bluuebunny/crossref_metadata_2025 huggingface dataset:
Domain wall pinning in precipitation hardenable NdFe11Ti-based high coercivity magnet alloys
Authors: Huang Sen-Huann , Chin Tsung-Shune
Published: July 2002

High coercivity precipitation hardenable ThMn12-type (1-12) melt spun alloys were successfully prepared by crystallizing the hard magnetic Nd2Fe14B (2-14-1) phase in the 1-12 matrix of the NdFe11Ti alloy doped with 0.2–0.4 mole fraction (x) of a Nd0.67B0.33 composition. Magnetic properties and a transmission electron microscopy microstructure of these alloys were studied. The domain wall pinning of these alloys was investigated by successively increasing applied magnetizing field and temperature dependence of coercivity at constant field. It was found that the coercivity arises from domain wall pinning of the dispersed 2-14-1 phase. Curve fitting with the Gaunt model depicts that weak pinning prevails at addition fractions of x≤0.25, while strong pinning prevails at addition fractions of x≥ (R18)0.3.
Measurement of breakdown voltages and V-I characteristics of sodium, potassium, cadmium, and zinc vapors using coaxial cylindrical electrodes
Authors: Rajasekaran K. , Naidu M. S.
Published: July 2002

Experimental results of breakdown voltages and V-I characteristics measured for the first time using coaxial cylindrical electrodes over the pressure range 0.006–0.72 kPa in sodium, potassium, cadmium, and zinc vapors are reported. The breakdown voltages in all the vapors are found to obey Paschen’s Law. The breakdown voltages in cadmium and zinc are substantially higher than those in alkaline sodium and potassium, directly in relation to their ionization potentials. The investigations also reveal that the V-I characteristics are pressure dependent and do not exhibit any negative current growth.
Investigation of GaAs/Si material by x-ray double-crystal diffraction
Authors: Li Chaorong , Mai Zhenhong , Cui Shufan , Zhou Junming , Wang Yutian
Published: July 2002

GaAs epilayer films on Si substrates grown by molecular-beam epitaxy were investigated by the x-ray double-crystal diffraction method. The rocking curves were recorded for different diffraction vectors of samples. The results show that the unit-cell volumes of GaAs epilayers are smaller than that of the GaAs bulk material. The strained-layer superlattice buffer layer can improve the quality of the film, especially in the surface lamella. The parameter W′ = Wexpt/(√‖γh‖/γ0/sin 2θB) is introduced to describe the quality of different depths of epilayers. As the x-ray incident angle is increased, W′ also increases, that is, the quality of the film deteriorates with increasing penetration distance of the x-ray beam. Therefore, W′ can be considered as a parameter that describes the degree of perfection of the epilayer along the depth below the surface. The cross-section transmission electron microscopy observations agree with the results of x-ray double-crystal diffraction.
Short-optical-pulse generation from gain-switched laser diodes with two oscillation modes
Authors: Kawaguchi Hitoshi , Carroll John. E.
Published: July 2002

The effect of two-wavelength oscillation for short-optical-pulse generation in laser diodes by sinusoidal current modulation has been investigated using a rate equation analysis. A high peak power and short pulse without a tail can be generated at the shorter wavelength λ2 with the help of carrier damping through carrier-photon conversion at the longer wavelength λ1. This can be obtained provided that the cw threshold current for λ1 is lower than that for λ2 and the gain g2 larger than g1 at the high carrier excitation levels that occur under the conditions of gain switching.
Crystal structures and light absorption spectra of 1,4-dithioketo-3,6-diphenyl-pyrrolo-[3,4-c]-pyrrole
Authors: Arita M. , Fukushima K. , Homma S. , Kura H. , Yamamoto H. , Okamura M.
Published: July 2002

1,4-dithioketo-3,6-diphenyl-pyrrolo-[3,4-c]-pyrrole, which is a good charge generation material for a near-infrared electrophotographic photoreceptor, has three polymorphs called the I, II, and III forms. The I and II forms are transformed into the III form after having been kept in suitable organic solvents. On the other hand, the III form is changed to the I and/or II forms by heat treatment above 320 °C. Among the three polymorphs, only the highly ordered III form shows the necessary and characteristic absorption in the near-infrared region.
Epitaxial Y1Ba2Cu3O7 thin films on CeO2 buffer layers on sapphire substrates
Authors: Denhoff M. W. , McCaffrey J. P.
Published: July 2002

Pulsed laser deposition has been used to deposit Y1Ba2Cu3O7 layer on CeO2 buffer layers on (11_02) sapphire. Both layers are epitaxial with the 〈110〉 direction of the CeO2 layer aligned with the 〈2_021〉 direction of the sapphire substrate. The c-axis Y1Ba2Cu3O7 layer has its 〈100〉 direction alligned with the 〈110〉 direction of the CeO2. Cross-sectional transmission electron microscopy shows the epitaxy to be coherent and the interfaces to be abrupt at an atomic level. The best films have a critical current of 9 × 106 A/cm2 at 4.2 K and lower microwave surface resistance than copper at 77 K and at a frequency of 31 GHz.
Proposed time-of-flight experiments across an amorphous semiconductor heterojunction
Authors: Shapiro Finley R.
Published: July 2002

It is proposed that time-of-flight experiments measuring the current flow across amorphous semiconductor heterojunctions can provide important information on these junctions. Simulations are presented which show the expected current flow across gradual heterojunctions of different steepness, and an abrupt heterojunction modeled as the limit of a gradual heterojunction becoming infinitely steep. An important question is whether experiments will show the same smooth, monotonic dependence on steepness that the simulations show. Once the experiments are performed, it will be possible to use simulation to help understand the results.
Functional minimization and one-dimensional profile inversion
Authors: Hodgson R. J. W.
Published: July 2002

