bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct and exchange-correlation carrier interaction effects in a resonant tunnel diode
Authors: Gawlinski E. , Dzurak T. , Tahir-Kheli R. A.
Published: July 2002

Results are presented of a density functional calculation of the effects due to both electron-electron direct and exchange-correlation interactions on the effective, single-electron potential, the conduction electron density profile, the device transmission coefficient, and the current-voltage characteristics of a GaAs-AlGaAs quantum-well tunnel diode. The calculation proceeds by self-consistently solving the Kohn–Sham and Poisson equations, accounting for the strong, electric-field-induced nonequilibrium effects by employing a spatially varying chemical potential which is essential for maintaining net charge neutrality. The exchange potential used is the Dirac local-density approximation and the correlation potential is determined from the Wigner interpolation formula. The results show a number of interesting effects: it is found that the direct, electrostatic repulsion due to the buildup of charge within the spacer layers extends far beyond the device, well into the contact layers. Furthermore, the depression of carrier density within the quantum well leads to a reduction in the exchange-correlation screening of the direct interaction. Consequently, the total band bending in the vicinity of the device is enhanced by the exchange-correlation interaction, a result in contradiction with a previous Hartree–Fock calculation [K. Bandara and D. Coon, Appl. Phys. Lett. 53, 1865 (1988)]. In the case of a resonantly biased quantum well, the formation of an exchange-correlation hole due to the population of the resonant level within the quantum well is also observed. Finally, elastic scattering effects have been modeled by including random noise in the barrier conduction band. This causes a broadening of the resonant level within the quantum well, which in turn leads to an enhanced current flow through the overbiased device, although this enhancement is not as large as that seen experimentally. This suggests that the enhanced current flow in the overbiased device is likely to be due to inelastic scattering processes that are not included in this model.
Wannier localization in GaAs/GaAlAs superlattices under electric field
Authors: Zhang Yaohui , Jiang Desheng , Li Feng , Zhou Junming , Mei Xiaobing
Published: July 2002

We have studied the Wannier–Stark effect in GaAs/GaAlAs short-period superlattices under applied electric field perpendicular to the layers by room- and low-temperature photocurrent measurements. The changes in the transition intensities with biasing are well fitted to a theoretical calculation based on the finite Kronig–Penney model on which the potential of an applied electric field is superposed. With increasing electric field, the 0h peak grows to a maximum while the −1h and +1h peaks monotonousely decrease. By a comparison of the spectra measured at different temperatures, the two peaks in the room temperature photocurrent spectra at relatively low electric field (1.0×104 V/cm) are identified to be caused by the Wannier localization effect instead of saddle-point excitons.
Tunneling between a two-dimensional electron gas and a two-dimensional hole gas
Authors: Jorke H.
Published: July 2002

Using tunneling probabilities from two-band model calculations, interband tunneling from a two-dimensional electron gas to a two-dimensional hole gas is examined. The tunneling current is found, both in the direct and in the indirect case, to decrease inversely with the lifetime τr of states occupied in the two-dimensional hole gas by tunneling. As with increasing temperature τr commonly decreases, the temperature dependence of interband tunneling between two-dimensional carrier gases is expected to be more pronounced than that between three-dimensional carrier gases. By use of a self-consistent approach, tunneling currents are calculated for the δn-δp doping structure in (100) silicon.
On the influence of thermal history on simple surface reactions
Authors: Wautelet M.
Published: July 2002

The kinetic equations for simple surface reactions are solved numerically. Emphasis is placed on the effects of changing the thermal history of the system. It is shown how the global reaction rates depend on the thermal history (initial and final temperatures, time constants) and the kinetic parameters of the reaction (activation energies).
‘‘Walls’’ of a paramagnetic gas in a magnetic field gradient
Authors: Freeman Gordon R.
Published: July 2002

A quantitative explanation is given for the recently reported ‘‘walls’’ formed by a paramagnetic gas in a magnetic field gradient, that can guide the flow of a diamagnetic gas down a negative field gradient, or reflect the flow from a positive field gradient.
Properties of the planar poly(3-octylthiophene)/aluminum Schottky barrier diode
Authors: Assadi A. , Svensson C. , Willander M. , Inganäs O.
Published: July 2002

Formation and characterization of planar polymer Schottky barrier diodes are presented. Electrical characteristics of planar aluminium-poly(3-octylthiophene) Schottky barrier diodes are studied with emphasis on the current transport mechanisms. The device exhibits nearly ideal diode behavior in dark with an ideality factor of n=1.2. Temperature dependence of the current-voltage characteristics of the diode is studied in the range 170–370 K. Agreement with the diffusion theory of metal-semiconductor rectification is demonstrated for high temperatures T≳300 K. For temperatures less than room temperatures tunneling is proposed to be the dominant current transport mechanism.
The critical current of Ag/YBa2Cu3O7−δ random bulk composites
Authors: Calabrese J. J. , Dubson M. A. , Garland J. C.
Published: July 2002

We have measured the current-voltage characteristics of bulk percolating Ag/YBa2Cu3O7−δ composites ranging in composition from 0.10 to 1.00 volume fraction superconductor at temperatures from 40 to 100 K. The dependence of the normal state resistivity on volume fraction is consistent with the percolation theory. The critical current densities of the composites exhibit a temperature dependence consistent with superconductor-normal metal-superconductor junction behavior. Our data suggest that the critical currents in these composites are limited by proximity coupling through Ag between the high-Tc grains.
Nb Josephson junction with a Hf/HfN double overlayer
Authors: Morohashi Shin’ichi , Imamura Takeshi , Hasuo Shinya
Published: July 2002

