bluuebunny/crossref_metadata_2025 huggingface dataset:
Picosecond time evolution of photoexcited hot-electron mobility in GaAs and the speed of photoresponse
Authors: Vengurlekar A. S. , Jha Sudhanshu S.
Published: July 2002

The transient mobility of hot electrons photoexcited in undoped GaAs by subpicosecond laser pulses is calculated. For this, we solve the time-dependent Boltzmann transport equation in the presence of a low-frequency, weak electric field. The attention is focused mainly on the role of intracentral Γ valley scattering in determining the delay in the mobility rise on the picosecond time scale, and the hot-electron energies are assumed to be below the thresholds for possible side-valley transfers (Γ→L,X). We consider the mobility response under two separate conditions of excited carrier density, namely, (1) low-density excitations for which the electron–longitudinal phonon (LO) Fröhlich interaction initially dominates in the carrier relaxation and (2) high-density excitations for which the electron-electron interaction is faster than all other collisions. The mobility of hot electrons is very small (<1000 cm2/V s) just after photogeneration. It rises to its maximum value with a time constant decided by the various scattering processes which are influenced by the values of the carrier density and the lattice temperature. We find that the mobility rise can be quite slow up to the scale of several picoseconds, even when the possible delay due to side-valley scattering is absent.
Observation of radiative and nonradiative tunneling in GaAs/AlxGa1−xAs heterojunction bipolar transistors with compositionally graded base-emitter heterojunctions
Authors: de Lyon T. J. , Casey H. C. , Enquist P. M. , Hutchby J. A. , SpringThorpe A. J.
Published: July 2002

A comparative experimental study of 77-K current gain and electroluminescent (EL) spectra in Npn GaAs/AlxGa1−xAs heterojunction bipolar transistors (HBTs) with either compositionally graded or abrupt base-emitter heterojunctions is reported. Shifting-peak spectra associated with radiative tunneling of carriers into the base-emitter heterojunction space-charge region are observed to dominate the 77-K EL spectra of HBTs with linearly graded emitters. The 77-K EL spectra of the abrupt HBTs are characterized by a peak whose energy position is invariant with respect to base-emitter bias and corresponds to recombination of electrons diffusing across the HBT base. Comparison of EL peak intensity and transistor base current indicates that the graded HBT current gain at 77 K is determined by nonradiative tunneling of electrons and holes to deep levels at the base-emitter junction. The loss of minority carriers to radiative and nonradiative tunneling current mechanisms in the graded HBT causes the 77-K current gain of the graded HBT to be significantly lower than that of the abrupt HBT.
Lattice vibration spectra of GaP1−xSbx and InP1−xSbx
Authors: Cherng Y. T. , Jaw D. H. , Jou M. J. , Stringfellow G. B.
Published: July 2002

Raman scattering spectra of ternary semiconductor alloys GaP1−xSbx and InP1−xSbx have been investigated in the spectral region from 150 to 450 cm−1 at room temperature. The optical phonons of both GaP1−xSbx and InP1−xSbx exhibit ‘‘two-mode’’ behavior over the whole composition range. A random element isodisplacement model is used to describe the behavior of the optical phonons of both alloy systems. The calculations of the dependence of the long-wavelength optical phonon frequencies on the composition are in good agreement with the experimental results.
Investigation of the (100)Si/amorphous insulator interface structure by a half-period image of a high-resolution electron microscope
Authors: Ohdomari Iwao , Kai Kazuhiko , Ueno Tomo , Suzuki Kazumasa
Published: July 2002

In order to understand the change in images due to imaging conditions, we have calculated the dependence of the intensity on defocus using a structure model. The contrast of images is strongest for c-Si under conditions for structure and reversed images and weakest for the half-period image. Intensity for an a-SiO2 region does not have a strong dependence on the defocus. The contrast of the half-period image for c-Si is almost comparable to that of a-SiO2. Consequently the periodic pattern for the c-Si region can best be discriminated from the random pattern of a-SiO2 under the condition of the half-period image. In addition, since the condition is sensitive to the thickness of the c-Si region, the identification of the transition region becomes easier by using the half-period image.
The intensifying effect of metallic screens on the sensitivity of x-ray films at 662 keV
Authors: Navon E. , Barnea G. , Dick C. E.
Published: July 2002

The relative photographic effect of electrons originating from 662-keV photons interacting in aluminum, copper, and lead foils was measured as a function of the foil thickness. Intensification factors on the sensitivity of Kodak AA x-ray films of up to 5.5, 4.6, and 8.7 were determined for aluminum, copper, and lead, respectively. The equilibrium thicknesses for back screens were found to be 40, 65, and 110 mg/cm2, respectively. For front screens, the equilibrium thickness is 110 mg/cm2 in all cases. The results were compared with the absorbed dose in the film’s emulsions, calculated by Monte Carlo methods and found to agree within 10%.
Finite-element analysis of radio-frequency quadrupole traps
Authors: Lunney M. David N. , Webb J. P. , Moore R. B.
Published: July 2002