Modern techniques of functional minimization are applied to the one-dimensional profile inversion problem. The procedure is applied to profiles that can be represented as a series of linear ramps. A band-limited knowledge of the transmission function is used to determine the parameters that describe the profile. It is found that simple profiles can be readily determined. For more involved profiles, the method of simulated annealing proves to be helpful in obtaining the correct profile.
Frequency dependence of thermal volume instabilities in high-frequency CO2 laser discharges
Authors: Wester R.
Published: July 2002

The influence of the excitation frequency on the development of thermal volume instabilities in high frequency discharges has been investigated within the scope of an analytical discharge model. Edge effects have been neglected. Stabilizing effects are the local reduction of the electric field strength when locally raising the conductivity, the electron-ion recombination, electron diffusion and heat conduction. The field reduction and the time averaged recombination coefficient depend on the frequency. In the frequency range of some 10 MHz the field reduction and the enhanced recombination are responsible for the stability of the discharges. With increasing frequency the field reduction is less pronounced because of the increasing displacement current leading to the situation that above some 100 MHz of excitation frequency the discharge is no longer stable even in the case of enhanced recombination.
Structure of hydrogen-induced planar defect in silicon by high-resolution electron microscopy
Authors: Muto Shunsuke , Takeda Seiji , Hirata Mitsuji , Tanabe Tetsuo
Published: July 2002

It has been known that introduction of hydrogen into silicon at moderate temperatures results in extended planar defects on {111} planes. The structure of the hydrogen-induced defects in silicon has been investigated by means of high-resolution transmission electron microscopy. As a result of the contrast analysis of the high-resolution images, with the aid of computer simulation, we propose a new structural model, which involves breaking of Si—Si bonds between layers of smaller spacing, connected with three bonds per atom, rather than those of larger spacing with one bond per atom. The broken bonds are considered to be saturated by hydrogen atoms.
Magnetic edge states in a corrugated quantum channel
Authors: Lent Craig S. , Leng Manhua
Published: July 2002

We calculate the band structure of a long ballistic channel whose width is modulated periodically in the presence of a perpendicular magnetic field. The channel is narrowed on one side only, the other wall remaining straight. At zero magnetic field, the periodic modulation of the width produces miniband gaps. As the magnetic field is increased, the gaps disappear. The vanishing of the miniband gaps is related to the suppression of backscattering in edge-state transport discussed by Büttiker [M. Büttiker, Phys. Rev. B 38, 9375 (1988)]. The band structure at high fields consists of free-electron-like bands associated with magnetic edge states, and flat bands associated with localized Landau levels. We calculate the wave functions and current densities associated with these states. The asymmetry in the walls causes electrons moving through the channel in one direction to have a different effective mass from electrons moving in the opposite direction.
Electrophotographic properties and ultraviolet light fatigue of dual- layered photoreceptors incorporating phthalocyanine and hole transport polymers
Authors: Enokida Toshio , Hirohashi Ryo , Kurata Ryuichiro
Published: July 2002

Dual-layered photoreceptors incorporating τ-form metal-free phthalocyanine (τ-H2Pc) for charge generation material and poly(methylphenylsilylene)(PMPS) for charge transport material(CTM) have been studied concerning their electric properties especially in the electrophotographic characteristics. The photoreceptor using PMPS exhibited high sensitivity; however, the fatigue due to ultraviolet(UV) light was observed. We compared them with well-known poly(N-vinylcarbazole) for CTM based on surface potentials, sensitivities, hole carrier mobilities, and conductivities. As a result of Gel permeation chromatography, Fourier transform infrared and x-ray photoelectron spectroscopy spectra before and after UV light irradiation, the PMPS was cleaved into lower molecular weight products and polymerized, which included cross-linking.
Effect of high-temperature treatment on optical-absorption bands in amorphous SiO2
Authors: Dohguchi Nobuyuki , Munekuni Shuji , Nishikawa Hiroyuki , Ohki Yoshimichi , Nagasawa Kaya
Published: July 2002

The intensity change in optical absorption at 3.8, 5.0, and 5.8 eV was measured for thermal treatment up to 1000 °C done on silica glass samples manufactured by various methods. It was found that these absorption bands change differently with heat, depending on the synthesis process of the sample. The 3.8-eV absorption band due to peroxy linkage is found to increase with high-temperature treatment when the sample contains dissolved oxygen molecules within the sample. For the sample with no oxygen molecules, high-temperaturetreatment does not alter the absorption intensity at 3.8 eV. The 5.0-eV absorption band is found to decrease by high-temperature treatment. In the case of an oxygen-containingsample, the reaction of oxygen molecules with oxygen vacancy sites is a cause of this decrease. The 5.1-eV band, which was thought to have no temperature dependence, is found to be annealed at a temperature region around 950 °C.
Intracavity laser absorption spectroscopic investigation of barium desorption from dispenser cathodes
Authors: Daniszewski E. , McCalmont J. , Chrostowski A. , Chaiken J.
Published: July 2002

