bluuebunny/crossref_metadata_2025 huggingface dataset:
Comprehensive investigation of polish-induced surface strain in 〈100〉 and 〈111〉 GaAs and InP
Authors: Hang Z. , Shen H. , Pollak Fred H.
Published: July 2002

This paper presents the results of a systematic and extensive investigation of polish-induced surface strain in 〈100〉 and 〈111〉 GaAs and InP using Raman scattering from the longitudinal optical (LO) phonon modes. By using various lines of an Ar-ion laser it was possible to accomplish nondestructive depth profiling. To account for the observed line-shape changes we have used a model which is based on the convolution of the penetration depth of the light and skin depth of the polish-induced surface strain. From such an analysis we have obtained the polish-induced surface strain, skin depth of the strain, and inhomogeneous broadening. For the 〈100〉 surface, the strain is about 2%–3% in both materials and the skin depth (100–500 Å) is relatively independent of particle size. In contrast, for the 〈111〉 surface, the average surface strain is only about 0.6% for GaAs and 1.2% for InP and the skin depth is of the order the particle size. The dependence of the strain skin depth on polish time also has been studied. A qualitative argument based on polish-induced bond breaking is proposed to explain why surface strain for 〈111〉 is considerably less than for 〈100〉 and why the strain is compressive for both surfaces. Using a one-dimensional diffusion model, we can successfully explain the depth dependence of the polish-induced strain and the polish time dependence of the damage skin depth. This analysis yields a diffusion coefficient for the polish-induced strain for the two surfaces. Our diffusion model is consistent with the conventional model of chemomechanical polishing of compound semiconductors.
Iodine-incorporated polystyrene for laser marking
Authors: Torres-Filho Afrânio , Franzan Antonio H.
Published: July 2002

An iodine-incorporated polymeric film, based on a solid-state charge-transfer complex between polystyrene and iodine, is described. The material prepared, originally red, can be marked (changing to transparent) by an Ar+ laser beam. Possible photochemical and photothermal mechanisms for such transformation are proposed. The laser print can be erased by exposing the film to I2 vapor. Besides its use as a laser-beam diagnostic material, possible future applications include optical storage devices.
HgI2 near-band-gap photoluminescence structure and its relationship to nuclear detector quality
Authors: Wong D. , Schlesinger T. E. , James R. B. , Ortale C. , van den Berg L. , Schnepple W. F.
Published: July 2002

The low-temperature photoluminescence spectra of several mercuric iodide detectors and off-stoichiometric bulk material have been characterized. Phonon energies have been determined with Raman spectroscopy over a range of temperatures. In earlier work some of the near-band-gap photoluminescence features were identified as phonon replicas. After careful examination of Raman and photoluminescence data, we find that one or perhaps more of these features is probably due to shallow electronic levels related to native defects. Suggestions as to the relationship between photoluminescence peaks and detector quality are made.
The investigation of lineage propagation in liquid-encapsulated Czochralski GaAs using cathodoluminescence imaging of cleaved wafers
Authors: Noad J. P.
Published: July 2002

A novel technique, using a combination of conventional KOH dislocation etching and cathodoluminescence imaging of cleaved wafers, has been used to investigate the propagation of lineage features in liquid-encapsulated Czochralski GaAs. Using this technique, three-dimensional pictures of these dislocation structures have been obtained.
Optical and electro-optic properties of cyanotolanes and cyanostilbenes: Potential infrared liquid crystals
Authors: Wu Shin-Tson , Cox Robert J.
Published: July 2002

Optical and electro-optic properties of some highly conjugated nematic liquid crystals (LCs): 4-cyano-4′-n-alkyltolanes (n-CDP) and 4-cyano-4′-n-alkylstilbene (n-CS) were studied at elevated temperature. Results are compared with 4-cyano-4′-n-pentylbiphenyl (5CB). These LCs exhibit large birefringence, small viscoelastic coefficient, and low threshold voltage. Their potential application for modulating visible and infrared radiation is addressed.
The effect of the entropy wave on sound and electromagnetic waves in ferromagnetic metals
Authors: Dewar G.
Published: July 2002

The role entropy plays on the interconversion of gigahertz sound waves and electromagnetic waves in ferromagnetic metals has been studied. In linearized form the heat flow equation leads to an entropy wave in the ferromagnet. For the simple configuration in which the microwave magnetic field and an applied, static magnetic field are parallel and in the plane of a ferromagnetic metal film, two pairs of terms arise which couple the entropy wave to the electromagnetic wave and the sound wave. The coupling to the electromagnetic wave is peculiar to ferromagnets and its primary effect is to modify the skin depth. The coupling to the sound wave controls whether the sound propagates under adiabatic or isothermal conditions. The frequency at which the transition from adiabatic to isothermal sound occurs can be low enough to affect the accuracy of experiments to measure the ferromagnet’s exchange stiffness constant by observing the spin wave/sound wave dispersion relation crossing.
dc and ac magnetic field effects in LaBaCuOx, YBa2Cu3O7−x, and other high-T
c superconductors
Authors: Flippen R. B. , Askew T. R.
Published: July 2002