A radio-frequency quadrupole ion trap is an axisymmetric arrangement of electrodes used to contain charged particles. The field between the electrodes must be calculated using numerical techniques, as practical implementations of the trap cause the potential distribution to deviate from the closed form. The finite-element method has been used to compute the electric field and a fourth-order numerical integration has been written to compute ion trajectories inside the trap. Together, these computations were used to study the injection of ions into traps. Results from injection simulations are compared with experimental observations.
Surface segregation mechanism during two-dimensional epitaxial growth: The case of dopants in Si and GaAs molecular-beam epitaxy
Authors: Andrieu S. , d’Avitaya F. Arnaud , Pfister J. C.
Published: July 2002

In this paper, we present a physical explanation for the dopant surface segregation during two-dimensional growth in molecular-beam epitaxy. It is shown that the only way to explain dopant behavior is to assume the climbing of dopant atoms over the steps on the surface, during the growth. An energetical analysis of such phenomenon is presented. Taking into account this mechanism during two-dimensional growth, two kinetic equations can be written for each layer. Resolution of the system provides analytical solutions, and the growth rate influence on the doping profile is justified. The applicability of this approach to several dopants both in GaAs and Si is discussed. It appears that the origin of this segregation phenomenon lies in the unfavorable energy situation for the incorporation of a dopant instead of a bulk material atom.
Metalorganic molecular-beam epitaxy of InGaP
Authors: Ozasa Kazunari , Yuri Masaaki , Tanaka Shigehisa , Matsunami Hiroyuki
Published: July 2002

To study the growth mechanism of phosphorus-based III-V ternaries in metalorganic molecular-beam epitaxy, epitaxial growth of In1−xGax P was carried out on GaAs(100) using triethylindium (TEIn), triethylgallium (TEGa), and phosphine under high vacuum (10−5 Torr). Three distinct stages were observed in the temperature dependence of growth rate and Ga composition x of In1−xGax P epilayers. At 390–520 °C, the growth rate and the Ga composition were independent of temperature. The growth rate was proportional to the group-III total flux of TEGa+TEIn, and the Ga composition to the flux ratio of TEGa/(TEGa+TEIn). Lower growth rates were observed with InP-rich compositions below 390 °C, and with GaP-rich compositions above 520 °C. By dividing the growth rate γ into the two growth rates of quasi-binaries [xγ for GaP and (1−x)γ for InP], the pyrolysis of TEGa with an apparent activation energy of 39 kcal/mol was found to limit the growth below 390 °C. At higher temperatures above 520 °C, In droplets were formed on the epilayer surfaces, suggesting that phosphorus evaporation governs the growth. Moreover, a new type of complex defect (InP crystallite partially surrounded by metal In) observed in some cases above 520 °C is reported for the first time.
Determination of high-field-enhanced emission rates with the constant capacitance-voltage transient technique
Authors: Chang M. B. , Tomokage H. , Shiau J. J. , Bube R. H. , Bravman J. C.
Published: July 2002

We propose a new method for determining the trap level, doping concentration profiles, and enhanced emission rates caused by a high field which is accurate even in the presence of high-trap concentrations with a nonuniform profile. The constant capacitance-voltage transient technique is applied in this method. The amplitude of the transient voltage and the reverse-bias voltage at the beginning of the emission cycle are used for the determination of trap level and doping concentration profiles, respectively. The field enhanced emission rate is determined from the initial slope of the transient signal. The midgap level in GaAs is measured in order to test this method. The effects of both junction leakage current and free-carrier tail on the trap concentration and emission rate measurements are discussed together with the high-field effect.
Current transport in a-Si:Ge alloy Schottky barriers
Authors: Sharma D. K. , Narasimhan K. L. , Kumar Shailendra , Arora B. M. , Paul W. , Turner W. A.
Published: July 2002

In this paper, we have investigated the temperature dependence of forward and reverse currents of a-Si:Ge:H-Pd barriers. In contrast to a-Si:H, we find that the diode quality factor is 2 and is independent of temperature. We have confirmed quantitatively that the forward current is recombination limited and the reverse current is generation limited. The barrier height ΦB=0.7 eV, which is half the measured optical gap. The frequency, bias, and temperature dependence of capacitance have also been investigated. From the capacitance measurements, we infer that the density of states near midgap is approximately 2×1017 cm−3 eV−1.
Emission spectroscopy diagnostics of a magnetron sputter discharge
Authors: Cook J. G. , Das S. R.
Published: July 2002

An emission spectroscopy study is made of an rf magnetron discharge used to sputter deposit CdTe in Ar. The dependence on gas pressure and rf power of the strongest Cd, Te, and Ar emission line intensities (I) is determined for both the negative glow and the positive column. It is shown that the sputtered atom density NCd (NTe) is proportional to ICd/IAr (ITe/IAr) as the rf power is varied at pressures near 0.5 Pa, and that such a relationship does not hold as the gas pressure is varied. From the power dependence of IAr it is deduced that Ar atoms are excited to emitting states directly from the ground state; no evidence for the influence of intermediate metastable states is observed.
Ionization of atomic oxygen on the surface of a specimen in plasma anodization
Authors: Matsumura Koki
Published: July 2002

