bluuebunny/crossref_metadata_2025 huggingface dataset:
1/f noise from levels in a linear or planar array
Authors: Morrison S. Roy
Published: July 2002

This contribution expands on the analysis of an earlier study with the same title. There it was shown that charge transfer across a double layer to and from a monoenergetic set of surface states would yield 1/f  noise if the fluctuations are strong enough for nonlinearity. It is proposed that the location of uncharged energy levels or sites fluctuates and can induce such nonlinearity. The uncharged species can randomly move far-from or close-to a charged species. If it is close to a charged species, the rate of charge transfer to it is low. Fluctuations in position thus result in significant fluctuations of charge transfer rates. With simplifications, the 1/f noise associated with ionosorption/desorption of O2 on a semiconductor is calculated as an example of this double-layer noise. The computed noise spectrum of carrier density fluctuations follows the 1/f  law over the frequency span predicted in the earlier study. A distribution of surface state energies leads to a substantial increase in the frequency span. In the example, noise from four discrete trapping energies (time constants) when summed yields 1/f  noise over 6 decades. The example describes carrier density fluctuations. It is suggested that mobility fluctuations may dominate in many cases, especially metals, because there will be strong carrier scattering by bulk (and possibly surface) double layers. The temperature dependence of double layer 1/f  noise is briefly discussed. The results for grain boundary noise by Madenach and Werner are shown to be consistent with the double-layer model, as is the temperature variation as discussed by Dutta and Horn [Rev. Mod. Phys. 53, 497 (1971)].
Performance characteristics of In0.2Ga0.8As/GaAs multiquantum-well lasers
Authors: Dutta N. K. , Wynn J. , Sivco D. L. , Cho A. Y. , Zydzik G. J.
Published: July 2002

The performance characteristics of ridge waveguide In0.2Ga0.8As/GaAs multiquantum-well lasers are reported. The lasers emit more than 50 mW/facet in the temperature range 20–100 °C in the fundamental transverse mode. The external differential quantum efficiency of 250-μm-long lasers is 0.4 mW/mA/facet. The internal optical loss is 14 cm−1. The optical gain is found to vary linearly with current. The increase in threshold current with increasing temperature in these lasers is primarily due to decreasing carrier lifetime (increased carrier loss) at high temperature. Increasing the heterobarrier height may further improve the high-temperature performance of these devices.
Be+ ion implantation in Ga0.96Al0.04Sb epitaxial layers
Authors: Pérotin M. , Gouskov L. , Luquet H. , Abiale Abi P. , Sabir A. , Pérez A.
Published: July 2002

Be ions are implanted into Te-doped Ga0.96Al0.04Sb layers grown by liquid-phase epitaxy. Be distribution is analyzed from secondary-ion mass spectrometry profiles and is found to be in good agreement with a computed simulation one. Hall-effect measurements show a complete electrical activity of the Be-implanted ions. Mesa devices are realized on the Ga0.96Al0.04Sb p+/Ga0.96Al0.04Sb n−/GaSb+ system: Be implantation leads to good quality junctions exhibiting homogeneous multiplication.
Rapid thermal annealing of high concentration mixed As/In- and P/In-implanted silicon single crystals
Authors: Shiryaev S. Yu. , Nylandsted Larsen A. , Safronov N.
Published: July 2002

The effect of group-V donor impurities on the behavior of indium atoms implanted into silicon single crystals has been studied by Rutherford backscattering spectrometry/channeling spectrometry, and differential Hall-effect/resistivity measurements. Flat arsenic or phosphorus profiles of concentrations between ∼1.4×1020 cm−3 and 3×1020 cm−3 were produced by As+ or P+ implantation followed by rapid thermal annealing (RTA) (20 s, 1100 °C). Subsequently In was implanted to peak concentrations of 1.7×1020 cm−3 or 3.5×1020 cm−3 and annealed by RTA (15 s, 700–1050 °C).Compared to single indium implants, the presence of the preimplanted group-V impurities is found to reduce the redistribution of the implanted indium atoms during RTA and to increase the concentration of indium atoms incorporated on (or close to) lattice sites (up to ∼2×1020 cm−3). The value of the indium substitutional fraction is found to be dependent on anneal temperature and type of donor impurity. A reduction in the free-electron concentration is observed in both the phosphorus and arsenic predoped samples at the same depths as that of the indium atoms.
Experimental study of intersubband infrared transitions in coupled quantum wells under an electric field
Authors: Liu H. C. , Buchanan M. , Wasilewski Z. R.
Published: July 2002

The infrared absorption of a multiple quantum-well structure with coupled wells is studied experimentally. The structure consists of 40 repeats of two coupled quantum wells with a wider doped GaAs well and a narrower undoped GaAs well and AlAs barriers. A strong absorption due to an intersubband transition in the wider wells is seen at about 0.14 eV, which shifts in transition energy when a negative bias is applied and decreases in absorption strength when a positive bias is applied. The shift is due to many-body effects on the transition energy when the electron density in the wider well is reduced, and the decrease is attributed to the blocking of the final state when the upper state in the wider well is populated.
The theory of ultrasoft magnetic films
Authors: Bouchaud J. P. , Zérah P. G.
Published: July 2002