Small (<300 Oe) dc magnetic fields are found to significantly lower the superconducting transition temperature Tc and change the shape of the magnetic flux exclusion M vs T curve in powder compactions of La2−xBaxCu3Oy, YBa2Cu3O7−x, and other high-Tc materials. dTc/dH of 0.02 to 0.08 deg/Oe with Hc1 less than 20 Oe near Tc are typical. The M vs T curve and the value of Hc1 are sample dependent. The results are interpreted in terms of the effect of particle size and size distribution on the material magnetic penetration depth. Measurements of the real and imaginary parts of the magnetic susceptibility show that the latter is frequency dependent over the range of 0.1–10 kHz when measured with an ac mutual inductance technique. Assuming that the material can be considered as a network of Josephson junctions, the temperature dependence of the imaginary component of the susceptibility can be used to calculate a value for the superconducting energy gap.
Magnetic and structural properties of melt-spun rare-earth transition-metal intermetallics with ThMn12 structure
Authors: Singleton E. W. , Strzeszewski J. , Hadjipanayis G. C. , Sellmyer D. J.
Published: July 2002

The magnetic and structural properties of melt-spun R8Fe84Ti8 with R=Nd, Sm, Dy, Gd and R8(Fe,Co)76[V(Mo)]16 with R=Nd, Sm have been studied with x-ray diffraction, transmission electron microscopy, and magnetic measurements. The tetragonal ThMn12-type structure was found in all alloys after annealing at about 700 °C. The Curie temperature (Tc) of the as-spun amorphous samples was in the range of 40–100 °C. Crystallized Nd8(Fe1−xCox)84Ti8 samples with the 1:12 structure have a Tc around 250 °C for x=0, reaching the value of 660 °C for x=0.5 and then decreasing again to 490 °C for x=1. ac susceptibility studies on Co-substituted samples showed magnetic transitions in the temperature range 100–200 K. The coercivity was found to be strongly dependent on the microstructure. The highest value of Hc (2 kOe) was obtained in Sm-Fe-Ti samples with a grain size about 500 Å. The upper value of Hc is low because of the presence of some α-Fe in crystallized ribbons.
Magnetic behavior and anomalous thermal expansion of Nd2(Fe1−xMnx)14B
Authors: Cheng Ben-pei , Fu Shou-can , Yang Ying-chang , James William J.
Published: July 2002

Magnetic properties of Nd2(Fe1−x Mnx) 14B, where x equals 0.00, 0.10, 0.20, 0.30, and 0.40, are presented. All of these compounds crystallize in the tetragonal structure, space group P42/mnm. X-ray diffraction experiments in a temperature range from 77 to 800 K have been carried out in order to study the anomalous thermal expansion by measuring the thermal variation of the lattice parameters a and c. The effect of substituting Fe with Mn on the thermal expansion anomalies of Nd2(Fe,Mn)14B is discussed in comparison with that of Nd2(Fe,Al)14B and Nd2(Fe,Co)14B.
Three-dimensional excess carrier distribution in semiconductor imaging arrays
Authors: Levy David , Schacham Samuel E.
Published: July 2002

The distribution of excess carriers in the three dimensions of a semiconductor in closely packed sensing arrays is analytically derived using a novel three-dimensional simulation. In addition to the introduction of lateral transport, the results show significant deviation from the distribution obtained out of the one-dimensional model, both in magnitude and gradients. Thus, the net flow of carriers is drastically different than previously predicted. The technical implications of the exact three-dimensional distribution on quantum efficiency and crosstalk is visualized. The effects of physical parameters such as absorption coefficient, diffusion length, array geometry, and detector structure are thoroughly investigated.
Damaged and damage-free hydrogenation of GaAs: The effect of reactor geometry
Authors: Jackson G. S. , Beberman J. , Feng M. S. , Hsieh K. C. , Holonyak N. , Verdeyen J.
Published: July 2002

The effects on GaAs hydrogenation of two different rf reactor types are investigated, one a parallel-plate reactor with a capacitively coupled discharge and the other an inductively coupled system. The atomic hydrogen, dissociated in the plasma of either system, passivates impurities in GaAs. The plasma in the capacitively coupled discharge reactor develops a large self-bias relative to the sample and large ion energies (∼100 eV), resulting in significant etching of the GaAs surface. In spite of the surface erosion, passivation of donors by hydrogen diffusing into the material is observed. The sample hydrogenated in the inductively coupled discharge (kTe/q <1–2 eV) is not etched, exhibiting, nevertheless, a comparable passivation of donors. Hydrogenation without surface damage is accomplished with the sample in the glow discharge of an inductively coupled reactor but not in a capacitively coupled discharge.
ac-dc conversion effect in ceramic superconductor BaPb1−x BixO3
Authors: Ikegawa Sumio , Honda Toshihisa , Ikeda Hiroshi , Maeda Atsutaka , Takagi Hidenori , Uchida Shin-ichi , Uchinokura Kunimitsu , Tanaka Shoji
Published: July 2002

The dc voltages (Vdc ) induced by an rf current of frequency 10 MHz in the ceramic superconductor BaPb1−x Bix O3 have been observed near the superconducting transition temperature(∼10 K). The Vdc is related to superconductivity because the Vdc decreases with increasing applied magnetic field. From the investigations using second-harmonic superposition on the rf current as well as differential resistance measurements, it is concluded that the Vdc is generated by an alternating current and its second-harmonic wave flowing through the sample with a nonlinear but symmetric current-voltage characteristic induced by the superconducting transition. Therefore, the observed Vdc induced by an rf current is not due to the reverse ac Josephson effect, which had been proposed previously.
Hot-carrier-induced degradation of metal-oxide-semiconductor field-effect transistors: Oxide charge versus interface traps
Authors: Choi Jeong Yeol , Ko Ping Keung , Hu Chenming , Scott William F.
Published: July 2002

