bluuebunny/crossref_metadata_2025 huggingface dataset:
Observation of large, untwinned orthorhombic domains in YBa2Cu3O7 single crystals
Authors: Wang Z. Z. , Ong N. P. , McGinn J. T.
Published: July 2002

The twinning pattern in single crystals of YBa2Cu3O7 has been studied by differential interference contrast microscopy and transmission electron microscopy. In 10% of crystals studied large untwinned orthorhombic [(b−a)/a=2.7%] domains exceeding 100×100 μm2 in area are observed. The structure of twin defects is described and the existence of two types of minority domains is inferred. We infer from the domain structures a mechanism for the growth of twinning patterns in single crystals.
Polycrystalline Si thin-film transistors using thermally crystallized low-pressure chemical vapor deposition a-Si films for the channel layer and P-doped microcrystalline Si films for the source and drain layers
Authors: Kobayashi Kazuhiro , Nijs John , Mertens Robert
Published: July 2002

We have fabricated thin-film transistors with a field-effect mobility of 17 cm2 /V s using thermally crystallized low-pressure chemical vapor deposition (LPCVD) a-Si films for the channel layer and P-doped microcrystalline Si films deposited by plasma CVD for the source and drain layers. The maximum processing temperature equals 630 °C. The characteristics of these films have been investigated as well. It is found that the grain size of the thermally crystallized LPCVD a-Si films increases and a {111} preferential orientation of the films becomes more pronounced as the film thickness increases. The average grain size amounts 440 nm on the long axis and 200 nm on the short axis for a film thickness of 460 nm. The conductivity of P-doped microcrystalline Si films deposited by plasma CVD at 270 °C is closely dependent on the deposition rate of the films and the grain size of the underlying channel polycrystalline Si films. By decreasing the deposition rate and using crystallized LPCVD a-Si films for the underlying channel layer, highly conductive P-doped microcrystalline Si films are realized.
The zinc pressure effect in chlorine-doped ZnSe grown by atmospheric metalorganic chemical vapor deposition
Authors: Kamata Atsushi , Uemoto Tsutomu , Hirahara Keijiro , Beppu Tatsuro
Published: July 2002

An n-type ZnSe has been grown by atmospheric metalorganic chemical vapor deposition in which hydrogen chloride was used as the chlorine-donor source. Epitaxial layers were evaluated by photoluminescence measurements and Hall measurements. An excitonic emission intensity at 4.2 K, which is a donor bound excitonic emission, increased with donor doping concentration increase. The electron carrier concentration varied with a quadratic dependence on the dopant concentration. Chlorine-doped ZnSe characteristics were revealed to be similar in regard to the relation between the electrical and luminescent properties, irrespective of dopant source materials. An increase in zinc partial pressure led to an increase in carrier concentration and the suppression of the self-activated emission intensity. A zinc excess growth condition was revealed to be effective for quality improvement for n-type ZnSe and suppression of the compensation effect, which made the carrier producing efficiency high.
An interface reaction mechanism for the dry oxidation of silicon
Authors: Moharir S. S. , Chandorkar A. N. , Vasi J.
Published: July 2002

We have developed a mathematical model for dry silicon oxidation in the thin-oxide regime based on the adsorption of oxygen at the Si-SiO2 interface, and fitted a whole range of data for (111) silicon. We propose that quasichemical bonding exists between oxygen and silicon at the Si-SiO2 interface before the final oxidation reaction takes place.
Low-temperature 3C-SiC heteroepitaxial film growth on Si by reactive-ion-beam deposition
Authors: Yamada Hiroshi
Published: July 2002

Heteroepitaxial growth of 3C-SiC on Si(111) and Si (100) at temperatures lower than 800 °C was investigated by using a low-temperature crystalline film formation method, reactive-ion-beam deposition. This method uses low-energy ionized species extracted from reactive electron-cyclotron-resonance plasma of SiH4 and C2H4. In the case of direct film growth on clean Si substrates, 3C-SiC film growth can be achieved at the low temperature of 770 °C±12° by adjusting the ion energy to 200 eV. To improve crystalline quality, Si homoepitaxial and Si-C transition layers, about 2–3 and 3–4 nm in thickness, respectively, were formed in the initial heteroepitaxial growth stage. Using these thin layers, 200-nm-thick 3C-SiC/Si(111) heteroepitaxial films with about 63 cm2 /V s (300 K) and about 21 cm2 /V s (700 K) in Hall mobility can be obtained at the same low temperature, although they included twins.
Positive temperature coefficient of resistance in metal-semiconductor contacts
Authors: Ito Kentaro , Fukami Tatsuo
Published: July 2002

Metal-semiconductor contacts were formed using vacuum-evaporated Au films on n-type ceramics. The surface of the ceramics was anodically oxidized prior to gold evaporation. It was found that the diode thus obtained, had the positive temperature coefficient of resistance under reverse bias. This effect was not only observed in the contact consisting of the Ba1−xSrxTiO3 ceramics at temperatures both above and below the Curie point, but also in that of nonferroelectric semiconducting oxide such as TiO2. The positive temperature coefficient effect was explained in terms of electron tunneling through the metal-insulator-semiconductor structure.
Sensitivity-enhanced electron holography and its application to magnetic recording investigations
Authors: Hasegawa Shuji , Kawasaki Takeshi , Endo Junji , Tonomura Akira , Honda Yukio , Futamoto Masaaki , Yoshida Kazuetsu , Kugiya Fumio , Koizumi Makoto
Published: July 2002