We propose a theoretical interpretation of the unusual magnetic properties of ultrasoft magnetic films. Effective-medium theory is shown to reproduce remarkably well the dependence of the low-frequency susceptibility with magnetic field. In order to understand the dynamical susceptibility, one needs to generalize the usual Landau–Lifshitz equation and introduce an anisotropic dissipative term. The two relaxation coefficients α1,α2 are determined by a fit of the experimental data. α2 is found to be large, perhaps reflecting the strong inhomogeneity of the local anisotropy field.
EL2 and anion antisite defects in plastically deformed GaAs
Authors: Hofmann D. M. , Meyer B. K. , Spaeth J.-M. , Wattenbach M. , Krüger J , Kisielowski-Kemmerich C. , Alexander H.
Published: July 2002

We report on optical absorption its magnetic circular dichroism (MCD), optically detected electron spin-resonance (ODESR), and electron nuclear double-resonance (ODENDOR) investigations of plastically deformed semi-insulating GaAs. By plastic deformation arsenic antisite defects are created which show a similar ODESR pattern as EL2 defects present in the material prior to deformation. EL2 and the new antisite defects can be distinguished by their different spectral dependence of the MCD. The new antisite defect formation starts at 2% deformation and is investigated as a function of the degree of deformation; additional EL2 defects are not created. With ODENDOR it is shown that the atomistic structure of the EL2 defects changes in the deformed GaAs.
Effect of interface state distribution on field effect conductance activation energy in hydrogenated amorphous silicon thin film transistors
Authors: Bae Byung-Seong , Lee Choochon
Published: July 2002

The gate voltage dependencies of conductance activation energy of source-drain current are investigated for hydrogenated amorphous silicon thin film transistor. We compared the calculated activation energy with experimental results and discussed the density of gap and interface states in hydrogenated amorphous silicon. The experimental results could be explained by the introduction of the interface state distribution with exponential tails near the conduction band edge in parallel with the bulk gap state distribution.
Selectively Se-doped AlGaAs/GaAs heterostructures with reduced D
X-center concentrations grown by molecular-beam epitaxy
Authors: Ishikawa Tomonori , Maeda Takeshi , Kondo Kazuo
Published: July 2002

We studied the DX centers in Se-doped Alx Ga1−xAs layers grown by molecular-beam epitaxy. The DX-center concentrations of these layers were considerably lower than in Si-doped layers because of their shallower DX-center energy levels. We also studied Se doping of AlGaAs layers, and applied Se doping to selectively doped AlGaAs/GaAs heterostructures to eliminate the influences of DX centers. By optimizing growth conditions, we obtained excellent two-dimensional electron gas characteristics comparable to those of conventional Si-doped heterostructures. Using Se-doped Al0.2 Ga0.8 As layers, we grew DX-center-free selectively doped AlGaAs/GaAs heterostructures having electron mobilities of 70 000 cm2 /V s at 77 K.
Effects of inelastic electron-phonon scattering on the resonant tunneling in double-barrier structure
Authors: Tyan Jyh-Haur , Lue Juh-Tzeng , Sheng Jian-Shang
Published: July 2002

The Breit–Wigner formula is exploited to calculate the tunneling transmission probability affected by longitudinal optical phonon scattering in multiple quantum wells composed of Ga1−xAlxAs compounds. A quantitative result shows that the resonance electron energy and the integrated total transmission probability through the potential barriers are not changed, while the transmission peak is reduced and the linewidth is broadened.
Comments on the dielectric theory: Non-Debye models and the superposition principle
Authors: Ferreira G. F. Leal , Gross B.
Published: July 2002

Nonexponential relaxations may be decomposed into a distribution of elementary exponential relaxations. Although of mathematical interest, these distributions may not have a physical sense if the elementary process of dipolar orientation itself is nonexponential, that is, non-Debye. We analyze non-Debye models using the superposition principle and assume that they admit a rate equation. In this case the rate itself results to be time dependent. Using the superposition principle as a guide, it then is possible to find the polarization for nonisothermal processes and even for time-varying electric fields. We finally comment on defect diffusion models devised to explain the dynamics of the polarization and depolarization unit, which seem not to be in accord with the superposition principle.
Measurement of refractive indices of homogeneous fibers with regular or irregular transverse sections
Authors: Hamza A. A. , Kabeel M. A.
Published: July 2002

Seven fibers of different cross-sectional shape are studied interferometrically using multiple-beam Fizeau fringes. These fibers are of circular, rectangular, triangular, trilobal, elliptical, kidney, and dog-bone cross-sectional shapes. The areas enclosed under the interference fringe shift is considered to represent the optical path difference integrated across the fiber. This principal is applied to nylon 6 fibers of trilobal cross-sectional shape. The described method is suitable for the measurement of refractive indices of any fiber with regular or irregular transverse sections. Microinterferograms are given for illustration.
Direct oxinitride synthesis by multipulse excimer laser irradiation of silicon wafers in a nitrogen-containing ambient environment
Authors: Crăciun V. , Mihăilescu I. N. , Oncioiu Gh. , Luches A. , Martino M. , Nassisi V. , Radiotis E. , Drigo A. V. , Ganatsios S.
Published: July 2002

The direct synthesis of silicon oxinitride films by multipulse excimer (λ=308 nm) laser irradiation in a nitrogen-containing ambient gas is reported featuring characteristics consistent with potential application in microelectronics.
Near-infrared optical properties of CoSi2 thin films
Authors: Duboz J. Y. , Badoz P. A. , Henz J. , von Känel H.
Published: July 2002

