bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature dependence of optical and electronic properties of moderately doped silicon at terahertz frequencies
Authors: Nashima S. , Morikawa O. , Takata K. , Hangyo M.
Published: July 2002

Complex conductivity of moderately P-doped silicon wafers (1.1±0.2 Ω cm at room temperature) has been measured by using a terahertz (THz) time-domain spectroscopy for the temperature and frequency ranges of 20–300 K and 0.2–1.1 THz, respectively. The strong frequency dependence of the complex conductivity due to the free carriers in the THz region is observed and it changes rapidly with temperature, which is interpreted in terms of the increase in mobility and freezing of the free carrier as analyzed by using the simple Drude model. The experimental data deviate slightly from the simple Drude model at low temperatures and becomes apparent with decreasing temperature.
Spatially modified layer properties related to the formation of gallium droplets on GaN(0001) surfaces during plasma-assisted molecular-beam epitaxy
Authors: Kruse C. , Einfeldt S. , Böttcher T. , Hommel D. , Rudloff D. , Christen J.
Published: July 2002

The surface morphology and the spatial distribution of defect-related luminescence of GaN(0001) layers grown by plasma-assisted molecular-beam epitaxy under gallium-rich conditions has been investigated. Droplets of liquid gallium form on the surface during growth and lead to distinct spiral hillocks under the droplet. The droplets are surrounded by extended voids which point to an incomplete gallium adlayer on the GaN surface during growth at the droplet boundary. Cathodoluminescence spectra indicate an enhanced intensity in the yellow spectral range for the GaN under the droplets which is attributed to a change in the local density of point defects in the layer.
Generation of fluxes of highly charged heavy ions from a picosecond laser-produced plasma
Authors: Badziak J. , Parys P. , Vankov A. B. , Wołowski J. , Woryna E.
Published: July 2002

The results of the investigations of ion emission from targets of medium and high atomic numbers irradiated by 1 ps laser pulse of intensity up to 5×1016 W/cm2 are presented. The generation of high energy (up to 1 MeV) highly charged heavy ions (Ta+38, Au+33), as well as Ar-like Ag ions and fully striped Al ions is demonstrated. Some properties of ion fluxes emitted from picosecond laser-produced high-z plasmas are determined.
Transport properties of Bi1−xSbx alloy nanowires synthesized by pressure injection
Authors: Lin Yu-Ming , Cronin S. B. , Rabin O. , Ying Jackie Y. , Dresselhaus M. S.
Published: July 2002

Various transport measurements are performed to assess the alloying and size effects in sub-100 nm Bi1−xSbx (0⩽x⩽0.15) nanowires. Temperature-dependent resistance measurements exhibit non-monotonic trends as x increases, and a theoretical model is presented to explain the features which are related to the unusual band structure of Bi1−xSbx systems. Magnetoresistance measurements of these Bi1−xSbx nanowires show interesting size-dependent behaviors similar to those in Bi nanowires.
Activation barriers for series of exothermic homologous reactions. VI. Reactions of lanthanide and transition metal atoms.
Authors: Blue Alan S. , Fontijn Arthur
Published: July 2002

Semiempirical configuration interaction (SECI) theory to predict activation barriers, E, as given by k(T)=ATn exp(−E(RT), has been applied to homologous series of lanthanide (LN) and transition metal (TM) atom oxidation reactions. This was achieved by considering as homologous series reactions of elements differing only by the number of electrons in one subshell. Comparison between SECI and experimental results leads to an average deviation for the LN+N2O reactions of 0.66 kJ mol−1, and up to 5.5 kJ mol−1 for other series. Thirty-one activation barriers are reported.
Application of higher order decouplings of the dilated electron propagator to Π2 CO−, Πg2 N2− and Πg2 C2H2− shape resonances
Authors: Mahalakshmi S. , Venkatnathan Arun , Mishra Manoj K.
Published: July 2002

The full third order (Σ3), quasi-particle third order (Σq3) and outer valence Green’s function (OVGF-A) decouplings of the bi-orthogonal dilated electron propagator have been implemented and results from their application to Π2 CO−, Πg2 N2−, and Πg2 C2H2− shape resonances are presented and compared with energies and widths obtained using the zeroth order (Σ0), quasiparticle second order (Σq2) and second order (Σ2) decouplings. The energies and widths from the various Σ3 decouplings for shape resonances are close to those obtained using the Σ2 approximant but the corresponding Feynman–Dyson amplitudes (FDAs) differ considerably. The differences between FDAs from different decouplings are analyzed to elicit the role of correlation and relaxation in the formation and decay of shape resonances.
Investigation of off-aligned exchange coupling by torque curve and ferromagnetic resonance
Authors: Layadi A.
Published: July 2002

Off-aligned exchange coupling in bilayer thin film is investigated by torque curve and ferromagnetic resonance (FMR). In off-aligned exchange coupling, the unidirectional anisotropy axis makes an angle β with the anisotropy axis of the ferromagnetic layer. The torque curves of the off-aligned exchange are shifted with respect to the ones of the aligned case (β=0). From the experimental measure of the shift angle α0 and of the torque curve slope at α0, one can determine independently the exchange anisotropy field HE and β values. A description of the FMR modes in such an off-aligned exchange coupling is given. The FMR mode position and linewidth are studied as a function of the anisotropy fields, of the off-aligned angle values, and of the applied field direction. The resonance frequency and frequency linewidth present particular features which will help to do the right interpretation of FMR spectra of these systems.
Elastic oscillations of cylindrical fuses
Authors: Mahan G. D. , Gladden J. R. , Maynard J. D.
Published: July 2002