We fabricated a Nb Josephson junction with a Nb/HfOx-Hf/HfN/Nb structure. The junction showed an excellent current-voltage characteristics (Vm = 40 mV), and these characteristics were not degraded with annealing at temperatures up to 350 °C. Each layer in the Hf/HfN double overlayer plays an important role in the junction structure. The Hf layer acts as a layer for the tunneling barrier formation and as an effective etch stop for a reactive ion etching process in junction fabrication. The HfN layer greatly contributes to the annealing durability of the junction by acting as an effective stop for grain boundary diffusion between the Nb and Hf layers.
Suitability of gap frequencies for the Josephson voltage standard
Authors: Frank Birgit , Meyer H. G.
Published: July 2002

We report theoretical investigations of Shapiro step formation at high microwave drive frequencies. A drive frequency equal to the gap frequency or its first subharmonic generates current-voltage characteristics that are especially well suited for Josephson voltage standards. Such drive frequencies increase the stability of the reference voltage and reduce the total number of junctions required to produce a given voltage. In contrast to conventional series-array voltage standards, the dc current bias has to be chosen on the order of the critical current.
Scattering from a conducting surface coated with multilayers of lossy dielectric material (transverse electric polarization)
Authors: Lin Chi-Sen , Yaqoob M. Tahir
Published: July 2002

A new method of moments solution is presented to find the scattered field from a two-dimensional conducting surface coated with one or more layers of lossy dielectric material of arbitrary thickness for transverse electric polarization of the incident field. A conduction current on the inner conducting surface and a volume polarization current in the dielectric material are considered. These two currents produce the scattered field, so the scattered field and the field related parameters are readily obtained. A set of E-field integral equations is developed by applying the boundary conditions at the conducting surface and in the dielectric material. These integral equations are solved by the method of moments. By considering the polarization of the dielectric, the effects of surface wave excitation are automatically included in the solution. An excellent agreement of results with the exact solution is achieved.
Optical and structural characterizations of ZnSe/ZnSSe superlattices grown by metalorganic chemical vapor deposition
Authors: Kuroda Yasuhide , Suemune Ikuo , Fujimoto Masahiro , Fujii Yoshihisa , Otsuka Nobuo , Nakamura Yoshio
Published: July 2002

ZnSe/ZnSSe superlattices (SLs) grown on GaAs substrates were studied with transmission electron microscopy and x-ray diffraction. Defects were observed in the initial growth stage, but they were recovered with the growth of short-period SL. The temperature dependent decrease of photoluminescence (PL) intensities improved in the short-period SL. Clear excitonic absorption peaks were observed in photocurrent spectra and the blue shift of the absorption peaks by the quantum confinement was in reasonable agreement with the calculated peak shift. In a SL with the well width of 93 Å, a biexciton PL peak was observed from the very low excitation power of less than 1 mW/cm2. Details of the biexciton properties are discussed.
Growth of CdS by atmospheric pressure metalorganic vapor-phase epitaxy at low temperature
Authors: Yodo Tokuo , Tanaka Shuhei
Published: July 2002

Single-crystalline epilayers (epitaxial layers) of undoped, phosphorus-, and iodine-doped CdS have been grown at 250–400 °C on (100)-oriented GaAs substrates by atmospheric pressure metalorganic vapor-phase epitaxy using dimethylcadmium and hydrogen sulfide as source materials. The premature reaction typically encountered with this source combination, as well as in the case of ZnSe epitaxial growth using dimethylzinc and hydrogen selenide, can be eliminated completely even at atmospheric pressure by controlling the respective flow velocities of the carrier gases, including the source gases, independently. The crystallographic structure of CdS epilayers is largely related to the VI/II source gas mole ratio, and changes from hexagonal into cubic (100) structure with decreasing VI/II ratio. From the x-ray-diffraction and photoluminescence measurements, an epilayer grown at 350 °C with a VI/II ratio of 2 has excellent crystalline quality with complete single-cubic (100)-type epitaxial structure. Also in correspondence with such changes of the crystallographic structure, it is clearly observed that the energy positions of the near-band-edge emissions shift 75, 96, and 101 meV, respectively, downwards at 300, 77, and 4.2 K. In addition, the fundamental data on cubic CdS have been obtained for the first time. It is concluded that a P impurity does not form a shallow acceptor level, but instead SA (self-activated) centers. An I impurity effectively forms a shallow donor level while preserving the high crystalline quality, and changes the crystallographic structure from cubic type into hexagonal type without generating SA centers. It is concluded that the doping alters both crystallographic structure and crystalline quality in the epitaxial growth of CdS.
Numerical simulation of cylindrical converging shocks in solids
Authors: Hiroe T. , Matsuo H. , Fujiwara K.
Published: July 2002

