bluuebunny/crossref_metadata_2025 huggingface dataset:
Impurity scattering limited mobility in a quantum well heterojunction
Authors: Lee Johnson , Spector Harold N. , Arora Vijay K.
Published: February 2003

We calculate the mobility of carriers in a quantum well structure when they are scattered by ionized impurities in the size-quantum limit (SQL) where the carriers are assumed to populate only the lowest quantized energy level. It is found that the probability of scattering due to ionized impurities decreases with the well thickness in contrast to the case of acoustic phonon scattering where the scattering probability is enhanced under the conditions of the SQL. The temperature and thickness dependence of the mobility depends critically on the screening of the Coulomb potential due to the presence of the ionized impurities.
Effective conductivity of regular conducting channeling textures in two dimensions
Authors: Nakamura Mitsunobu
Published: February 2003

Composite materials exist, which are composed of elongated conductors and granular insulators. For the effective conductivity of such materials, the ordinary effective medium theory and the random resistor network models cannot be efficiently applied. As an approach to the problem, we compute by the finite element method the effective conductivity of triangular, square, and hexagonal channeling textures, composed of continuous conductive channels and islands of insulators. As shown by the results, the effective conductivities of the three patterns are nearly equal when the channel widths of the textures are the same. And compared with a granular conductor-insulator composite material, the three textures have a very conductive geometrical configuration, because neither island nor dead end conducting regions exist in the three patterns. If we accumulate such data for the effective conductivity of materials with a definite composite structure, we can predict the outline of the geometrical configuration of a composite material or inhomogeneous medium by measurement of the conductivity and volume components.
The capacitance of rf sputtered hydrogenated amorphous silicon, Schottky barrier diodes
Authors: Fernandez-Canque H. L. , Allison J. , Thompson M. J.
Published: February 2003

A generalized interpretation of the capacitance/conductance behavior in a hydrogenated amorphous silicon Schottky barrier is introduced. This approach takes into account the influence of voltage, temperature, frequency, and light intensity on the capacitance and conductance characteristics of a Schottky barrier junction and on a complete device. From the various different considered cases it is possible to obtain information on the barrier profile, depletion width of the barrier, and density of states in the gap. The model proposed provides a method of obtaining the ‘‘active’’ charge that effectively determines the capacitance in the barrier. Comparison of theoretical predictions based on the model with experimental data from capacitance and conductance measurements of reactively sputtered, hydrogenated a-Si:H-metal Schottky barrier structures as a function of temperature voltage, frequency, and illumination shows good agreement.
Low-resistance contacts to p-type Li-diffused CdTe
Authors: Lee Chun-teh , Bube Richard H.
Published: February 2003

Reproducible low-resistance contacts to p-type CdTe single crystals have been made by diffusion of Li into the CdTe surface before evaporation of Au as the contact metal. Diffusion produces a surface hole density of about 1019 cm−3 at room temperature; this results in a contact resistivity of the order of 0.01 Ω cm2, the lowest value reported to date for p-type CdTe. The high diffusivity of Li results in a degradation of the contacts even at room temperature, with the degradation rate critically dependent on the temperature used for Li diffusion. The optimum temperature appears to be about 280 °C; contacts formed on surfaces diffused with Li at this temperature show a contact resistivity of 0.025 Ω cm2 after 5 months.
Far infrared frequency response of a Josephson junction in a self-pumped mixer
Authors: Henaux J-C. , Vernet G. , Adde R.
Published: February 2003

A continuous measurement of the far-infrared frequency response of a point contact Josephson junction is performed between 0.7 and 2 THz. The response at increasing frequencies present three characteristic regions with variations proportional to f−2, f−4, f−6. They illustrate the losses introduced successively at increasing frequencies by the resistively shunted junction model, the junction RC time constant and the attenuation of the Josephson current above the gap frequency.
Effect of nonparabolicity on amplification of eigenmode acoustic waves in piezoelectric semiconductor films
Authors: Wu Chhi-Chong , Tsai Jensan
Published: February 2003

Amplification characteristics of eigenmode acoustic waves in piezoelectric semiconductor films have been investigated quantum mechanically in the GHz frequency region. The energy-band structure of piezoelectric semiconductors is assumed to be nonparabolic. Numerical results show that the amplification coefficient oscillates with the frequency according to the mode of acoustic waves and the thickness of semiconductor films. Moreover, the amplification coefficient depends on the band structure of materials, the electronic screening effect, the temperature, and the applied electric field.
Dry oxidation of silicon: A new model of growth including relaxation of stress by viscous flow
Authors: Fargeix A. , Ghibaudo G.
Published: February 2003

This paper deals with a model of silicon oxidation including stress relaxation by viscous flow during growth. Based on a Deal–Grove process and a Maxwellian stress relaxation approach, an integrodifferential equation giving the inverse growth rate dt/deox vs eox is established. Valid in any case of thickness growth rate dependence, it allows us to fit dry silicon oxidation data on a wide range of oxidation temperature (780–980 °C).
The maximum efficiency of solar energy conversion devices
Authors: Byrd J. William , Adler Carl G.
Published: February 2003