The sensitivity for electron-phase measurement in electron holography has been improved to better than 2π/100 by the application of digital interferometry at the optical reconstruction stage. This enables quantitative measurement of magnetic flux as small as (1/100)(h/e)(=4.1×10−17 Wb), hitherto undetectable, with high spatial resolution. With this technique, we have observed the distribution of leakage magnetic field from a thin cross section of a perpendicularly magnetized recording film (cobalt-chromium) with a recording density as high as 300 kFCI (85 nm bit length), the highest density ever directly observed.
Magnetic properties of granular Co-polymer thin films
Authors: Laurent C. , Mauri D. , Kay E. , Parkin S. S. P.
Published: July 2002

Composite cobalt-polymer thin films are created by simultaneous metal sputtering and plasma polymerization of propane. The magnetic properties are investigated as a function of Co volume fraction. At low concentration, Co forms very small isolated clusters (∼10 Å) which behave superparamagnetically down to <6 K. At 0.22 ±0.05 Co volume fraction an electrical percolation threshold and a transition to ferromagnetic behavior is observed.
Dynamic depth profile measurements of implanted deuterium in nickel
Authors: Petitpierre O. , Möller W. , Scherzer B. M. U.
Published: July 2002

Depth profiles of 10-keV deuterium implanted in nickel were obtained during implantation through elastic recoil detection between 233 and 313 K. The profiles were allowed to reach saturation at each measured temperature. At the lowest temperature, measurements with various implantation fluxes were performed. Aside from surface peaks, the depth profiles show a uniform density of deuterium in the implanted layer and the shape of these profiles is independent of the sample temperature or implantation fluence or flux. The temperature and fluence dependence could be successfully reproduced with a trapping-detrapping model considering three different trap binding energies. Two of the model parameters are in good agreement with previous calculations performed to reproduce reemission measurements.
Theory and practice of proximity correction by secondary exposure
Authors: Leen Todd K.
Published: July 2002

This article examines the theory and practice of correcting proximity effect in direct write electron beam lithography by the introduction of a second diffuse, image-complement exposure. The common point-spread function for energy deposition in the substrate is used in formulating a solution to the inverse scattering problem, and the solution is expressed as a power series in the backscatter coefficient. The ghost technique is shown to constitute an approximation to this solution. This mathematical exposition clearly indicates the power of the technique for providing very accurate, point-by-point correction of proximity effect. Application of the procedure to nonlinear resists in a shaped-beam exposure tool is given.
Fabrication of buried-heterostructure diode lasers using i
n s
i
t
u Mg diffusion
Authors: Mukai Seiji , Kaneko Yasuyuki , Watanabe Masanobu , Itoh Hideo , Yajima Hiroyoshi
Published: July 2002

An in situ diffusion technique is developed to simplify the diode-laser fabrication process. In this technique Mg is diffused into double-heterostructure wafers during their liquid-phase-epitaxial growth process through an in situ formed diffusion mask, which makes separate mask-formation and diffusion processes unnecessary. Buried-heterostructure lasers with low threshold and high efficiency are fabricated utilizing this simplified process.
Fine line aluminum etching in air and in solution using a tunable dye laser
Authors: Contolini Robert J. , Alspector Joshua
Published: July 2002

We report results of using a pulsed, tunable laser to etch fine patterned aluminum lines on a silicon integrated circuit. Wavelengths from 2850 and 5730 Å were investigated for aluminum etching, both in air and in solution. Air ablation at the shortest wavelength was found to be most effective in selectively removing aluminum while least damaging the underlying silicon dioxide insulator layer. Complimentary metal oxide semiconductor inverter test circuits worked successfully after laser etching of selected aluminum links.
The dependence of silicon selective epitaxial growth rates on masking oxide thickness
Authors: Friedrich J. A. , Kastelic M. , Neudeck G. W. , Takoudis C. G.
Published: July 2002

Growth rates in selective epitaxial depositions (SEG) and epitaxial lateral overgrowth (ELO) in the SiCl2H2-HCl-H2 system were studied as a function of masking oxide thickness. Enhanced growth was observed on wafers with thin (80 nm), as compared to thick (>300 nm), masking oxides. The higher growth rates on wafers with thin oxides were attributed to their higher surface temperature. The higher surface temperature for wafers with thin oxides is demonstrated to be due to decreased radiant heat transfer as compared to wafers with thicker oxides. The dependence of oxide thickness on growth rates was global, meaning that the bulk or large area field oxide thickness, and not the local oxide thickness in the immediate vicinity of the seed window, determined the growth rates. Hence, the dependence of growth rates on masking oxide thickness is critical in understanding, designing, and comparing experiments studying epitaxial deposition processes, but is less critical for technological applications of SEG and ELO.
High-pressure oxidation of titanium disilicide/polycrystalline silicon composite films
Authors: Rosner S. J. , Amano Jun , Turner J. E. , Laderman S. L. , Dervan A.
Published: July 2002

The oxidation of titanium disilicide on polycrystalline silicon-coated substrates by steam oxidation at pressures up to 25 atm has been investigated. Films were examined by Rutherford backscattering spectrometry and transmission electron microscopy. At low temperatures, the formation of a silicon dioxide surface layer is limited by the transport of silicon to the reacting interface, resulting in rapid oxidation/decomposition of the silicide. At temperatures greater than 750 °C, a metal-free oxide was obtained, allowing the formation of a self-passivated self-aligned silicide structure appropriate for very-large-scale-integrated circuit applications.
Investigation of the interface grading in III-V heterostructures by double-crystal diffractometry
Authors: Ferrari C. , Franzosi P.
Published: July 2002