Cylindrically converging shock waves in solids have been analyzed by the random choice method (RCM). A Riemann solver for fluidlike solids with the Grüneisen-type equation of state is constructed and incorporated into the RCM. It is then applied to the cylindrical shock tube problems for solid copper with driving pressures of 20 and 200 GPa. The numerical results are compared with those of the finite difference method (FDM). The shock speed is smaller and the discontinuity at the shock front is smeared out due to the artificial viscosity in the FDM calculation. Spatial distributions of pressure, density, and particle velocity calculated by the RCM show that the steepness at the shock front is maintained both in the converging and reflecting stages. It is shown that the pressure on the shock front and the total energy contained in the central circular area are much larger in the reflecting stage than in the focusing stage. The dimensional analysis has shown that the similarity solution exists; however the numerical result shows that the flow does not fall within the similarity regime in the region of calculation. It suggests that the self-similar flow is only limited in extreme proximity to the axis.
Electrical-transport properties and microwave device performance of sputtered TlCaBaCuO superconducting thin films
Authors: Subramanyam G. , Kapoor V. J. , Chorey C. M. , Bhasin K. B.
Published: July 2002

Tl-Ca-Ba-Cu-O high-temperature superconducting thin films were deposited on lanthanum aluminate substrates, by rf magnetron sputtering and postannealing methods. A reproducible fabrication process with low-resistance metal contacts has been established for high-Tc and high-Jc TlCaBaCuO thin films after patterning using standard microelectronic photolithography and wet chemical etching techniques. Low-resistance gold contacts on TlCaBaCuO thin films were obtained by annealing in an oxygen flow of 1 l/min followed by a slow furnace cooling. Specific contact resistivity was approximately 10−10 Ω cm2 below 77 K. High transition temperatures as high as 100 K, and current density at zero magnetic field greater than 105 A/cm2 are routinely obtained in 0.3–0.5 μm TlCaBaCuO thin films. The morphology studies of the films using scanning electron microscopy show the correlation between Jc and the microstructure of the films. Films with featureless morphology have larger zero-field transport currents. The microwave properties of TlCaBaCuO thin films were investigated by designing, fabricating, and characterizing microstrip ring resonators with a fundamental resonance frequency of 12 GHz on 10-mil-thick lanthanum aluminate (LaAlO3) substrates. Ring resonators with a superconducting ground plane of 0.3 μm thickness and a gold ground plane of 1 μm thickness were fabricated and characterized in the temperature range of 60–95 K. Typical unloaded quality factors Q for the ring resonators at 12 GHz were above 1500 at 65 K, compared to an unloaded Q of 370 for a gold ring resonator. A surface resistance as low as 1.5 mΩ at 12 GHz and 77 K was obtained in 0.3 μm TlCaBaCuO thin films using the ring resonator Q measurements. Typical values of penetration depth at 0 K in the TlCaBaCuO thin films were determined to be between 7000 and 8000 Å using the temperature variation of resonance frequency measurements.
Magnetic properties of superconducting YBa2Cu3Ox permanent magnets prepared by the melt process
Authors: Gotoh S. , Murakami M. , Fujimoto H. , Koshizuka N.
Published: July 2002

Demagnetizing curves after field cooling were measured in the melt processed YBa2Cu3Ox superconductors using a vibrating sample magnetometer and a SQUID magnetometer. The curves showed that the samples worked as strong bulk permanent magnets. This is attributed to the strong flux pinning of the bulk superconductors and is well explained in terms of the Bean–London model. The magnetic properties of the permanent magnet can be continuously changed using the field-cooling technique. The magnet properties of the melt-powder–melt-growth processed YBa2Cu3Ox with 1.5 mm thickness obtained at 5 K after field cooling in 10 kOe are as follows: the residual flux densities Br are 9.6 kG (H∥ c) and 8.5 kG (H⊥ c); the coercive forces bHc are 33 kOe (H∥ c) and 17 kOe (H⊥ c); and the maximum energy product, (BH)max, are 110 MGOe (H∥ c) and 49 MGOe (H⊥ c).
Influence of thin protective InAs layers on the optical quality of AlGaAs and quantum wells
Authors: Tsai K. L. , Chang K. H. , Lee C. P. , Huang K. F. , Chang Y. , Fan J. C. , Liu D. G.
Published: July 2002

Influence of a thin protective but subsequently evaporated InAs layer on the regrowth of AlGaAs has been studied. It was found that although most of the InAs could be evaporated by thermal desorption, some would react with Al0.36Ga0.64As to form InAlGaAs. These InAlGaAs islands act as potential wells for carrier recombination and dominate the photoluminescence spectrum. Transmission electron microscopy photographs show that dislocations are formed near the islands. These defects are caused by lattice mismatch between AlGaAs and InAlGaAs. These islands and defects strongly affect the optical quality of surrounding Al0.36Ga0.64As and quantum wells.
Raman spectroscopic characterization of KrF-laser-irradiated silicon
Authors: Holz L. , Semjonow A. , Lenz K. , Lau A. , Richter W. , Wilhelm H.
Published: July 2002

High-fluence KrF-laser-irradiated silicon wafers exhibit a wealth of surface structures, which are different depending on the medium present above the surface during treatment with ultraviolet light. A special surface feature, appearing after treatment under water and in air, is analyzed with a Raman microprobe spectrometer. It is found to consist of leaflike formed silicon structures located above but still attached to the treated surface. During Raman scattering measurements the temperature of these morphological peculiarity rises considerably even at low cw probe laser powers because of geometrically limited thermal conductivity. It is shown that the temperatures, which were derived from the Stokes–to–anti-Stokes scattering intensity ratio are more reliable than those extracted from line shifts since the stress developing inside the Raman laser-heated leaflike microstructures is not known. A Raman microprobe scan of a damage spot, generated by UV treatment under water, reveals in the most cases an enhanced Raman intensity (factor of 10) in comparison with untreated areas. This enhancement is even larger at surface spots of smaller (≤1 μm) sizes and is attributed to the field enhancement of the incident and scattered radiation field caused by geometrical resonances.
Electromigration-induced drift failure of via contacts in multilevel metallization
Authors: Oates A. S. , Nkansah F. , Chittipeddi S.
Published: July 2002