A fast current pulse causes a material to heat and undergo rapid expansion. We calculate the response of a cylindrically shaped material to a pulse on the microsecond time scale. The first step is to obtain the breathing modes of elastic oscillation of the cylinder. These modes are calculated using a Rayleigh–Ritz variational method introduced by Demarest for cubes. The boundary conditions are derived, which give the amplitude of each elastic mode in response to the sudden heating. The results are illustrated by calculations on a station arrester made of a ZnO ceramic.
Crystalline orientation effects on the electronic transport properties of LaMnOy thin films
Authors: Zhang J. H. , Ming N. B. , Li X. G.
Published: July 2002

We have grown epitaxial and polycrystalline LaMnOy thin films on a LaAlO3 substrate by the off-axis magnetron sputtering technique and investigated the crystalline orientation effects on the electronic transport properties. Lattice mismatch, crystalline quality, resistivity, resistivity transition temperature Tp, and magnetoresistance (MR) in epitaxial films exhibit crystalline orientation dependence. The largest Tp and MR are observed in the (111) oriented films. In the polycrystalline films, the Tp is smaller than that of the (011)/(111) oriented films but higher than that of the (001) oriented films. The MR increases with decreasing temperature in contrast to that of the epitaxial films in which the MR experiences a peak near Tp. Oxygen annealing decreases MR and resistivity, and increases Tp in the order: (111)<(011)<(001)<(polycrystalline). The above results suggest that the structure and composition of the epitaxial films improve in the order: (001)<(011)<(111).
Characterization of metal-containing carbon films using Raman scattering
Authors: Huang Q. F. , Yoon S. F. , Rusli  , Chew K. , Ahn J.
Published: July 2002

Metal-containing carbon (Me-C:H) films were deposited using the electron cyclotron resonance chemical vapor deposition technique in conjunction with a metal screen-grid system. Four sets of Me-C:H films were analyzed using Raman scattering. Two sets were molybdenum-containing carbon (Mo-C:H) films deposited at fixed dc bias (at different CH4/Ar ratios), and at fixed CH4/Ar ratio (at different dc bias). Another two sets of nickel-containing carbon (Ni-C:H) films were deposited at fixed rf power, but at a different CH4/Ar ratio, with and without postgrowth thermal annealing at 200 °C. All films showed the characteristic G and D peaks except for those with high metal content. The D peak is very pronounced in the Ni-C:H films, and both the G and D peaks follow an opposite trend; downshifting and upshifting in wave number, respectively, as the CH4/Ar ratio was increased. In the case of Mo-C:H films deposited at fixed dc bias, both peaks downshifted in wave number, following an increase in the CH4/Ar ratio. The G peak full width at half maximum for both the Ni- and Mo-C:H films increased slightly with an increase in CH4/Ar ratio, consistent with the variation in the relative integrated intensity of the D to G peak (ID/IG). Thermal annealing experiments conducted on the film samples revealed relatively stable characteristics with a minor effect on the film structure. The results showed that the impinging ion energy plays an important role in the structural properties of the Me-C:H films.
Aging behavior of porous silicon electrochemically etched with the aid of Zn
Authors: Suh K. Y. , Kim Y. S. , Lee Hong H.
Published: July 2002

Aging behavior of red, green, and blue photoluminescence from porous silicon formed by electrochemical etching aided with zinc has been studied over a 3 month time span. Time-resolved photoluminescence spectra and decay dynamics have revealed that there are two radiating states in Zn-aided porous silicon. One is the quantum confinement and the other is the oxygen-related defect. For green emission, the wavelength shifts from 520 to 420 nm and its photoluminescence spectra and decay behavior become very similar to those of blue emission.
Submicron nickel deposition on silicon from an electrolytic solution controlled by near-field optics
Authors: Diesinger H. , Bsiesy A. , Hérino R.
Published: July 2002

The application of a near-field optical device to the electrochemical deposition of submicron nickel dots on silicon is demonstrated. The silicon–electrolyte junction behaves like a Schottky diode where the electrolyte plays the role of the metal. The junction is reverse biased so that only a negligible dark current is flowing across the junction. The optical tip of the near-field device is used as a local lightsource to control a photocurrent on a submicron scale, which allows one to create submicron objects of nickel by locally triggering the electrochemical reduction of nickel ions. The effect of the lateral diffusion of the photogenerated carriers on the form of the deposited nickel dots is described by a two-dimensional carrier diffusion model.
Single-electron charging phenomena in silicon nanopillars with and without silicon nitride tunnel barriers
Authors: Pooley D. M. , Ahmed H. , Mizuta H. , Nakazato K.
Published: July 2002

Electron transport in silicon nanopillars has been studied for pillars with zero, one, or two silicon nitride barrier layers of 2 nm thickness. Evidence of Coulomb blockade is presented and the role of the silicon nitride layers is discussed. Wide zero current regions are observed for some devices with two silicon nitride tunnel barriers and these are attributed to the formation of fully depleted quantum dots.
Interaction of guided optical waves and magnetostatic forward volume waves in a double-layered waveguide under inclined magnetic field
Authors: Xinwen Si , Gongqiang Liu , Wenkang Zhang
Published: July 2002