The production of work by devices receiving radiant energy and interacting with a local environment is discussed. Provision is made for the device to radiate at a temperature different from the local environmental temperature. The resulting conversion efficiency is discussed in terms of the radiant source, emitting and environmental temperatures. The environment is seen to play a pivotal role in the production of work. Extrema in the efficiency function are examined and no true maxima are found to exist. However, there are optimum choices for the emitter temperature if we hold the environmental temperature constant, and conversely. A case is demonstrated for which the device may absorb an amount of heat from the environment and perform an equal amount of work.
Ablation of electrode surfaces in high power diodes
Authors: Sincerny P. , Gilman C. , Stringfield R. , Friedman M. , Wilson A.
Published: February 2003

The ablation of electrode surfaces has been observed for several materials illuminated by radiation from an imploding wire array. The experiments were done on the PITHON 5-TW generator. A plasma boundary at ne=5×1018/cm3 expands at velocities up to 10 cm/μs from the surface. Calculations suggest early vacuum-ultraviolet radiation ablates the electrode surface. Hydrogen is the dominant element forming a coating on the electrode surface.
Formation of partially coherent antimony precipitates in ion implanted thermally annealed silicon
Authors: Pennycook S. J. , Narayan J. , Holland O. W.
Published: February 2003

Thermal annealing of a supersaturated solid solution of antimony in silicon results in the formation of partially coherent antimony precipitates. Transmission electron microscopy and microdiffraction studies show the precipitates to be bounded by {112} Si surfaces with the {111} Si and {1̄012} Sb planes coherent across the interface. The role of dislocations in the growth of the precipitates is discussed.
High pressure structural phase transition in AgGaTe2
Authors: Qadri S. B. , Rek Z. , Webb A. W. , Skelton E. F. , Wolf S. A.
Published: February 2003

From in situ diffraction measurements of synchrotron produced x radiation, we have found that AgGaTe2 transforms from the tetragonal, chalcopyrite structure to a face-centered cubic structure at 4.0±0.5 GPa. The resistivity shows a minimum near this pressure, but the material retains its semiconducting nature.
On models of phosphorus diffusion in silicon
Authors: Hu S. M. , Fahey P. , Dutton R. W.
Published: February 2003

Various phenomena associated with phosphorus diffusion in silicon are reviewed and prominent models are critiqued. It is shown that these models are either fundamentally unsound, or are inconsistent with observed phenomena. A consistent model is proposed in which two mechanisms are operating simultaneously, namely, the vacancy mechanism for the slower diffusing component, and the interstitialcy mechanism for the faster diffusing component. It is assumed that phosphorus exists in silicon in both the substitutional and the interstitialcy species, and that both are shallow donors. The conversion between the two species is relatively slow, giving rise to the so-called kinked concentration profile. Diffusion via a partial interstitialcy mechanism leads to a supersaturation of self-interstitials.
Fourier–Bessel representation of periodic electrostatic systems of juxtaposed coaxial cylinders separated by finite gaps
Authors: van der Merwe J. P.
Published: February 2003

An iterative procedure is described by means of which the potential distribution can be found in axially symmetrical periodic configurations of juxtaposed coaxial electrodes. The solution is in the form of Fourier–Bessel series, and the procedure involves the potential calculation in the gap by an overrelaxation process in respect of points located on a mesh covering a small region which includes a cross section of the gap. The gap potential is represented either by a polynomial or by the sum of a linear function and a Fourier series. Using this method, the errors on axial potentials are found to be approximately two orders of magnitude smaller than those on potentials calculated by assuming that the potential in a gap is a linear function. Compared to the relaxation method, the present procedure represents a considerable saving on computing time and memory.
Amplification of Bleustein–Gulyaev waves in cadmium sulfide
Authors: Palanichamy P. , Singh S. P.
Published: February 2003

The propagation of Bleustein–Gulyaev waves in the presence of a dc electric field in the vacuum baked piezoelectric semiconducting crystals of class 6 has been studied theoretically. By solving the partial differential equations representing the electron–acoustic wave interaction in the piezoelectric semiconducting region, and the Laplace’s equation in the vacuum region separately and fulfilling the relevant boundary conditions, we obtain an expression for the amplification coefficient. The effects of carrier diffusion, resistivity, and carrier drift velocity on the amplification coefficient have been studied based on numerical calculations for the semiconducting CdS sample. It has been observed that, compared to Rayleigh waves, the Bleustein–Gulyaev waves give a much higher amplification.
The current-voltage characteristic of magnetron sputtering systems
Authors: Westwood W. D. , Maniv S. , Scanlon P. J.
Published: February 2003

The I-V characteristic of dc and rf magnetron sputtering systems has been shown to fit an expression of the form I=β(V−V0)2, where V0 is the minimum voltage necessary to maintain a discharge. New experimental data is presented for a dc planar magnetron with Al, Cd2Sn, Cr, and CdSe targets in argon discharges and for a dc Research S-gun with an Al target in argon and argon/oxygen discharges. Literature data for planar, S-gun, and cylindrical magnetrons has also been shown to fit the above expression; for rf magnetrons, I is the rms current and V is the target self-bias voltage. V0 decreases from about 400 V at 0.1 Pa to 250 V at 1 Pa and then decreases at higher pressures. β increases from about 50 to ≤300 A/kV2 as the pressure increases from 0.1 to 10 Pa. The actual values of V0 and β depend on the system, target, and sputtering gas. It is shown that the I∝V2 dependence is due to a space-charge-limited electron current in the magnetron geometry which reduces the electron mobility by several orders of magnitude from the zero magnetic field value; the mobility ratio depends on the electron-atom collision frequency.
The effect of stress relief on magnetic distributions in ion-implanted garnet films
Authors: Shiomi S. , Shir C. C.
Published: February 2003

