated in detail based on the results of cross-sectional and plan-view transmission electron microscope observations and analysis of the growth kinetics.
Annealing dynamics of molecular-beam epitaxial GaAs grown at 200 °C
Authors: Look D. C. , Walters D. C. , Robinson G. D. , Sizelove J. R. , Mier M. G. , Stutz C. E.
Published: July 2002

By separating a 2-μm-thick molecular-beam-epitaxial GaAs layer grown at 200 °C from its 650-μm-thick substrate, we have been able to obtain accurate Hall-effect and conductivity data as functions of annealing temperature from 300 to 600 °C. At a measurement temperature of 300 K, analysis confirms that hopping conduction is much stronger than band conduction for all annealing temperatures. However, at higher measurement temperatures (up to 500 K), the band conduction becomes comparable, and a detailed analysis yields the donor and acceptor concentrations and the donor activation energy. Also, an independent absorption study yields the total and charged AsGa concentrations. Comparisons of all of these quantities as a function of annealing temperature TA show a new feature of the annealing dynamics, namely, that the dominant acceptor (probably VGa related) strongly decreases and then increases as TA is increased from 350 to 450 °C. Above 450 °C, ND, NA, and [AsGa] all decrease, as is known from previous studies.
X-ray damage to optical components using a laser-plasma source
Authors: Elton R. C. , Billings D.-M. , Grun J. , Young F. C. , Manka C. K. , Ripin B. H. , Burris H. R. , Resnick J. , Ripin D. J. , Millard J. R.
Published: July 2002

X-ray damage to optical surfaces consisting of melting, fracturing, cracking, and cratering is produced, and then analyzed using interference contrast microscopy and stylus profilometery. The test samples are irradiated by 0.5–1.6 keV x rays at fluence levels up to 5.5 cal/cm2. The x rays originate from L-shell transitions in copper ions, produced when 1.25-μm-thick targets are irradiated at 1.3 kJ energy by a 1.054 μm wavelength laser. The x-ray emission is found to be nearly isotropic over 2π sr, while the plasma mass-flow distribution is peaked along the laser axis. Hence, contamination of the test sample by target debris or plasma is greatly reduced by placing the samples off axis from the laser beam, in addition to the use of beryllium shields.
Nitrogen doping in hydrogenated amorphous silicon
Authors: Zhou Jiang-Huai , Yamaguchi Kengou , Yamamoto Yoshikazu , Shimizu Tatsuo
Published: July 2002

The doping effect of N in hydrogenated amorphous silicon (a-Si:H) is studied. The absence of a thickness dependence of the conductivity of N-doped samples provides convincing evidence that the doping effect of N in a-Si:H is a bulk property. The similarity between the effect of N doping and that of P doping found in the conductivity and the photoconductivity decay indicates that N can act as an effective donor in a-Si:H and that N doping is also of substitutional type; however, the solid-phase doping efficiency of N is estimated to be at least three orders of magnitude lower than that of P.
Electrical and optical properties of GaInAsP grown by gas-source molecular beam epitaxy
Authors: Tappura K.
Published: July 2002

GaxIn1−xAsyP1−y layers were grown on InP substrates by gas-source molecular beam epitaxy in order to study the electrical and optical properties of the quaternaries. Hall mobilities and carrier concentrations of Si- and Be-doped quaternary layers were compared in the alloys for different wavelengths. Smaller hole concentrations were observed for the alloy compositions close to InP than for those close to GaInAs grown with the same Be cell temperature. In addition, the highest achievable hole concentration was found to be a function of the alloy composition. Possible reasons for the observations are discussed. The influence of pregrowth treatments on the measured Hall mobilities and carrier concentrations due to the changes in the substrate-epilayer interfacial conductivity was studied. Room-temperature photoluminescence results are also presented.
Interdiffusion study of amorphous Ni–Si multilayer at low temperature
Authors: Wang W. H. , Bai H. Y. , Wang W. K.
Published: July 2002

Little is known about the interdiffusion in the amorphous Ni–Si multilayer due to the lack of suitable experimental method. In this paper, the interdiffusion phenomena in the amorphous Ni–Si multilayer are investigated by an in situ x-ray diffraction technique. The temperature-dependent interdiffusivity obtained by monitoring the decay of the first-order modulation peak as a function of annealing time can be described in terms of the Arrhenius relation. The effective interdiffusivities can be expressed as De(T)=2.13 ×10−17 exp[−(0.61±0.02)/kBT] m2/s (423–613 K). A retarded interstitial diffusion mechanism is suggested to explain the diffusion process in the amorphous multilayer films.
Observation of a very high electron current extraction mode in a hollow cathode discharge
Authors: Hershcovitch Ady
Published: July 2002

Earlier results by Hershcovitch, Kovarik, and Prelec in J. Appl. Phys. 67, 671 (1990) proved that, in a low-pressure operating mode, hollow cathode discharges can have a two-component electron population, one of which is that of ‘‘fast’’ electrons having an energy corresponding to the cathode potential and a thermal spread of about 0.13 eV, which could form a basis for an excellent electron gun. Investigations of extracted electron currents in this low pressure mode indicate the existence of a narrow pressure range characterized by very high electron current extraction.
Determination of quadratic nonlinear optical coefficient of AlxGa1−xAs system by the method of reflected second harmonics
Authors: Ohashi M. , Kondo T. , Ito R. , Fukatsu S. , Shiraki Y. , Kumata K. , Kano S. S.
Published: July 2002