Intracavity laser absorption spectroscopy was used to measure the number density of neutral ground state barium atoms desorbed from an operating dispenser cathode. The measurement suggests an order of magnitude value of 108 atoms/cm3 at a distance of 5 cm from the emitting surface. This is the first direct state selective measurement of the barium density near to the surface of an operating cathode which can be directly traced to conventional multipass absorption spectroscopy. The value we obtain is consistent with results reported by other workers using less direct methods and allows more detailed statements to be made concerning the chemical state of the Ba at the instant of desorption.
Mechanism for homogenizing electrical properties of semi-insulating GaAs during ingot annealing
Authors: Suemitsu Maki , Terada Koji , Nishijima Masaaki , Miyamoto Nobuo
Published: July 2002

Concentrations of total ionized point defects, neutral and ionized EL2, carbon acceptor, and other shallow donor and acceptor levels in as-grown and as-annealed semi-insulating GaAs crystals were characterized using nuclear magnetic resonance, multiwavelength near-infrared photoabsorption, and Fourier-transformed infrared photoabsorption. In as-grown crystals, shallow donors (XD) and acceptors (XA) of about 2×1015 cm−3 concentration were found to exist. The net donor concentration (NXD − NXA) of these levels showed an excellent positive correlation with the carbon acceptor in its distribution within the wafer, implying the donor’s carbon-acceptor-related origin. An anneal at 850 °C for 24 h diminished these levels. By regarding the intrinsic donor as VAs, the improvement in electrical uniformity during ingot annealing is explained in terms of an annihilation of both intrinsic acceptors and precursors for SiAs acceptors.
MeV proton elastic backscattering analysis of silicon nitride and oxide layers on silicon
Authors: Weilin Jiang , Peiran Zhu , Aihua Dong , Shiduan Yin
Published: July 2002

A simple method for the analysis of concentration ratios N/Si and O/Si in silicon nitride and oxide layers on silicon substrate is presented. 1.95-MeV proton elastic backscattering was used to determine the composition and density. A comparison with 2.1-MeV helium Rutherford backscattering measurements is given. Results are in good agreement with each other. The method is especially useful to analyze samples of 20 000 Å or thicker layers. We conclude that these two techniques are complementary for the measurements of samples with different thickness. A brief discussion has been given on results.
Tribological behavior of C—F bonds in plasma-synthesized fluoropolymers analyzed by polarized infrared microspectroscopy
Authors: Sugimoto Iwao , Miyake Shojiro
Published: July 2002

Tribological structural changes in plasma-produced fluoropolymers are investigated by polarized microinfrared spectroscopy. The olefinic structures, which arise from the defluorination of fluorocarbon frameworks by friction, are enhanced in the friction products remaining in the severely rubbed trace. The C—F bond softening, indicated by a downward shift in the C—F stretching peak, is confirmed in the friction products, comparing with unrubbed film. The degree of bond softening in the friction products increases with increasing the degree of rubbing severeness. Polarization analyses of the C—F stretching band reveal that the carbon frameworks of the friction products remaining in the vigorously rubbed trace are oriented in the rubbing direction.
Auger electron and x-ray photoelectron spectroscopy of monocrystalline layers of KTa1−xNbxO3 grown by liquid-phase epitaxy
Authors: Gutmann R. , Hulliger J. , Hauert R. , Moser E. M.
Published: July 2002

Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), and electron microprobe analysis (EMA) were applied to investigate the chemical composition, impurities, and the homogeneity of thin para- and ferroelectric epitaxial KTa1−xNbxO3 (KTN) layers grown by liquid-phase epitaxy using a KTN-KF flux. AES indicated no Ta/Nb fluctuations within the layer plane and in the growth direction. XPS and EMA determined a F incorporation of 0.8–0.9 mol % for as-grown and 0.6 mol % for annealed samples. Valence analyses with XPS and electron paramagnetic resonance (EPR) revealed only the regular valence state for the B atoms of a (I,V)ABO3 perovskite lattice. An unexpected splitting of the K 2p doublet peak was found for as-grown layers. Structural defects observed by optical microscopy and x-ray topography were attributed to lattice relaxation effects. Optical waveguiding could be achieved for para- and ferroelectric layers.
Linewidth enhancement factor and carrier-induced differential index in InGaAs separate confinement multi-quantum-well lasers
Authors: Grabmaier A. , Fuchs G. , Hangleiter A. , Glew R. W. , Greene P. D. , Whiteaway J. E. A.
Published: July 2002

Quantum-well lasers can achieve a low spectral linewidth because of their high differential gain, leading to a lower linewidth enhancement factor α than for bulk lasers. The differential refractive index and the gain of InGaAs separate confinement multi-quantum-well lasers with two different quaternary barrier layers, have been determined from the spontaneous emission spectra below threshold. The measured value of the α factor is about 2.8 up to 3.5 at the gain maximum for both laser structures. The refractive index and the gain spectra are connected via the Kramers–Kronig relation. Therefore, the differential refractive index and the α factor have been deduced from calculated gain spectra with an additional contribution of the intraband transitions of the free carriers.
Wave interactions with generalized Cantor bar fractal multilayers
Authors: Sun Xiaoguang , Jaggard Dwight L.
Published: July 2002

The reflection and transmission properties of finely divided fractal layers are investigated and characterized. The results for electromagnetic or optical waves normally incident upon generalized Cantor bar fractal multilayers are found for various fractal dimensions and stages of growth. A new exact self-similar algorithm is described which makes use of the self-similarity of the structures to clearly display the underlying physics. This fractal computational scheme provides the reflection and transmission coefficients for fractally distributed layers with extreme economy when compared to traditional approaches. Finally, a method for extracting fractal descriptors from scattered data is discussed. High- and low- frequency regimes are examined.
Theory of operation of the quantum-well injection laser without k selection
Authors: Taylor G. W.
Published: July 2002