Magnetization distributions around a circular nonimplanted disk in an ion-implanted garnet film are calculated through numerical integration of the Landau–Lifshitz–Gilbert equation. In addition to uniform stress-induced in-plane anisotropy in the implanted region, the effect of stress relief near the edge of nonimplanted disk is taken into account. Calculation results show that magnetization distributions are strongly affected by the stress distribution near the edge not only in the region close to the implantation edge where charged walls are formed but also in the region rather far away from the edge. With proper choice of stress distribution, the present calculation can reproduce the ‘‘propeller-like’’ domain wall pattern which is experimentally observed by the Bitter technique. This suggests that the stress distribution near the implantation edge might be determined by comparing calculation results of magnetization distributions with experimental observations of domain wall pattern.
Molecular beam epitaxial growth of InGaAlP visible laser diodes operating at 0.66–0.68 μm at room temperatures
Authors: Asahi H. , Kawamura Y. , Nagai H.
Published: February 2003

The room temperature pulsed operation of In0.49Ga0.31Al0.20P/In0.49Ga0.51−x AlxP/In0.49Ga0.31Al0.20P(x=0.00–0.03) double heterostructure (DH) laser diodes have been achieved for the first time. The lasing wavelength was 0.66–0.68 μm with a threshold current density of 2.6–3.6×104A/cm2 at 26 °C. These results were achieved by growing DH wafers by molecular beam epitaxy (MBE). Key points in the successful MBE growth of these DH wafers were, first, the realization of low resistance p-type and n-type InGaAlP layers by reducing contamination in the growth chamber. This was done by installing a substrate loading room with an interlock valve and a substrate transfer mechanism. The second was the realization of an abrupt p-n junction by the use of Si instead of Sn as an n-type dopant.
Photoluminescence in GaAs doping superlattices
Authors: Jung Helmut , Künzel Harald , Döhler Gottfried H. , Ploog Klaus
Published: February 2003

The influence of excitation density and excitation energy on the low-temperature photoluminescence spectra of GaAs doping superlattices has been studied in detail. In addition to the strongly tunable luminescence across the indirect gap in real space, which is the specific recombination process in doping superlattices, luminescence lines near the band gap of bulk GaAs, originating from vertical electron-hole recombination processes, are observed. The relative intensities of these vertical luminescence transitions increase at excitation energies close to the bulk band gap and also at high excitation densities. We explain this increase by a simple model based on the classical evaluation of the relaxation kinetics of photoexcited carriers in momentum and real space. The significant result of our investigation is the observation that the luminescence efficiency in GaAs doping superlattices remains constant if the excitation density is varied. Consequently, the relative weight of nonradiative recombination processes is not increasing if the recombination lifetimes are enhanced by several orders of magnitude by lowering the value of the effective gap.
Electrical properties of Au-Cu-doped Si Schottky diode
Authors: Tōyama Naotake
Published: February 2003

Current-voltage measurement and photoelectric measurement were carried out in copper-doped silicon Schottky diode. Although the current of Schottky diode varies remarkably with copper diffusion temperature, it is found out that the variation of current takes a maximum and a minimum at diffusion temperatures of about 1000 and 1100 °C, respectively. Such variation of current exceedingly corresponds well to that of the lattice strain of copper-doped silicon crystal which has been revealed by x-ray measurement. It is also shown that the saturation current and the shunt resistance of Schottky diode can be obtained by photoelectric measurement even in a sample which has a large excess current component, viz., a larger n value than unity. As a result, it is found out that the effective Richardson constant and the shunt resistance are changed mainly by the lattice strain due to copper introduction.
Investigation of the Al/TiSi2/Si contact system
Authors: Ting Chung Yu , Wittmer Marc
Published: February 2003

We have studied the thermal stability of the Al/TiSi2/Si contact system with Rutherford backscattering and glancing-angle x-ray diffraction. The results show that this sytem is thermally stable up to 550 °C for 30 min annealing. At higher annealing temperatures Al starts to react with TiSi2 by forming the Ti7Al5Si12 ternary compound. Electrical measurements on shallow junction diodes with Al/TiSi2/Si contacts show that in contrast to the thermal stability results the device junctions were all shorted after annealing for 30 min at 400 °C. Investigation of the failure mechanism with scanning electron microscopy and electron microprobe reveals that even during low temperature annealing the Si diffuses through the TiSi2 and dissolves into the Al top layer. At the same time Al diffuses through the TiSi2, penetrates into the silicon substrate, and shorts device junctions. These processes are particularly amplified by a large area ratio of Al pad to Si contact opening.
Generation-annealing kinetics and atomic models of a compensating donor in the surface space charge layer of oxidized silicon
Authors: Sah Chih-Tang , Sun Jack Yuan-Chen , Tzou Joseph Jeng-Tao
Published: February 2003