The noncollinear interaction between the guided optical waves (GOWs) and magnetostatic forward volume waves (MSFVWs) is theoretically studied in a double-layered waveguide under inclined magnetic field. The diffraction efficiency (DE) and the mode-conversion efficiency of GOWs are calculated numerically at the different inclination angles of the field. The results indicate that the double-layered waveguide, in which the top magnetic layer is made of the Bi-doped YIG film, can enhance the DE of GOWs. Under the phase-matching conditions, the DE may be greatly enhanced by using an appropriately inclined magnetic field in the double-layered waveguide. In addition, by varying the inclination angle of the field and the interval of the double-layered waveguide, the magneto-optical (MO) coupling between the GOWs and MSFVWs can be adjusted in the larger range. It is possible to improve the performances of the MO waveguide devices more effectively.
Plastic deformation at high temperatures of pure and Mn-doped GaSb
Authors: Plaza J. L. , Diéguez E. , Jiménez-Melendo M. , Domı́nguez-Rodrı́guez A.
Published: July 2002

In this work the plastic behavior of GaSb and Mn-doped GaSb at high temperature has been analyzed. Several experiments at different constant load and temperatures around 500 °C were carried out. The parameters used in the Haasen model have been obtained experimentally and compared with the ones obtained from simulations.
Optical and transport properties of Sb-doped SrTiO3 thin films
Authors: Wang Huan-hua , Cui Da-fu , Dai Sou-yu , Lu Hui-bin , Zhou Yue-liang , Chen Zheng-hao , Yang Guo-zhen
Published: July 2002

Optically transparent SrTi1−xSbxO3 (=0.05, 0.10, 0.15, and 0.20) thin films with transmittances higher than 85% in the visible region have been grown on SrTiO3 substrates by pulsed-laser deposition. Unless overdoped, the films possess a single-crystal phase and impurity conduction. The temperature dependence of the resistivities shows a metal–semiconductor transition for the film with x=0.05, and semiconducting behaviors for the films with x=0.10 and 0.15. The overdoped film with x=0.20 is an insulator. Sb concentration has a dominant effect on the electrical properties of the films, and the Anderson localization is probably the mechanism. X-ray photoelectron spectroscopy results indicate that the Sb impurity atoms provide donor electrons to form impurity states within the band gap, which is responsible for the electrical localized impurity. The wide band gap and the low density of states in the conduction band result in the transparency of the films. The disorder increases with Sb concentration, which is the main origin of the evolution of the electrical properties.
Electric-field-induced polarization in the ergodic and nonergodic states of PbMg1/3Nb2/3O3 relaxor
Authors: Dkhil B. , Kiat J. M.
Published: July 2002

We report results obtained from polarization measurements on PbMg1/3Nb2/3O3 single crystal under static electric field, in both field cooling and field switching after zero field cooling processes. In the field cooling process, two kinds of regime are observed depending on the field strength, i.e., above and below threshold value Et≈1.7 kV/cm. From the low field regime results we have extracted both linear and nonlinear susceptibilities, which exhibit an anomaly close to the freezing temperature. In the field switching after zero field cooling experiments, a local polarization corresponding to the appearance of polar nuclei develops up to a critical value where the nuclei collapse into macroscopic ferroelectric macrodomains.
The effect of strain in InP/InGaAs quantum-well infrared photodetectors on the operating wavelength
Authors: Gusakov Y. , Finkman E. , Bahir G. , Ritter D.
Published: July 2002

We report on InP/InGaAs quantum-well infrared photodetectors (QWIPs) that cover the spectral range from 8 to 11 μm. The only previously reported operating wavelength for QWIPs of the same material system was around 8 μm. The higher operating wavelengths were achieved by including the strain as an additional band gap engineering parameter. According to our calculations, the InP/InGaAs lattice-mismatched multiple quantum well structures are suitable for design QWIPs covering the 5.5–11 μm range. We demonstrate five different QWIP structures with bound-to-bound and bound-to-continuum transitions for photodetection in the 8–12 μm atmospheric window. The calculations are in very good agreement with the experimental data. We found that the InP/InGaAs material system is more flexible than GaAs/AlGaAs because it has an additional degree of freedom—the strain for band gap engineering design.
Identification of aging mechanisms in the optical and electrical characteristics of light-emitting diodes
Authors: Pursiainen Otto , Linder Norbert , Jaeger Arndt , Oberschmid Raimund , Streubel Klaus
Published: July 2002

We report new methods of identifying the effects of aging on the light–current (L–I) and current–voltage (I–V) characteristics of AlInGaP light-emitting diodes (LEDs). We believe that these methods are also applicable to other III–V compound semiconductors. We observe a broadening of the nonlinear range of the L–I characteristic accompanied by a shift to higher currents in the I–V characteristic. These features can be attributed to an increase of nonradiative recombination processes in the active layer. A second process, however, can lead to an increase of the LED output power. We conclude from an analysis of the current dependence that this process is due to a different mechanism.
Isotropic Raman scattering of HF in dense gas and liquid SF6: Study of the motional narrowing effect
Authors: Padilla A. , Pérez J. , Hernández A. Calvo
Published: July 2002