Whether hot-carrier-induced degradation of metal-oxide-semiconductor field-effect transistors is caused by charge trapping in the oxide or interface-trap generation is a subject of considerable interest. We show that both processes take place in the hot-carrier-induced degradation. The relative importance of the two mechanisms depends on the stressing condition and the electron-trap density in the oxide. Charge trapping may be a dominant mechanism for devices with high trap density in the gate oxide. When subjected to severe degradation either by very-high-voltage stressing or by long-term stressing, the degradation of n-channel transistors seems to be mostly due to charge trapping as a result of oxide-trap generation by channel hot electrons. Under pulse stress, if the gate voltage turns off in the presence of high drain voltage, the ratio of charge trapping to interface-trap generation appears to be larger than under dc stress. This may be due to the generation of oxide traps by electron-hole recombination in the oxide. For a normal good oxide fabricated in the state-of-the-art technology under the worst-case dc bias condition or under pulse stress with inverterlike waveforms, hot-electron trapping contributes less than 10% to the device degradation and interface-trap generation is the dominant mechanism of device degradation.
Light emission from high bias Al-AlOx-Au tunnel junctions
Authors: Shu Q. Q. , Wen W. J. , Xu S. J.
Published: July 2002

An observation of the Al-AlOx-Au light emitting tunneling junctions deposited on the underlayers of CaF2 has been made. The applied bias can be up to 5.12 V at room temperature, and the efficiencies were in the 10−4 range and one order higher than before. The emission spectra are characterized by the cutoff frequency near 3.26 eV and the lack of the emission from the radiative mode of surface plasmon polariton.
New photoconductive gain mechanism by electric field modulation in multiquantum-well heterostructures
Authors: Capasso Federico , Ripamonti Giancarlo , Tsang W. T. , Hutchinson Albert L. , Chu S. N. G.
Published: July 2002

A new type of photoconductivity in semiconductor heterojunctions has been observed. The structures are InP/In0.47Ga0.53As forward-biased multiquantum-well p-n junctions grown by chemical-beam epitaxy. This phenomenon manifests itself in a photocurrent proportional to the dark differential conductance. This effect is associated with the partial screening of the electric field in the wells induced, at constant bias, by photogenerated carriers in the wells. The resulting increase of the field in the barriers leads to enhanced injection and photocurrent gain.
The kinetics of contact noise of Naβ″ alumina
Authors: Kuo Chu Kun , Brophy James J.
Published: July 2002

The kinetics of interfacial chemical reaction noise at sodium amalgam, NaI in propylene carbonate, and aqueous NaNO3 contacts to Naβ″ alumina are examined by determining the time, temperature, and sodium ion concentration dependence of the noise. The rate constant for the reaction noise is smallest for the NaI propylene carbonate contacts, 2.0×10−4 s−1, increases with sodium concentration, and has a thermal activation energy of 0.5 eV. Contact noise is interpreted in terms of ionic shot noise at the interface during the buildup of the electric double layer.
The effect of mass and pole strength on the levitation height of a magnet over a superconductor
Authors: Williams Richard , Matey J. R. , Arie Y. , Rathee J.
Published: July 2002

We have measured the effect of the mass and pole strength of a magnet on its equilibrium levitation height z over a superconducting disk of YBa2Cu3O7. A simple image force model gives the observed dependence of z on the mass and pole strength, but not the observed proportionality factor.
Thermochemical heat of ablation of solid carbon
Authors: Klein Claude A. , Berry Michael J. , Miles Perry A.
Published: July 2002

The thermochemical heat of ablation of carbon, HA, is usually set equal to 32 kJ/g as derived from the JANAF tables. There is, however, some uncertainty since JANAF-recommended values for heats of vaporization and partial vapor pressures differ from the results of a detailed analysis that was carried out at the Lawrence Livermore National Laboratory (LLNL). We find that the LLNL model yields carbon-vaporization enthalpies that are appreciably lower than the JANAF-based values. In this light, we examine experimental data generated in the course of a comprehensive investigation of laser-interaction effects in graphite and conclude that our experiments are indicative of an HA equal to 31.0±1.6 kJ/g.
Interband transitions of ZnTe-ZnSe superlattices prepared on GaAs (100) by hot wall epitaxy
Authors: Yang H. , Ishida A. , Fujiyasu H. , Kuwabara H.
Published: July 2002

Photoluminescence measurements of ZnTe-ZnSe superlattices prepared on GaAs (100) substrates by hot wall epitaxy method were carried out. Free- and bound-exciton lines due to the interband transitions of the superlattices were observed for the first time. Absorption spectra of the reflection and the transmission modes were measured to confirm the exciton lines. A theoretical calculation based on the envelope function scheme of superlattices is presented to explain the structure dependence of the photoluminescence data, taking strain effects into account.
Rutherford backscattering spectroscopy studies of ion transport in anodic oxides of Al/GaAs
Authors: Teare S. W. , Fischer C. W.
Published: July 2002

Anodic oxidation of thin Al films on GaAs beyond the exhaustion point is shown to induce substrate GaAs migration into and through the Al oxide layer. Continued anodization results in a triple-layer structure composed of a surface GaAs oxide layer superimposed on top of a mixed Al oxide layer on a substrate GaAs oxide layer. The thicknesses and composition of these Al/GaAs composite oxides are measured using Rutherford backscattering spectrometry and are related to the specific final anodic voltages. The results show that, upon completion of the anodization of the Al layer, the Ga and or As ions drift under the action of the anodic field through the Al oxide. Eventually a new oxide is formed at the GaAs/oxide interface and also at the electrolyte/oxide interface in the ratio of 64:36.
Surface modification of a-Si:H with a scanning tunneling microscope operated in air
Authors: Jahanmir J. , West P. E. , Hsieh S. , Rhodin T. N.
Published: July 2002