Experimental evidence of the generation of a shallow bulk donor center in the surface space-charge layer of oxidized silicon by exposure to a high dose of 10-keV electron is first summarized. An extensive new study of the generation and annealing kinetics of a similar bulk donor in p-Si metal-oxide-semiconductor capacitors subjected to as much as 20 C/cm2 avalanche electron injection is then reported. The generation kinetics from 180 to 298 K is first order with a constant total donor concentration of about 1×1017 cm−3 which is independent of both injection temperature and voltage, and a generation cross section given by 8.6×10−18 exp(−113 meV/kT) cm2, which increases with injection voltage. Rapid annealing begins at 50 °C following a second-order kinetics from 50 °C to 150 °C with an annealing rate given by 4.2×10−7 exp(−1.07 eV/kT) cm3/sec. Analyses of the results suggest that a bulk oxygen donor is the origin, and the bimolecular annealing kinetics involves hydrogen bonding of the oxygen donor dangling bonds.
Scanning internal photoemission studies of sodium-contaminated metal-oxide-semiconductor capacitors
Authors: Bouthillier T. M. , Young L. , Tsoi H. Y.
Published: February 2003

Following DiStefano and also Williams and Woods we have used scanning internal photoemission to map barrier inhomogeneities in sodium-contaminated Al/SiO2/Si Metal-Oxide-Semiconductor capacitors. A computer controlled system was used with a He/Cd laser. A well-known and striking result of the previous work is that peaks tend to be found in the internal photoemission. In some cases these peaks have been attributed to the segregation of an initially uniform sodium ion distribution into clusters of a few μm diameter. This clustering occurred during a low temperature anneal under positive gate bias. The mechanism for the supposed segregation is of considerable interest. One possibility is that the segregation maps pre-existing inhomogeneities either in the silicon substrate or in the oxide. Another mechanism, proposed by Williams and Woods, involves the image force lowering of the potential energy of the sodium ions. The lowering is increased as the induced electron charge density in the silicon increases with progressive clustering. This positive feedback was proposed to lead to instability. A thermodynamic development of the model by Wojtowcz led to the concept of two-dimensional phase transitions in the sodium distribution. In the present work we report the result that peaks can be produced by a low temperature anneal with the sodium either at the Al/SiO2 interface or drifted to the Si/SiO2 interface. In the first case, the sodium must be drifted to the silicon side before the peaks appear. This may show that nucleation centers are produced by the anneal and mapped by the sodium. Alternatively, if un-nucleated segregation occurs it must be a function of sodium in SiO2 rather than of sodium near the Si/SiO2 interface. Correlation with weak spot breakdown was again observed and the effects of using HCl oxides were studied.
Interface states and internal photoemission in p-type GaAs metal-oxide-semiconductor surfaces
Authors: Kashkarov P. K. , Kazior T. E. , Lagowski J. , Gatos H. C.
Published: February 2003

An interface photodischarge study of p-type GaAs metal-oxide-semiconductor (MOS) structures revealed the presence of deep interface states and shallow donors and acceptors which were previously observed in n-type GaAs MOS through sub-band-gap photoionization transitions. For higher photon energies internal photoemission was observed, i.e., injection of electrons to the conduction band of the oxide from either the metal (Au) or from the GaAs valence band; the threshold energies were found to be 3.25 and 3.7±0.1 eV, respectively. The measured photoemission current exhibited a thermal activation energy of about 0.06 eV, which is consistent with a hopping mechanism of electron transport in the oxide.
Size and temperature effects on thermoelectric power of β-tin thin films
Authors: Das V. Damodara , Mohanty Jyotish Chandra
Published: February 2003

Tin thin films of thicknesses in the range 500–7000 Å have been prepared by vacuum deposition at room temperature at a pressure of 5×10−5 Torr on glass substrates. Thermal electromotive forces (emfs) of these films have been measured after aging as a function of temperature difference. It is found that the thermoelectric power of the films is independent of temperature in the range studied (300–425 °K). It is also found that the thermoelectric power of the films obeys the inverse thickness dependence predicted by size effect theories. The electronic mean free path is evaluated to be 530 Å.
Sources of acoustic emission in superconducting magnets
Authors: Tsukamoto O. , Iwasa Y.
Published: February 2003

Origins of acoustic emission (AE) in superconducting wires have been investigated. Our experimental results indicate that wire motion is a dominant source of AE in current-carrying wires, both superconducting and nonsuperconducting. Furthermore, the results show that flux motion, except during flux jumping, produces no discernable acoustic signals. Both of these conclusions differ from the conclusions of earlier AE results which attributed the major source of AE signals in superconductors and superconducting magnets to flux motion. A simple model based on frictional sliding of conductor is presented to interpret acoustic data; agreement between theory and experiment is good.
Thermal stability of Pb-alloy Josephson junction electrode materials. VIII. Effects of Au addition to Pb-Bi counterelectrodes
Authors: Murakami Masanori , Huang H.-C. W. , Kircher C. J.
Published: February 2003