Much effort has been expended to improve metal sidewall coverage of via contacts in multilevel metallization schemes because of the possibility of an enhanced rate of electromigration failure at the sidewall. Multilayered conductors, which incorporate a refractory material beneath an Al alloy layer, will be more resistant to these voiding failures. These metallizations are not ideal, however, because of the discontinuities in the flux of electromigrating atoms at the Al/refractory interfaces of the via, which render the interfaces vulnerable to voiding. This paper examines the relative importance of electromigration at the sidewall and metal interface of vias containing AlSiCu/TiN multilayer conductors. Our results demonstrate that voiding failure is not associated with poor metal step coverage, and that the interface between the metal levels is the region most vulnerable to voiding. Formation of voids between the metal levels occurs by drift of the Al layer away from the Al/TiN interface, and there is a strong dependence of failure on the direction of electron flow through the via. This directional dependence arises because the Al drift velocity is determined by the current density in the stripes attached to the via. We present an expression for the via failure time that incorporates the stripe current density.
Structural and electrical characteristics of Ge and Se implanted InP after rapid thermal annealing
Authors: Kringho/j P. , Hansen J. L. , Shiryaev S. Yu.
Published: July 2002

The electrical activation of Ge and Se implanted into <100≳ InP at elevated temperatures and the annealing of the implantation-induced disorder have been investigated by differential Hall/resistivity measurements, Rutherford backscattering spectrometry, and transmission electron microscopy. At implantation temperatures below 170 °C, an amorphous layer is created by the implantation process. After recrystallization by rapid thermal annealing of the amorphized layer, a localized defect band was found, which gives rise to a dip (M shape) in the carrier density profile. This band is believed to be caused by a stoichiometric imbalance of In and P. For implantation temperatures above 170 °C, the samples remain crystalline during implantation and as a result, no localized defect band is observed.
Thermomagnetic study of the high-temperature oxidation behavior of Nd-Fe-B permanent magnets and powders
Authors: Lemarchand D. , Delamare J. , Vigier P.
Published: July 2002

Thermomagnetic measurements were used to determine the oxidation kinetics of bulk and powdered Nd-Fe-B magnets under a pressure of 1 Pa in the 360–600 °C temperature range. Those conditions are roughly similar to those undergone by sintered or rapidly quenched magnets during heat treatment. The first step of the oxidation kinetics obeys a parabolic law for bulk magnets and a cubic one for powders, with activation energies in the range 65–78 and 35–50 kJ/mol, respectively. Some anomalies in these patterns related to time or temperature are discussed.
Thermal donor formation and annihilation in oxygen-implanted float-zone silicon
Authors: Hahn S. , Stein H. J. , Shatas S. C. , Ponce F. A.
Published: July 2002

The formation and annihilation behaviors of thermal donors in 16O+-, 18O+-, or 16O++12C+-implanted float-zone silicon have been investigated with secondary ion mass spectrometry, spreading resistance probe, Hall effect, and transmission electron microscopy. Various oxygen or carbon+oxygen-implanted samples were laser annealed to remove implant damage and subjected to furnace annealing at 450 °C for up to 100 h to activate oxygen-related thermal donors. Oxygen concentrations at the peak of the implanted profiles exceed the maximum for Czochralski Si by an order of magnitude. It is found that the third to fourth power dependence of thermal donor formation on oxygen generally observed for Czochralski Si does not hold for the higher oxygen concentration in the implanted layer. Annihilation characteristics of thermal donors formed in the oxygen implanted layers were investigated by the rapid thermal annealing technique. A rapid thermal anneal at 1150 °C for 30 s was required to remove all the thermal donors. Based upon the annihilation kinetics data, it is tentatively concluded that both old and new thermal donors exist in the oxygen-implanted layer. For carbon+oxygen-coimplanted samples, the data have shown that carbon greatly increases the new thermal donor concentration in the implanted layer. Finally, precipitate morphologies for both oxygen-only- and carbon+oxygen-coimplanted samples after a 450 °C furnace annealing were investigated by high resolution electron microscopy. In the case of oxygen-implant-only samples, predominant precipitate morphologies are needlelike while platelet defects predominate for carbon+oxygen-coimplanted samples. Since carbon increases the formation rate of new thermal donors, it is unlikely that they are distinctly related to needlelike precipitates as claimed in previous studies.
Phase conjugation by degenerate four-wave mixing in a planar waveguide with a nonlinear cladding
Authors: Chen Bao Xue , Kobayashi Shunsuke
Published: July 2002

A novel analytical consideration is presented for dealing with phase conjugation by degenerate four-TE wave mixing in a planar waveguide bounded by a nonlinear cladding, in which both phase-conjugate power coupling and intensity-dependent field distributions are discussed. New wave solutions for signal and phase-conjugation reflections are obtained with anomalous power-dependent field distributions, and are used to specific numerical example based on a nematic liquid crystal.
Simulation of ion transport through curved-solenoid macroparticle filters
Authors: Davis C. A. , Donnelly I. J.
Published: July 2002