A scanning tunneling microscope was applied to the lithographic microprocessing of amorphous materials in air. Phase transformations were induced in the thin-film a-Si:H on silicon by low-energy electron irradiation. Electronic characterization of the surface before and after the phase transformation indicated a change in the local conductivity directly below the tip. Submicrometer lines were formed on these thin films by application of multiple, 10-V, 35-μs voltage pulses between the tip and the sample. The lines were imaged with the STM in the imaging mode. The linewidths written on a-Si:H corresponded to the average tip radii used in the experiments, e.g., approximately 500–5000 Å.
Optical oscillator strengths for germanium, tin, and lead
Authors: Ganas P. S.
Published: July 2002

A semiempirical analytical atomic independent-particle-model potential adjusted to experimental single-particle energy levels is used to generate wave functions for the valence and excited states of Ge i, Sn i, and Pb i. Using the Born approximation and LS coupling we calculate optical oscillator strengths for excitations from the ground states 4p2(3P0) of Ge i, 5p2(3P0) of Sn i, and 6p2(3P0) of Pb i. The results are compared to experimental and theoretical data.
Surface modification of silicon by partially ionized beam deposited aluminum
Authors: Srinivasan Radhika , Murarka Shyam P. , Lu T.-M.
Published: July 2002

We investigated the electrical characteristics of thin aluminum films, deposited using the newly developed partially ionized beam deposition technique on single-crystal silicon substrates. The occurrence of an n-type surface layer on an otherwise p-type substrate was observed in samples of ultrathin films (10–50 Å). The presence of this ‘‘inversion’’ layer was found to be a strong function of deposition conditions, substrate resistivity, and thickness of the aluminum overlayers.
Characterization of InP/GaAs/Si structures grown by atmospheric pressure metalorganic chemical vapor deposition
Authors: Pearton S. J. , Short K. T. , Macrander A. T. , Abernathy C. R. , Mazzi V. P. , Haegel N. M. , Al-Jassim M. M. , Vernon S. M. , Haven V. E.
Published: July 2002

The thickness dependence of material quality of InP-GaAs-Si structures grown by atmospheric pressure metalorganic chemical vapor deposition was investigated. The InP thickness was varied from 1–4 μm, and that of the GaAs from 0.1–4 μm. For a given thickness of InP, its ion channeling yield and x-ray peak width were essentially independent of the GaAs layer thickness. The InP x-ray peak widths were typically 400–440 arcsec for 4-μm-thick layers grown on GaAs. The GaAs x-ray widths in turn varied from 320–1000 arcsec for layer thicknesses from 0.1–4 μm. Cross-sectional transmission electron microscopy showed high defect densities at both the InP-GaAs and GaAs-Si interfaces. In 4-μm-thick InP layers the average threading dislocation density was in the range (3–8)×108 cm−2 with a stacking fault density within the range (0.4–2)×108 cm2. The He+ ion channeling yield near the InP surface was similar to that of bulk InP (χmin∼4%), but rose rapidly toward the InP-GaAs heterointerface where it was typically around 50% for 1-μm-thick InP layers. All samples showed room-temperature luminescence, while at 4.4 K, exciton-related transitions, whose intensity was a function of the InP thickness, were observed.
Optical absorption and structure of thermally annealed gallium selenide thin films
Authors: De Blasi C. , Manno D. , Micocci G. , Tepore A.
Published: July 2002

A systematic investigation of the effects of thermal annealing on the optical absorption and structure of evaporated GaSe thin films is reported. The optical gap is determined in films annealed at various temperatures and for different periods of time. The variation of the optical gap is tentatively explained as due to the annealing of the unsaturated bonds present in the amorphous solid. An electron microscopic investigation shows that a gradual amorphous-polycrystalline transformation occurs in films treated at temperatures higher than 500 K.
A new family of thermal donors generated around 450 °C in phosphorus-doped Czochralski silicon
Authors: Kamiura Yoichi , Hashimoto Fumio , Yoneta Minoru
Published: July 2002

We have discovered a new family of oxygen-related double donors [new thermal donors (NTD’s)] generated around 450 °C in phosphorus-doped Czochralski silicon by combining deep-level transient spectroscopy with Hall measurements. This new family was well distinguished from the normal family of thermal donors (TD’s) currently studied so far. Our results have shown that both families of thermal donors exhibit qualitatively the same kinetic behavior. Namely, as the annealing time increases, their ionization energy of levels continuously decrease with their densities increasing until the maxima and then become constant with their densities decreasing. However, there are significantly quantitative differences between the both families; NTD’s have shallower levels, considerably smaller generation rates, and higher thermal stability than TD’s. Sufficiently prolonged annealing for more than 105 min around 450 °C or short donor-killing annealing for 20 min at 650 °C completely annihilates TD’s, leaving only NTD’s, of which the most stable and therefore most shallow species have been suggested by our Hall measurements to have donor levels at 0.04 and 0.09 eV below the conduction-band edge. The density of interstitial oxygen still continues to decrease even after prolonged annealing for more than 105 min, where NTD’s are present in a stable condition in a concentration of 1×1015 cm−3. NTD’s may correlate with the NL10 electron paramagnetic resonance center because of similarities in their generation kinetics. We have suggested a hypothesis that NTD’s have similar defect structures as TD’s and that an unknown nucleus involved in the core of NTD’s plays an essential role in lowering their ionization energy of levels and generation rates and also in stabilizing their donor activity.
Creation of TlCaBaCuO fine features by a wet process
Authors: Shih I. , Qiu C. X.
Published: July 2002