In previous studies, strain-relaxation-induced changes in film microstructure, such as grain rotation, hillock formation, and dislocation slip bands, were observed after repeated thermal cycling between 298 and 4.2 K in 0.4-μm-thick ε-phase Pb-Bi films that are used as the counterelectrode material of experimental Pb-alloy Josephson junction devices. In the present paper, the effects of small additions of Au (1–8 nm thickness) to the Pb-Bi films on the changes in the film microstructure were studied by using x-ray diffraction, and scanning and transmission electron microscopy. It was found that the changes in microstructure observed in the Pb-Bi films were significantly reduced by the Au addition, although the average level of strain relaxation in the Pb-Bi alloy films upon thermal cycling between 298 and 4.2 K was not influenced by the Au addition. Experimental junctions were made using fine-grained Pb-In-Au films prepared at 77 K as the base electrode material, and Pb-Bi or Pb-Bi-Au films prepared at 273 K as the counterelectrode material. The junctions were cycled 200 times between 298 and 4.2 K. The junction failure level was observed to be reduced by a factor of ∼10 times compared to that of control samples by using Pb-Bi-Au films with 1-nm-thick Au as the counterelectrode material. An additional order of magnitude reduction in the junction failure level was obtained by increasing the Au thickness to 8 nm. The results indicate that reducing the changes in microstructure of the counterelectrode material reduces the incidence of junction failure upon repeated cycling between 298 and 4.2 K. However, adding Au to Pb-Bi counterelectrodes also causes an increase in the low-bias tunneling current. This increase in current, which is believed to be due to the presence of nonsuperconductive Pb3Au compounds in the vicinity of the tunnel barrier, would be undesirable for some device applications.
Intermetallic compound formation in thin-film and in bulk samples of the Ni-Si binary system
Authors: Tu K. N. , Ottaviani G. , Gösele U. , Föll H.
Published: February 2003

In this study, we attempt to clarify the difference between interdiffusion in thin-film and in bulk samples, and we have chosen the Ni-Si binary system for experimentation. A major difference is in the behavior of intermetallic compound formation; while the compounds form sequentially in thin films, they tend to appear simultaneously in bulk samples. The essence of sequential formation is the absence of the other stable phases during the growth of a specific one. We have used cross-sectional lattice imaging of the interface between a NiSi film and a Si to confirm the absence of NiSi2 at the interface. Other differences between the sequential growth of a compound in the thin-film Ni-Si samples and the simultaneous growth of several compounds in the bulk Ni-Si samples have been compared and discussed.
Space charge distributions near interfaces during kinetic processes
Authors: Yan M. F. , Cannon R. M. , Bowen H. K.
Published: February 2003

For a variety of kinetic processes or transient conditions, such as grain boundary migration, formation of new surfaces at low temperatures, and quenching, there is insufficient time for solute redistribution around the interface. Under these conditions vacancy migration may be rapid. We analyze two limiting cases of constrained equilibria in which the vacancy distribution satisfies a minimum free energy under the constraint of no solute redistribution. The two cases are where the solute-vacancy association is at local equilibrium or is invariant. The resulting space charge potentials around the interface are often similar to that for the fully equilibrated case, if the bulk potential is controlled by vacancy equilibration. The differences in the electrostatic potentials among the constrained and complete equilibrium cases increase with decreasing temperature. The differences can also be increased if there are appreciable non-Coulombic solute-boundary interactions. Furthermore, we analyze the times, temperatures, or kinetic conditions under which these approximations are useful.
Leaky surface-elastic waves on both flat and strongly corrugated surfaces for isotropic, nondissipative media
Authors: Glass N. E. , Maradudin A. A.
Published: February 2003

The dispersion relation for Rayleigh waves propagating across a grating, on the surface of a semi-infinite, nondissipative, isotropic elastic medium was recently calculated by Rayleigh’s method and equivalently by a formally exact method based on Green’s theorem. Now, using a complex wave-vector k or complex frequency ω in the present work, we continue the solutions of the dispersion relation into the radiative region of the kω-plane (i.e., above the bulk transverse sound line) and into the first frequency-gap on the boundary of the Brillouin zone caused by the grating periodicity. Here the solutions for the surface waves have components that radiate outwardly into the bulk. The acoustic attenuation for the Rayleigh waves, calculated from the imaginary part of complex k, agrees very well with experiment: all the observed peaks, including those missed by previous perturbation scattering theories, are found. Moreover, a branch is found in the dispersion relation, to which a corresponding complex solution is also found for the flat surface, between the bulk transverse and longitudinal sound lines, that represents an intrinsically leaky flat-surface wave or surface resonance. The principal peak in the Rayleigh wave attenuation can be associated with an interaction between the Rayleigh wave and this new intrinsically leaky wave.
Deep levels in InGaAsP/InP p+n diodes grown by vapor phase epitaxy
Authors: Macrander A. T. , Johnston W. D.
Published: February 2003

Deep level transient spectroscopy measurements have been made on nominally undoped n-InP. Results for electron traps and for hole traps are reported for samples with space charge densities equal to 1.6, 3.7, and 8.7×1016 cm−3. The p+ quaternary top layer was doped with Zn. A hole trap labeled H1 having an activation energy of 0.18 eV and a hole capture cross section (obtained from emission data) of 5×10−16 cm2 was found in the 1.6×1016 cm−3 material. The concentration of this trap was 1.2×1013 cm−3. No hole traps with concentrations in excess of 2 ×1013 cm−3 were found in any of the samples studied. An electron trap labeled E1 was detected in the 1.6×1016 cm−3 material. The concentration found was 5×1012 cm−3. An electron capture rate of 3×104 s−1 was directly measured for E1 at 241 K. Differences between emission and capture data can be reconciled if the E1 trap interacts with the L conduction band minimum. An electron trap labeled E2 was observed in all the samples studied. A line shape analysis showed that the broad E2 peak was not due solely to a single exponential transient. The concentration of the E2 trap was found to be 1×1013 cm−3 at depths greater than 0.15 μm from the interface; within 0.15 μm of the interface, it was found to be ∼1015 cm−3. A value of 0.6 eV was found for the E2 emission activation energy. Electron capture was too fast to measure directly. A value of 10−14 cm2 was obtained for the capture cross section from emission data. It is concluded that the E2 trap interacts with the Γ conduction band minimum. A significant hole capture rate was inferred for the E2 trap; the ratio of the hole capture rate to the electron capture rate was inferred to be 3 for a 1.0-A/cm2, 10-μs injection pulse. It is concluded that of the three traps studied only E2 may play a significant role in optoelectronic devices.
Electrical properties of Fe in GaAs
Authors: Kleverman M. , Omling P. , Ledebo L-Å. , Grimmeiss H. G.
Published: February 2003