The quantum-well laser is described in terms of the appropriate quasi-Fermi levels and Einstein coefficient for stimulated emission. Emission frequencies, thresholds currents temperature dependencies, and linewidths are determined as a function of the quantum-well parameters, the photon lifetime, the temperature, and the emission coefficient. Correlation with existing data is demonstrated.
Wear improvements induced by thermally grown oxide layers and by nitrogen ion implantation
Authors: Reinbold Rolland A. , Kohser Ronald A. , Hale Edward B.
Published: July 2002

Mild steels which have been either thermally oxidized near 300 °C or implanted with nitrogen ions have been wear tested using a modified Falex Lubricant Testing machine. Both these treatments cause similar, much reduced wear rates which are about an order of magnitude better than in untreated samples. Specimens worn after treatments by both methods have been examined in detail using scanning electron microscopy and Auger spectroscopy. It is concluded that the wear induced by oxidation is the same as the wear induced by nitrogen ion implantation. Both of these treatments acted to initiate favorable sustained oxide wear and confirm the Initiator/Sustainer model. Additional studies have been done on oxidized samples using a variety of sample processing techniques and sequences including oxide layer stripping, wear recycling, and annealing. These studies clearly show that favorable wear results were caused by the grown oxide layer and not by the heat treatment. Also, it has been found that the favorable oxide wear can be stopped and started numerous times since it is able to reinitiate and sustain itself. However, if a worn oxide layer is stripped from a sample just prior to the wear run, favorable wear does not occur unless the sample was oxidized or favorably worn in the last few weeks. This occurs because wear favorable chemistry at the oxide/metal interface anneals at room temperature. Other discussions of the wear initiating and sustaining processes are presented.
Interaction of a harmonic wave with a dynamically transforming inhomogeneity
Authors: Mikata Yozo , Nemat-Nasser S.
Published: July 2002

The elastodynamic response of the transformation-toughened ceramics under a time-harmonic stress wave is investigated. A phenomenological model is proposed to describe the situation, which involves the interaction between an incident stress wave and a dynamic inhomogeneity with a stress-induced martensitic transformation. The most important assumption made in this model is that the stress-induced transformation can be treated as completely reversible. The solution for this model is obtained by combining solutions to a scattering problem, a dynamic inhomogeneity problem, and a static inhomogeneity problem. An exact closed form solution is obtained for the dynamic inhomogeneity problem. The numerical results for the zirconia-toughened ceramics suggest that, under the high-frequency dynamic loading, the transformation-toughened ceramics might lose its toughness due to a relatively large tension field caused by the dynamically transforming zirconia particle.
On the relationship between the surface composition of the substrate and the Schottky barrier height in Au/n-CdTe contacts
Authors: Van Meirhaeghe R. L. , van de Walle R. , Laflère W. H. , Cardon F.
Published: July 2002

The variation of the Schottky barrier height ΦB of Au/n-CdTe contacts with the Cd/Te ratio at the substrate’s surface has been investigated. X-ray photoelectron spectroscopy measurements show that this ratio increases with the anneal temperature Ta up to 330 °C. The Schottky barrier height reaches a maximum for near stoichiometric substrates. Mixed regions of Te and Au, due to etching and subsequent surface disruption by Au, determine ΦB at low Ta. The ΦB value as expected for the ideal Au/n-CdTe contact (following the work-function model) is found for stoichiometric surfaces. At high Ta an increasing nonstoichiometry produces decreasing ΦB values. Our measurements show that the interfacial reactivity decreases with the number of defects. This offers us a general explanation for the observed ΦB behavior, based upon reactivity at nonstoichiometric surfaces.
Characterization of growth interruption interface by mobility profiling
Authors: Takebe T. , Shirakawa T. , Murai S. , Tada K.
Published: July 2002

A mobility profiling technique using a field-effect transistor has been successfully applied to characterize the growth interruption interfaces of organometallic vapor-phase epitaxial Si-doped n-GaAs layers. The interface was formed by interrupting the supply of TMGa and SiH4 for certain lengths of time under a pressure of flowing AsH3. The 30-s interruption interface showed a decrease in the carrier concentration and an increase in the mobility, as obtained from the gate capacitance-voltage and transconductance-voltage characteristics. A quantitative analysis led us to a conclusion that the interface in question is not compensated by acceptor impurities or defects, in contrast with an easy conclusion usually deduced only from the carrier concentration profile, but has an effective reduction of Si doping level. A secondary-ion mass spectroscopic (SIMS) depth analysis of Si and C atoms supported the above-mentioned conclusion. The 60-s interruption, however, showed an extremely low drain current, which was caused by overcompensation of Si by C pileup at the interface, as confirmed from the SIMS depth profile. Thus, it was found that electrical compensation of the interface rapidly proceeds during 30–60-s interruption. The mobility profiling, therefore, provides a sensitive and powerful tool for growth interruption analysis.
The nonproportionality of interface-trap generation to hole trapping efficiency in metal-oxide-silicon devices
Authors: Chen I. C. , Wei C. C. , Teng C. W.
Published: July 2002