The interface grading in III-V compound single heterostructures has been investigated by using the double-crystal diffractometry. Theoretical rocking curves have been calculated for the particular example of InGaAs/InP slightly mismatched heterostructures, assuming the 004 reflection and the CuKα1 radiation. It has been found that the Pendellosung fringe intensity is the most suitable and sensitive parameter to determine the type and amount of the lattice parameter gradient close to the interface. Rocking curves have been experimentally measured for a variety of single heterostructures and a satisfactory agreement between experimental and theoretical profiles has been obtained when the correct interface shape was assumed.
Controlled p-type impurity doping of HgTe-CdTe superlattices during molecular-beam-epitaxial growth
Authors: Peterman D. J. , Wroge M. L. , Morris B. J. , Leopold D. J. , Broerman J. G.
Published: July 2002

We report identification of a reliable p-type impurity dopant that can be used during molecular-beam-epitaxial (MBE) growth of HgTe-CdTe superlattices. Silver doping during the epitaxial growth of (100)-oriented HgTe-CdTe superlattices is shown to yield reproducible hole concentrations in the range of 1016–1018 cm−3. When normalized by the growth rate, the hole concentrations show an exponential dependence on the temperature of the Ag effusion cell. The diffusion of Ag in step-doped junctions was studied by use of secondary-ion mass spectrometry. The diffusion coefficient of Ag at the low MBE growth temperatures was found to be in the range of (1–5)×10−13 cm2/s. These values are comparable to recently reported values in MBE-grown (Hg,Cd)Te alloys and suggest that strain does not produce any new diffusion paths in the superlattices.
Role of silicon and oxygen impurities in gallium antimonide grain boundary
Authors: Roy U. N. , Basu S.
Published: July 2002

Grain-boundary barrier heights in polycrystalline gallium antimonide were shown to be due to the segregation of silicon and oxygen impurities as determined by electron probe microanalysis. From the variation of zero bias conductance with temperature the barrier height was measured for both n- and p-type bicrystals. The barrier heights were found to occur due to the depletion and accumulation layers in the vicinity of the grain boundary for n- and p-type samples, respectively. Reduction of barrier height after hydrogen annealing at 500 °C was observed.
Dynamic current oscillations in a metal-oxide-semiconductor surface potential well
Authors: Lou L. F.
Published: July 2002

Novel oscillatory behavior has been observed in metal-oxide-semiconductor (MOS) capacitors at low temperatures. These observations were made by applying a voltage ramp to an MOS capacitor fabricated on p-type silicon. The silicon surface was driven from accumulation, through depletion, and into the avalanche regime, repetitively. The surface potential well fills with electrons as avalanche multiplication occurs during ramp-up, and emits those electrons into the bulk silicon as the well depth decreases during ramp-down. The filling and emission processes induce displacement current oscillations, which indicates that dynamically quantized two-dimensional subbands have been observed.
Study on the dependence of electrical properties on dislocation levels in InSb films vacuum deposited on glass
Authors: Iida Shosan
Published: July 2002

The absorption coefficient, as a function of photon energy, of vacuum-deposited indium antimonide (InSb) films on a glass substrate produced by varying the evaporation source material temperature and flash evaporation time interval was determined with Kramers–Kronig analysis developed by Roessler [D. M. Roessler, Br. J. Appl. Phys. 16, 1119 (1965)]. The absorption coefficients can be determined by the analysis without restriction due to a glass substrate which is opaque to below around 0.31 eV of infrared rays (InSb band gap around 0.2 eV is in this opaque region) because the analysis can determine the coefficients from only reflectance data without transmittance data of the film. Therefore, the analysis was conducted with measured reflectance of the films at room temperature. Results of the analysis showed that dislocation levels, which are in good agreement with both the Read and Broudy models for In and Sb dislocations, exist in the films. The Hall coefficient and Hall mobility of the films at room temperature decrease with an increase of the number of transitions between levels, such as transitions from the valence band to a dislocation level, from a dislocation level to any other dislocation level, and from a dislocation level to the conduction band. Deposition conditions for producing high-quality InSb film should be given so that the generation of dislocation levels is suppressed or eliminated from the results. From the above analytical results, the analysis may give more detailed information, such as peaks that correspond to the energy of carrier transitions in the absorption coefficient as a function of photon energy, in comparison with a method of straight determination of the transition energies from only reflectance or transmittance data. Other wide applications of this analytical method are expected.
Defect-related dielectric breakdown, charge trapping, and interface-state generation of gate oxides grown on zone-melting-recrystallized silicon-on-insulator films
Authors: Lee Chun-Teh , Chen Chenson K.
Published: July 2002

Dielectric breakdown has been investigated for gate oxides grown on 0.3- and 1-μm-thick zone-melting-recrystallized (ZMR) silicon-on-insulator films, and also for oxides on 0.65- and 0.84-μm-thick films thinned from 1-μm-thick films by thermal oxidation. In addition, charge trapping and interface-state generation have been studied for 1-μm-thick ZMR films. The gate oxide grown on a 1-μm-thick ZMR film is significantly better than that grown on a 0.3-μm-thick ZMR film. The weak spots for the breakdown of gate oxides are identified and correlated with defects in the ZMR films by optical Nomarski interference contrast microscopy and scanning electron microscopy. In comparison to its counterpart on bulk Si, the gate oxide grown on a 1-μm-thick ZMR film is characterized by a slightly lower breakdown field, larger positive charge generation, higher electron trapping, and larger interface-state generation.
Propagation loss of surface acoustic waves on a monolithic metal-insulator-semiconductor structure
Authors: Mitsutsuka S. , Okamoto T. , Niitsuma T. , Minagawa S.
Published: July 2002