Ion transport through curved-solenoid macroparticle filters is investigated using a parabolic potential model of the electric field. Consideration of the ion equations of motion shows that the filter efficiency will increase with the relative radius of curvature of the solenoid and decrease with the relative length of the input region. If the magnetic field is constant in the input region, transport efficiencies of up to 100% are predicted. We argue that the observed effect of axial magnetic field on the angular distribution of ions emitted from the cathode spot can be explained by electric fields changing ion trajectories after emission, rather than a change in spot behavior. Detailed calculations give the energy and angular distributions with which the ions exit the filter. Focusing effects are observed and seen to affect the ion transport−particularly when the ions are not emitted on the filter axis.
Magnetoresistance peaks in the neighborhood of coercivity in magneto-optical recording media
Authors: Hajjar Roger A. , Mansuripur M.
Published: July 2002

Perpendicular magnetoresistance data performed on magneto-optical samples with uniaxial magnetic anisotropy (perpendicular to the film plane) show a change of the resistance ΔR/R when the applied field reaches the coercive field. The various mechanisms that can lead to this phenomenon are investigated based on different magneto-optical films. In particular, the interaction of magnetic domains and domain walls with the electric current is interesting. Separating the two effects is important to understanding of the various galvanomagnetic and magnetic processes in these films. Three different mechanisms are considered in order to explain the data: The first mechanism is associated with the Hall effect, the second mechanism involves the anisotropic resistivity, and the third mechanism is related to the s-d scattering effect. Some of the experimental results are explained by modeling the current and electric-field distribution in these films. In the simulations the film is modeled by a two- or three-dimensional lattice with each branch in the lattice having its own resistivity tensor in order to simulate magnetic domains and domain walls in the film.
High-resistivity GaSb grown by molecular-beam epitaxy
Authors: Polyakov A. Y. , Stam M. , Milnes A. G. , Wilson R. G. , Fang Z. Q. , Rai-Choudhury P. , Hillard R. J.
Published: July 2002

GaSb undoped layers grown by molecular-beam epitaxy on GaSb or on semi-insulating GaAs substrates at temperatures between 600 and 630 °C are shown to have carrier concentrations in the low 1013 cm−3 range, corresponding to almost intrinsic conditions. The materials have been characterized using current-voltage, capacitance-voltage, Hall effect, photoluminescence, thermally stimulated current, and secondary-ion mass spectrometry. Bulk GaSb (n type) is also found to have converted to high-resistance p type after a heat treatment at 630 °C. Speculations are offered for the responsible mechanism, but a definitive explanation does not exist at this time.
Dynamic light scattering measurements of high-pressure viscosity utilizing a diamond anvil cell
Authors: Herbst C. A. , King H. E. , Gao Z. , Ou-Yang H. D.
Published: July 2002

Dynamic light scattering (DLS) is a widely used and powerful technique for studying the dynamics of fluids. We demonstrate here the first use of DLS in the diamond anvil cell. Using 91 nm polystyrene spheres suspended in methanol in the chamber of a diamond anvil cell, we show that the viscosity of the fluid can be accurately measured using this technique. Measurements up to 2.90 GPa are reported. Previous reports of DLS measurements have used large-volume pressure cells that limited the data to moderate pressures, but with the diamond anvil cell no such limitations exist. However, a significant difficulty in DLS measurements with the diamond cell comes from the small size of the pressure chamber. Not only does this lead to a weak scattered intensity, but scattering from the sample is combined with partly coherent scattering from the diamond/air and diamond/sample interfaces, thus complicating data interpretation. We show how this heterodyne component can bias the measured diffusion coefficients and then demonstrate a straightforward procedure by which this heterodyne component can be minimized. The resulting diffusion coefficients (ranging from 10−8 to 10−10 cm2 s−1), recalculated as viscosity, are found to have an average precision of 2.5% and are in excellent agreement with literature values.
Photoemission study on the formation of Mo contacts to CuInSe2
Authors: Nelson A. J. , Niles D. W. , Kazmerski L. L. , Rioux D. , Patel R. , Höchst H.
Published: July 2002

Synchrotron radiation soft-x-ray photoemission spectroscopy was used to investigate the development of the electronic structure at the Mo/CuInSe2 interface. Mo overlayers were e-beam deposited in steps on single-crystal n-type CuInSe2 at ambient temperature. Photoemission measurements were acquired after each growth in order to observe changes in the valence-band electronic structure as well as changes in the In 4d, Se 3d, and Mo 4d core lines. Photoemission measurements on the valence-band and core lines were also obtained after annealing. The results were used to correlate the interface chemistry with the electronic structure at this interface and to directly determine the maximum possible Schottky barrier height φb to be ≤0.2 eV at the Mo/CuInSe2 junction before annealing, thus showing that this contact is essentially ohmic.
Photoluminescence investigations of Cd1−xMnxTe under hydrostatic pressure
Authors: Jiang S. , Shen S. C. , Li G. H.
Published: July 2002