The behavior of the species of oxidation dominating the oxide growth in plasma anodization of Al is investigated in this paper. The relationship between the current efficiency and the plasma parameters was observed under the different anodizing conditions with changing the construction of the discharge electrodes and the discharge current in order to clarify the factors contributing to the anodization. The formula of the current efficiency was tentatively derived from a rough model of the growth process of the oxide film with an approximation. The formula, in practice, was consistent with the experimental results. Consequently, it was suggested that the rate-limiting step in the oxide growth is due to the supply of the atomic oxygens from the plasma to the surface of the specimen and also to their ionization.
Ion kinetics study of a high-efficiency, high-energy hydrogen fluoride chain chemical laser initiated by an intense electron beam
Authors: Ashidate Shu-ichi , Obara Minoru
Published: July 2002

The operational characteristics of intense electron-beam (e-beam) initiated hydrogen fluoride (HF) chain chemical lasers were theoretically analyzed with a new computer code including both neutral and ionic reactions. The gas mixture used is F2/H2/SF6/O2. Both theoretical HF laser output energy and pulse width were in good agreement with those of the experiment. Using this code, we calculated the performance characteristics as a function of e-beam current pulse width, initial total gas pressure, H2 partial pressure, O2 partial pressure, and gas temperature. In order to optimize the total gas pressure, we introduced a new parameter which shows the effect of the pressure rise by the exothermic chemical reactions. The optimum total gas pressure of 850 Torr was predicted in our system. Moreover, by lowering the initial gas temperature from 300 to 220 K both the output energy and the chemical efficiency were improved.
X-ray interference in quantum-well laser structures
Authors: Wie C. R.
Published: July 2002

X-ray interference effects are observed in the simulated rocking curves of quantum-well laser structures. It is shown that the interference effects appear in the cladding layer peak of rocking curves for a generic sample structure of a thin heterojunction layer of composition A cladded with two thicker layers of composition B. Depending on the detailed layer structure and the lattice mismatch, the sandwiched quantum-well layer can be as thin as 2–3 Å in order to affect the interference structure of the cladding layer peak. For a given mismatch, the interference effect occurs around a certain minimum thickness and similar interference structures appear periodically with increasing quantum-well layer thickness. This effect can be used to estimate the quantum-well layer thickness with a high accuracy. A simple model is used to calculate the thickness period as a function of lattice misfit and diffraction geometry. The calculation results explain the simulation results.
The electroelastic constants of quartz determined by the resonator method
Authors: Hruska Carl K. , Brendel Remi
Published: July 2002

One hundred and thirty-four new observations of the resonance frequency shift in quartz plate resonators caused by a dc electric field have been used to determine, by least-squares fit, one pure component and five combinations of the remaining seven components of the electroelastic tensor components of alpha quartz. The work is done in the framework of the nonlinear theory of dielectrics. Comparison is made with similar values obtained independently using a different experimental method. A substantial improvement in the degree of agreement has been achieved with respect to earlier results [J. Appl. Phys. 55, 608 (1984)] which are also superseded by this work.
Double-layered overwritable magneto-optic disk with magnetic recording and magneto-optic reproducing
Authors: Ishii Osamu , Yoshimura Fumikatsu , Nonaka Koutarou , Hatakeyama Iwao
Published: July 2002

This communication describes an overwritable magneto-optic disk with a double-layered medium consisting of magnetic recording (low coercivity Hc and high Curie temperature Tc) and reproducing (high Hc and low Tc) layers. After a magnetic head writes data on the recording layer, a focused laser beam from the optic head irradiates a recorded track to transfer the bits to the reproducing layer with a width equal to that of the laser beam. The printed bits on the reproducing layer are read with the magneto-optic head. By repeating the above operations, the overwrite process is achieved.
Photoluminescence of CuAlxGa1−xSe2 crystals grown by chemical vapor transport
Authors: Sugiyama Koichi , Iwasaki Satoshi , Endo Tamio , Miyake Hideto
Published: July 2002

The photoluminescence (PL) characteristics have been studied for the CuAlxGa1−x Se2 chalcopyrite quaternary crystals grown by an iodine transport technique. The PL measurements at 77 K reveal the existence of three types of emission bands, which are attributed to transitions involving localized states: shallow acceptors, deep donors, and deep acceptors, respectively. The origin of the shallow acceptors is tentatively assigned to Se interstitials and that of the deep donors to iodine impurities. All the measured crystals are p type and the hole mobility at room temperature decreases with x (≲0.3).
Unified approach to the temporal evolution of surface profiles in solid etch and deposition processes
Authors: Gallatin G. M. , Zarowin C. B.
Published: July 2002

The differential equation describing the temporal evolution of solid surfaces subject to etching or depositon is derived. Its general properties are discussed and solutions to particular problems are obtained. The differential equation explicitly shows the evolution of the shape of the surface to be the product of a geometric factor which is common to all etch/deposition processes and a rate factor which depends on the physics of the process considered. The rate factor must in general be derived from first principles. Here we limit consideration to rate factors that describe isotropic and unidirectional processes, as well as linear combinations of these two processes. The properties of the evolution of surface profiles are studied in detail for each case. A unidirectional etch with a rate factor dependent on the local surface curvature is shown to produce good agreement with the observed shapes of deep isolation trenches in silicon. Finally, the surface evolution equation is used to expore the ability of certain processes to smooth and polish initially rough surfaces.
Steady-state bulk trap-modulated hopping conduction in doped linear low-density polyethylene
Authors: Nath R. , Perlman M. M.
Published: July 2002