A theory for the propagation loss of surface acoustic waves on a monolithic metal-insulator-semiconductor structure is developed. We derive the theory for the case where an epitaxial layer of semiconductor on a heavily doped substrate is used. The experimental results obtained by using Sezawa waves on a monolithic ZnO/SiO2/Si structure are compared with the theoretical predictions. The theoretical values are in good agreement with the experimental values in regard to the bias-voltage characteristics, the temperature characteristics, and the effects of the impurity concentration and the thickness of the epitaxial layer. It is shown that the surface-acoustic-wave propagation loss is considerably sensitive not only to the impurity concentration but also to the thickness of the epitaxial layer.
Interstitial and substitutional Zn in InP and InGaAsP
Authors: van Gurp G. J. , van Dongen T. , Fontijn G. M. , Jacobs J. M. , Tjaden D. L. A.
Published: July 2002

Closed-ampoule Zn diffusion in InP results in a net acceptor concentration that is much smaller than the Zn concentration. After subsequent annealing of InP in an atmosphere without Zn, the Zn and net acceptor concentrations have become almost identical, due to a decreased Zn concentration and an increased net acceptor concentration. The annealing treatment gives rise to a decreased contact resistivity. The diffusion depth has not changed. Annealing with a SiN cap on the InP surface does not have this effect on the concentrations. These annealing effects also take place in InGaAsP on InP layers. The results can be explained quantitatively by assuming that Zn is incorporated as both substitutional acceptors and interstitial donors and that only the interstitial Zn is driven out by the annealing, owing to its large diffusion coefficient. Profiles calculated with this interstitial-substitutional model can be fitted to experimental profiles assuming Zn to diffuse as singly ionized interstitial donors. This model can also describe earlier reported results on Zn diffusion in n-type InP for which a profile cutoff is found at a depth where the acceptor concentration equals the background donor concentration and in which the acceptor solubility is higher than in undoped InP.
Effect of the detailed growth conditions on the injection efficiency of (N)AlGaAs-(p+)GaAs heterojunctions produced by molecular-beam epitaxy
Authors: Khamsehpour B. , Singer K. E.
Published: July 2002

Abrupt (N)AlGaAs-(p+ )GaAs heterojunction diodes were grown by molecular-beam epitaxy. It was found that the position with respect to the heterointerface at which the substrate temperature was changed from that for the growth of (p+ )GaAs to that for the growth of (N)AlGaAs had a significant effect on the injection efficiency of the devices. By initiating the substrate temperature rise right at the start of the (N)AlGaAs growth, heterojunction bipolar transistors with an abrupt (N)Al0.18 Ga0.82 As-(p+ )GaAs emitter-base junction having current gains of between 60 and 70 were fabricated. These relatively high-current gains are argued to be due to the effects of hot-electron injection into the base.
Effects of band-gap narrowing on common-emitter current gain of GaAs homojunction bipolar transistors
Authors: Liou J. J.
Published: July 2002

GaAs homojunction bipolar transistors (GaAs BTs) are attractive because of their manufacturability and high electron mobility. This paper theoretically investigates the band-gap narrowing effects on the common-emitter current gain β of GaAs BTs based on recently reported band-gap-narrowing results for GaAs taking into account interactions between free carriers and dopant ions. It is shown that, benefitting from the band-gap contractions, an n+/ p+ /n GaAs BT can possess good β as well as high cutoff frequency, contrasting with the conventional concept that n+ /p/n doping in a GaAs BT is needed in order to obtain high β. Experimental results reported in literature regarding n+ /p+ /n GaAs BTs are also discussed.
Alloy fluctuation effects on the carrier emission from the Fe acceptor doped in liquid-phase-epitaxy-grown In0.49Ga0.51P
Authors: Takanohashi T.
Published: July 2002

We used microscopic model of disordered atomic arrangements to analyze the thermal emission properties of holes from an Fe acceptor doped in liquid-phase-epitaxy-grown In0.49Ga0.51P. The nonexponential properties of hole emission are well explained by the discretely broadened activation-energy model. The effective width of the broadened level is 90 meV. This communication shows that the activation energy of an Fe acceptor with an arbitrary composition of InGaP can be predicted by the broadening parameter introduced in this study.
Scanning tunneling microscope imaging technique for weakly bonded surface deposits
Authors: Jericho M. H. , Blackford B. L. , Dahn D. C.
Published: July 2002

An imaging mode for a scanning tunneling microscope is described in which the tunneling needle is periodically withdrawn from the surface under study in order to reduce the elastic interaction effects between needle and substrate during imaging. Examples of images of weakly bonded surface deposits that could not be imaged with the conventional sweep method are presented. The technique also makes it possible to first manipulate and subsequently image deposits that are weakly bonded to a substrate.
Metal drilling with a CO2 laser beam. II. Analysis of aluminum drilling experiments
Authors: Armon E. , Hill M. , Spalding I. J. , Zvirin Y.
Published: July 2002