The isotropic Raman spectra of HF diluted in dense gas and liquid SF6 have been calculated and compared with existing experimental data. The motional narrowing that arises in the transition from dense gas to liquid phase has been studied globally and line-by-line. The influence of mixing and memory effects and the role played by the different terms of the solute–solvent interaction are especially considered.
Subsurface impurities in Pd(111) studied by scanning tunneling microscopy
Authors: Rose M. K. , Borg A. , Mitsui T. , Ogletree D. F. , Salmeron M.
Published: July 2002

Low concentrations of three distinct impurity species beneath the Pd(111) surface are studied by STM. The subsurface impurities are distinguished by their image contrast, diffusion properties, and interactions with adsorbed molecules. Isolated subsurface impurities appear at low gap resistance (<≈ MΩ) as three-fold symmetric modulations of the Pd 1×1 surface corrugation. One impurity type is found to occupy substitutional sites in the layer below the surface. Based on Auger spectroscopy this species is identified as sulfur. The other two species are found to occupy octahedral interstitial sites immediately below the surface layer. Two-dimensional diffusion of the interstitial impurities occurs below room temperature. The onset temperature for diffusion is lowered dramatically in the presence of surface adsorbates. Quantitative measures of the diffusion barriers are consistent with surface facilitated diffusion of interstitial oxygen and carbon atoms. The mobile impurities interact with adsorbed atoms and molecules, limiting surface diffusion, nucleating island growth, and serving as active sites for surface reactions.
Nonmagnetic spinguides and spin transport in semiconductors
Authors: Gurzhi R. N. , Kalinenko A. N. , Kopeliovich A. I. , Yanovskiı̆ A. V.
Published: July 2002

The construction of a spinguide—a semiconductor channel with walls consisting of a dilute magnetic semiconductor with very large Zeeman splitting and transmitting electrons only with one type of polarization—is proposed. Such channels can be sources of spin-polarized current in nonmagnetic conductors. They can be used for creating fast switches of the spin-polarization direction of the electric current and for transmitting spin polarization over large distances (even larger than the spin-flip length). The selective transparency of the walls gives rise to new size transport effects.
Ferroelectric plasma cathode with a control grid
Authors: Dunaevsky A. , Krasik Ya. E. , Felsteiner J. , Sternlieb A.
Published: July 2002

Experimental results of high-current electron beam generation in a planar diode with a ferroelectric plasma cathode and a control grid are presented. The plasma is formed as a result of noncomplete discharge on the surface of a BaTiO3 sample when a driving pulse is applied to its rear electrode. This noncomplete surface discharge leads also to the appearance of fast plasma flows which fill the anode–cathode gap prior to the application of the accelerating electric field. The measured plasma densities and flow velocities allow us to estimate the bias potential of the control grid which is needed for the suppression of the plasma flows. The dependence of the plasma density on the grid potential is presented. Using the control grid, operation of the diode with the ferroelectric plasma cathode is achieved with negligible plasma prefilling of the anode–cathode gap.
Quantum-interference characteristics of a 25 nm trench-type InGaAs/InAlAs quantum-wire field-effect transistor
Authors: Sugaya T. , Bird J. P. , Ogura M. , Sugiyama Y. , Ferry D. K. , Jang K.-Y.
Published: July 2002

We study the quantum-interference characteristics of a 25 nm, trench-type, InGaAs quantum-wire field-effect transistor realized by selective epitaxy, and find very different behavior from that typically exhibited by disordered wires. The amplitude of the magnetoresistance fluctuations is exponentially suppressed at high fields, where evidence of an Aharonov–Bohm effect is observed. The exponential suppression appears to be consistent with theoretical predictions for the influence of magnetic field on the scattering rate in clean wires, while the Aharonov–Bohm effect points to an interference process in which the one-dimensional subbands of the wire themselves constitute well-resolved paths for electron interference.
SU
(N)
skyrmions from harmonic maps S2→Gr(2,N)
Authors: Wospakrik H. J. , Zakrzewski W. J.
Published: July 2002

We construct multiskyrmion fields of the SU(N) Skyrme models by using harmonic maps of S2 to the Grassmannian Gr(2,N), which we express in terms of rank-2 projectors. Within this construction we derive some approximate spherically symmetric solutions of SU(N) Skyrme models and show that their energies are marginally higher than those for the rank-one cases. We also discuss the possibility of generating exact spherically symmetric solutions using this construction. In particular, we present arguments which suggest that the only solutions obtained in this way are embeddings.
Observation of oscillating behavior in the reflectance difference spectra of oxidized Si(001) surfaces
Authors: Matsudo Tatsuo , Ohta Tomohiro , Yasuda Tetsuji , Nishizawa Masayasu , Miyata Noriyuki , Yamasaki Satoshi , Shklyaev Alexander A. , Ichikawa Masakazu
Published: July 2002

Layer-by-layer oxidation of Si(001)-(2×1) surfaces was observed using the reflectance difference (RD) spectroscopy. Distinctive features in the RD spectra appeared near the E1 (3.3 eV) and E2 (4.2 eV) transition energies of Si. The polarity of these features was repeatedly reversed as the oxide thickness was increased to 4 monolayers (MLs). Oscillation of the RD amplitude near the E1 transition energy was observed in real time during the oxidation process. A half period of the oscillation corresponds to the oxidation of 1 ML. These results demonstrate the possibility of in situ counting and control of the number of oxidized layers.
Analysis of the admittance-frequency and capacitance–voltage of dense SnO2⋅CoO-based varistor ceramics
Authors: Bueno P. R. , Oliveira M. M. , Bacelar-Junior W. K. , Leite E. R. , Longo E. , Garcia-Belmonte G. , Bisquert J.
Published: July 2002