During the study of the formation of TlBaCaCuO from rf-sputtered Ba-Ca-Cu-O films (Ba:Ca-Cu=2:2:3 in target) it was found that the rf-sputtered materials were relatively unstable in water, in photoresist developer, and even in room atmosphere. To overcome the severe undercutting effect during the chemical etching process resulting from the instability, a Cu protective layer with a thickness of 100–150 Å was adopted for the fine-line patterning. Using a positive photoresist technique, 3-μm lines have been successfully produced. Lines with a width of 150 μm also have been produced on ZrO2 substrates and superconductivity was observed after a heat treatment in an environment containing O2 and Tl gas.
Atom probe studies of the composition of low-temperature oxides on (100) silicon and gallium arsenide surfaces
Authors: Grovenor C. R. M. , Cerezo A.
Published: July 2002

Pulsed laser atom probe microanalysis has been used to investigate the stoichiometry of low-temperature oxides on silicon and gallium arsenide. The composition of hydrophobic oxides grown on silicon after cleaning in hydrofluoric acid solutions is shown to tend to SiO as the oxide layer thickens. By contrast, hydrophilic oxides grown by low-temperature chemical treatments have a layered structure, SiO2 /SiO/Si. Low-temperature air-grown and chemical oxides on GaAs have a composition (GaAs)2O3, and are covered by a layer of adsorbed water. This same composition is also approached by thermal oxides grown between 300 and 400 °C in a low partial pressure of oxygen.
Epitaxial CoGa and textured CoAs contacts on Ga1−xAlxAs fabricated by molecular-beam epitaxy
Authors: Palmstro/m C. J. , Fimland B.-O. , Sands T. , Garrison K. C. , Bartynski R. A.
Published: July 2002

Films of CoGa and CoAs have been deposited on Ga1−xAlxAs surfaces. Control of the Ga1−xAlxAs surface prior to CoGa deposition results in the preferential formation of two epitaxial orientations, either (100)[011]CoGa∥(100)[011]Ga1−xAlxAs or (110)[001]CoGa∥(100)[01̄1̄]Ga1−xAlxAs. The crystalline quality of (100)-oriented CoGa was good as determined by Rutherford backscattering with channeling measurements, χmin∼7%, and cross-sectional transmission electron microscopy. The (110)CoGa films did not have as good a crystalline quality, χmin∼41%. CoAs films were found to be highly textured, but not single crystal. Schottky barrier diodes fabricated from CoGa/Ga1−xAlxAs and CoAs/Ga1−xAlxAs showed good characteristics with low ideality factors, n<1.15. In general CoGa contacts had a ∼0.1 eV lower barrier height than CoAs.
Structural depth profiling of iron oxide thin films using grazing incidence asymmetric Bragg x-ray diffraction
Authors: Toney Michael F. , Brennan Sean
Published: July 2002

X-ray depth profiling in a grazing incidence asymmetric Bragg geometry is used to obtain the depth-dependent structure of a nominally γ-Fe2O3 thin film, which was oxidized from an Fe3O4 film. As the incidence angle is varied from angles less than the critical angle for total external reflection to angles greater than the critical angle, the x-ray penetration depth increases from about 20 to several thousand angstroms. The observed diffraction originates from this region of variable depth and a structural depth profile of the thin film can be obtained by measuring the diffraction pattern as a function of incidence angle. The iron oxide film is found to have a 45-Å-thick surface layer of α-Fe2O3; beneath this layer the film is predominantly γ-Fe2O3 but also contains about 2.6 at. % α-Fe2O3. These data, together with previous chemical and magnetic data, suggest that during oxidation of the Fe3O4 film the surface layer forms by the outward diffusion of Fe ions and their subsequent oxidization to α-Fe2O3. One possible explanation of the 2.6% α-Fe2O3 in the bulk of the film is that the Fe3O4 film contains small nuclei of material that are structurally similar to α-Fe2O3. During the oxidation to form γ-Fe2O3, these then grow to form small grains of α-Fe2O3 that are observed.
Temperature behavior of the coercivity of a magnetically hard alloy Pt0.7Ni0.3Fe
Authors: Chen X. , Gaunt P.
Published: July 2002

The kinks of a Bloch wall at some lamellar junctions are attributed to the reduction of the demagnetizing energy. An improved method is developed to calculate Hc(T), the coercive field.
Dynamic fragmentation model with internal damage
Authors: Yatom H. , Ruppin R.
Published: July 2002

Fragment sizes obtained in an explosive fragmentation process are evaluated by energy balance considerations. The kinetic energy which drives the fragmentation process is calculated in a more elaborate way than in previous work. The contribution of the formation of internal cracks within the fragments to the energy balance is also taken into account by invoking results from percolation theory. It is found that when internal damage is included, the calculated fragment sizes are considerably larger than those derived from the simplified model of uncracked fragments.
Calculation of the transverse acoustoelectric voltage in a piezoelectric-extrinsic semiconductor structure
Authors: Lippens P. E. , Lannoo M. , Pouliquen J. F.
Published: July 2002

The transverse acoustoelectric voltage (TAV) is calculated for a piezoelectric-extrinsic semiconductor structure. Using a small-signal expansion an analytical but rather complicated expression is obtained and computed for the LiNbO3/n-Si system. New and simple expressions are given, respectively, for high and low conductivities. In the latter case the TAV can reverse sign as a function of the conductivity and the frequency. This effect is explained from the second-order variations of the majority carrier concentration. The influence of the air gap between the piezoelectric and the semiconductor is also studied.
Time domain reflection methods for dielectric measurements to 10 GHz
Authors: Cole R. H. , Berberian J. G. , Mashimo S. , Chryssikos G. , Burns A. , Tombari E.
Published: July 2002