The penetration time, crater top radius, and melted zone for aluminum plates drilled with a CO2 laser beam have been measured and analyzed on the basis of various assumptions concerning absorptivity of the liquid metal, attenuation by the metal vapor and heat exchange with the vapor. By comparison with the experimental data it is shown that each of the interaction parameters must lie within a predetermined range in order to correlate all the experimental measurements. This ascertains the reliability of the theoretical approach and yields estimates of the a priori unknown parameters for the specific exposure conditions.
Infrared properties of diabase glass and wool
Authors: Ljungdahl Gösta , Ribbing Carl G.
Published: July 2002

Results from infrared reflectance and collimated transmittance of a diabase glass are presented and compared with data for wool, prepared from the same glass. Using very thin glass slices it proved possible to establish a lower limit to the extinction coefficient k (1200 cm−1)≥0.043 where the glass exhibits a low reflectance minimum and the wool transmittance a sharp maximum, related, but not identical to, the classical Christiansen effect. With this low limit to the extinction coefficient of the glass material, a fivefold transmittance enhancement of the wool in comparison to glass is confirmed. As a tentative explanation it is suggested that the rapid quenching of the glass fibers causes a reduction of the k value. It is also demonstrated that the wool transmittance maximum at 1200 cm−1 decreases exponentially with sample thickness, significantly faster than a secondary maximum at 2240 cm−1. Dispersion analysis of the bulk glass reflectance was performed using four Lorentz oscillator terms. The resonance frequencies obtained from the dispersion analysis can be related to the vibration modes of the sodium-silicate glasses, considering the presence of both network-forming and modifying impurities.
Effect of matrix composition and impact angle on the fractional ion yield of Be+ sputtered from oxygen-bombarded silicon and compound semiconductors
Authors: Homma Yoshikazu , Wittmaack Klaus
Published: July 2002

Using two different secondary ion mass spectrometers we have determined fractional ion yields of Be+ sputtered from seven beryllium-implanted semiconductor matrices (Si, GaAs, AlxGa1−x, InGaAs, and InP) by O+2 bombardment. The measurements were performed at five different impact angles θ ranging from near-normal beam incidence, i.e., θ=2°, to θ=42°. The fractional yields δY+Be show a strong matrix dependent variation (up to a factor of more than 100) as well as a pronounced θ dependence. Even though the two instruments differ considerably with respect to the geometry and the strength of the secondary ion extraction field, the matrix-dependent variations in δY+Be were almost the same for the same θ. On the basis of these findings previously reported discrepancies in the magnitude of the Be matrix effect can be attributed almost completely to the θ dependence of the ionization probability. Moreover, it is shown that a universal relationship between the ion yield δY+ and the matrix sputtering yield Y cannot be established because of functional dependence δY+(Y,θ) is different for each impact angle. Further evidence in this respect is obtained from the Y dependence of the ionization probability of Be+, derived by roughly correcting the measured fractional ion yields for θ-dependent variations in transmission of the employed quadrupole based instrument. A first-order correction to the Be+ matrix effect can be obtained from the O+ intensity measured quasisimultaneously with the Be+ intensity.
Electronic transport investigation of arsenic-implanted silicon. II. Annealing kinetics of defects
Authors: Christofides Constantinos , Ghibaudo Gerard , Jaouen Herve
Published: July 2002

A study of the effects of the annealing temperature and time on arsenic-implanted silicon films is reported. ac and dc Hall-effect measurements as a function of temperature and frequency have been employed to characterize arsenic-implanted silicon films. The method of spreading resistance has also been used, allowing measurement of the resistance of the implantation damage layer as a function of depth. These techniques allow one to probe the annihilation processes of damage layer defects as a function of annealing conditions (i.e., temperature and time). The activation energy of the recovery process of the ionic implantation damage, found to be about 0.6 eV, is attributed to a local reconstruction of the implanted layer.
Electrical characterization of GaAs/Al0.30Ga0.70 As p+-n heterojunctions grown by metalorganic vapor phase epitaxy
Authors: Tischler M. A. , Baratte H. , Kuech T. F. , Wang P. J.
Published: July 2002

Electrical transport measurements are very sensitive to the structure of a heterojunction. This sensitivity is used in conjunction with a realistic model for the band diagram to determine the position of the dopant junction relative to the metallurgical junction. This electrical technique involves the determination of an effective barrier height from temperature-dependent I-V measurements and comparison with calculated barrier heights. The sensitivity of the electrical characteristics to the device structure can often be greater than that of secondary ion mass spectroscopy or C-V profiling. GaAs/Al0.30Ga0.70 As p+-n heterojunctions grown under a variety of conditions are used to demonstrate this technique. Growth conditions which produce abrupt zinc profiles are discussed.
Graphoepitaxial growth of germanium on the textured natural crystalline surface relief duplicated on a foreign substrate
Authors: Kanata T. , Takakura H. , Hamakawa Y. , Kubota K.
Published: July 2002

A series of experimental trials was made on the oriented nucleation in the graphoepitaxial growth of germanium. The graphoepitaxial growth was performed from a germanium/metal eutectic alloy solution by scanning a cw argon-ion laser on a silicon-dioxide/tantalum/nickel substrate having a surface of pyramidal relief duplicated from the textured surface of (100) single-crystalline silicon. In the germanium/metal system, the germanium can be grown at relatively low temperatures in the 300–400 °C range by the eutectic effect. The laser-induced recrystallization of an eutectic alloy started at the bottom of the valleys and moved up to the top through the germanium/metal alloy phase. Then the metal was left on the top of the pyramids. When the laser scan was repeated, the surface became flat, and its crystallographic orientation was epitaxially controlled by the surface relief of the substrate.
Useful design relationships for the engineering of thermodynamically stable strained-layer structures
Authors: Vawter G. Allen , Myers D. R.
Published: July 2002