The susceptibility to hole trapping of the gate oxide of a metal-oxide-silicon (MOS) device is not necessarily proportional to the efficiency of interface trap generation at the Si-SiO2 interface, which is widely believed due to the recombination of electrons and trapped holes in the oxide close to the interface. In this study, an oxide given a high-temperature (1000 °C) anneal, which increases the hole trapping efficiency of the oxide, is shown to have much less generated interface traps compared to a normal oxide (without high-temperature annealing) upon exposing to ionizing radiation with subsequent electron injection, or high-field injection alone. Under high-field tunneling injection, the electron fluence required to create a certain density of interface trap is an order of magnitude higher for the annealed oxide compared to the normal oxide. These results could provide a possible direction for improving the reliability of the gate oxide of a MOS field-effect transistor.
Low-temperature mesotaxy of ion beam synthesized ErSi2
Authors: Golanski A. , Park J. L. , Pennycook S. J. , White C. W.
Published: July 2002

High doses (7×1016–1.3×1017/cm2) of 170-keV Er+ ions were implanted into single-crystal Si at an implantation temperature of Ti=520 °C. During Er implantation ErSi2 crystallizes as coherent precipitates within a crystalline Si matrix. During the subsequent annealing at 800 °C a discontinuous buried layer of the single crystalline ErSi2 is formed. Implanted and annealed samples were subsequently reimplanted with 170-keV Er+ ions at 250<Ti<520 °C. The second implantation results in a mesotaxial growth of the previously formed buried single-crystal ErSi2 layer for implantation temperatures Ti≳300 °C where ion beam induced, defect mediated diffusion of Er atoms in the Si matrix occurs during the implantation process.
Characteristics of a sputtered Y-Ba-Cu-O thin-film dc superconducting quantum interference device prepared by rf sputtering
Authors: Goto Toshinari , Ying Xing Bao , Park Chan Hoon , Takeda Yuji , Usami Koichi , Kobayashi Tadayuki
Published: July 2002

A dc superconducting quantum interference device (SQUID) is fabricated on an amorphous Y-Ba-Cu-O film by a photolithographic technique and successive post-annealing treatment. The SQUID shows periodic and symmetric behavior in the voltage versus magnetic-flux curves (V-Φ curves). No multiple periodicities are observed. The transfer function ∂V/∂Φ for output voltage is about 90 and 20 μV/Φ0 at 4.2 and 56 K, respectively. It is expected that the SQUID contains only two symmetric active Josephson junctions.
Growth of pseudomorphic insulating HoF3 layers on Si(111)
Authors: Griffiths C. L. , Macdonald J. E. , Williams R. H.
Published: July 2002

We report the successful growth of pseudomorphic, trigonal structured HoF3 insulating layers, stable at room temperature, on the Si(111) surface. Normally the tysonite structure is only stable at temperatures above 1070 °C [R. E. Thoma and G. D. Brunton, Sov. Phys. Crystallogr. 18, 473 (1966)]. A phase transition to the lower-temperature orthorhombic structure is observed for a thickness of around 12 Å, consistent with the relaxation of elastic strain in the insulating layer.
A novel approach for including band-structure effects in a Monte Carlo simulation of electron transport in silicon
Authors: Vogelsang Th. , Hänsch W.
Published: July 2002

We present a novel approach for including the effects of realistic silicon band structure in the simulation of electron transport with a Monte Carlo method. This will be achieved by an electron effective-mass and energy–over–wave-vector relation, which are derived directly from the density of states. Consistent with this model, the scattering rates as well as the equations of motion are determined by the density of states. With our approach the computation tables in three-dimensional momentum space can be replaced by one-dimensional tables in energy space. The necessary amount of memory size and table lookup time is therefore significantly reduced. The number of free parameters in our model is not higher than in the full band-structure model. We show by comparison with full band-structure Monte Carlo and experimental results that there is no loss in physical meaning by the use of the new method.
Layer thickness variations and x-ray diffraction patterns: A general treatment
Authors: Hollanders Mark A. , Thijsse Barend J.
Published: July 2002

Using a columnar approximation, the effect of random layer thickness variations in a compositionally modulated material on the x-ray diffraction pattern is expressed in terms of their distribution function. It is demonstrated that the Fourier transform of this distribution function appears in a function describing the effective phase relations between the individual layers. Features of multilayer diffraction patterns, such as the presence or absence of superlattice peaks, are explained. It is also shown that when the Fourier transform of the thickness variation distribution changes sign from positive to negative, the superlattice peaks change position from integral to half-integral order. The effects of thickness variations are compared with those of interface roughness.
Characterization of metalorganic chemical vapor deposition grown GaAs on Si by means of x-ray scattering radiography
Authors: Suzuki Yoshifumi , Chikaura Yoshinori
Published: July 2002

Lattice mismatched heteroepitaxial layer GaAs on Si grown by metalorganic chemical-vapor deposition have a crystal mosaicity which gives a local rocking curve of x-ray diffraction as broad as several hundreds of sec in arc. Since, for such a locally imperfect crystal, conventional x-ray topography provides little significant information, x-ray scattering radiography has been applied to characterizing a GaAs layer on silicon. Microcomputer-assisted x-ray scattering radiography enabled us to observe a quantitative orientation distribution for the specimen. The internal structure of the epitaxial layer was quite different from that of the substrate. A dislocation or a bundle of dislocations observed in the Si substrate did not propagate through the GaAs epitaxial layer. Lattice planes in the epitaxial layer and the substrate were found to vary their orientation 6 min in arc and 2–3 min in arc, respectively, in a specimen of 6×6 mm2 dimensions. The bending is concave. The bending mechanism is explained primarily by the difference in thermal expansion coefficients. It is proposed that climb motion of misfit dislocations may cause the lattice bending of the epitaxial layer.
Reaction of oxygen with in situ H2S-treated GaAs (001) surfaces
Authors: Kawanishi H. , Sugimoto Y. , Akita K.
Published: July 2002