A mathematical model is developed for trap-modulated, steady-state, hopping transport of space-charge-limited carriers, injected into linear low-density polyethylene, doped with oxidized low-density polyethylene. Poole field lowering of the trap depth is also included. The hopping sites are carbonyl groups provided by the dopant, lying in the amorphous regions of the sample. We assume band-tail or band conduction, i.e., little or no energy barrier to transport within the crystalline regions, and deep traps located at the crystalline-amorphous matrix boundaries. Two adjustable parameters, the hopping and trap site separations, are used to give good agreement with the experimental current-applied field characteristics in the temperature range 50–85 °C for fields less than 4×105 V/cm, and hopping site concentrations of 2×1019/cm3 and 4×1019/cm3. For the latter concentration, (corresponding to a separation of about 28 Å) at temperatures (35–60 °C) that are too low to thermally detrap injected carriers (that are trapped before reaching the steady state), conduction takes place by hopping in the amorphous regions over an energy barrier of 0.30 eV. At elevated temperatures (60–85 °C), detrapping contributes to the steady-state current. The activation energy in this latter temperature range is 1.17 eV (at 2×105 V/cm). The final current, field, and temperature equation shows that the hopping and trap energies are additive on a semilog plot of I/T vs 1/T. Thus, the field-lowered trap depth is 0.87 eV. This result agrees well with a previously determined crystalline-amorphous trap depth in virgin linear low-density polyethylene.
Anomalous electrical behavior of n-type GaAs
Authors: Benzaquen M. , Walsh D. , Benzaquen R. , Kunysz A.
Published: July 2002

Hall data are presented for two n-type GaAs epilayers of different origin with dissimilar thickness, grown by metalorganic chemical vapor deposition. Both the Hall mobility and Hall electronic concentration were analyzed for each sample on the basis of a complete electrical transport model. The results for a 3-μm-thick sample, which was also the purest, were in good agreement with theory in the whole temperature range, without accounting for depletion effects. The other sample, 9 μm thick and more heavily doped, showed an increase of the Hall electronic concentration above 200 K, along with a depressed room-temperature Hall mobility. As for previous studies in InP, this behavior is well described by the presence of a deep center or complex of unknown origin.
Effects of doping-density gradients on band-gap narrowing in silicon and GaAs devices
Authors: Lowney Jeremiah R. , Bennett Herbert S.
Published: July 2002

The limitations of the theory for band-gap narrowing, which is based on uniform material, are considered in devices that have steep doping gradients. Validity criteria are derived that place upper bounds on the dopant and carrier density gradients for the application of the results from uniform theory. The existence of wave-function tailing beyond the potential barriers that occur in devices is studied. At room temperature the effects due to these tails are usually small, but at low temperatures they can become very significant.
Magnon Brillouin scattering in FeSi sputtered films
Authors: Yoshihara Akira , Haneda Yoichi , Shimada Yutaka , Fujimura Tadao
Published: July 2002

Thermally excited spin waves in sputtered FeSi films (2.6 wt. % of Si) have been studied at room temperature by Brillouin scattering in external magnetic fields of up to 4.0 kOe. Scattering from the Damon–Eshbach surface mode and the standing spin waves has been observed. The magnetic constants of the FeSi films are determined as follows: γ/2π =2.87±0.06 GHz/kOe, g=2.05±0.04, 4πMs=19.9±0.4 kG, 4πMb=20.1±0.4 kG, and Db=1.18±0.24×10−9 Oe cm2. Here, the subscripts s and b refer to surface and bulk, respectively.
An analytical solution to predict the drive-in of N- and P-well implants in high-temperature process steps
Authors: Maldonado C. D.
Published: July 2002

The linear two-dimensional boundary-value problem that governs the redistribution of low-dose N- and P-well implants during high-temperature drive cycles in inert and oxidizing ambients is solved analytically in this paper. The oxide growth rate that appears in the defining equations of the boundary-value problem is made independent of time by subdividing the process step into smaller time intervals and replacing the oxide growth in each interval by its average value. The resultant boundary-value problem was then solved such that the solution evolves from a specified initial distribution, using the Green’s function technique. By using the final impurity distribution in a prior interval of time as the initial distribution in a subsequent interval, in a sequential manner, a hierarchy of solutions is generated that spans the entire process step. The program for generating this hierarchy of solutions was applied to two examples pertaining to the drive-in of N- and P-well implants. The obtained results were, for all practical purposes, identical to those of the romansii (redistribution and oxidation modeling analysis by simulation in II dimensions) program, thus confirming the validity of the analytical solution. Because the discretized system of equations becomes stiff for high-temperature (1165 °C) drive cycles, the CPU times obtained on the DEC(8800) computer with the analytical solution of this paper were at least two orders of magnitude smaller than those obtained with the romansii program. In regions where the two-dimensional simulations can be reasonably approximated by one-dimensional profiles, the obtained correlation with the SUPREM3 (Stanford University Process Engineering Models 3) predictions was excellent.
Interface structure of a-Si:H/ZnS multilayer films elucidated from electron-spin resonance and infrared-absorption measurements
Authors: Morimoto Akiharu , Mizushima Kazuyoshi , Shimizu Tatsuo
Published: July 2002