Transmission and reflection measurements in the energy range 0.5–1 eV have been performed on thin CoSi2 films grown by molecular-beam epitaxy on Si(111). For film thicknesses above 200 Å, the transmission factor decreases exponentially with film thickness, with an optical attenuation length of 180 Å nearly independent of photon energy. Deviations from this law for film thicknesses below 200 Å are explained by reflection effects. These data, supplemented by reflection measurements, can be fitted by theoretical calculations of the transmission and reflection factors, thus leading to the determination of the CoSi2 optical indexes. The energy dependence of the real and imaginary indexes is found to be consistent with the Drude model. Some interesting aspects of this intraband absorption either in ultrathin films or at low temperature are presented.
Study of the Co-Ge/GaAs contact system
Authors: Genut M. , Eizenberg M.
Published: July 2002

The interfacial reactions between thin films of cobalt and germanium and (001)-oriented GaAs substrates in two configurations, Co/Ge/GaAs and Ge/Co/GaAs, were studied. The microstructure and phase formation, as analyzed by transmission electron microscopy, x-ray diffraction, and Auger electron spectroscopy, were correlated with the electrical properties of these contacts, as determined by current-voltage and capacitance-voltage measurements. At low temperatures, 250≤T<325 °C, the only reaction that was monitored was the formation of Co5Ge7 at the outer interface, while the GaAs substrate remained intact. The growth of Co5Ge7 was diffusion limited with an activation energy of ∼0.7 eV. At the temperature range of 325–400 °C for both metalizations epitaxial Co2GaAs was formed on top of the GaAs beneath the Co5Ge7 layer. For the Ge/Co/GaAs metalization this was accompanied (at 400 °C) by solid-phase epitaxial growth of Ge precipitates on the GaAs surface. Contacts produced in this annealing regime were rectifying with nearly ideal thermionic emission behavior. The Co2GaAs phase was unstable at higher temperatures (500–600 °C), and the reaction products were two ternary phases, with compositions of Co2GeGa and Co2GeAs. These compounds were spatially separated—the Co2GeGa layer on top of the Co2GeAs phase. Contacts produced at the high-temperature regime (>400 °C) had very low effective barriers and on an n+ GaAs substrate became ohmic.
X-ray photoelectron spectroscopy study of thin Ag overlayers on YBa2Cu3O7−x: Effects of oxygen annealing
Authors: Niedermann Ph. , Grande A. P. , Grepstad J. K. , Triscone J.-M. , Karkut M. G. , Brunner O. , Antognazza L. , Sadowski W. , Scheel H. J. , Fischer O/.
Published: July 2002

X-ray photoelectron spectroscopy was used to examine vapor deposited Ag overlayers on YBa2Cu3O7−x thin films and cleaved single-crystal surfaces (x=1), including the effects of subsequent heat treatment in oxygen. The core level spectra of the present tetragonal crystals were found to closely resemble those previously reported for nominally orthorhombic superconducting samples. Minor differences, notably an increased fraction of Cu in the +1 oxidation state and a slightly higher binding energy of the Ba 3d levels, may be attributed to the lower oxygen content of the tetragonal semiconducting phase. Deposition of Ag on clean monocrystal surfaces was found to cause some disruption of CuO bonds at the Ag/YBa2Cu3O7−x interface. We also find weak indications of surface band bending (i.e., Schottky barrier formation) from a uniform shift in the measured binding energies of the substrate core levels upon Ag deposition. Heat treatment in pure oxygen (1 h at 500 °C) of Ag-coated superconducting thin films was found to reduce efficiently the amount of superficial contaminant phases, initially present on the air-exposed thin-film surfaces, and to cause diffusion of Ag to a depth of ∼20 nm into the volume of the material.
Novel electrical and annealing properties of defects in electron irradiated silicon p+-n junctions
Authors: Wang F. P. , Sun H. H. , Lu F.
Published: July 2002

Novel results on defect annealing behavior and minority-carrier lifetime control in electron irradiated silicon p+-n junctions are presented. Two mechanisms are found to be involved in the annealing process of the divacancies; one dominates in the lower temperature range (from 240 to 300 °C) and the other dominates in the higher temperature range (from 320 to 360 °C). A defect labeld as E3 with an energy level at 0.37 eV below the conduction band is found to be an efficient recombination channel responsible for minority carrier lifetime control. The activation energy for dissociation of the defect E3 obtained from the annealing study is 1.7 eV, and the frequency factor is 2.8×109 s−1. Annealing of electron irradiated samples at about 300 °C, or performing the electron irradiation at a similar high temperature is found to increase the concentration of the defect E3, and stabilize the carrier lifetime. These processes might be useful to improve the thermal stability of devices like high-voltage rectifiers and thyristors.
Parametric studies of dynamic powder consolidation using a particle-level numerical model
Authors: Williamson R. L.
Published: July 2002