The reaction of oxygen with H2S-treated GaAs (001) surfaces was studied using Auger electron spectroscopy and reflection high-energy electron diffraction. GaAs surfaces in situ treated with H2S gas were exposed to pure oxygen gas with and without simultaneous light illumination of a halogen lamp. It was shown that the oxygen uptake on a H2S-treated surface is much less than that on an untreated bare GaAs surface. Surfaces exposed to oxygen were heated in an ultrahigh-vacuum environment in order to study the desorption of the reacted oxygen. The oxygen Auger signal was found to easily disappear when the surface was heated to 520 °C, leaving sulfur atoms on the surface. The oxide formed on a bare GaAs surface with light illumination was found to be relatively thick; it did not desorb completely until it was heated to about 550 °C. These results indicate that oxide on a H2S-treated surface is formed only on the top surface.
InGaAs-GaAs-AlGaAs strained-layer laser with heavy silicon doping
Authors: Sin Y. K. , Hsieh K. Y. , Lee J. H. , Hwang Y. , Kolbas R. M.
Published: July 2002

Photoluminescence characteristics of uniformly silicon- and beryllium-doped pseudomorphic InGaAs-GaAs-AlGaAs single- and multiple-quantum-well heterostructures grown by molecular-beam epitaxy are studied. Red shifts in the photoluminescence peaks are obtained from uniformly silicon-doped single-quantum-well samples with respect to undoped samples. Uniformly beryllium-doped InGaAs-GaAs multiple quantum wells totally intermix during materials growth. Also, the effect on laser performance (laser thresholds and emission spectra) by silicon doping is demonstrated with an InGaAs-GaAs-AlGaAs strained-layer laser (grown by molecular-beam epitaxy) with a heavily silicon-doped quantum well. The low laser threshold, kink in light versus current, shift in emission wavelength, and two emission peaks are observed, and these characteristics are believed to be due to heavy silicon doping.
Electric field and Doppler emission profile measurements in an obstructed hydrogen discharge
Authors: Ganguly B. N. , Garscadden Alan
Published: July 2002

Spatially resolved electric field, emission intensity, and linewidth profiles have been measured in a dc low current, low pressure obstructed hydrogen discharge with a planar electrode configuration. The polarization-dependent Stark splitting of the Hβ line has been used to measure the electric field. The axial electric field was high over the entire interelectrode space. The radial variations of electric field and emission intensity show that the discharge is almost annular. The Hα spectra indicate that, except in a plasma region at an edge of the anode, heavy-particle excitations exceed electron-impact excitation and that the kinetic energy of much of the excited atomic hydrogen was as high as 450 eV. This dc discharge exhibits current-voltage oscillations which appear to be caused by the periodic collapse of the wall sheath. For these discharge conditions, the Hβ Stark spectrum yields electric field measurements with an accuracy of better than 5%.
Comment on ‘‘Coupled ac photocurrent and photothermal reflectance response theory of semiconducting p-n junctions I and II’’ [J. Appl. Phys. 66, 5572 and 5584 (1989)]
Authors: Sablikov V. A.
Published: July 2002

It is shown that the recent theory of photothermal phenomena in semiconductor p-n junctions by Mandelis is incorrect because it ignores the heat generated by the photocurrent passing the junction barrier (the Peltier heat). The relative contribution of heat sources caused by the current and by carrier recombination to the total heating is discussed for open circuit and short circuit regimes.
Rapid thermal annealing effect on near-surface stoichiometry of GaAs by heavy-ion Rutherford backscattering
Authors: Gagnon G. , Houdayer A. , Currie J. F. , Azelmad A.
Published: July 2002

We have studied the near-surface stoichiometry profiles of GaAs wafers subjected to rapid thermal annealing in a forming gas environment using the Rutherford backscattering (RBS) technique with a 33-MeV 16O beam. Our measured profiles quantify the extent of arsenic loss at uncapped wafer surfaces for high-temperature anneals. We have observed that a two-temperature step anneal results in a stoichiometry profile which is nearly RBS indistinguishable from that of an unannealed wafer.
Observation of galvanomagnetic voltages at a magnetic domain wall in Ni-Fe films
Authors: Gopalaswamy S. , Berger L.
Published: July 2002

A Ni81Fe19 film of 110 nm thickness is traversed by a dc current density normal to the easy axis. Two sharp tungsten wires serve as potential probes, distant by 210 μm along the easy axis. A charged wall, oriented at an angle to the easy axis, is made to creep slowly across the sample by applying dc easy axis and 60-Hz hard axis magnetic fields. The dc voltage between the probes is found to vary whenever the wall passes by the probes. The variation has the form of a voltage peak of ≂40 μV typical height. These peaks are caused by the planar Hall effect, in combination with a canting of the domain magnetization near the charged wall. In the case of a current parallel to the easy axis and normal to the line joining the probes, a steplike voltage variation ≤150 μV is observed for an uncharged wall in the presence of a dc hard axis field. Planar Hall effect and (field induced) domain canting are again responsible.
Magnetic properties and local ordering during thermal annealing of amorphous Fe75Ni5B15Si5 films
Authors: Oliver S. A. , Harris V. G. , Vittoria C. , Elam W. T. , Kim K. H. , Hamdeh H. H. , Alhabash M.
Published: July 2002