Multilayer films consisting of hydrogenated amorphous silicon and zincsulfide (a-Si:H/ZnS) were prepared by glow-discharge decomposition of silane gas and diethylsulfur-diethylzinc gas mixture. Since a-Si:H/ZnS multilayer films do not have Si atoms in their barrier layer, they have an advantage of easy characterization of the a-Si:H well layer by using electron-spin resonance and infrared absorption. These measurements revealed that in an interface region within a distance of 10 nm from the interface, H atoms in a-Si:H are incorporated in the form of dihydride rather than in the form of monohydride. In accordance with the H bonding scheme, it was also found that the interface region in a-Si:H within a distance of several nanometers from the interface has a large Si dangling bond density of the order of 1018 cm−3. Transport properties in these films were also investigated.
Influence of high-temperature thermal treatment on edge-defined film-fed growth silicon
Authors: Pivac B. , Desnica U. V.
Published: July 2002

Various polycrystalline silicon ribbons, grown with the edge-defined film-fed growth (EFG) technique, are annealed at the temperatures from 450 to 1250 °C. The EFG ribbon growth technique introduces high C and O concentration which results in specific annealing behavior due to defect interactions. It is shown that oxygen in-diffusion during the crystal growth produces an oxygen-rich layer close to the surface of the ribbon, containing mostly SiOx agglomerates unstable at higher temperatures. Carbon concentration that exceeds the oxygen concentration causes a formation of high-temperature [C,O] complexes which could not be found in Si material with an inverted carbon-to-oxygen concentration ratio.
Experimental evidence for a second-donor level of gold in silicon
Authors: Jang Sheng-Lyang , Bosman Gijs
Published: July 2002

The resistance and the low-frequency voltage noise of a silicon p+-p−-p+ device doped with boron and gold were measured as a function of temperature. The data indicate that gold produces two energy levels at 0.267 and 0.336 eV above the valence band, respectively. The observation is explained in terms of double-donor centers interacting with the valence band.
The computer simulation of the internal friction peaks associated with the oscillation of geometric kinks along the nonscrew dislocation in the atmosphere of nonlinear power dissipating interstitials
Authors: Ogurtani Tarik Ö. , Seeger Alfred K.
Published: July 2002

The effects of the nonlinear power dissipation on the strength and the position of the cold-work internal friction peaks associated with the oscillation of geometric kinks in the atmosphere of paraelastic interstitials have been investigated by the novel numerical study of the related mathematical macromodel. The present macroscopic model of internal friction is described by a second-order ordinary differential equation with a nonlinear Debye-type dissipative drag term. This system shows not only dissipative resonance behavior, but it also results in unusually sharp energy dissipations, like the Cherenkov radiation, when the kink velocity exceeds the Snoek jump velocity of interstitials at high external driving force amplitudes.
Plastic yielding at crack tips
Authors: Altan S. Burhanettin , Eringen A. Cemal
Published: July 2002

Small-scale plastic yielding at crack tips is studied by means of nonlocal elasticity. Plastic lines along the crack line of a mode III crack modeled by an array of dislocations. It is shown that plastic yield begins after a definite value of load as a consequence of nonlocality. The length of plastic zone and the dislocation distribution are determined as functions of the applied load. The results are in good agreement with experimental observations
Similarity transformations for decaying wall charge fields in a spherical shell
Authors: Curzon F. L.
Published: July 2002

It is shown that ohmic dissipation of wall charges causes the electric field inside a spherical insulating shell to decay with a characteristic time constant, t0 =2aηε0 , where η is the surface resistance of the shell, a is its radius, and ε0 is the permittivity of a vacuum. It is demonstrated that the electric potential inside the shell at time t can be constructed by means of similarity transformations which are generated by multiplying the initial charge densities by a factor f and lengths by f 2 where f=exp(−t/2t0 ). Using this method the potential near the centers of oppositely charged disks of wall charge of radius b (b≪a) is calculated in terms of analytic expressions for the case where the externally applied field is absent. It is pointed out that the latter solution can be generalized to yield the potential distribution generated by small wall charge spots which have rotationally symmetric charge distributions. It is anticipated that the results will be useful for further studies of external electrode discharges in gases in insulating containers, Examples include low-frequency electric field sensors and gas-filled cavities in solid insulators.
The dynamics of free, straight dislocation pairs. I. Screw dislocations
Authors: Eykholt R. , Trugman S. A. , Srolovitz D. J.
Published: July 2002

Analytic expressions are derived for the motion of a pair of interacting, straight, parallel (or antiparallel) screw dislocations in an applied stress field. Analysis of the equations of motion of the dislocations shows that, under most circumstances, the velocity of a dislocation is proportional to the driving force (i.e., the motion is overdamped), and, in this limit, the results are exact. However, when the two dislocations are very close together, inertial terms begin to play a role, and the resultant ‘‘finite-mass’’ corrections are treated perturbatively. For the case of antiparallel screw dislocations, a capture cross section exists and is given by the product of the shear modulus and the Burgers vector over the applied stress. Based on these results, a simple statistical analysis of the motion of a large number of screw dislocations is presented.
A conversion electron Mössbauer spectroscopy and transmission electron microscopy study of monocrystalline iron implanted with nitrogen
Authors: Terwagne G. , VanTendeloo G. , Donnelly S. E.
Published: July 2002