A numerical simulation approach is used to investigate various aspects of dynamic metal powder consolidation. A two-dimensional continuum model is employed where only a few powder particles, and the interparticle voids, are considered. Consolidation is achieved by introducing large compressive stress waves in type 304 stainless-steel powder material using a high-velocity flyer plate. The effects of stress-wave amplitude on the particle deformation, consolidation rate, and temperature field are discussed based on the results of simulations using projectile impact velocities of 0.5, 1.0, and 2.0 km/s. It is demonstrated that increases in stress-wave amplitude result in higher surface temperatures leading to more extensive interparticle bonding. The 0.5 km/s impact results in full densification but is insufficient to create particle melting and bonding; the 2.0 km/s impact results in extensive interparticle melting. The effects of simple variations in the initial particle geometry are investigated by considering monosized and bimodal particle distributions and a matrix of identical hollow particles. Because each of these simulations correspond to a different initial density, the results are used to examine the effects of initial void fraction on energy deposition in the powder material during consolidation. It is shown that the average internal energy of the consolidated particles increases substantially as the initial void fraction is increased. In a final simulation, argon is placed in the regions between particles to investigate the effects of interstitial gases on the temperature field during consolidation. Shock compression of the gas results in increased surface temperatures and more extensive interparticle melting; for the materials and consolidation conditions considered, however, it is not a predominant energy deposition mechanism.
Opto-optical modulation in nematic liquid crystals
Authors: Sugimura A. , Takahashi Y. , Uda H. , Sonomura H. , Naito H. , Okuda M.
Published: July 2002

A new type of opto-optical modulation effect in nematic liquid crystals is experimentally observed. The transmitted intensity of a He-Ne laser beam passing through a liquid crystal sample while applying a dc voltage is modulated by illuminating the sample with a xenon flash lamp pulse. The response time is fast, of the order of several milliseconds. The modulated state lasts for about 500 ms. A modulated intensity of light as large as ten times the unmodulated one is obtained. The physical origin of this effect is also discussed.
GaAs phase effect on interfacial drain current of a 400-μm-wide gate Si-implanted MESFET
Authors: Saito Yasuyuki
Published: July 2002

Using substrates from different composition liquid-encapsulated Czochralski-grown crystal boules, the 1.5 μm×400-μm wide-gate metal-semiconductor field-effect-transistors (MESFETs) drain current (Id)-drain voltage (Vd) characteristic at near pinch-off bias was observed as a low-frequency oscillation (LFO) Id-Vd curve. This process indicates the interfacial behavior of the MESFET’s Id between GaAs crystal bulk and the Si-implanted electrically active channel layer. As a result, both the LFO behavior and the Id-Vd curve at the interfacial layer were dependent on the substrate GaAs composition but were not dependent on its impurity boron concentration. Large Id-LFO was observed for the substrates from near- or stoichiometric GaAs melts and compared with the Id-LFO for As-rich melts. With the As-rich melt samples, small Id-LFO was observed for both low carbon concentration (nondetectable) and high carbon concentration (≂2×1016 cm−3) in the substrates. From the result and discussion of the LFO model, Id-LFO is not caused by the deep center but by the interaction among both the electron carrier (in this case), and the deep center and electrical potential profile. This is formed by imposed electric bias force and nonbias potential profile of both the electrically active impurity doping profile of process and the mixed band structure of substrate bulk, and occurs because the Id-LFO is small on an As-rich substrate which can have many native deep-center EL2s.
Reflecting boundary conditions for graded p-n junctions
Authors: Schacham S. E.
Published: July 2002

In a graded junction, the formalism for handling reflecting boundary conditions must be modified. Since a significant drift term is present, zero recombination velocity at the surface does not imply a zero excess carrier gradient but rather zero overall flux. A model for analyzing p-n junctions fabricated by implantation or diffusion is presented, assuming the dominant recombination mechanism in the graded region is Auger. The model enables optimization of diode design. By proper selection of parameters, mainly by reducing surface concentration or by increasing the steepness of the dopant profile, it is possible to drastically reduce the saturation current generated by the graded region.
Investigation of ‘‘connectivity’’ in silver-ceramic superconductor composites by their field screening property
Authors: Reich S. , Nabutovsky V. M.
Published: July 2002

In this paper we outline an experimental method and a theoretical framework by which the strength of weak superconducting links in granular ceramic systems is compared and measured. This new method is based on dc measurement of screening properties of superconducting materials and renders a simultaneous determination of the critical magnetic field and the penetration length. In particular, the method is applied to a series of newly developed nonrandom silver-YBa2Cu3O7−δ composites. By measuring the field screening property in these materials, the effectiveness of various sintering processes can be judged.
Superconductivity and crystallinity of Ba2Y1Cu3O7−δ thin films prepared by pulsed laser deposition with substrate bias voltage
Authors: Izumi H. , Ohata K. , Hase T. , Suzuki K. , Morishita T. , Tanaka S.
Published: July 2002

Substrate bias voltages were found to be significantly effective in preparing high-quality laser-deposited superconducting Ba2Y1Cu3O7−δ films at reduced substrate temperatures. The zero-resistance temperature of the biased films, positive bias being more effective than negative, decreased very slightly when the substrate temperature was lowered, whereas that of the unbiased films decreased considerably. In addition, the surface morphology and c-axis orientation have been improved by applying substrate bias voltages. Bias voltages within ±500 V hardly affect the composition of the resulting films so that stoichiometric films have been obtained from a stoichiometric target. A time-resolved optical observation revealed that a short time emission, probably being oxygen plasma, occurred in a few μs after the laser pulse impingement. The improvement in crystallinity of the resulting films is attributed to this emission. The velocity of emissive species in the plume was determined to be 6×105 cm/s. Under positive-biased conditions slower components with a velocity of 3×105 cm/s or less were also observed.
Assessment of the structural quality of CdTe/Cd1−xZnxTe strained superlattices by high-resolution x-ray diffraction and photoluminescence studies
Authors: Ponchet A. , Lentz G. , Tuffigo H. , Magnea N. , Mariette H. , Gentile P.
Published: July 2002