The evolution of magnetic properties and local atomic ordering during thermal annealing has been studied for amorphous Fe75Ni5B15Si5 thin films. Resistivity, vibrating sample magnetometer (VSM), ferromagnetic resonance (FMR), extended x-ray absorption fine structure (EXAFS), and Mössbauer effect (ME) measurements were taken on samples annealed at various temperatures ranging to film crystallization. The as-deposited samples are in a close-packed structure with little short-range order. Samples annealed above 200 °C show ordering of the boron shell, but no indication of long-range ordering. With the exception of the anisotropy and coercive fields, no change in the magnetic or microwave magnetic parameters is observed for these samples prior to crystallization. Samples annealed above 400 °C show indications of crystallization for all measurements.
Solid-liquid interfacial energy of the Bi0.7Pb0.3SrCaCu1.8Ox glass
Authors: Nishi Yoshitake , Manabe Toyohisa , Watanabe Shigemi , Igarashi Akira , Mikagi Kaoru
Published: July 2002

The solid-liquid interfacial energy is estimated by use of the nucleation frequency of isothermal crystallization on aging in Bi0.7Pb0.3SrCaCu1.8Ox glassy samples above glass transition temperature. The value of solid-liquid interfacial energy Q is about 74.7 mJ/m2. The Q value is often expressed by use of enthalpy change ΔHf, Avogadro’s number N and molar volume V; Q = CΔHf/(N1/3V2/3). The constant C obtained is 0.38, which is between 0.32 for covalent bonded elements and 0.45 for metals.
Polarization reversal and thermally stimulated discharge current in a vinylidene fluoride trifluoroethylene copolymer
Authors: Guy I. L. , Das-Gupta D. K.
Published: July 2002

Polarization reversal in a ferroelectric copolymer of vinylidene fluoride and trifluoroethylene is observed in a circuit with a large time constant. The contributions of the ferroelectric and nonferroelectric phases in the copolymer can be identified in the reversal currents. If the copolymer is poled at high temperature, then reversal currents measured subsequently at lower temperatures display an asymmetry which is consistent with the accumulation of space charge in the copolymer. Shifts in successive reversal currents indicate that this space-charge accumulation dissipates slowly during polarization reversal. Thermally stimulated discharge currents from poled samples, and from samples with partially reversed polarization, indicate that there may be two populations of dipoles in the copolymer which are affected to different degrees by the space charge.
Natural buffer layer in DyBa2Cu3O7−x films grown on Si by molecular beam epitaxy
Authors: Nordman C. A. , Wang T. , Chandrasekhar N. , Beauchamp K. M. , Achutharaman V. S. , Schulze R. K. , Spalding G. C. , Lin Z-H. , Evans J. F. , Goldman A. M.
Published: July 2002

Growth of a natural buffer layer has been observed for DyBa2Cu3O7−x films grown on Si substrates. The best DyBa2Cu3O7−x film, grown by molecular beam epitaxy with ozone as a source of activated oxygen, was 2300-Å thick, highly c-axis oriented, and had a resistive-transition onset at 90 K and zero resistance by 70 K. The natural buffer layer, which grew at the interface of the DyBa2Cu3O7−x film and the Si substrate, consisted of Si, Ba, and O. Transmission electron microscopy on this film revealed a 150-Å amorphous layer, whereas Auger electron spectroscopy depth profiling showed 400 Å of chemical interdiffusion.
Effects of in situ treatment on InGaAs/InP heterointerfaces produced by organometallic chemical vapor deposition regrowth
Authors: Hong W-P. , Caneau C. , Hayes J. R. , Bhat R. , Chang G. K. , Nguyen C. , Jeong Y. H. , Hadjipanteli S. , Illiadis A. A.
Published: July 2002

The properties of heterostructures containing an InGaAs/InP heterointerface generated by organometallic chemical vapor deposition regrowth have been investigated. Regrowth of InGaAs on InP was carried out after different sample preparations including wet chemical etching and in situ treatment prior to the regrowth. The electrical properties of the heterointerface were studied by performing deep-level transient spectroscopy measurements. An electron trap was observed in the interface region of the samples either in situ etched with HCl gas or annealed under PH3 overpressure. Temporal pulse response measurements were employed to study the effects of this electron trap on the optical performance of p-i-n photodetectors containing this regrown heterointerface.
Low-threshold GaAs/AlGaAs quantum-well lasers grown by organometallic vapor-phase epitaxy using trimethylamine alane
Authors: Hobson W. S. , van der Ziel J. P. , Levi A. F. J. , O’Gorman J. , Abernathy C. R. , Geva M. , Luther L. C. , Swaminathan V.
Published: July 2002

We have utilized a new aluminum source, trimethylamine alane (TMAA), in the growth of graded-index separate-confinement heterostructure single quantum-well GaAs/AlGaAs laser structures by low pressure (30 Torr) organometallic vapor-phase epitaxy. We find lower carbon and oxygen incorporation in AlGaAs epilayers using TMAA since it does not contain a direct Al–C bond and it is not susceptible to the formation of volatile Al–O containing compounds. The oxygen and carbon concentrations were below the detection limits (< 5 × 1016 cm−3 and < 3 × 1016 cm−3, respectively) of the secondary ion mass spectrometry measurements. Broad-area lasers with 10-nm quantum wells and Al0.45Ga0.55As cladding layers exhibited threshold current densities of 140 A cm−2 for cavity lengths of 1 mm, internal quantum efficiencies of 81%, and intrinsic losses of 1.6 cm−1. These results demonstrate that extremely high-quality AlGaAs and GaAs quantum wells can be grown with TMAA.
Photoinduced changes in the optical absorption of gallium arsenide doping superlattices
Authors: Tobin Mary S. , Bruno John D.
Published: July 2002