Monocrystalline films of α-iron were implanted at room temperature with nitrogen to different doses. The transmission electron microscopy and conversion electron Mössbauer spectroscopy measurements have shown clearly that the two techniques are complementary in determining the nitride phases present in the implanted films. At low doses (lower than 5×1016 ions/cm2) the α′-martensite is formed with the implanted nitrogen occupying octahedral sites. At higher doses (greater than 5×1016 ions/cm2) two phases which are more compact and progressively richer in nitrogen are observed, ε-Fe3N and ε-Fe2+xN.
Low-temperature (600–650 °C) silicon epitaxy by excimer laser-assisted chemical vapor deposition
Authors: Yamada A. , Satoh A. , Konagai M. , Takahashi K.
Published: July 2002

High-quality Si epitaxial films have been grown at low temperatures of 600–650 °C using an ArF/XeF excimer laser irradiated normal to the substrate. Crystallinity of the deposited films was characterized by reflection high-energy electron diffraction, Rutherford backscattering, Raman scattering, and secondary ion mass spectroscopy measurements. It was found that the laser irradiation on the growing surface was very effective for the improvement of both film crystallinity and electrical properties. A theoretical analysis of heat diffusion was carried out to clarify the effect of laser irradiation on the film quality. It was found that the photothermal effect of laser irradiation was a dominant factor in the improvement of the film crystallinity.
A possible mechanism of electron injection for the threshold voltage shift of metal-oxide-semiconductor field-effect transistors at low voltage
Authors: Tanimoto Satoshi , Mihara Teruyoshi , Asada Kunihiro , Sugano Takuo
Published: July 2002

A new possible model for hot-electron injection into the gate oxide of a metal-oxide-semiconductor field effect transistor at the drain voltage lower than the Si-SiO2 effective barrier height is proposed, taking into account the high-energy phonon scattering and impact ionization of electrons in the channel. Experimental confirmation of the model has been performed by measuring the temperature dependence of the threshold voltage shift of metal-oxide-semiconductor field-effect transistors with a floating gate for the temperature range of 100–300 K.
Device applications of vanadium-doped silicon-dioxide
Authors: DeLima J. J. , Snell A. J. , Krishna K. V. , Owen A. E. , Hawryliw A. , Thompson R.
Published: July 2002

This study has been undertaken in an attempt to investigate the possible applications of transition-metal-doped amorphous silicon-dioxide in floating-gate avalanche-metal/silicon-dioxide/silicon-type nonvolatile memories, with the objective of developing an electrically erasable programmable read-only memory structure with low WRITE and ERASE voltages, (e.g., ≂5 V) which does not depend for its operation on the very thin tunneling oxides (i.e., ≤80 Å) currently used and which are a major source of device instability and degradation. Results are presented for 200-Å-thick vanadium-doped silicon-dioxide films which show reproducible current-voltage characteristics at much reduced voltages compared with conventional thin thermal oxides.
Surface kinetics and growth interruption in molecular-beam epitaxy of compound semiconductors: A computer simulation study
Authors: Ghaisas S. V. , Madhukar A.
Published: July 2002

The dynamics of the growth front smoothness recovery following growth interruption in molecular-beam epitaxy of III-V compounds is examined via Monte Carlo computer simulations. Results are obtained as a function of the substrate temperature and group-V pressure and found to be remarkably similar to the behavior of the reflection high-energy electron diffraction (RHEED) specular beam intensity recovery measured near the first out-of-phase condition. An initial fast smoothness recovery is shown to be a combined effect of rapid interlayer movement of essentially isolated group-III atoms and the continued dissociative adsorption of the group-V molecules. The temperature dependence of the short time constant representing the fast initial recovery of the RHEED specular beam intensity thus does not necessarily provide a measure of the group-III surface diffusion coefficient. Results are also presented for the smoothness recovery behavior of Alx Ga1−x As alloys. The consequences of the differences in Ga and Al kinetic rates for the chemical nature (lateral and in the growth direction) of normal and inverted interfaces formed following growth interruption are discussed. The findings support earlier interpretations of the photoluminescence data on Alx Ga1−x As quantum well structures grown employing growth interruption.
Crystallization of amorphous Ti-Si alloy thin films: Microstructure and resistivity
Authors: Raaijmakers Ivo J. M. M. , van Ommen Alfred H. , Reader Alec H.
Published: July 2002

Cosputtered amorphous thin films consisting of Ti and Si were crystallized to the C49 TiSi2 phase at temperatures of about 390 °C. Prolonged annealing of the crystalline C49 TiSi2 phase at higher temperatures resulted in a gradual decrease in resistivity. We investigated the changes in microstructure which were associated with this slow decrease of the resistivity of the C49 phase. In situ resistivity and Hall-effect measurements, electron microscopy, and x-ray diffraction were used. It was demonstrated that the slow decrease in resistivity of the crystalline C49 phase was associated with a decreasing stacking fault density (typically 2×106 cm−1) and a decreasing density of point defects. The presence of point defects was found to be related to stoichiometry deviations. Polymorphous crystallization of a slightly Si-rich sample was found to result in a supersaturated solid solution of Si in C49 TiSi2. It was proposed that the phase field of the C49 phase is significantly wider than that of the equilibrium C54 phase. The reproducably low resistivity of the C54 TiSi2 polytype was due to the elimination of practically all stacking faults and point defects.
Anomalous transport in random superconducting composite systems
Authors: Yu K. W.
Published: July 2002