We present a detailed analysis of x-ray double-diffraction rocking-curve measurements and low-temperature photoluminescence spectroscopy of (001) CdTe-CdxZn1−xTe strained-layer superlattices grown by molecular-beam epitaxy. The presence of very sharp satellite reflections demonstrate smooth interfaces with a well-defined modulation of both composition and perpendicular stress. Using a kinematical step model, the thickness, strain, and composition of the wells and the barriers are extracted. It is shown that fluctuations of 1 monolayer of the average period can be reproducibly obtained in such superlattices, in excellent agreement with the in situ reflection of high-energy electron diffraction oscillations measurements. The structural perfection of these superlattices is confirmed by the optical spectra which exhibit sharp excitonic transitions.
Effects of using the more accurate intrinsic concentration on bipolar transistor modeling
Authors: Liou J. J. , Yuan J. S. , Wong W. W.
Published: July 2002

A more accurate intrinsic concentration was suggested recently. Discrepancies between using the conventional and the more accurate intrinsic concentrations on bipolar transistor modeling are assessed in this study. Our calculations show that the conventional intrinsic concentration overestimates the collector and base currents by a factor of 1.5 to 2 but affects less severely the steady-state current gain.
Photoluminescence spectroscopy of CdTe epilayers grown by rf magnetron sputtering
Authors: Das S. R. , Cook J. G. , Rowell N. L. , Aouadi M. S.
Published: July 2002

Photoluminescence spectra are measured for sputter-deposited, heteroepitaxial (100)CdTe layers of thicknesses up to 14 μm grown on (100)KBr substrates. Three emission bands, at 0.81, 1.00, and 1.41 eV, are observed. From comparison of the photoluminescence spectra of the epilayers with those of several bulk single-crystal and polycrystalline samples, the origin of the 1.41-eV band, reported previously by many workers, is correlated to structural defects arising from lattice mismatch with the substrate. It is concluded that the 0.81- and 1.00-eV bands are due to defect levels resulting from nonstoichiometric growth. The injection level and temperature dependence of the photoluminescence suggest that the 1.41- and 0.81-eV emissions are donor-acceptor transitions whereas the 1.00- eV emission is a conduction-band-acceptor transition.
A combination of rapid thermal processing and photochemical deposition for the growth of SiO2 suitable for InP device applications
Authors: Licoppe C. , Wattine F. , Meriadec C. , Flicstein J. , Nissim Y. I.
Published: July 2002

A combination of ultraviolet and infrared lamps is used to obtain the growth of SiO2 on InP substrates at low temperature under rapid thermal processing conditions. Thorough infrared spectroscopy characterization of the dielectric layers shows that the ultraviolet-assisted growth process without mercury sensitization leads to good quality silica interspersed with oxygen-deficient inclusions. Rapid annealing improves them so as to be suitable for InP-based field-effect devices, with interface trap density around 5×1011 cm−2. A study of the interface trap density made with this technique shows the relevance of fast thermal processing, even at low growth temperatures, for the improvement of these devices.
Amorphization and regrowth in Si/CoSi2/Si heterostructures
Authors: Maex Karen , White Alice E. , Short K. T. , Hsieh Yong-Fen , Hull R. , Osenbach J. W. , Praefcke H. C.
Published: July 2002

Reduction of the defect density in the Si overlayer of Si/CoSi2/Si heterostructures fabricated by mesotaxy has been achieved by selective amorphization and regrowth of the Si. Layer-by-layer regrowth of the silicide with an activation energy of 1.14 eV has also been clearly shown.
Formation and behavior of BGaVAs complex defects in gallium arsenide grown by liquid-encapsulated Czochralski method
Authors: Orito Fumio , Fujii Katsushi , Okada Yasumasa
Published: July 2002

The effect of wafer annealing on lattice parameter of liquid-encapsulated Czochralski (LEC) grown undoped semi-insulating GaAs crystals is investigated, showing that wafer annealing increases the lattice parameter from an anomalous state below that predicted by Vegard’s law. The sheet-carrier concentration of a silicon-implanted layer formed on undoped semi-insulating GaAs increases with the increase in lattice parameter caused by the wafer annealing. The reduction of BGaVAs complex defects is a reasonable explanation for the increase in lattice parameter and sheet-carrier concentration. In LEC-grown silicon-doped GaAs crystals, no anomalous reduction of lattice parameter is observed in as-grown crystals. It is speculated that the silicon introduced into the crystal from the melt fills the VAs vacancies in the GaAs crystal before BGaVAs forms. BGaVAs complex defects in undoped GaAs crystal must be formed during the post-growth cooling process.
Domain erasure and formation in direct overwrite magneto-optic recording
Authors: Schultz Mark D. , Kryder Mark H.
Published: July 2002