Linear absorption coefficients and photoinduced changes in the absorption coefficient are experimentally determined for two doping superlattice structures. The linear values are compared with the values for a semi-insulating and an n-doped substrate of GaAs. The results for the absorption and light-induced absorption changes are qualitatively consistent with a Franz–Keldysh analysis.
Topographic contrast of monatomic surface steps on Si(100) in secondary electron microscopy
Authors: Drucker Jeff
Published: July 2002

A phenomenonological model of topographic contrast in secondary electron microscopy is presented. This model involves exponential attenuation of isotropically generated secondary electrons. The effect of primary beam diameter and the material dependent secondary electron attenuation length on secondary electron images is demonstrated by explicitly computing linescans of images of straight surface steps. These computed linescans are directly compared with those obtained from monatomic surface steps on Si(100) imaged at normal incidence in an ultrahigh-vacuum scanning transmission electron microscope. An asymmetry in the experimental linescan cannot be fit by any combination of model parameters suggesting that this contrast is not simply due to surface topography. A simple explanation for the contrast reversal observed in secondary electron images of surface steps when the primary beam changes direction from the upstairs to the downstairs direction is presented. The possibility of determining secondary electron emission parameters and extracting surface chemical and electronic information using high spatial resolution secondary and Auger electron imaging is briefly discussed.
Native-oxide-masked Si impurity-induced layer disordering of AlxGa1−xAs-AlyGa1−yAs-AlzGa1−zAs quantum-well heterostructures
Authors: El-Zein N. , Holonyak N. , Kish F. A. , Sugg A. R. , Richard T. A. , Dallesasse J. M. , Smith S. C. , Burnham R. D.
Published: July 2002

Data are presented showing that the native oxide that can be formed on high Al composition AlxGa1−xAs (x≳0.7) confining layers commonly employed on AlxGa1−xAs-AlyGa1−yAs-AlzGa1−zAs (y≳z) superlattices or quantum-well heterostructures serves as an effective mask against Si diffusion, and thus impurity-induced layer disordering. The high-quality native oxide is produced by the conversion of high-composition AlxGa1−xAs (x≳0.7) confining layers via H2O vapor oxidation (≳400 °C) in N2 carrier gas.
Optoelectronic measurement of semiconductor surfaces and interfaces with femtosecond optics
Authors: Zhang X.-C. , Auston D. H.
Published: July 2002

The basic concepts and preliminary applications of optically induced electromagnetic radiation from semiconductor surfaces and interfaces by using femtosecond optics are discussed. This submillimeter-wave radiation provides a novel optoelectronic technique to study semiconductor electronic surface and interface properties with a contactless approach. The amplitude and phase of the electromagnetic radiation from the semiconductor surfaces depend on carrier mobility, impurity doping concentration, and strength and polarity of the static internal field. A large selection of bulk, epitaxial layer and superlattice samples from III-V, II-VI and group-IV semiconductors has been tested. The orientation and strength of the static built-in fields of a wide range of semiconductor surfaces, such as surface depletion, metal/semiconductor Schottky, p-n junction and strain-induced piezoelectric fields, can be determined and estimated.
Evolution of vacancy ordering and defect structure in epitaxial YSi2−x thin films on (111)Si
Authors: Lee T. L. , Chen L. J. , Chen F. R.
Published: July 2002

The evolution of vacancy ordering and defect structure in epitaxial YSi2−x thin films on (111)Si have been studied by both conventional and high-resolution transmission electron microscopy. Epitaxial YSi2−x with an ordered vacancy structure was grown on (111)Si by rapid thermal annealing. In samples annealed at 500 °C for 120 s epitaxial YSi2−x was found to form. After annealing at 600 °C for 15 s, the appearance of additional diffraction spots is attributed to the formation of an ordered vacancy superstructure in the epitaxial YSi2−x thin films. In samples annealed at 600 °C for longer time or higher temperatures, the splitting of extra diffraction spots is correlated to the formation of an out-of-step structure. Streaking of the split diffraction spots in the diffraction pattern is attributed to the presence of an out-of-step structure with a range of M values. The M was found to settle down to 2 after high-temperature and/or long time annealing. Planar defects in YSi2−x films were analyzed to be stacking faults on {101̄0} planes with 1/6 〈1̄21̄3〉 displacement vectors. Computer simulation was carried out to determine the atomic structure of stacking fault. The simulated images are seen to match rather well with experimental images taken under two different values of defocus.
Phenomenological analysis of the magnetocrystalline anisotropy of the Co sublattice in some rhombohedral and hexagonal intermetallic structures derived from the CaCu5 unit cell
Authors: Pareti L. , Solzi M. , Marusi G.
Published: July 2002

A comparative study of the saturation magnetization, Curie temperature, and magnetocrystalline anisotropy in several rhombohedral and hexagonal Y-Co compounds was done. The considered phases YCo3, Y2Co7, Y5Co19 (rhombohedrals), YCo5+z, and Y2Co17 (hexagonals) are all derived from the hexagonal CaCu5 unit. The variation of the magnetic properties in the different compounds was found to be strongly correlated to the cobalt content. In particular the Co sublattice anisotropy varies linearly with the Co content in the phases, while it seems to be not affected by structural changes (rhombohedral-hexagonal). The highest anisotropy of Co was found in YCo5, every modification of the CaCu5 cell resulting in a weakening of the overall axial anisotropy. An evaluation of the strength of the Co anisotropy in the 2c, 3g, and dumbbell sites was done using a phenomenological model.