GaAs has been doped with Fe by diffusion and by liquid-phase epitaxy. The deep level introduced has an optical cross section for excitation of holes to the valence band with one threshold at 0.46 eV and another at about 0.85 eV. By combining those data with previous measurements of internal transitions between the ground state and an excited state, the level position in the gap is established. Optical excitation of electrons to the conduction band is below the limit of detection. The cross section for capture of electrons is nearly temperature independent with a value of about 10−19 cm2 at 200 K, and the thermal activation energy for emission of holes is 0.54 eV after T2 correction.
Quantum freeze-out effect in a size-limited intrinsic transport
Authors: Arora Vijay K. , Spector Harold N.
Published: February 2003

The size-limited resistivity of intrinsic thin films is calculated theoretically in the size-quantum limit (SQL), where the film thickness d is comparable to the de Broglie wavelength λD of the electrons (λD≥d). The variation of the intrinsic carrier concentration with the film thickness is taken into account. We find that in the SQL, the ratio of the thin film resistivity to the bulk resistivity increases exponentially with decreasing film thickness. This arises because of the increase in the effective band gap of an intrinsic thin film with film thickness as a result of size quantization.
Origin of negative temperature coefficient of resistivity in polycrystalline Ti-N films
Authors: Igasaki Yasuhiro , Mitsuhashi Hiroji
Published: February 2003

A negative temperature coefficient of electrical resistivity (TCR) has been observed in Ti-N films prepared by reactive evaporation or sputtering. Some samples measured had a resistivity minimum and the minimum temperature changing with varying nitrogen contents. To study the origin of this anomalous temperature dependence of resistivity, the crystallographic structures of Ti-N films were measured by x-ray diffraction. The resistivity data could be analyzed in terms of the existing theory based on the structural Kondo effect. The results demonstrated that the negative TCR originated from higher concentration of interstitial nitrogen atoms in the Ti-Nx solid-solution phase, and nitrogen vacancies and/or intrinsic stacking faults in the fcc TiNx compounds.
Electrical and optical properties of Be-doped InP grown by molecular beam epitaxy
Authors: Kawamura Y. , Asahi H. , Nagai H.
Published: February 2003

Beryllium-doped InP layers have been grown on (100) InP substrates by molecular beam epitaxy. Room temperature hole concentrations as high as 6×1018 cm−3 have been successfully achieved. The activation energy (∼14 meV) of Be acceptor in InP with the room temperature hole concentrations of ∼1017 cm−3 is smaller than those of Zn(∼30 meV) and Cd(∼38 meV) acceptors in InP with the same hole concentrations. The photoluminescence spectrum at 77 K has a near band emission (1.41 eV) and a Be-related emission (1.38 eV). InGaAs/InP double heterostructure laser diodes were also successfully fabricated by using Be as a p-type dopant, and room temperature pulse operation has been achieved in these laser diodes.
Grain size dependence of mobility in polycrystalline n-indium phosphide
Authors: Roy J. N. , Basu S. , Bose D. N.
Published: February 2003

Polycrystalline n-indium phosphide (InP) with grain sizes varying from 15 to 2000 μm has been prepared by iodine chemical reaction and synthesis solute diffusion (SSD) techniques. The variation of electron mobility and hence electron mean free path with grain size has been determined from conductivity and Hall effect studies, taking into account the effect of compensation as discussed by Jensen. The results show that electron mobility at 300 K increases from 29 to 691 cm2/V s with grain sizes increasing from 15 to 2000 μm. While for a single crystal the electron mobility varied with temperature between 160–300 K as T−2.25, for polycrystalline InP the variation was T−2.44 (2000 μm in grain size) and T−2.97 (200 μm in grain size) showing the effect of grain boundary scattering. The impurity activation energies have also been determined and were found to increase with a decrease of grain size.
Heterojunction-induced phenomena in Hall effect and photoconductivity measurements of epitaxial AlxGa1−xAs
Authors: Collins Douglas M. , Mars Dan E. , Fischer B. , Kocot C.
Published: February 2003