The erase and write processes in single layer direct-overwrite magneto-optic recording materials were investigated utilizing a stroboscopic microscope system with 10-nsec time resolution. The effects of thermal magnetization reduction are addressed and limited by image subtraction techniques. With this technique the erase process is shown to be a collapse process which occurs during heating, rather than cooling. Galvanometer driven beam scanning is utilized to write and erase ‘‘stripe’’ domains at velocities up to 5 m/s. Scanning write and scanning continuous beam erase are investigated stroboscopically, providing surprising new data on these processes. The erase process for a ‘‘stripe’’ domain is shown to proceed from the end of the domain, and in front of the approaching erase laser beam. Jitter in the leading edge of the written domain is observed, and may be responsible for the noise levels observed in these materials. The data indicate that the erase process is driven by a combination of temperature and temperature gradient. The write behavior can be explained by either a post-laser pulse nucleation or by movement of the trailing domain wall.
Photovoltaic properties of iodine-doped magnesium tetraphenylporphyrin sandwich cells. Optimization of doping, and dark electrical properties
Authors: Nevin W. A. , Chamberlain G. A.
Published: July 2002

By fabricating, doping, and testing sandwich cells of the structure Al/Al2O3 /magnesium tetraphenylporphyrin (MgTPP)/Au under high vacuum, without contact with the atmosphere, the effect of iodine doping on the dark and photovoltaic response has been determined. The properties were found to be extremely sensitive to small variations in iodine concentration, and a method of doping was developed to give highly reproducible devices with optimum photovoltaic efficiency for this system. The doped device behaves as a metal-insulator-semiconductor structure in which a depletion layer of thickness ∼100 nm and carrier concentration ∼1016 cm3 is formed in the porphyrin near the Al-Al2O3/MgTPP interface. From analysis of the time dependence of the electrical properties after doping, a value of 1×10−15 cm2/s is obtained for the diffusion coefficient of iodine in the MgTPP film. Rectification of the dark characteristics is observed only for optimized devices, with a rectification ratio of 240 obtained for a cell having a 200-nm-thick porphyrin layer. Current transport at moderate field strengths appears to be space-charge limited in the presence of a discrete trapping level in the porphyrin, enhanced at higher fields by Poole–Frenkel emission in the oxide layer.
Structural stability of heat-treated W/C and W/B4C multilayers
Authors: Jankowski A. F. , Schrawyer L. R. , Wall M. A.
Published: July 2002

The utilization of W/C and W/B4C multilayer structures as Bragg diffractors rests in their reflective efficiency and dependability, both of which rely on the stability of the layered structure. The layers within the vapor deposited multilayers, often amorphous, are typically metastable, hence susceptible to thermally induced structural change. In fact, crystallization and compound formation are known to occur in annealed multilayer systems. In this study, multilayers of W/C and W/B4C were vacuum heat treated, then structurally examined. A comparison between the pre- and post-heat-treated structures of the two multilayer systems is accomplished using diffraction, depth profiling, and microscopy. Our results indicate structural stability in the W/B4C multilayers, after heat treatment, in comparison with structural degradation noted in the W/C system.
Carbonization process for low-temperature growth of 3C-SiC by the gas-source molecular-beam epitaxial method
Authors: Motoyama Shin-ichi , Morikawa Norikazu , Nasu Masaaki , Kaneda Shigeo
Published: July 2002

Using the carbonization process, single-crystalline SiC films were grown at substrate temperature (Tsub) in the range of 750–1050 °C by the gas-source molecular-beam epitaxial method. This process was performed by using C2H4 gas and a special growth method in which the temperature was raised at a predetermined rate (RT) during growth. To realize the growth of single-crystalline carbonized films, it was found that a C2H4 gas pressure PC2H4=8×10−5 Torr and rising rate RT=25–25/3 °C/min were necessary. After the carbonization process, essential growth of SiC films using SiHCl3 and C2H4 gases in the range of gas pressure ratios PSiHCl3/PC2H4= (1)/(3) –5 (PSiHCl3=1–5×10−5 Torr) at Tsub=1000 °C was performed. In these all experimental ranges, single-crystalline 3C-SiC films could be grown.
The electroelastic tensor of quartz determined by the resonator method
Authors: Hruska Carl K.
Published: July 2002

The complete electroelastic tensor of quartz has been calculated—for the first time—exclusively using the data obtained by the resonator method. Its eight independent components were obtained by the least-squares fit to 184 observations of the dc-field-induced change in the resonance frequency of the extentional mode of rods and thickness modes of plates. Simultaneously, an attempt has been made to calculate the eight independent components of the electrostrictive tensor and the only independent component of the third-order permittivity tensor of quartz. Only seven values have been obtained here; three of them are linear combinations of these quantities. A comparison made with similar tensors as calculated from the transit-time experiment [Kittinger, Tichy, and Friedel, J. Appl. Phys. 60, 1465 (1986)] yields excellent agreement for the electroelastic tensor. Differences between the corresponding tensor components are comparable with their standard errors. The comparisons available for the electrostrictive tensor are considerably less encouraging. No comparison for the third-order permittivity (disregarded in the analysis of the transit-time experiment) could be made.
Investigation of magnetic and electrical properties of the Ho0.85Tb0.15Fe2−xCox system
Authors: Dhilsha K. R. , Rao K. V. S. Rama
Published: July 2002

X-ray diffraction studies carried out on a Ho0.85Tb0.15Fe2−xCox (x=0–2.0) system revealed that all the compositions investigated retained the C15-type cubic Laves phase structure. Magnetization and electrical resistivity measurements were carried out in the temperature range 77–750 K. The Curie temperature was found to increase initially from 630 K for x=0 to a value of 690 K for x=0.5 and then decrease to 130 K for x=2.0. Several anomalies observed in the resistivity measurements have been identified corresponding to spin reorientations occurring in this system. Some of these spin reorientations have also been observed in the magnetization measurements.
Mechanism of negative-bias-temperature instability
Authors: Blat C. E. , Nicollian E. H. , Poindexter E. H.
Published: July 2002