Total reflection methods and instrumentation for their use are described for measurements of dielectric permittivity and loss at frequencies to 10 GHz or more. Several cell designs are shown, together with analyses of their performance. Procedures are given for correcting effects of wave propagation in the cells and residual reflections in the cells by bilinear analysis with calibrations using dielectrics of known permittivity. Representative results are presented for highly polar liquids, dilute solutions of polar molecules in nonpolar solvents, electrolyte solutions, and ionic glasses with appreciable ohmic conduction.
Structure and electron transport anomalies in InSe-In6Se7 composite
Authors: Vitta Satish
Published: July 2002

Rapid solidification of an equiatomic In-Se alloy resulted in the formation of an equilibrium InSe-In6Se7 phase mixture. The InSe phase was found to be polytypic and exhibited the structural variants 2H, 3H, and 4H. The 4H polytype was found to be in considerably higher proportion compared to 2H and 3H types. The In6Se7 phase was found to be hexagonal with a=0.8919 nm and c=1.4273 nm. Both In6Se7 and the polytypes of InSe could be identified with the space group P61. The conductivity σ variation with temperature was found to be similar to that observed in disordered semiconducting materials. For temperatures >200 K, ln σ decreased linearly with T−1, phonon-assisted carrier excitation. For temperatures <200 K, ln σ decrease followed T−1/3 behavior, representative of variable-range hopping conduction of electrons.
Radio-frequency probe for plasma conductivity measurement. I. Theoretical study
Authors: Zeller P. , Pointu A. M.
Published: July 2002

Radio-frequency impedance variation of a finite length coil surrounding a plasma column is theoretically related to plasma complex conductivity. Calculations use two dimensions and do not need perturbation approximation. Their application range is discussed and methods are proposed to deduce from measurements the plasma electron density and effective collision frequency.
Nonlinear curved fiber coupler
Authors: Jakubczyk Z. , Tremblay R. , Vallée R.
Published: July 2002

The switching capability of a nonlinear curved directional coupler based on single-mode glass fibers is analyzed. The beam-propagation method is used to visualize the evolution of an optical field along a coupling region.
Analysis of single polaron hopping in ac conductivity of amorphous Ge20SbxSe80−x glasses
Authors: Mehra R. M. , Kumar Rajesh , Mathur P. C.
Published: July 2002

The results for the ac conductivity over temperature range (298–500 K) and frequency range (102–107 Hz) for the Ge-Sb-Se glasses with different compositions are presented. These glasses exhibit a strong temperature dependence of ac conductivity and of its frequency exponent s. The results are discussed in the light of the correlated barrier hopping model for ac conduction. All the features observed are interpreted by taking into account the contribution of both single polarons and bipolarons. It is shown that the single polarons dominate the hopping transport process in the measured temperature range. The effect of the addition of Sb is also discussed in terms of the present model. The energy levels and densities of the defect for Ge-Sb-Se glasses are deduced from the comparison between the theoretical and experimental results.
Time-resolved luminescence from the AlGaAs layer of AlGaAs/GaAs heterostructures
Authors: Christanell R. , Höpfel R. A.
Published: July 2002

The luminescence of optically injected carriers in the thin AlGaAs layer of AlGaAs/GaAs single heterostructures is studied with femtosecond time resolution by using a ‘‘population-correlation’’ technique. We observe lifetimes of the combined electron-hole populations of 5–11 ps depending on the layer thickness of the different samples. We find that the dominating process for carrier transfer is ‘‘thermal’’ emission of carriers limited by ambipolar diffusion.
Charge trapping/generation and reliability for high-performance tantalum oxide capacitors
Authors: Byeon S. G. , Tzeng Y.
Published: July 2002

Charge trapping/generation behavior and reliability of recently developed high-performance sputtered/anodized tantalum oxide films in structures of Al–tantalum-oxide–Ta metal-insulator-metal (MIM) capacitors under constant current stress are studied by observing the voltage-time and time-to-breakdown characteristics in comparison with those of the usual tantalum oxide MIM capacitors prepared by either anodization or reactive sputtering. The dominant charge trapping/generation in the anodized tantalum oxide films is either slow electron trapping under current stress on the Ta bottom electrodes or positive charge generation under current stress on the Al top electrodes. Positive charge generation due to oxygen vacancies after fast electron trapping is dominant in the sputtered tantalum oxide films which show defect-related breakdown phenomena. The sputtered/anodized tantalum oxide demonstrates much superior reliability because of its less charge trapping/generation and better enduring property under charge injection compared with the anodized or the sputtered tantalum oxide films.
Preferred orientation effects in coevaporated films of DyBa2Cu3O7−x superconductors
Authors: Budhani R. C. , Xu Youwen , Wiesmann H. , Ruckman M. W. , Sabatini R. L.
Published: July 2002

Thermal coevaporation has been used to deposit thin films of Dy-Ba-Cu-O compounds on magnesium oxide substrates. The as-deposited films crystallize into a randomly oriented polycrystalline phase on annealing at 900 °C. Further annealing at higher temperatures results in a c-axis-oriented material. Effects of the structural changes on the superconducting behavior of the films have been evaluated with resistivity and magnetization measurements. The c-axis-oriented films show sharper resistive transition and improved diamagnetic shielding.
Output power and efficiencies of slab laser systems
Authors: Eicher J. , Hodgson N. , Weber H.
Published: July 2002