This article describes the admittance-frequency feature of a class of SnO2⋅CoO-based polycrystalline ceramics with high nonlinear current–voltage characteristics (nonlinear coefficients above 50). Broad relaxation peaks caused by the presence of deep trap states were characterized based on the admittance response of different systems doped with La2O3, Pr2O3, and CeO2. The calculation of the energy of this deep trap level revealed not only that all the compositions share the same value but also that this value could be attributed to an oxygen vacancy or to CoSn▾ like defects. The values of barrier height and density of states obtained from a capacitance–voltage analysis are in good agreement with the nonlinear coefficients. The highest nonlinear coefficients are found in compositions with greater barrier height values and higher density of deep trap states at the grain boundary interface.
Composition control of Hf1−xSixO2 films deposited on Si by chemical-vapor deposition using amide precursors
Authors: Hendrix B. C. , Borovik A. S. , Xu C. , Roeder J. F. , Baum T. H. , Bevan M. J. , Visokay M. R. , Chambers J. J. , Rotondaro A. L. P. , Bu H. , Colombo L.
Published: July 2002

Hafnium silicate (Hf1−xSixO2) films were deposited by metalorganic chemical-vapor deposition with composition x ranging from 0 to 1 using amide precursors in an organic solvent. The liquid precursors, tetrakis(diethylamido)hafnium, Hf[N(C2H5)2]4, and tetrakis(dimethylamido)silicon, Si[N(CH3)2]4, are compatible when mixed in solution, have high elemental purity, and exhibit a low halogen content. Thin oxide films were deposited with these precursors over a range of wafer temperatures from 400 to 600 °C with very low carbon and nitrogen incorporation. Control of the film composition is attained by changing the ratio of silicon concentration to hafnium concentration in the precursor solution for specific deposition conditions. Composition and growth rate are reported as a function of process condition. Interfacial layers of less than 10 Å were observed by high-resolution transmission electron microscopy.
Wavelength demodulation using optically quenched lasers
Authors: Parker Michael A.
Published: July 2002

Gain quenched lasers can satisfy the requirements for all-optical switches in communications and computing systems. Hitherto, these devices have lacked optical gain between the input beam and output beam, and have been limited to switching amplitude modulated optical signals. A simple model based on the laser rate equations demonstrates that quenched devices can convert wavelength modulated signals into amplitude modulated ones with programmable optical gain. The discussion includes the effect of carrier injection, laser construction, and type of heterostructure.
Effect of implanted metal impurities on superconducting tungsten films
Authors: Young B. A. , Saab T. , Cabrera B. , Miller A. J. , Brink P. L. , Castle J. P.
Published: July 2002

The superconducting transition temperature of more than 30 thin-film tungsten samples was measured using a dilution refrigerator. The samples were fabricated using a 99.999% pure tungsten target and a dc magnetron sputtering system. Individual films were then doped with metal impurity ions using an accurate ion implantation technique. The effect of the metal–ion doping on the superconducting transition temperature was measured for samples with superconducting transitions in the range of 40–150 mK. Magnetic dopant species including Ni, Co, and Fe resulted in suppressed values of the tungsten Tc. The suppression was linear with increasing dopant concentration, for concentrations up to tens of ppm. For higher concentrations of magnetic atoms, the data are consistent with the Abrikosov–Gor'kov theory [Soviet Physics JETP 12, 1243 (1961)] modified by antiferromagnetic impurity–impurity interactions. By contrast, tungsten films implanted with Mg or Cr showed little change in Tc after doping. In this article, we present data from cryogenic experiments on these films. We also present x-ray diffraction (XRD) spectra for a subset of the films. Our XRD data confirm that the observed suppression in Tc for the magnetically doped samples is not due to any structural changes (e.g., lattice distortion or damage) induced by the implantation process.
Density of states in the gap of amorphous semiconductors determined from modulated photocurrent measurements in the recombination regime
Authors: Koropecki R. R. , Schmidt J. A. , Arce R.
Published: July 2002

An experimental technique to study the energy profile of localized states in the gap of amorphous semiconductors is proposed. The method is based on the relationship between the recombination lifetime and the density of states (DOS) at the quasi-Fermi level for trapped carriers. We use the modulated photocurrent experiment in the recombination-limited regime as a convenient method to measure the recombination lifetime. Measurements performed as a function of temperature allow the DOS above the Fermi energy to be determined. The accuracy and limitations of the method are studied by means of computer simulations. The experimental technique is applied to obtain the density of defect states of a hydrogenated amorphous silicon sample.
Character of defects at an ion-irradiated buried thin-film interface
Authors: Kalyanaraman R. , Haynes T. E. , Holland O. W. , Gilmer G. H.
Published: July 2002