Although negative-bias-temperature instability in metal-oxide-semiconductor integrated circuits has been minimized empirically, the exact mechanism is unknown. We argue in this paper that the mechanism of negative-bias-temperature instability can be modeled by a first-order electrochemical reaction between hydrogenated trivalent silicon, a neutral water-related species located in the oxide near the Si-SiO2 interface, and holes at the silicon surface to form neutral trivalent silicon and a positively charged water-related species. To show that such a reaction describes the phenomenon, we show that (1) water must be present in the oxide near the Si-SiO2 interface, (2) induced interface and oxide-fixed charge densities are equal, (3) the saturation interface-trap and oxide-fixed charge densities depend on the initial hole concentration at the silicon surface or aging field, (4) the buildup of these charge densities follows first-order reaction kinetics, and (5) time constants for this charge buildup are independent of aging field. The measurements which are done to demonstrate these features combine room-temperature charge measurement using the Q-C method with current measurements during accelerated aging.
Sources of donor impurities in undoped GaAs grown using arsine and trimethylgallium
Authors: Watkins S. P. , Haacke G.
Published: July 2002

Magnetophotoluminescence spectroscopy (MPL) has been used to ascertain the source of donor impurities in high-purity GaAs grown by atmospheric pressure metalorganic vapor deposition using arsine and trimethylgallium. A linear correlation between absolute MPL intensity and net carrier concentration for high-purity n-type epilayers over the concentration range 1×1014–2×1015 cm−3 provided an unambiguous method for identifying the source of donor impurities by comparing epilayers grown with different source batches. Batch-to-batch variations in the quality of films grown with eight different arsine cylinders were traced directly to the presence of varying amounts of a Ge-containing contaminant in the arsine.
Cathodoluminescence study of diamond films grown by microwave plasma assisted chemical vapor deposition
Authors: Yacobi B. G. , Badzian A. R. , Badzian T.
Published: July 2002

Diamond films, produced by microwave plasma assisted chemical vapor deposition, were studied using cathodoluminescence (CL) scanning electron microscopy and spectroscopy techniques. Luminescence intensities of the observed prominent peaks at 420, 445, and 738 nm were found to vary widely as a function of both the deposition conditions and the location in the same sample. Additional peaks and shoulders at 464, 483, 500, 514, and 532 nm were also observed in some regions of diamond films deposited using the higher (i.e., 1%) CH4/H2 concentration and the substrate temperatures below 950 °C. Strong variations in CL intensities in different regions of the same sample were observed, indicating substantial variations in the distribution of defects and impurities in these diamond films. Luminescence due to the boron in a doped sample was also observed, and it was concluded that the higher CL intensity in that sample compared to other samples was due to the reduced defect densities and not due to the boron.
Determination of roughness correlations in multilayer films for x-ray mirrors
Authors: Savage D. E. , Kleiner J. , Schimke N. , Phang Y.-H. , Jankowski T. , Jacobs J. , Kariotis R. , Lagally M. G.
Published: July 2002

Interfacial roughness in multilayer films may be random or correlated, i.e., replicated from layer to layer. It is shown that these can be separated and quantified using x-ray diffraction rocking curves and a straightforward analysis. The lateral correlation length along the interfaces can additionally be determined. A quantitative evaluation for W/C multilayers shows that correlated roughness contributes significantly to the total roughness, even at length scales that are surprisingly short, of the order 2–6 nm.
Differential ion damage and its annealing behavior in AlAs/GaAs heterostructures
Authors: Cullis A. G. , Smith P. W. , Jacobson D. C. , Poate J. M.
Published: July 2002

The nature of differential ion damage in AlAs-GaAs epitaxial heterostructures is explored using conventional and high-resolution transmission electron microscopy, together with Rutherford backscattering spectrometry. By use of Si+ ion implantation, the rapid buildup of lattice damage in GaAs, and the relative resistance of AlAs to structure breakdown is highlighted. The ion dose levels required for bulk amorphization of the two materials differ by at least two orders of magnitude. The way in which lattice disorder changes near the AlAs/GaAs interface is studied in detail and it is demonstrated that the AlAs layer, which remains crystalline up to high ion doses, promotes in situ annealing of narrow zones of GaAs crystal adjacent to both of its interfaces. These crystalline GaAs zones show substantially enhanced resistance to ion damage accumulation but they contain planar defects and are finally rendered amorphous after extended ion bombardment. During this process, defects propagate into the edges of the AlAs layer which are then progressively amorphized in an apparently heterogeneous (boundary-dependent) manner. In addition, it is shown that GaAs in other regions of the sample is amorphized by a mechanism which at first leaves nanometer-scale blocks of crystal isolated within the newly formed amorphous material, although these blocks are then rapidly broken down by further bombardment. The way in which the implantation-damaged layers restructure during annealing treatment is also described. Up to ∼320 nm of amorphous GaAs beneath the AlAs layer can be regrown as a single crystal by the motion of two opposing growth interfaces during annealing at 800 °C.
X-ray diffraction from d spacing gradients along ion-implanted zones
Authors: Rao Satish I. , Houska C. R.
Published: July 2002