Recent studies have provided sufficient knowledge about the dominant failure mechanisms for lattice-mismatched strained-layer heterostuctures to permit the design of thermodynamically stable strained-layer systems for device applications. We have developed procedures that summarize this knowledge for the working device designer, and apply these relationships to the design of ion-implanted, strained-layer, quantum-well lasers.
Perturbational method for impurity level splitting in the random GaAs1−cPc alloy system
Authors: Hasbun Javier E. , Roth Laura M.
Published: July 2002

A simple perturbational method is used to calculate the impurity level splitting in the random GaAs1−cPc alloy system. For impurities that take the Ga site we calculate the splitting due to the nearest-neighbor disordered anion shell. For impurities that take the As or P site, we calculate the splitting due to the second-nearest-neighbor disordered anion shell. We present results for the splittings as a function of impurity levels in the alloy gap using the Vogl, Hjalmarson, and Dow ten-band model [J. Phys. Chem. Solids 44, 365 (1983)] for semiconductors in the virtual crystal approximation. We compare our work with experiment when possible.
Electronic defect structure in TiO and MnO
Authors: Khowash P. K. , Ellis D. E.
Published: July 2002

The electronic structure, charge distribution, magnetic moment, and binding energies are studied in transition-metal monoxides using the discrete variational method in the embedded scheme within the local density formalism. Defect structures such as 1:0, 2:1, 4:1, and 7:2 (vacancy:interstitial ratio) were evaluated with respect to the ideal structure. Ti loses its moment in the 4:1 structure as the 3d electrons are depopulated in the process of redistribution. Mn shows the highest magnetic moment as in the atomic case but varies over a range of 2.23–4.96 μB depending upon the defect structure. Our calculations predict greater stability for the 2:1 defect structure in TiO and MnO. The interstitial metal ion tends to be in a trivalent state in accord with experiments.
Unipolar corona space charge in wire-plane geometry: A first principles numerical computation
Authors: Li J.-R. , Wintle H. J.
Published: July 2002

We have calculated the space-charge-perturbed ion flow for the wire-plane geometry using coordinate inversion and a finite-difference method to retain the boundary at infinity. The results agree in outline with earlier finite element work, but they show a smooth variation of charge density with angle close to the wire. This suggests that the earlier work [J. L. Davis and J. F. Hoburg, J. Electrostat. 18, 1 (1986)] contains an error. We also show that the commonly used Deutsch assumption that field lines preserve their shape is not particularly good. We note that all calculations, good and poor, reproduce the well-established Warburg (cosine power law) dependence of current density and field on the ground plane, but that careful work is needed to establish the conditions near the emitting wire.
Reduction of the density profile of a field-reversed configuration plasma from detailed interferometric measurements
Authors: Okada S. , Kiso Y. , Goto S. , Ishimura T.
Published: July 2002

In order to obtain a detailed density profile of a field-reversed configuration (FRC) plasma, fast-response multichannel heterodyne quadrature interferometers are constructed. Using these interferometers and assuming a rigid-body radial shift motion of the plasma, a spatially fine-grained line integrated density (∫ n dl) profile at its axial midplane is measured. A radial density profile n(r) is reduced from spline fitting of ∫ n dl. The n(r) is found to be nearly an even function of u(=r2/R2−1, R is the magnetic axis radius) as expected. The n(r) is also obtained by the fitting of a line integral of a model n(r) consisting of a modified rigid rotor (RR) profile which can describe the density steepening near the separatrix of the FRC plasma. When the plasma is fat (xs =separatrix radius/coil inner radius=0.63), the density profile is very near to the RR profile itself given by sech2 (Ku), where K is a constant. When the plasma is slender (xs =0.43), the modification is somewhat pronounced. In both cases n(r) at r=R is flatter but near to the RR profile, and the scale length of the density gradient at the separatrix is about twice the ion gyroradius. Detailed error analyses of the fitting parameters are done to show the range of allowed profiles. Although the fitting is accomplished very well (root-mean-square excursion of the fitted ∫ n dl from the measured one is from 1.9% to 2.5%), much variation of n(r) is still possible.
Kelvin functions for determination of magnetic susceptibility in nonmagnetic metals
Authors: Jardim Renato Figueiredo , Laks Bernardo
Published: July 2002

A method to calculate the real and imaginary parts of the magnetic permeability and susceptibility of nonmagnetic metals by using Kelvin functions is presented. The exact treatment is shown for the massive cylindrical geometry. An expression for a hollow circular cylinder is discussed and expanded to the thin-shell limit.
Nature of interfaces and oxidation processes in Ge+-implanted Si
Authors: Srivatsa A. R. , Sharan S. , Holland O. W. , Narayan J.
Published: July 2002