In order to investigate the nature of defects produced by ion irradiation through a heterostructure, a silicon-on-insulator substrate with a buried SiO2 layer at a depth of ∼1.5 μm was irradiated. The implantation was done using 2 MeV Si+28 ions in the dose range of 0.2–1×1016 cm−2. The subsequent defect analysis was performed using the Au labeling technique. Besides the presence of an expected excess of vacancy-type defects in the Si overlayer (VSiex), an additional vacancy excess peak was observed at the frontside of the buried interface (VIntex). The VIntex is found to increase linearly with increasing dose of the high-energy implant. The presence of this VIntex peak near the interface is also predicted by the TRIM Monte Carlo code. Additional Monte Carlo simulations of damage production via high-energy implantation in Si/X-type structures show that the nature of the defects at the front Si/X interface can be changed from vacancy to interstitial-type by increasing the mass of atoms in the buried thin-film, X. These experiments provide quantitative verification of nonuniform defect production at an ion-irradiated buried interface in Si.
Optical properties and photoexcitations of an organic blue emitter embedded in a polymeric active matrix
Authors: Giovanella U. , Botta C. , Gurioli M. , Papagni A. , Tubino R. , Maiorana S. , Del Buttero P. , Alderighi D. , Kudrna J.
Published: July 2002

The doping of a widely used active polymeric matrix, the polyvinyl carbazole (PVK), with an organic blue emitter has been studied by both continuous wave and time resolved photoluminescence spectroscopy. It is found that the overall emission efficiency of the blend is controlled by two processes: the resonant transfer from the donor to the acceptor and the hopping between the donor sites. Because of the observed spectral variations of the emission spectrum of PVK (donor) with the temperature, both processes exhibit a strong, albeit opposite temperature dependence. The existence of the hopping process accounts for the sharp increase of the transfer efficiency with the concentration, not predicted by the Foerster theory.
Surface photovoltage in quantum well structures
Authors: Ruda H. , Shik A.
Published: July 2002

A theoretical expression for surface photovoltage VSPV in semiconductor structures with a single or series of quantum wells in the space charge region is derived. The cases of both linear and quadratic recombination in the quantum wells are considered. For photon energies ℏω less than the band gap of the barrier layer Eg1, the photovoltage spectrum VSPV(ω) is determined by the absorption spectrum in quantum wells, whereas for ℏω>Eg1, VSPV=const(ω). The model results are in good agreement with experimental data.
A two-dimensional nonlinear photonic crystal for strong second harmonic generation
Authors: Shi B. , Jiang Z. M. , Zhou X. F. , Wang X.
Published: July 2002

Detailed numerical analysis and computer simulation of a two-dimensional defective photonic crystal structure fabricated with nonlinear optical materials are carried out. The localized states in the band gap and electric field distributions of such a structure were calculated by the finite-difference time-domain method, and demonstrated a greatly enhanced second harmonic generation with an efficiency of about 4 orders of magnitude higher than that in an ordinary nonlinear crystal.
Radiofrequency sustained double layer in a plasma reactor
Authors: Annaratone B. M. , Allen J. E.
Published: July 2002

This article presents experimental evidence of a coupling of power between the rf supply and a collisionless plasma in a capacitively coupled plasma reactor. The reactor is driven in plasma sheath resonance to let high rf currents circulate in the system. These currents allow the formation of strong rf fields inside the nonuniform plasma leading to a double layer with a mechanism similar to the rf plasma sheath at the electrodes. Electrons accelerated by the double layer are very effective in ionizing, because of the increased cross section, and create a dense plasma at low pressures. The power is consequently transferred by the ions accelerated in the electrode sheath to the substrate to be processed with high improvement in both performance and process rate. Diagnostics include a retarding field analyzer on the grounded electrode to measure the energy spectrum of ions hitting the substrate and a capacitive probe to obtain the rf potential variations in the plasma.
Interface roughness in SiGe quantum-cascade structures from x-ray reflectivity studies
Authors: Roch T. , Medun̆a M. , Stangl J. , Hesse A. , Lechner R. T. , Bauer G. , Dehlinger G. , Diehl L. , Gennser U. , Müller E. , Grützmacher D.
Published: July 2002

We have investigated the structural properties of Si/SiGe electroluiminescent quantum-cascade structures, by means of x-ray reflectivity and diffraction. The cascade structures were grown at a comparatively low temperature of T=350 °C to avoid misfit dislcoation formation. Despite an overall thickness of the cascade structures of about 9000 Å and Ge contents of up to more than 40% in some of the SiGe wells, the entire stack of layers is indeed pseudomorphic with respect to the Si substrate. The analysis of x-ray reflectivity data yields a rather small rms interface roughness, which increases only slightly from 2 to 2.9 Å from the bottom to the top of the cascade structures. From x-ray reflectivity maps we obtain in addition the vertical and lateral correlation of the interface roughness. It turns out that for long range interface fluctuations the vertical correlation length is larger than for short range fluctuations.
Measurement of reflective liquid crystal displays
Authors: Tang S. T. , Kwok H. S.
Published: July 2002

Cell gap thickness is one of the most important design parameters for liquid crystal displays (LCD). Existing measurement methods only apply to transmittive LC cells. These methods are obviously unsuitable for measuring the cell gaps of reflective LCDs with internal reflectors. This kind of LCD includes single polarizer reflective displays and liquid crystal on silicon displays. The objective of this article is to introduce various reflective methods of LCD cell characterization that are both applicable to transmittive and reflective LCDs.
Evidence for a large enrichment of interstitial oxygen atoms in the nanometer-thick metal layer at the NbO/Nb (110) interface
Authors: Arfaoui I. , Guillot C. , Cousty J. , Antoine C.
Published: July 2002