The photoluminescence of Cd1−xMnxTe with x=0.25, 0.40, and 0.60 is investigated at 77 K and different pressures. The pressure coefficients of the photoluminescence bands Cd0.75Mn0.25Te and Cd0.6Mn0.4Te are found to be positive and the magnitudes are about 8×10−3 eV/kbar, which is in good agreement with the pressure coefficients of the interband transition. The pressure coefficient of the photoluminescence bands for Cd0.4Mn0.6Te is found to be −6×10−3 eV/kbar, which is quite different from the pressure coefficient of the interband transition. The possible transition mechanism is discussed in terms of group theory and crystal field theory.
Phase transformation of titanium silicide as measured by ellipsometry
Authors: Sikora Robert , Lundy Walter
Published: July 2002

The phase transition of sputter deposited titanium silicide from the metastable C49 phase to the stable C54 phase is detected through the use of ellipsometry and compared to the more common method of detection by sheet resistance changes. Effective medium theory is used to show how ellipsometry can be used to detect both compositional and microstructural changes in composite films via changes in the films dielectric function. The advantage of the ellipsometric technique over other methods is it’s noncontact nature which makes it suitable for measuring phase changes in situ.
An amorphous silicon/silicon-carbide double barrier structure with 2.66 peak to valley current ratio negative resistance
Authors: Fang Y. K. , Chen K. H. , Wu K. S. , Liu C. R. , Hwang J. D.
Published: July 2002

Amorphous silicon/silicon-carbide double barrier structure with 2.66 peak to valley ratio single negative resistance and 1.146/1.174 double negative resistance under room temperature are studied. Theoretical analysis and experimental investigation employed to raise peak to valley current ratio and to obtain multiple negative resistances current-voltage curve are also included.
A highly sensitive infrared spectroscopic method for buried thin low-index films
Authors: Brendel R.
Published: July 2002

A technique for the infrared spectroscopy of thin low-index films buried in a high-index material is introduced. The measurement technique applies a grazing incidence transmission of p-polarized light. The sensitivity enhancement over a transmission measurement is treated analytically for the thin film limit and is verified numerically by the simulation of spectra of ultrathin silicon oxide films within silicon as produced by wafer bonding. The technique can also be applied to hydrogen platelets within heavily hydrogenated silicon.
Enhancement of flux pinning in Bi2Sr2CaCu2O8 by 180 MeV Cu11+ irradiation
Authors: Kumakura H. , Ikeda S. , Kitaguchi H. , Togano K. , Maeda H. , Kase J. , Morimoto T. , Okayasu S. , Kazumata Y.
Published: July 2002

180 MeV Cu11+ irradiation was done on the c-axis grain oriented Bi2Sr2CaCu2O8 tapes. Irradiation enhanced hysteresis in dc magnetization curves, especially in high magnetic fields. The irreversibility line can be moved to higher field by irradiation. Transport Jc is also enhanced by the irradiation of the small fluences. The irradiation produced large (∼100 nm) and small (∼5 nm) defects. They are effective for flux pinning in Bi2Sr2CaCu2O8.
Carriers induced at the end of a quantum well
Authors: Stern Frank , Laux Steven E.
Published: July 2002

The charge distribution of carriers induced at the end of a quantum well by an auxiliary confining potential perpendicular to the plane of the well has been calculated for two examples. The first example considers a selectively doped layer grown epitaxially on a cleaved quantum well structure. The induced electron density in this case is found to be approximately proportional to the width of the well, with an additional charge from the dopants that project outside the well and with a cutoff at very small well widths as the quantum state is driven above the band offset. The second example considers the effect of surface pinning of the Fermi level above the conduction band edge of InAs.
Flux pinning in high-temperature superconducting multicore wires based on Bi2Sr2CaCu2Ox
Authors: Löhle J. , Mattenberger K. , Vogt O. , Wachter P.
Published: July 2002

Using the powder-in-tube technique superconducting 19-core wires have been produced with several diameters (down to 1/10 mm) and a length of some hundred meters. These wires show critical current densities of about 13500 A/cm2 in zero magnetic field and 6000 A/cm2 in a parallel field of 10 T at 4.2 K, respectively. For high magnetic field application it is necessary to understand the flux pinning mechanism. For this purpose the dissipative flux motion below Tc has been studied. The results of dc measurements were parametrized in the framework of flux creep. Using the Anderson model [published in Phys. Rev. Lett. 9, 309 (1962)], we find an activation energy inversely proportional to the square root of the magnetic field.
Far-infrared measurements of the mobility and carrier concentration in lightly doped GaAs on Si(100)
Authors: Morley S. , Zahn D. R. T. , Eickhoff T. , Richter W. , Woolf D. A. , Westwood D. I. , Williams R. H.
Published: July 2002

GaAs layers with thicknesses from 1 to 8 μm were grown by molecular-beam epitaxy onto Si(100) substrates. These epitaxial layers were lightly doped with Si (ND≂2×1016 cm−3). The determination of accurate numbers for the carrier concentrations and mobilities in the GaAs is complicated by the low doping and the dimensions of the films. However, a new approach in IR spectroscopy that combines a conventional reflectance measurement from 50 to 500 cm−1 with a transmittance measurement in the very far-infrared range from 12 to 62 cm−1 is demonstrated to provide precise information on both carrier concentrations and mobilities. A comparison of the results obtained at room temperature from IR and Hall measurements reveals that the nondestructive IR technique is an easy to perform and excellent characterization tool for the Ga As layers.
Observation of natural oxide growth on silicon facets using an atomic force microscope with current measurement
Authors: Hosaka Sumio , Koyanagi Hajime , Hasegawa Tsuyoshi , Hosoki Shigeyuki , Hiraiwa Atsushi
Published: July 2002