Temperature-dependent Hall effect measurements are reported for n-type, Si-doped Al0.32Ga0.68As films grown on semi-insulating GaAs substrates. Results are presented for films grown with and without undoped Al0.32Ga0.68As buffer layers. For T≥200 K, the free electron concentration in these Si-doped films has an exponential dependence on temperature with an activation energy of ∼93 meV. The temperature-independent free-electron concentration observed for T≤100 K is due to conduction in the GaAs substrate near the substrate-epilayer interface (i.e., a two-dimensional electron gas). Hall mobilities measured in thin (≤5 μm) AlxGa1−xAs films, particularly at low temperatures, can be dominated by this conduction mechanism and are thus invalid as a measure of the transport properties of the AlxGa1−xAs films. In addition, photoconductivity data are presented which show that the persistent photoconductivity effect observed in these films is due primarily to charge separation at the AlxGa1−xAs/GaAs heterojunction.
Electron transport properties in rutile from 6 to 40 K
Authors: DeFord John W. , Johnson Owen W.
Published: February 2003

Electrical conductivity mechanisms in single crystal rutile (TiO2) between 6 and 40 K have been studied in Nb-doped and Nb+H-doped material by means of electrical resistance and Hall effect measurements. In this range, three scattering mechanisms were found to be important: neutral and ionized impurities and acoustic phonons. In the region from approximately 12 to 25 K the electrical conductivity was found to be strictly exponential in 1/T, indicating acoustic phonon limited scattering, and yielding the donor trapping energies for Nb and H (20.0±0.1 and 4.4±0.1 meV, respectively). With the acoustic phonon limited mobility written as μ=μ0/T3/2, μ0 was found to be (1.2±0.1)×104 and (3.9±0.4)×10−4 cm2(K)3/2/V s in the ‘‘a’’ and ‘‘c’’ directions, respectively. Although qualitative agreement with existing theories on neutral and ionized impurity scattering is obtained, quantitative agreement requires an improved theory taking anisotropy into account. It was also found that the ratio of ‘‘c’’ to ‘‘a’’ mobility is a function of temperature and doping. The electron effective mass was estimated to be ∼12.5 m0.
Electrical characteristics of an anisotropic semiconductor sample of circular shape with finite contacts
Authors: Versnel W.
Published: February 2003

The circular anisotropic Van der Pauw configuration with four equal finite edge contacts, symmetrical in respect of two orthogonal axes, is analyzed. Applying Schwarz-Christoffel transformations, the potential problem of this structure is solved. The numerical calculations have been reduced to those of regular definite integrals. Furthermore, simple approximative formulae have been found, which describe the electrical characteristics of the structure. It is shown that a pocket calculator is sufficient for determining specific resistivities ρ1 and ρ2 from measurements.
Analysis of parallel Schottky contacts by differential internal photoemission spectroscopy
Authors: Okumura T. , Tu K. N.
Published: February 2003

A differential analysis of internal photoemission spectroscopy has been developed for the study of nonuniformity in a Schottky contact. The analysis is capable of revealing the presence of a high-low parallel contact in a spectroscopic manner. It has been applied to a discrete parallel contact consisting of Pd2Si and NiSi as well as a nonuniform contact of Pd on Si in the as-deposited state. The nonuniformity in the latter case is due to the existence of high barrier regions (0.86 eV) in parallel to those of Pd2Si (0.74 eV) and it disappears after a subsequent annealing at 250 or 450 °C.
Modeling of hydrogenated amorphous silicon Schottky structures using capacitance-voltage and conductance-voltage measurements
Authors: Lahri R. , Han M. K. , Anderson W. A.
Published: February 2003

The conduction process in a-Si:H Schottky structures (metal-I-N+/substrate) is controlled primarily by the intrinsic (I) layer. This layer acts as a photoconductive insulator sandwiched between the bottom injecting contact and top blocking contact. A model incorporating this dual behavior of the I layer has been proposed to develop equations for the terminal dark current, capacitance (C), and conductance-voltage (G-V) characteristics of these structures. The results of dark C-V and G-V computations have been compared with the experimental data. The basic features of dark and illuminated G-V and illuminated C-V data have also been explained on the basis of this model.
Ion implantation and thermal annealing of α-Al2O3 single crystals
Authors: Naramoto H. , White C. W. , Williams J. M. , McHargue C. J. , Holland O. W. , Abraham M. M. , Appleton B. R.
Published: February 2003

The effects of ion implantation and post-implantation thermal annealing of α-Al2O3 have been characterized using ion scattering-channeling techniques, and correlated with electron paramagnetic resonance (EPR) and microhardness measurements. Although most of the work was done on 52Cr implanted specimens, preliminary results have been obtained also for implanted 90Zr and 48Ti. For Cr implantation, the Al2O3 lattice damage saturates at relatively low doses, but the near-surface region never becomes amorphous. A preferential annealing behavior begins in the Al sublattice after ∼800 °C annealing, and in the oxygen sublattice, only after 1000 °C annealing. Lattice location measurements show that after annealing to 1500 °C, Cr is greater than 95% substitutional in the Al sublattice. Above 1500 °C, implanted Cr atoms redistribute by substitutional diffusion processes. EPR measurements show that part, if not all, of the implanted Cr is trivalent and substitutional after annealing to 1600 °C. Microhardness measurements are consistent with alloy formation in the process of ion implantation followed by thermal annealing.
Redistribution of As during Pd2Si formation: Electrical measurements
Authors: Wittmer M. , Ting C.-Y. , Tu K. N.
Published: February 2003