We have studied anomalous diffusion in the random superconducting network (RSN) with a wide distribution of conductivity. We consider a composite medium of superconducting and normal conducting regions in which the normal conducting component obeys a transfer-rate distribution of the form W−(1+α) (0<α<1). In the static (dc) case below the percolation threshold pc, one finds that the dc conductivity varies as (pc−p)−s′ in the vicinity of pc with s′=1/α. Above the percolation threshold and in the RSN limit, the superconducting component is considered to possess a large but finite transfer rate Ws. In this limit, the dc conductivity follows the p=pc behavior for small Ws, crossing over to the behavior of ordinary percolation at a crossover value of the superconducting transfer rate Ws,co, which is found to vary as (p−pc)−(1+α)/α. The results are in good accord with scaling relations. Right at the percolation threshold, the frequency-dependent conductivity is calculated in the RSN limit. The real part of the conductivity (σR) at low frequencies initially follows the dc behavior, crossing over to the behavior σR∼ω1−α at high frequencies. The crossover frequencies are estimated for various relevant regions. The imaginary part of the conductivity (σI) has even more complex behaviors. At high frequencies, σI varies as ω1−α, being the same as the real part. The results are in accord with the scaling relations generalized to finite frequencies. The model is also numerically solved in the effective medium approximation to compare with the analytic results. Good agreements are found.
Laser-enhanced plasma anodization
Authors: Matsumura Koki
Published: July 2002

The enhancement of the growth rate of Al2O3 has been observed during plasma anodization accompanied by optical excitation with low-power visible argon-ion laser light. The increase of the current efficiency with light is approximately 20% of the efficiency without it. This enhancement of the oxide growth rate is considered to arise from promoting the generation rate of atomic oxygen, which contributes to the anodization as oxidizing species, in the plasma sheath near the specimen and/or on the specimen surface irradiated by the laser light. Although most of the atomic oxygen is regarded to be generated by the dissociation of molecular oxygens colliding with plasma electrons, the laser excitation might help the cumulative dissociation of molecular oxygens.
Microscopic origin of anelastic relaxations in polyethylene oxide-sodium thiocyanate complexes
Authors: Bartolotta A. , Bonetti E. , Carini G. , DiMarco G.
Published: July 2002

The temperature behavior (100–400 K) of the mechanical characteristics (internal friction and resonant frequency) of polyethyleneoxide-NaSCN polymeric electrolytes reveals the presence of anelastic relaxations, which arise from local and cooperative microscopic motions. The low-temperature γ relaxation is explained in terms of a relaxation time distribution, which is interpreted as arising from random deviations in the local arrangement of the relaxing particles. Moreover, the elastic and anelastic features, as a function of the salt content, give some insight concerning their microscopic origin and the connection between the structure and the fast ion dynamics in this kind of systems.
Resonant tunneling time delay and quantum well sheet density
Authors: Bandara K. M. S. V. , Coon D. D. , Zhao Hong
Published: July 2002

Time delays, dwell times, resonant state lifetimes, and electron sheet densities associated with tunneling through quantum well structures are analyzed from a scattering theory (S-matrix) viewpoint. Some of the results differ from intuitively motivated expressions which have appeared in the resonant tunneling literature. It is shown that the sheet density is given by a formula similar to the Tsu–Esaki formula [Appl. Phys. Lett. 22, 562 (1973)] for current density. Sheet density and dwell time are related to Hermitian matrices which are expressed in terms of the S-matrix and in terms of partial widths associated with resonant states.
Properties of the two-dimensional electron gas in modulation-doped GaInAs(P)/InP structures grown by low-pressure metalorganic vapor-phase epitaxy
Authors: Grützmacher D. , Meyer R. , Balk P. , Berg C. , Schäpers T. , Lüth H. , Zachau M. , Koch F.
Published: July 2002

This paper is concerned with the characteristics of the two-dimensional electron gas (2DEG) at modulation-doped GaInAs/InP and GaInAsP/InP heterojunctions and GaInAs/InP single-quantum-well structures grown by low-pressure metalorganic vapor-phase epitaxy (LP-MOVPE) at 20 hPa. Using trimethyl-In, trimethyl-Ga, AsH3, and PH3 as source materials, this process permits the deposition of very uniform films with abrupt interfaces and doping profiles. We give the first detailed analysis of modulation-doped structures by classical Hall effect, Shubnikov–de Haas, and quantum Hall-effect measurements. Study of the scattering mechanisms of the 2DEG in modulation-doped GaInAs/InP and GaInAsP/InP structures reveals a small interface roughness and a low impurity content at the interfaces. Electron mobilities at 4.2 K up to 189 000 cm2/V s for a GaInAs/InP and 72 000 cm2/V s for a GaInAsP/InP heterojunction as well as values as high as 170 000 cm2/V s for a GaInAs/InP quantum well structure demonstrate the excellent control of the growth process and the quality of the material attainable by LP-MOVPE.
Effects of gold on YBa2Cu3O7−x at elevated temperatures
Authors: Ray II Roger D. , Hellstrom Eric E.
Published: July 2002