Natural oxide growth on silicon facets is observed through an atomic force microscope (AFM) with current measurement. The sample is prepared by means of cleaning and heating a silicon (111) surface with direct electric heating in an ultrahigh vacuum, which creates various facets formed by step bunching. The silicon facets and steps can be observed with the AFM in air. The silicon surface structure and the current distribution can simultaneously be obtained. The results clarify that natural oxide growth on a few special high-index-orientation silicon facets is smaller than that on the other silicon facets ({111}, {110}, {100}, etc.).
Liquid-metal Couette flow with a two-dimensional periodic static surface and a transverse magnetic field
Authors: Beatty David J. , Walker John S. , Brown Samuel H. , Sondergaard Neal A.
Published: July 2002

The liquid-metal flow between a smooth moving wall and a two-dimensional, periodic, static wall with a uniform magnetic field that is perpendicular to both walls is treated. This problem models the flow in a liquid-metal sliding electrical contact with extremely large electric currents. The periodic static wall models the surface of a metal-fiber brush. The flow for a two-dimensional static wall is very different from that for a smooth static wall and involves large electrically driven spatial oscillations of the velocity, with swirling motion around the hills and valleys of the periodic surface. Solutions are presented (1) for large magnetic-field strength and arbitrary dimensionless periodic wall height, and (2) for arbitrary magnetic-field strength and small periodic wall height. Comparison of the two solutions indicates that viscous effects reduce the large velocity oscillations for typical electrical contacts.
Gallium acceptor incorporation in molecular beam epitaxial germanium on GaAs
Authors: Wood Colin E. C.
Published: July 2002

Conditions for ≤1021 cm−3 gallium doped p-type germanium films on vicinal (100) GaAs substrates are reported. Steady state gallium concentrations are linearly related to incident fluxes. Between 470 and 650 °C, incorporation is by thermodynamic distribution between accumulated surface concentrations and growing films. The distribution function favors higher incorporation with increasing temperature, however surface concentrations are significantly reduced by desorption above 550 °C. Kinetic limitations produce a retrograde temperature dependence of the distribution below ∼460 °C.
A new circuit model for tunneling related trapping at insulator-semiconductor interfaces in accumulation
Authors: Mui D. S. L. , Reed J. , Biswas D. , Morkoç H.
Published: July 2002

We have investigated the effects due to the capture of tunneling electrons by interface traps to the measured capacitance, Cm, and equivalent series resistance, Rm, of insulator-semiconductor interfaces in metal-insulator-semiconductor (MIS) capacitors in accumulation. A new circuit model taking into account the capture of tunneling electrons by interface traps is derived. Theoretical and experimental results of Si3N4/Si/GaAs, Si3N4/epi-Si, and SiO2/epi-Si MIS capacitors are compared. The Si, Si3N4, and SiO2 layers investigated were deposited in situ by electron cyclotron resonance generated plasma in an ultrahigh vacuum chemical vapor deposition chamber. Frequency dispersion of both Cm and Rm can be adequately explained by the new circuit model.
Self-consistent Monte Carlo particle transport with model quantum tunneling dynamics: Application to the intrinsic bistability of a symmetric double-barrier structure
Authors: Salvino R. E. , Buot F. A.
Published: July 2002

The intrinsic bistability in a symmetric resonant tunneling device (RTD) is simulated by the ensemble particle Monte Carlo technique, coupled with a simple model of the space- and time-dependent particle quantum dynamics inside the double-barrier region of the RTD. This model particle quantum dynamics is based upon the phase-time delay, which is obtained from a piecewise-linear-potential Airy function approach to the calculation of the transmission amplitude. An unambiguous hysteresis in the negative differential resistance (NDR) region of the current-voltage (I-V) characteristic is observed for a symmetric AlGaAs/GaAs double-barrier structure. The dynamical accumulation of carriers in the well is seen to be the cause of this marked bistability/hysteresis. However, the plateau-like features of the I-V curve are not resolved, although oscillations in the quantum well carrier density in the NDR are prominent. This article strongly suggests that a more accurate treatment of the space- and time-dependent particle quantum dynamics across the RTD is of paramount importance.
A new 1/f noise model for metal-oxide-semiconductor field-effect transistors in saturation and deep saturation
Authors: Zhu Y. , Deen M. J. , Kleinpenning T. G. M.
Published: July 2002

A new 1/f noise model for metal-oxide-semiconductor field-effect transistors (MOSFETs) in saturation and deep saturation based on the Hooge’s mobility fluctuation (MF) noise expression is presented. The new model uses detailed one-dimensional expressions of carrier number per unit length n(x) and channel potential V(x) varying with channel position x to calculate the gate referred noise spectral density SVG(f) in both saturation and deep saturation. The analytic variation of both n(x) and V(x) with x has been corroborated with a two-dimensional device simulator. In addition, new formulas for 1/f noise in MOSFETs based on the number fluctuation (NF) model are also presented. The theoretical results of SVG(f) and the drain current noise spectral density SID(f) versus biasing voltages, using the MF model, are in better agreement to the experimental results than the theoretical results of SVG(f) and SID(f) based on the NF model.
Magnetic hysteresis of a rectangular lattice of interacting single-domain ferromagnetic spheres
Authors: Lam John
Published: July 2002