Three kinematic diffraction models are described for interpreting diffraction profiles from ion-implanted samples. Each deals with relatively large d spacing gradients. The first treats the full zone as coherent which requires a direct summation of the Fourier series. The Bragg intensity band from the full zone is applied to implanted zones that are subjected to elastic constraints without incoherent interfaces. For high-fluence samples, and foreign interstitials, a static attenuation term becomes important and is included in all models. This term was not included in previous publications by the authors. The last two models deal with finite subgrain elements that may be connected in a continuous way with interfaces. With a linear element model, slope discontinuities give a sawtooth appearance of the d spacing curve. These discontinuities are eliminated by employing a sinusoidal variation in d spacing in a third model. The additional smoothing does not provide significant changes in the fine structure of the measured intensity. The parameters that determine line shape are: ΔM, the total change in the attenuation factor M within a subgrain, and s = N3l(Δd/〈d〉) which contains three additional independent parameters. These are the subgrain size, the order of the Bragg peak l, and the fractional changes in d spacing. The static lattice displacements can be large enough to introduce an asymmetry of the diffraction profiles from individual elements. This occurs when ΔM is greater than 0.15. Although this factor has been introduced only into the linear element model, a similar asymmetry should be observed with a sinusoidal variation in d spacing.
Li and Sb doping effects on the growth behavior of ZnS on GaP substrates
Authors: Fuke Shunro , Sugihara Yoshihide , Maezawa Chikako , Kuwahara Kazuhiro , Imai Tetsuji
Published: July 2002

The effects of impurities (Li and Sb) introduced into the carrier gas on the growth rate and crystallinity are investigated for the vapor-phase epitaxial growth of ZnS on GaP substrates. In the case of Sb incorporation, a clear dependence of the growth rate on polar planes has not been obtained. On the other hand, Li incorporation to the growth ambient causes an increase of the growth rate on (111)A plane and a decrease on (111)B plane. This result is analogous to that observed in case of In doping and is in contrast with the iodine doping effects. These impurity effects are found to depend on the combination between the ionization polarity of impurity elements and the polarity of the substrate orientation.
The stability of stretching and accelerating plastic sheets. I
Authors: Romero Louis A.
Published: July 2002

The equations governing the linearized stability of a perfectly plastic sheet that is isotropically stretching in the horizontal direction and accelerating in the vertical direction are derived. The equations are analyzed for the case where the vertical acceleration is zero. The stability of the sheet depends on a dimensionless parameter Γ that measures the ratio of the inertial forces to the plastic forces. This parameter decreases as the sheet stretches. The sheet is stable provided Γ is large. When Γ is small, the sheet is unstable to symmetrical disturbances. There is no sharply defined most unstable wavelength, but the most unstable wavelengths range between 10 and 1/Γ times the thickness of the sheet.
Dual-ion-beam sputter deposition of TiN films
Authors: Valentini A. , Quaranta F. , Penza M. , Vasanelli L. , Battaglin G.
Published: July 2002

A dual-ion-beam technique for the deposition of TiN thin films is described. The metal-atom flux is supplied by sputtering a titanium target with an inert ion beam, while the reactive flux is supplied directly to the growing film by a low-energy ion beam. Results are presented for titanium films deposited at room temperature under a range of N+2 ion bombardment to form TiN. Analysis gives the incorporation of nitrogen, the background gas contamination, and the optical and electrical properties of TiN films.
Measurement of a population inversion on the 551.4-nm transition in an optically pumped Ti vapor laser
Authors: Ninomiya H. , Takashima N. , Hirata K.
Published: July 2002

A population inversion density on the Ti 551.4-nm (3D01−3F2) transition in a N2 -laser-pumped Ti-vapor laser has been estimated from measurements of an optical gain on the laser transition, length of the laser medium, and temperature in the vapor to determine the linewidth. Ti vapor is generated by irradiation of a pulsed YAG laser light of 1 J/pulse energy and then the Ti atoms are optically pumped by a N2 laser of 0.2 mJ/cm2 intensity. It has been experimentally observed that, in pure Ti vapor, the population of Ti (3d24s2 3F2) is about 8×1013/cm3, the temperature in the vapor is about 9000 K, the population inversion on the 551.4-nm transition is about 1.5×1011/cm3, and the absorption cross section of the N2 -laser light at 337.044 nm by a Ti atom is 3.0×10−15 cm2.
Band-edge photorefractivity in semiconductors: Theory and experiment
Authors: Partovi Afshin , Garmire Elsa M.
Published: July 2002

At wavelengths close to the band edge, strong photorefractive gratings using the Franz–Keldysh electrorefractive effect can be written in semiconductors. Two-beam-coupling exponential gain coefficients as high as Γ=16.3 cm−1 have been obtained in GaAs by combining the electrorefractive photorefractive grating with the conventional electro-optic photorefractive grating and using the moving grating technique to enhance the photorefractive space-charge field. A method for calculation of the gain coefficient near the band edge of materials is presented. The method is applied to GaAs and the results are compared to the experimental data. Reasonable agreement with experiment has been achieved. An optimal spectral range (910 nm<λ<930 nm) for near-band-edge photorefractivity in GaAs has been found. Conventional theories of photorefractivity based on Kukhtarev’s equations are found to be sufficient for calculation of the photorefractive space-charge field near the band edge. Predictions of the gain coefficient near the band edge using the moving grating technique are presented. Other methods of increasing the photorefractive gain such as the temperature-dependent resonance in InP:Fe are also discussed.