Starting with the known relations for rod systems, the efficiencies and the output power of a slab system are derived as a function of the small-signal gain and the resonator losses. Taking into account the beam overlap and beam enlargement it turns out that higher extraction efficiencies can be achieved in slab systems compared to equivalent rod systems. Under the assumption of the same excitation power and equal losses in both systems this results in a higher output power and a lower lasing threshold in slabs. These advantages can be realized provided that the pumping arrangement of slab systems is optimized similar to rod systems.
Gamma-ray irradiation effect in amorphous hydrogenated silicon
Authors: Imagawa O. , Yasuda K. , Yoshida A.
Published: July 2002

The gamma-ray irradiation effect in undoped amorphous hydrogenated silicon (a-Si:H) films has been investigated. The total dose was in the range of 1016–1017 photons/cm2. The dark conductivity and photoconductivity increase, and the Fermi level Ef moves downwards beyond the middle of the gap. The defects introduced are predominantly unoccupied dangling bonds (D+), and a remarkable increase of neutral dangling bonds (D0) was not observed. The fundamental difference between gamma-ray and visible-light (the Staebler–Wronski effect) irradiation is due to the difference in the generation of neutral dangling bonds (D0).
Transport length, quantum efficiency, and trap density measurement in Bi12SiO2
Authors: dos Santos Paulo Acioly M. , Garcia Paulo Magno , Frejlich Jaime
Published: July 2002

We report the measurement of diffusion transport length LD, quantum efficiency φ for photoelectron generation, and the Debye screening length and associated trap density NA in an undoped Bi12SiO20 (BSO) photorefractive crystal. The method is based on the optical erasing of holographically recorded gratings in the crystal. The measurement of the diffraction efficiency evolution is considerably facilitated profitting from polarization properties of anisotropic diffraction in BSO-type crystals in a self-diffraction experiment. Data processing is carried out using simple linear regression techniques for experimental conditions in two limiting situations: far from and well into trap saturation conditions. We prove that optical erasure closely verifies the decay law predicted by theory even if a highly contrasted pattern of light is used for recording. We measured NA=6.3×1016 cm−3, agreeing in order of magnitude, with already reported values, but found out LD=0.1 μm, which is too much lower than data in literature for an electron-based charge transport material as this one.
High-dose magnesium implantations in InP activated by rapid thermal annealing
Authors: van Berlo W. H. , Landgren G.
Published: July 2002

Highly doped, near 1019 cm−3, p-type layers have been obtained in InP by ion implantation of magnesium and the use of rapid thermal annealing with proximity encapsulation. The resulting doping profiles can be qualitatively accounted for by considering the interstitial/substitutional diffusion model and the stoichiometric imbalance created by implantation-induced knock-on of phosphorus. The upper limit for substitutional incorporation of magnesium is found to be of the order of 1019 cm−3. Although coimplantation of P and Mg has an effect on the activation and distribution of Mg, it is not as important as in the case of As/Mg in GaAs. The results have important implications for the design of implanted contacts to optoelectronic devices.
Solid-state epitaxy of osmium silicide on (111)Si under reducing atmosphere
Authors: Chang Y. S. , Chou M. L.
Published: July 2002

Under a mixed hydrogen/argon atmosphere epitaxial osmium silicide has been successfully grown on (111)Si for the first time. A new process of electroless deposited osmium film on Si subsequent with a suitable two-step hydrogen annealing scheme was developed for the formation of epitaxial osmium silicide. Polycrystalline silicides of Os2Si3 and OsSi2 were found in all cases of single annealing, and the grain size increased with annealing temperature. While in the developed two-step annealing scheme single-crystalline silicide can form; the first step annealing was found to be critical to determine epitaxy. The epitaxial silicide was identified to be OsSi2 of orthorhombic structure. The orientation relationships between epitaxial OsSi2 and Si were found to be (040)OsSi2∥(22̄0)Si, and [102̄] OsSi2∥ [111] Si.
Investigation of the normal zone along a superstabilized superconducting solenoid
Authors: Devred Arnaud
Published: July 2002

Construction of large thin-walled superconducting solenoids for high-energy particle detectors has required the development of superstabilized superconductors, in which a multifilamentary superconducting composite is inserted in a large aluminum tape. The transition to the normal resistive state of such a conductor is accompanied by a redistribution of current, which, due to the size of the normal matrix, is long compared with the thermal phenomena and greatly affects the propagation velocity of the normal zone. Having modeled the electromagnetic behavior of a layer of superstabilized conductors during transition, we numerically solve the equation for current diffusion in the superstabilizer and establish an implicit equation for propagation velocity. We then investigate two limiting cases relating to low and high velocities. In both cases, we derive a simplified form of the implicit equation and, by considering the physical interpretation of the phenomena, we determine the application domain. Finally, we show that for superstabilized conductors there is a wide overlap of the two domains and that the two simplified equations for propagation velocity reduce to a single formula valid for all cases.
Formation of PtSi in the presence of Al and a Cr barrier layer
Authors: Chang Chin-An
Published: July 2002

The effect of Cr as a barrier between PtSi and Al is studied by analyzing the reactions of the Al/Cr/Pt/Si (2000 Å/1000 Å/1000 Å/Si substrate) structures. Electrical measurement shows a rapid rise in sheet resistance after annealing at 400 °C. Structural analysis shows extensive reactions between Al and Cr at such temperatures. The PtSi formed remains little changed until 550 °C, and is converted to PtAl2 at higher temperatures. The results are compared with those using W, Ti-W, and carbon barriers, and the roles of barrier materials on the stability of the Al/PtSi metallurgy are discussed.
AuBe/p-InGaAsP contact formed by rapid thermal processing
Authors: Katz A. , Thomas P. M. , Chu S. N. G. , Lee J. W. , Dautremont-Smith W. C.
Published: July 2002