The quadratic nonlinear optical coefficient in the AlGaAs system has been systematically measured as a function of the alloy composition at the fundamental wavelength of 1.064 μm by the method of reflected harmonics. The harmonic waves from the thin-film samples are analyzed considering various interferences including multiple reflections. The experimental results show a reduction of the magnitude of the second-harmonic coefficient with increasing Al content in the AlGaAs system. This tendency is consistent with Miller’s rule.
Electronic transport properties and thickness dependence of the giant magnetoresistance in Co/Cu multilayers
Authors: Eckl Th. , Reiss G. , Brückl H. , Hoffmann H.
Published: July 2002

The transport properties of electrons in Co/Cu multilayered thin films are of special interest for the giant magnetoresistance (GMR) of this system. The magnitude of this effect depends on the mean free paths and on the strength of the interface scattering which in turn are strongly related to film structure. In this article, we discuss the results of resistance and magnetoresistance measurements carried out during film growth. We characterize the electronic transport parameters of these films and the growth mechanism of the layers. The new technique of the in situ measurement of the magnetoresistance furthermore provides a tool to find correlations of the growth mechanism with the dependence of the GMR on the Co thickness.
Radiation-induced segregation of nitrogen implanted into iron
Authors: Jagielski J. , Moncoffre N. , Marest G. , Thomé L. , Barcz A. J. , Gawlik G. , Rosinski W.
Published: July 2002

Nitrogen redistribution toward the sample surface during the implantation processes performed at temperatures ranging from room temperature to 250 °C was studied for pure iron by means of nuclear reaction analysis and secondary-ion-mass spectrometry. The role of carbon and radiation defects was investigated. The results reveal the importance of radiation defects on nitrogen migration and trapping. The migration mechanism was identified as a radiation-induced segregation.
Photopyroelectric deconvolution of bulk and surface optical-absorption and nonradiative energy conversion efficiency spectra in Ti:Al2O3 crystals
Authors: Vanniasinkam J. , Mandelis A. , Buddhudu S. , Kokta M.
Published: July 2002

The extension of an earlier monolithic photopyroelectric spectroscopic model [A. Mandelis et al., Phys. Rev. B 48, 6808 (1993)] to include surface and bulk optical absorptions and the subsequent optical-to-thermal (nonradiative) energy conversion efficiencies associated with these sites has allowed the self-consistent determination of visible spectra of these quantities, using a very sensitive noncontact experimental configuration to obtain in-phase and quadrature photopyroelectric spectra of Ti:sapphire crystals of two thicknesses and figures of merit.
Charged defect states in intrinsic hydrogenated amorphous silicon films
Authors: Güneş Mehmet , Wronski Christopher R. , McMahon T. J.
Published: July 2002

Steady-state photoconductivity, sub-band-gap absorption and electron spin resonance (ESR) measurements were carried out on annealed and light soaked intrinsic hydrogenated amorphous silicon (a-Si:H) films. The experimental results were modeled using detailed numerical analysis. The defect densities derived from the sub-band-gap absorption in the light soaked films were correlated with the ESR spin densities. Self-consistent fitting of the data was obtained using a gap state distribution which consists of positively charged defect states above, negatively charged defect states below and neutral defect states at about the midgap. Both the annealed and the light degraded states are modeled using the same gap states which increase upon light soaking and have a slight increase in the ratio of the neutral to charged defect densities. These results on intrinsic a-Si:H are consistent with proposed charged defect models and clearly indicate the importance of charged defect states in determining sub-band-gap absorption as well as its correlation with neutral dangling bonds.
Monte Carlo study of electron transport in strained silicon-carbon alloy
Authors: Ershov M. , Ryzhii V.
Published: July 2002

Electron transport characteristics of strained Si1−yCy random alloy grown on a Si (100) substrate are studied theoretically using the Monte Carlo technique. The value of alloy scattering potential has a strong influence on the low-field electron mobility. Valley repopulation effect combined with decreased scattering rate of electrons in strained Si1−yCy material can give rise to the increase of in-plane drift electron velocity with carbon concentration, in spite of the enhancement of alloy scattering. Electron transport characteristics have been calculated over a wide range of electric fields and temperatures.
Electrical characterization of instabilities in 6H silicon carbide metal-oxide-semiconductor capacitors
Authors: Raynaud Christophe , Autran Jean-Luc , Balland Bernard , Guillot Gérard , Jaussaud Claude , Billon Thierry
Published: July 2002