We have studied the nature of the interfaces between silicon dioxide and germanium-rich layer (SiO2/GexSi1−x) in Ge+-ion implanted and oxidized Si (100) samples. A series of implants were used to study the interfacial roughness as a function of implant dose. Oxidations were carried out at temperatures both above and below the viscous flow point of silicon dioxide (SiO2). In each case, the SiO2/GexSi1−x interface was found to be sharper on an atomic scale compared to the oxide/silicon (SiO2/Si) interface in virgin Si formed after similar oxidation treatments. An enhancement in oxidation was found for the implanted samples over the virgin silicon samples. This enhancement was greater for oxidation carried out at 900 °C for 30 min compared to that at 1000 °C for 20 min. At the higher implant doses, predominantly 60° misfit dislocations were observed at the GexSi1−x/Si interface. The mechanism of oxidation leading to these phenomena is discussed in detail.
Maximum lateral dimensions of laser-induced oxidation of thin tellurium films: A negative feedback effect
Authors: Wautelet M.
Published: July 2002

Thin tellurium films are deposited on glass and irradiated by a continuous Ar+ laser beam. The maximum dimension of the laser-oxidized zone d is measured as a function of the laser beam power P. The temperature T at the end of 180 s of irradiation is measured by an interferometric method. It is found that T is independent of P between 1.3 and 2.4 W. This correlates with the variation of d with P, at constant T, due to negative feedback between optical absorption and oxidation.
On the relaxation oscillation in copper-vapor lasers
Authors: Taniguchi Hiroshi , Saito Hiroshi
Published: July 2002

The possibility of relaxation oscillations in the laser output of a discharge-pumped copper (CuCl) vapor laser is explained qualitatively considering resonance-radiation trapping and collisional effects for experimental results.
Abnormal electron-spin-resonance spectra on [Ca,Y](Ti,Al)O3 perovskite single crystals
Authors: Becker Wolf-Jürgen
Published: July 2002

The X-band electron-spin-resonance spectra of Fe-doped [Ca,Y](Ti,Al)O3 perovskite single crystals show five resonant lines. Two of the five lines have an inverse phase in the first-derivative curve. The possibility of emission transition of a paramagnetic ion in an anisotropic environment and/or in the presence of oscillating distortions is discussed in this paper.
Electron density of the prepinched phase of a cerium (Z=58) vacuum spark plasma obtained from line emission measurements around 1 keV
Authors: Finkenthal M. , Stutman D. , Shalom A. Bar
Published: July 2002

Time-integrated space-resolved spectra emitted from vacuum spark cerium plasmas have been recorded in the 10–15 Å range. Photometric calibration of the spectrograph components, i.e., the RbAP crystal, a noise blocking filter, and the Kodak SC5 photographic plates used to record the spectra, made possible an estimate of absolute brightnesses of individual lines. The electron density of the emitting plasma has been evaluated, comparing experimental line ratios with those predicted by a density-dependent collisional-radiative model in which optical depth effects have been included. The conclusions of the present work are that the emitting plasma dimension is 200–500 μm and the electron density of this region is in the range 7×1019 –3×1020 cm−3.
Modulational instability of a lower hybrid wave in a plasma slab
Authors: Konar S. , Jain V. K. , Tripathi V. K.
Published: July 2002

The modulational instability of a lower hybrid pump is studied in a plasma slab. The coupled mode equations are solved using perturbation technique and growth rate for the four-wave process is obtained. It is found that the instability is possible only for quasimode frequency ω>ωpi. The growth rate increases with pump frequency and mode number, and is quite significant for moderate pump fields.
Photoacoustic monitoring of magnetite-crystal formation from iron(III) hydroxide acetate: Comparison with ESR results
Authors: Iacovacci M. , da Silva E. C. , Vargas H. , Pinheiro E. A. , Galembeck F. , Miranda L. C. M.
Published: July 2002

The formation of crystalline magnetite by 1-h heat treatment of iron(III) hydroxide acetate is described. This amorphous-crystalline solid transformation is monitored by electron-spin resonance and photoacoustic spectroscopies. No significant changes were detected for samples heated below 190 °C. Above this temperature both techniques presented results following a definite pattern, namely, the enhancement of ion mobility leading to particle growth and crystallization for a temperature up to 240 °C and the onset of magnetic ordering of magnetite near this temperature.
Temperature-dependent transmission extended electron energy-loss fine structure of aluminum
Authors: Disko Mark M. , Meitzner George , Ahn Channing C. , Krivanek Ondrej L.
Published: July 2002

Inelastic electron scattering experiments in a transmission electron microscope provide a probe of core electron excitations that have binding energies below 2 keV, and that are localized within submicron diameter sample volumes. Extended electron energy-loss fine-structure measurements which show the variation with temperature of the mean squared relative displacement of aluminum yield a localized measurement of the Debye temperature which is in excellent agreement with macroscopic measurements.
Superconducting transition and Raman spectrum of Y1Ba2Cu3O7−x prepared by polymeric precursor synthesis
Authors: Lee H. K. , Kim D. , Suck S. I.
Published: July 2002

High-Tc superconducting Y1Ba2Cu3O7−x bulk samples were prepared by polymeric precursor synthesis. Resistance, x-ray diffraction, and Raman scattering measurements were performed for sample characterization. The bulk specimen exhibited a sharp superconducting transition at 94.5 K with a 10%–90% transition width of 0.5 K. Four Raman active phonon modes were observed at frequences of 150, 337, 440, and 502 cm−1 in the 120–700 cm−1 region.
Insensitivity of YBa2Cu3O7−x to ionizing radiation
Authors: Clinard F. W. , Foltyn E. M. , Livak R. J. , Peterson D. E. , Coghlan W. A. , Hobbs L. W.
Published: July 2002