We have investigated the redistribution of As during Pd2Si formation with electrical measurements. Our results are in agreement with the earlier findings that part of the shallow implanted As is pushed ahead by the moving silicide-silicon interface at 250 °C. We show that, owing to the As redistribution, Pd2Si contacts can be formed to shallow junction diodes without altering the junction properties, because the junction is displaced by the approaching silicide-silicon interface. We also demonstrate that the increase in the As concentration beneath the silicide-silicon interface reduces contact resistance. Finally, we discuss the use of the As redistribution to adjust the barrier height of Schottky diodes and other applications in submicron integrated circuit technology.
Radiation damage in neutron transmutation-doped silicon. I. Electron paramagnetic resonance study
Authors: Sahu K. , Reddy T. Rs.
Published: February 2003

The removal of the radiation damage in neutron transmutation-doped silicon during the isochronal annealing from a temperature of 423–1223 K has been monitored by electron paramagnetic resonance spectroscopy. The dominant defect centers have been identified to be P1, A2, A4, A8, and A11. Complete decay of all the defect centers has been found to take place on annealing at 923 K, where a complete recovery of conduction electron spin resonance signal also takes place.
Radiation damage in neutron transmutation-doped silicon. II. Infrared study
Authors: Sahu K. , Abha  , Reddy T. Rs. , Warrier A. V. R.
Published: February 2003

Infrared absorption study of the annealing behavior of defects in neutron transmutation-doped silicon is reported in this paper. Infrared absorption measurements were carried out in the region 10 000–400 cm−1. This has shown the presence of extended band edge tailing, divacancy associated bands (5882, 2900, and 2760 cm−1) and higher order bands (1300–700 cm−1) at different stages of isochronal annealing from 423 to 873 K. The study of higher order bands under illumination with monochromatic light of wavelength varying from 0.5 to 1.5 μm has helped in understanding the nature of the transitions responsible for higher order bands. These bands disappear on annealing at 873 K, and no new bands appear on further annealing the sample to 1223 K. By correlating the present results with our earlier electron paramagnetic resonance results, we have postulated the formation of voids at higher temperatures of isochronal annealing.
Effects of preparation conditions and low-temperature ion irradiation on superconductivity and electrical resistivity of amorphous (Mo0.6Ru0.4)1−xBx films
Authors: Söldner L. , Adrian H. , Bieger J. , Brenner K. , Nölscher C. , Saemann-Ischenko G.
Published: February 2003

Thin amorphous films of superconducting (Mo0.6Ru0.4)1−xBx were prepared by magnetron sputtering in an ultrahigh vacuum (UHV) system. The superconducting properties and normal state resistivities ρ of films condensed at 77 K are discussed. We find a strong dependence on the sputter conditions of the low-temperature resistivity ρLT =ρ (25 K) and its variation upon irradiation with 20-MeV sulphur ions, although the superconducting critical temperature Tc and the temperature dependence of ρ are not strongly influenced for all films prepared. Whereas films sputtered with argon pressures below ∼10−2 mbar have resistivities of about 100 μΩ cm which are reduced 2–3% by irradiation, films sputtered with higher argon pressures have resistivities up to 1000 μΩ cm and show irradiation-induced decreases of almost 70%. Independent of this behavior, the x-ray diffraction patterns appear nearly identical, and Tc increases 6–10% with irradiation. Assuming that irradiation defects reduce the structural short-range order, the effects observed with low-resistance films could be explained by a smearing of the structure factor S(k) and an enhancement of the electronic density of states at the Fermi level N(EF). Our results suggest that the structure of high-resistance films has initially a reduced density which is increased by irradiation.
Elastic modulus in composition-modulated silver-palladium and copper-gold foils
Authors: Henein G. E. , Hilliard J. E.
Published: February 2003

The biaxial elastic modulus Y[111] has been measured by bulge testing in Ag-Pd and Cu-Au thin foils containing one-dimensional composition modulations with wavelengths ranging from 0.9 to 5.5 nm. For the Ag-Pd foils having wavelengths of 2.0–3.0 nm, the modulus was up to 2.3 times greater than that of homogeneous foils of the same average composition. The increase was found to be proportional to the square of the amplitude of the modulation. In foils containing modulations of wavelengths less than 2.0 nm or greater than 3.0 nm, the modulus was the same as that of homogeneous foils. It was observed that the deformation was elastic but non-Hookean. For the Cu-Au modulated foils no modulus enhancement was observed: The modulus for any wavelength was in good agreement with that calculated from the bulk elastic constants.
Attenuation and velocity of waves propagating along a steel-steel interface
Authors: Kumar Vijai
Published: February 2003

Measurements of attenuation and velocity of propagation of interfacial waves along steel-steel interface are reported. The bonding at the interface is varied by the application of external load normal to the plane interface. These measurements are interpreted in the framework of a theoretical model of a loosely bonded solid-solid interface.
Thin-film transistors fabricated in solid-phase-recrystallized Si films on fused silica substrates
Authors: Tsaur B-Y. , Fan John C. C. , Turner G. W. , Geis M. W. , Silversmith D. J. , Mountain R. W.
Published: February 2003

Solid-phase recrystallization of Si films prepared by chemical vapor deposition on fused silica substrates has been accomplished by transient heating on a graphite strip heater. This process increases the grain size from ∼50 nm to ∼1 μm. Thin-film transistors fabricated in the recrystallized films exhibit surface electron mobilities of 15–20 cm2/V s and on:off current ratios in excess of 105 for a voltage swing of 10 V.