The effect is investigated of interparticle interaction on the Stoner–Wohlfarth theory of magnetic hysteresis in single-domain particles. A model of interacting, identical, single-domain, ferromagnetic spheres in a three-dimensional rectangular lattice is studied. The anisotropy energy of the spheres is taken to be magnetocrystalline. Under the assumption that the magnetizations on the identical spheres are identical, the magnetostatic lattice interaction energy is calculated exactly in closed form. An exact formula is derived for the critical magnetic field as a function of the packing fraction of the spheres. The formula is also applicable to a lattice of aligned prolate spheroids if the dipole interaction is dominant. It is deduced that the coercive force of a specimen of compacted spherical particles should have no dependence on the packing fraction, while that of a specimen of compacted acicular particles should decrease linearly with increasing packing fraction. The deduction is compared with published experimental data.
Re-evaluation of spin-dependent cross sections of solutes in ferromagnetic hosts
Authors: Stearns Mary Beth
Published: July 2002

The resistivity data of ferromagnetic alloys has been re-evaluated taking into account that the conduction electrons in 3d ferromagnetics are predominantly polarized d-like electrons with high net polarization. This drastically changes the previously derived values of solute cross sections and scattering rates ratios of the majority and minority electrons. In particular, it removes the perplexing result of previous analyses that the spin-up and spin-down cross sections of sp solute atoms were not equal. Moreover, since past analyses of scattering, transport effects, etc., in 3d ferromagnetics have assumed that the conduction electrons are sp-like, all these results should also be critically re-examined to determine their validity.
Magnetic behavior and structure of the halogen-doped fullerene C60
Authors: Sekine Hisashi , Maeda Hiroshi , Kosuge Michio , Tanaka Yoshiaki , Tokumoto Madoka
Published: July 2002

We simultaneously doped bromine and iodine (electron acceptors) into C60 (fullerene) which is known to become superconductive by doping alkali metals (electron donors). The simultaneous doping of bromine and iodine into C60 brought about a hysteresis in the magnetic moment versus magnetic field curves as well as a structural change when the molar ratio of IBr (the 1:1 compound of iodine and bromine) to C60 is over about 2.5.
Metalorganic molecular beam epitaxial growth and characterization of CdSe/ZnSe strained-layer single quantum wells and superlattices on GaAs substrates
Authors: Fujita Shizuo , Wu Yi-hong , Kawakami Yoichi , Fujita Shigeo
Published: July 2002

Reflection high-energy electron diffraction (RHEED) oscillations that continued up to three cycles were observed during metalorganic molecular-beam epitaxial growth of CdSe on a ZnSe buffer grown on a GaAs substrate, showing two-dimensional layer-by-layer growth despite the large lattice mismatch (6.85%). Based on this result, we could definitely control the growth of CdSe/ZnSe strained-layer single quantum wells with well widths of 1–3 monolayers and of short-period superlattices under in situ RHEED monitoring. Optical properties strongly demonstrated the successful formation of well-defined structures consisting of these highly strained II-VI semiconductor multilayers.
Reply to ‘‘Comment on ‘A Comment on dielectric theory: Differential equations and permittivity’ ’’
Authors: Kliem H.
Published: July 2002

It is emphasized that in the comment of J. M. Alison on my communication [J. Appl. Phys. 70, 1861 (1991)] the time dependent coefficient f(t) in the equation of motion has been mistaken for the dielectric decay function φ(t).
Asymptotic theory of power transport by guided modes in two parallel, identical planar dielectric waveguides
Authors: Seshadri S. R.
Published: July 2002

An asymptotic treatment of power transport by guided modes in two parallel, identical planar dielectric waveguides is presented in the weak coupling limit. The small parameter is the factor by which the field amplitude decays from one waveguide to the other. The maximum power is transferred from one waveguide to the other periodically in the propagation direction, the spatial period being known as the interaction length. When the power in one waveguide is a maximum, there is a small amount of residual, undesirable power in the other waveguide. This cross talk is intrinsic to a coupled system. It is shown that the product of the intrinsic cross talk and the interaction length is a constant depending only on the parameters of the corresponding uncoupled waveguide. Also, this constant is identical to the transverse electric mode and the transverse magnetic mode. This cross-talk relation shows that the intrinsic cross talk can be reduced only at the expense of increasing the device dimensions.
Polarization effects on laser-induced growth of optically anisotropic CuTe thin films
Authors: Hanus F. , Wautelet M. , Laude L. D.
Published: July 2002

CuTe thin films are synthesized onto glass substrates by scanning an Ar+ laser beam on vacuum deposited sandwich films of Cu and Te in 1:1 stoichiometric ratio. At a laser power greater than the threshold power for synthesis to occur, laser irradiation results in large synthesized areas (1 cm2) whose optical properties are demonstrated to be highly anisotropic, like CuTe, which is known to be birefringent and pleiochroic. It is demonstrated experimentally that the optical anisotropy of these laser-synthesized CuTe films depends on the wavelength, power, and polarization of the laser beam. The synthesized blade-like crystallites are preferentially oriented. It is argued that their preferential orientation is due to a combination of the high-energy gradient and the relative orientation of the laser beam polarization with respect to the scanning direction.