The high-temperature superconductor YBa2Cu3O7−x has been irradiated in a transmission electron microscope to investigate the effect of high doses of ionizing energy on the microstructure of this material. Electrons of energies low enough to avoid knock-on displacement damage (80 and 100 keV) were used to achieve radiation doses of 1×1012 Gy at 115 K and 2×1013 Gy at room temperature. Using the criteria of twin fading and formation of extended defects, no microstructural damage was observed. These results indicate that YBa2Cu3O7−x is extremely resistant to damage by radiolytic processes.
Trapping of deuterium by helium bubbles and defects in ion-implanted tantalum
Authors: Lee S. R. , Myers S. M. , Spulak R. G.
Published: July 2002

Nuclear reaction analysis and ion implantation techniques were used to investigate the trapping of deuterium (D) by He bubbles and implantation defects in Ta. A series of four complementary temperature ramp experiments have enabled us to determine that: (1) the binding enthalpy of D at trap sites associated with He bubbles in Ta is 0.53±0.05 eV relative to solution sites; (2) the binding enthalpies of D at implantation defects in Ta are 0.53±0.10, 0.42±0.10, and 0.33±0.10 eV; and (3) the approximate number of He bubble trap sites produced per He atom implanted into Ta is 0.45 for mean He atomic fractions ranging from 1.5% to 2.5%. The measured binding enthalpies are compared with effective-medium theory calculations of the binding enthalpies of both hydrogen chemisorption sites and monovacancy sites containing from one to six trapped hydrogen atoms. This comparison suggests that the strongest 0.53-eV traps associated with implanted He are bubbles which trap hydrogen on their interior surface via a chemisorptionlike mechanism. The strong 0.53-eV defect trap sites are probably vacancy clusters, whereas the 0.42-eV defect traps appear to be monovacancy sites containing one to two hydrogen atoms, and the 0.33-eV sites appear to be monovacancy sites containing three to six hydrogen atoms.
Structural and electrical properties of B- and Ge-implanted Si
Authors: Turan R. , Hugsted B. , Lo/nsjo/ O. M. , Finstad T. G.
Published: July 2002

Ge diffusion after solid-phase epitaxy of Si amorphized by Ge++ implantation has been measured by backscattering spectrometry. Asymmetrically enhanced diffusion is observed for 〈111〉-oriented samples annealed at 1050 °C. A high concentration of twins observed by cross-section transmission electron microscopy seems to be connected to the enhancement. There is a large difference in Ge diffusion as well as defect structure between 〈100〉- and 〈111〉-oriented samples. Hole mobilities and sheet resistivities have been measured and compared for B- and B+Ge-implanted samples. The effect of Ge on the electrical properties is small.
Filamentary structure and transport in corrugated InGaAs/InP superlattices grown by vapor levitation epitaxy
Authors: Allen S. J. , Bastos P. , Cox H. M. , DeRosa F. , Hwang D. M. , Nazar L.
Published: July 2002

Periodic stimulation of a growth instability on (001) vicinal surfaces of InP and InGaAs induces a corrugated growth interface. When this interface is incorporated into a superlattice the two-dimensional quantum well coalesces into a periodic structure comprised of InGaAs filaments buried in an InP matrix. We have measured the transport in this system by contactless submillimeter wave spectroscopy and show that the electron motion is confined to these filaments, and we have determined the electron density and mobility in these submicrometer filaments.
Spectrally agile far-infrared detector using an n-i-p-i superlattice
Authors: Ruden P. P. , Marttila C. A. , Werner T. , Carroll J. E.
Published: July 2002

We propose a spectrally agile far-infrared detector based on an InSb n-i-p-i superlattice. We show that the spectral response of the detector can be tuned with an applied electrical bias that modulates the tunneling-assisted interband absorption coefficient by changing the internal electric fields. Calculations for several possible superlattice designs are presented and the limitation on the design parameters imposed by the tunneling current is discussed. It is shown that the detector can distinguish between blackbodies with temperatures in the range of 200–400 K independent of the distance between the object and the detector. We also present a simple discussion of the response time that can be expected from such a detector and of the noise sources that will limit its performance.
Microfabrication of WO3-based microelectrochemical devices
Authors: Schloh Martin O. , Leventis Nicholas , Wrighton Mark S.
Published: July 2002

A new photolithographic process for the patterning of WO3 is reported. A layer of sputtered polycrystalline WO3 can be patterned by a combination of photolithographic and dry etching processes to selectively cover a fraction of eight Pt microelectrodes each ∼50 μm long, 2 μm wide, and 0.3 μm thick, and spaced 1.2 μm apart. The modified microelectrode arrays were characterized by electrochemistry, surface profilometry, and scanning electron microscopy. A pair of microelectrodes connected by WO3 comprises a microelectrochemical transistor with pH-dependent electrical characteristics based on the pH and potential dependent conductivity of WO3 associated with the reversible electrochemical reaction WO3+nH++ne−⇄HnWO3.
Quantum-confined piezoelectric effect
Authors: Khurgin Jacob
Published: July 2002

A new type of piezoelectric effect, based on strain-induced changes in confinement of the carriers in the asymmetric quantum well structures is described theoretically. This effect can exist in materials that in a bulk form possess a center of inversion symmetry and therefore do not exhibit conventional piezoelectric properties. The magnitude of the piezoelectric coefficient in GaAs/AlGaAs structures is estimated to be a few percent of that in quartz. The various schemes for its enhancement, including possible applications of quantum wires, are discussed.