The oxide/metal interface induced by surface segregation of oxygen during the annealing of a Nb single crystal in UHV has been studied by photoemission spectroscopy with synchrotron radiation. With 260 and 350 eV photons, four well-resolved peaks A, B, C, D are found in spectra within the 200–210 eV range of binding energy. One couple of peaks (A and C) is associated with 3d5/2 and 3d3/2 core levels of Nb atoms in the metal while the other one (B and D), shifted by 1.4 eV when compared to A and C, corresponds to 3d levels of oxidized Nb atoms. The metal peak A at 202.3 eV is formed by three 3d5/2 components: a peak due to a metallic state (202.1 eV) and two components shifted by 0.2 and 0.5 eV, which are attributed to Nb6O and Nb4O compounds due to interstitial atoms of oxygen, respectively. The estimated concentration of the interstitial oxygen atoms in the nanometer-thick metal skin underlying the NbO/Nb interface corresponds to a large enrichment when compared to the one in the Nb bulk.
Calculation of the electrostatic-potential distribution in ohmic elliptical cylinders fed by a dipole source
Authors: Evrard R. , Schmeits M. , Troquet J.
Published: July 2002

We have developed an analytical method based on Mathieu functions to solve Poisson’s equation in homogeneous right elliptical cylinders. We apply the method to a detailed study of the electric-potential distribution in the bulk and on the surface of ohmic conductors of such a shape, fed by a current dipole located at any inside position. Contrary to a common opinion in electrocardiology, the potential contour map on the surface of cylinders of pronounced ellipticity has more than one maximum and one minimum if the dipole is located close and parallel to the symmetry plane containing the axes of greatest lengths, i.e., the ellipse major axis and the cylinder axis. The extrema are located near the intersection with the plane normal to the previous one and containing the dipole axis. We discuss the cases of cylinders with different ellipticity and dimension ratio, focusing on the evolution of the number and position of the surface-potential extrema as a function of the location and orientation of the dipole with respect to the nearby boundary.
Dynamic steady state during cyclic diffusional phase transformations
Authors: Schuh Christopher A.
Published: July 2002

The problem of cyclic diffusional charging/discharging of a plane sheet specimen is analyzed theoretically, for the unique case where chemical diffusion propagates moving phase boundaries. This cyclic variation of the classical Stefan moving boundary problem introduces additional complexities associated with the interaction and annihilation of phase boundaries. Using a finite difference method with local mesh adaptations to allow for the moving phase boundaries, the dynamic steady state condition has been investigated as a function of the cycle duration and shape, and with various equilibrium concentrations at the phase boundaries. Two main classes of steady state behavior are observed, involving either complete phase transformations on each cycle (type-C steady state) or incomplete transformations where the specimen remains primarily in one phase, only partially transforming on each cycle (type-I steady state). Maps of the steady state character have been developed for various conditions, and the results of many simulations are synthesized into guidelines for prediction of the steady state.
Enhanced channel mobility of 4H–SiC metal–oxide–semiconductor transistors fabricated with standard polycrystalline silicon technology and gate-oxide nitridation
Authors: Schörner Reinhold , Friedrichs Peter , Peters Dethard , Stephani Dietrich , Dimitrijev Sima , Jamet Philippe
Published: July 2002

This work presents improved channel mobility of n-channel metal–oxide–semiconductor field-effect transistors (MOSFETs) on 4H–SiC, achieved by gate-oxide nitridation in nitric oxide. Lateral enhancement mode MOSFETs were fabricated using standard polycrystalline silicon gate process and 900 °C annealing for the source and drain contacts. The low field mobility of these MOSFETs was as high as 48 cm2/Vs together with a threshold voltage of 0.6 V, while the interface state density—determined from the subthreshold slope—was about 3×1011 eV−1 cm−2. The 43-nm-thick gate oxide of coprocessed metal–oxide–semiconductor structures exhibited a breakdown field strength of 9 MV/cm.
Depth distributions and damage characteristics of protons implanted in n-type GaAs
Authors: Zavada J. M. , Jenkinson H. A. , Wilson R. G. , Sadana D. K.
Published: July 2002

Depth distributions of 300-keV protons implanted in n-type GaAs and characteristics of the associated damage in the crystalline material have been obtained. Range profiles of the implanted 1H ions as a function of substrate implantation temperature have been determined using secondary ion mass spectrometry for fluences of 5×1014 and 5×1015 cm−2. The projected range for the protons was approximately 2.7 μm for the room temperature implants, but a significant rearrangement of the 1H atoms occurred during elevated temperature implantation. While cross-sectional transmission electron microscopy showed no evidence of crystal damage in as-implanted wafers, plan-view measurements revealed platelike damage structures in the surface region (< 1μm).
Analysis of fluid light valve control layers for high-definition television large picture projection
Authors: Tepe R.
Published: July 2002

Here, proceeding from a previous study, the deformation problem of a viscose fluid is analyzed under simplified conditions as regards the physical model. This viscose fluid is used as the light control organ in the light valve method of large-screen television projection. By using simple approximate relationship, the important properties, such as dynamic behavior, frequency response, stability behavior, and resolution limit of the control layer and their dependence on material and system parameter are discussed in detail. The theoretical knowledge obtained from this analysis agrees to a large extent with the experimental results.
Magnetoacoustic resonance in antiferromagnetic insulators in ‘‘moderate’’ and strong magnetic fields
Authors: Maugin G. A. , Sioké-Rainaldy J.
Published: July 2002