Capacitance, charge, and current measurements have been performed on p-type 6H-SiC metal-oxide-semiconductor capacitors in order to study electrical instabilities in the SiO2/6H-SiC system and the behavior of the inversion layer at different temperatures. The analysis of hysteresis and deformation of capacitance-voltage curves shows the presence of interface states and oxide traps with a density of approximately 5–7×1010 eV−1 cm−2 in the midgap and a peak of 3×1012 eV−1 cm−2 at E=Ev+0.53 eV. Ionic contamination of the oxide layer has also been investigated, by thermally stimulated ionic current: A mobile charge concentration in the range of 1012 cm−2 was found. Finally, it is shown, by charge-voltage measurements, that the minority-carrier generation is assisted by deep levels during the formation of the inversion layer.
Growth, physical properties, and adhesion of copper-polyphenylquinoxaline interfaces
Authors: Pireaux J. J. , Grégoire Ch. , Bellard L. , Cros A. , Torres J. , Palleau J. , Templier F. , Nechstchein J. , Lazare S.
Published: July 2002

Monochromatized x-ray photoelectron spectroscopy, contact angle measurements, and peeling tests have been used to investigate the physicochemical surface properties of polyphenylquinoxaline (PPQ) and of copper-PPQ interfaces. The surface composition and oxygen content of a polymer that was deliberately oxidized by ultraviolet exposure in air were determined, and monitored during the anneal (up to 400 °C) of this thermostable polymer. Subsequent copper deposition in the monolayer range and film growth is characterized by small cluster formation, before percolation into a conducting metallic layer. Further anneal of the Cu-PPQ interface is seen to promote diffusion of Cu into the polymer, and to catalytically degrade the interface by oxidizing the polymer. These observations are correlated with peeling test measurements on the same Cu-PPQ interfaces: UV treatment combined with an anneal process are shown to be deleterious to the mechanical properties of the interface.
Influence of radio-frequency sputtering and crystallization parameters on the structure of the BiGa-DyIG garnet films for magneto-optical recording
Authors: Braïk Y. , Le Gall H.
Published: July 2002

The dependence of the crystalline structure on crystallization temperature, argon pressure, and rf power have been investigated in detail. Three ranges of annealing temperature were found. In the first and second ones, the film structures are, respectively, amorphous and perfectly polycrystalline, while in the last case an evolution to a textured state occurs. It has been observed that although for large rf power the formation of spurious phases is observed, there is only a small change in the overall composition of the films. On the contrary, for different values of the argon pressure only the garnet phase is observed, but with large stoichiometry changes.
Structural characterization for epitaxial Fe/Pt(001) multilayer
Authors: Sakurai Makoto
Published: July 2002

The structure for the epitaxial Fe/Pt(001) multilayer deposited in an ultrahigh-vacuum chamber is studied using a four-circle x-ray diffractometer. The Fe layer of the multilayer undergoes a structural transition with varying Fe layer thickness. Specular and nonspecular x-ray-diffraction patterns show a strong correlation between the structural transition and disorder. The linewidth of satellite peaks increases with the distance from fundamental reflection. The behavior of the increase becomes pronounced for the Fe layer thickness beyond 12.6 Å. The lateral linewidth is explained by a mosaic structure and correlated roughness. The correlated fluctuation increases with Fe layer thickness. Amplitudes of uncorrelated fluctuation and cumulative fluctuation are small for the Fe layer thickness less than 8.4 Å and increase with Fe layer thickness.
Energy of positive ions absorbed by negatively pulsed electrodes in two and three component plasmas
Authors: Amin Ali , Kim Hyun-Soo , Yi Seungjun , Lonngren Karl E. , Alexeff Igor
Published: July 2002

The temporal variation of the energy of positive ions deposited in metal electrodes inserted in a plasma to which a negative voltage step is applied is computed. Effects of impurity positive or negative ions upon the plasma source ion implantation process are calculated.
1/f noise in amorphous silicon nip and pin diodes
Authors: Wieczorek H.
Published: July 2002

In this article noise measurements on amorphous silicon nip and pin diodes are presented and discussed with regard to standard models for flicker noise. It is shown that 1/f noise is present in the dark forward current of a-Si:H diodes as well as in the photocurrent at low forward or reverse bias. The dependence of the noise power spectral density on dark current and photocurrent density, diode area, thickness, and current aging leads us to the conclusion that fluctuations in the electron injection current at the n+ contact are the reason for 1/f noise. This model is further supported by the current and frequency dependence of the shot noise in the photocurrent. We assume that the trapping of carriers switches on and off current filaments in the diode interface layer.
Description of the thermalization process of the sputtered atoms in a glow discharge using a three-dimensional Monte Carlo method
Authors: Bogaerts Annemie , van Straaten Mark , Gijbels Renaat
Published: July 2002

A three-dimensional Monte Carlo model is developed to simulate the thermalization process of atoms sputtered from the cathode in a glow discharge cell. A comparison is made with a simplified analytical thermalization model and the relative importance of different interaction potentials and scattering assumptions on quantities related to thermalization is investigated. Typical results of the thermalization model are (i) the thermalization profile (which gives the distribution of the thermalized sputtered atoms), (ii) the relative amount of atoms that can reach the backplate of the discharge cell without being thermalized, and (iii) the relative amount of backscattering to the cathode. The influence of gas pressure, kind of gas, and cathode material on the thermalization process is also investigated.