Alloyed ohmic contacts of AuBe (1% Be by weight) to 5×1018 cm−3 Zn-doped p-InGaAsP (λg=1.3 μm) were fabricated by rapid thermal processing and its performance was compared to those of the contacts formed by conventional furnace heating. The specific contact resistance decreased from a value of 4.9×10−4 Ω cm2 as-deposited to a value of 4.9×10−7 Ω cm2 as a result of rapid thermal processing at 420 °C for 30 s. This value was much lower than the value of 3.9×10−6 Ω cm2 obtained as a result of furnace heat treatment at 420 °C for 10 min. Rapid thermal processing at higher temperatures caused a sharp increase of the specific contact resistance. Auger depth profiling indicated that the degradation of the contact electrical performance at temperatures of 450 °C or higher were caused by intensive localized interactions between the AuBe and the InGaAsP and out-diffusion of all the quaternary elements toward the surface of the contact. The effective stress in the alloyed layer, normalized to the initial AuBe thickness of 80 nm, was tensile with a value of 7×109 dyn cm−2, and was less sensitive to the alloying parameters (time and temperature) than was the contact resistance.
Metallurgical study of Ni/GaAs contacts. I. Experimental determination of the solid portion of the Ni-Ga-As ternary-phase diagram
Authors: Guérin R. , Guivarc’h A.
Published: July 2002

X-ray diffraction on powders and single crystals has been performed to determine the limits of homogeneity and crystallographic data of metallic ternary phases which occur in the bulk Ni-Ga-As system and to draw the solid portion of the phase diagram. The samples were prepared in closed, small-volume containers to prevent the formation of gas-phase products. Five ternary phases which crystallize in hexagonal symmetry and are all structurally derived from the NiAs type were evidenced. Among them, three phases show hexagonal superlattices: a(3)1/2×3c, 2a×4c, and 3a×2c which denote ordered structures. Neither nickel nor ternary phases are in thermodynamic equilibrium with GaAs, in contrast to the binaries NiGa, Ni2 Ga3, and NiAs which are. The bulk-phase diagram determined in this study provides a framework within which most of the experimental data concerning the products of reactions at Ni/GaAs interfaces can be understood.
Microstructure-property correlations in the Bi(Pb)-Sr-Ca-Cu-O superconducting system
Authors: Ramesh R. , Green S. M. , Mei Yu , Manzi A. E. , Luo H. L.
Published: July 2002

The microstructure of solid-state processed (Bi,Pb)-Sr-Ca-Cu-O ceramics was characterized using transmission electron microscopy techniques. A strong sensitivity of the transport properties to small deviations in the nominal Bi-Ca ratio is evidenced. Significant differences in the microstructure are shown to correlate to the changes in the transport properties. It is suggested that the microstructure can be predicted by combining the results of resistivity, Meissner, and shielding experiments.
Ultrashallow diffused n+p junction using antimony for device applications
Authors: Söderbärg A. , Grelsson Ö. , Magnusson U.
Published: July 2002

Experimental characteristics of ultrashallow n+p junctions manufactured by vacuum evaporation of antimony (Sb) and silicon (Si), followed by heat treatments to recrystallize the amorphous silicon, are presented. It is found that the n+p junction is located less than 300 Å inside the crystalline silicon and that all Sb is redistributed within the regrown film. Comparisons with Schottky (Sb-Si) diodes show that with a heat treatment at 900 °C, the diodes convert fully from Schottky type to n+p type. Furthermore, normally off-type junction field-effect transistors have been fabricated using these n+p junctions as gate junctions, and the characteristics are presented together with data concerning threshold voltage variations. Also, the subthreshold characteristics of these junction field-effect transistors are presented. The behavior in the subthreshold region is found to be excellent.
Sequential power transfer between stripes of a diode laser array via photorefractive two-wave mixing in BaTiO3
Authors: MacCormack S. , Eason R. W.
Published: July 2002

We report the transfer of 48% of the incident power from a semiconductor laser array into a diffraction-limited beam by means of photorefractive coherent beam combination in BaTiO3, using a progressive two-wave mixing geometry. A single-element, photorefractive beam combiner is described which should allow the transfer of 88% of the power of a suitable array into a single diffraction-limited beam.
Boron doping of silicon by ArF excimer laser irradiation in B2H6
Authors: Matsumoto S. , Yoshioka S. , Wada J. , Inui S. , Uwasawa K.
Published: July 2002

Boron doping of silicon using a pulsed ArF excimer laser (λ=193 nm, FWHM=17 ns) with B2H6 has been investigated. Doping atoms are supplied mainly from both thermal and photochemical decomposition of the adsorbed layers on the surface. UV laser irradiation realizes both high surface carrier concentration (1×1021 cm−3) and a very shallow junction (0.1 μm). Diodes fabricated by laser doping show good electrical characteristics (n factor=1.10, reverse current density=1×10−7 A/cm2 at −5 V). Thermal annealing improves the reverse current density (3×10−9 A/cm2 at −5 V). A numerical calculation of boron concentration profiles has been performed by solving the diffusion equation in the melted region, which is evaluated by the heat conduction equation. From this calculation the diffusion coefficient of boron in liquid phase silicon (3×10−4 cm2/s) is obtained.