The magnetoacoustic resonance between phonons and magnons is studied analytically on the basis of a set of linearized magnetoelastic equations, which was previously deduced from a rotationally invariant nonlinear theory for uniaxial antiferromagnets of the easy-axis type. More specifically, the present paper investigates the less studied case where the bias magnetic field is either ‘‘moderate’’ or strong relative to some material parameter. Various types of dispersion and magnetoacoustic resonance couplings are exhibited depending on whether waves propagate along the direction of or orthogonal to the symmetry axis. In some cases a fast transverse elastic mode couples with both upper and lower magnon branches, while longitudinal and slow transverse elastic modes travel independently. In another case both fast and slow transverse elastic modes couple with both upper and lower magnon branches. In the case that most closely resembles the case of ferromagnets, left-circularly polarized transverse phonons and magnons couple at both high and low magnetoacoustic resonance points, while the right-circularly polarized transverse phonons are only rendered slightly dispersive for small wave numbers. These coupled dispersion behaviors are studied analytically (asymptotics) in terms of a small parameter which represents globally magnetoelastic couplings. This paper concludes the study of magnetoacoustic resonance in antiferromagnetic insulators which was started in a previous paper concerned with the case of weak bias magnetic fields.
Chemical shift imaging by spin-echo modified Fourier method
Authors: Satoh K. , Kose K. , Inouye T. , Yasuoka H.
Published: July 2002

A method for measuring spatially resolved high-resolution nuclear magnetic resonance spectra for a spatially heterogeneous complex object has been examined by making images of several phantoms. The factors which determine the image quality are discussed from both theoretical and experimental viewpoints. Especially, the effects of field inhomogeneity, originating from magnet inhomogeneity and nonuniform magnetic susceptibility of the object itself, are examined in detail. The indirect spin-spin coupling effect on imaging results is theoretically discussed. Although mathematical treatments are given for three-dimensional objects, actual measurements were performed for spatially limited two-dimensional regions by slicing the three-dimensional objects using a selective excitation technique. The results show that the present method is feasible for practical chemical shift imaging purposes.
Effects of doping on polysilicon etch rate in a fluorine-containing plasma
Authors: Baldi L. , Beardo D.
Published: July 2002

The effects of doping on the polysilicon etch rate in a CF4-CF3Cl-O2 planar plasma reactor are described. The effect is related only to the active carrier concentration and not to the total doping level. No significant change in etch rate was observed for carrier concentrations below 1019 cm−3. At higher concentrations the etch rate rapidly increases for phosphorus and arsenic doping and decreases for boron. A qualitative model, which explains experimental results, is described.
Dehydrogenation studies of amorphous silicon
Authors: Woodyard James R. , Bowen David R. , Gonzalez-Hernandez J. , Lee Sichen , Martin Denis , Tsu Raphael
Published: July 2002

The dehydrogenation of highly photoconductive amorphous silicon films has been studied using 15N,p nuclear reaction hydrogen depth profiling and isochronal anneals at temperatures between 300 and 500 °C. The studies shown that neither diffusion nor a first-order reaction are the rate limiting dehydrogenation mechanism for hydrogen concentrations between 5 and 40 at. %. Dehydrogenation is not rate limited by processes at the surface. The studies suggest that for concentrations above 5 at. % the dehydrogenation may be explained by second-order reaction kinetics involving the reordering of bonds. Below about 5 at. % a first-order process leading to dangling silicon bonds appears to dominate.
Conditions for uniform growth of GaAs by metalorganic chemical vapor deposition in a vertical reactor
Authors: Costrini G. , Coleman J. J.
Published: July 2002

The uniformity of epitaxial growth of GaAs by metalorganic chemical vapor deposition in a vertical-flow rotating-disk reactor has been investigated. Observations of the thickness of the epitaxial layer versus radial distance on the susceptor surface are made for various conditions of carrier gas flow and growth temperature. A model is proposed in consideration of hydrodynamic and thermal boundary layer effects at the susceptor surface. The effects of a parasitic processes in the limit of smaller boundary layers and transition to source input rate-limited growth in the limit of thicker boundary layers are described.
Exact solution for the peripheral photoresponse of a p-n junction
Authors: Sander L. M.
Published: July 2002

An exact analytical solution is given for the photoresponse of a p-n junction on a thick semiconductor due to lateral diffusion of minority carriers.
The effect of Fowler–Nordheim tunneling current on thin SiO2 metal-oxide-semiconductor capacitors
Authors: Hosoi Takashi , Akizawa Mitsuru , Matsumoto Satoru
Published: July 2002

p-type metal-oxide-semiconductor (MOS) capacitors with various oxide thickness (less than 200 Å) are stressed by Fowler–Nordheim (F–N) tunneling constant current with negative gate bias, and high frequency and low frequency capacitance-voltage (C-V) characteristics have been used to investigate the charge trapping phenomenon in thermally grown thin SiO2 films. Under constant current stress, high frequency C-V curve shifts negatively, and flatband votage shifts ΔVFB don’t saturate even at large injected charge F. In order to explain this behavior, we propose the expression, ΔVFB =A[1− exp(−σF)]+KF. The first term indicates hole trapping by the preexisting traps and the second term means the generation factor due to traps generated under stress. A fitting parameter A is nearly in proportion to the square of SiO2 thickness. This can be interpreted with the uniform distribution of bulk hole traps throughout the SiO2. Both capture cross section σ and generation factor K rapidly decrease with decreasing SiO2 thickness. From the results of low frequency C-V characteristics, the interface states with very high density of the order of 1013/cm2 eV are generated over a wide range of band gap.