The interaction between Au and YBa2Cu3O7−x from 800 to 878 °C in 1 atm O2 was studied. Over this temperature range, Cu and small amounts of Ba were removed from the 123 leaving 211 and presumably BaCuO2. CuO crystals were present on the Au surface after the experiments. For 4-h anneals Cu diffused primarily along the surface of the Au and through Au grain boundaries. Under the same conditions, Cu was also removed from DyBa2Cu3O7−x forming CuO crystals on the Au surface.
Ambient temperature thermal conductivity of YBa2Cu3O7−x
Authors: Williams R. K. , Graves R. S. , Kroeger D. M. , Marsh G. C. , Scarbrough J. O. , Brynestad J.
Published: July 2002

A comparative method was used to measure the thermal conductivity λ of a YBa2Cu3O7−x sample over the temperature range 305–360 K. Using one sample, data were obtained at two different x levels. Surprisingly, the smaller x value (higher Tc) produced a lower thermal conductivity. This observation is discussed in terms of scattering of phonons by point defects and electrons.
Turnover temperatures of ST-cut quartz with sputtered-deposited thin layers of SiO2 and ZnO
Authors: Perelman I. , Kornblit L. , Gorodetsky G. , Rokhlin S. I.
Published: July 2002

The effect of sputter-deposited thin layers of ZnO and SiO2 on the turnover temperature of an ST-cut quartz surface-acoustic-wave delay line is studied. Upward shifts of the turnover temperature are obtained with SiO2 . Downward shifts are obtained for ZnO. It was found that the turnover temperature is linearly dependent on the thickness of the overlays over the temperature range −90–80 °C.
Resonant and nonresonant decay instability of a Langmuir wave in a plasma cylinder
Authors: Konar Swapan , Jain V. K.
Published: July 2002

The parametric decay of a Langmuir wave into a Langmuir wave and an ion-acoustic wave is studied in a plasma cylinder. A dispersion relation is obtained using the perturbation technique. In a plasma with comparable electron and ion temperatures nonlinear Landau damping takes over the decay process. The growth rate is found to be dependent on the transverse extent of the plasma.
Study of the interdiffusion of GaAs-AlGaAs interfaces during rapid thermal annealing of ion-implanted structures
Authors: Kahen K. B. , Rajeswaran G.
Published: July 2002

The phenomenon of transient-enhanced interdiffusion of GaAs-AlGaAs interfaces during rapid thermal annealing of ion-implanted heterostructures is studied. It is shown that the important properties that influence the degree of interdiffusion are the temperature, the concentration of excess vacancies, and the ability of the vacancies to diffuse freely. A model is presented to explain these observations; it is based on the solution of coupled diffusion equations involving excess vacancy and Al distributions following ion implantation. Both initial distributions are obtained from the solution of a three-dimensional Monte Carlo simulation of ion implantation into a heterostructure sample. The model is found to be in excellent agreement with several sets of experiments. More specifically, it is shown to be valid for as-implanted vacancy concentrations below 6×1019 cm−3.
Generation of high-number densities of iodine monofluoride in a supersonic flow
Authors: Helms C. A. , Hanko L. , Healey K. , Hager G. , Perram G. P.
Published: July 2002

Iodine monofluoride, a promising visible chemical laser candidate, has been chemically produced at number densities exceeding 1×1015 molecules/cm3 in a supersonic flow. Combustion of nitric oxide and molecular fluorine produced atomic fluorine at an efficiency of 20%–30%, independent of flow conditions. The subsequent transonic reaction of atomic fluorine with molecular iodine to produce a stable flow of IF(X1Σ+) was mixing limited and complete within 10 μs. The low-pressure (3 Torr), low-temperature (300 K) flow environment should be suitable for lasing.
Transfer loss in acoustic charge transport devices due to electron traps induced by proton bombardment
Authors: Janes D. , Hoskins M. J. , Brophy M. J.
Published: July 2002

An experiment is described in which electron traps are introduced into an acoustic charge transport (ACT) channel in a controlled manner by proton bombardment. The characteristics of the electron traps, including activation energies, capture cross sections, and concentration profiles, are measured using deep-level transient spectroscopy. The transfer performance of the ACT device is evaluated through measurements of the periodic pulse degradation and the frequency response characteristics of the device. Comparisons are made with the theoretically predicted dependence of transfer loss on trap parameters. The use of traps induced by proton bombardment allows the effects of trapping loss to be isolated from the other response characteristics of the ACT device and therefore provides a detailed picture of the behavior of trap-related transfer loss. The results of this study illustrate the dependence of trapping loss on trap concentration and provide a means for correlating ACT device response characteristics to specific trapping levels.
Epitaxy of germanium using germane in the presence of tetramethylgermanium
Authors: Venkatasubramanian R. , Pickett R. T. , Timmons M. L.
Published: July 2002

Epitaxial germanium (Ge) growth from germane (GeH4) has been investigated in the presence of organometallic tetramethylgermanium (TMGe) in the temperature range of 675–825 °C. Under the growth conditions employed, the growth of Ge is essentially mass-transport limited with an optimum growth temperature of 725 °C. The presence of TMGe does not increase Ge growth rates but lowers background-carrier concentrations in undoped n-type Ge layers. This reduction in background-carrier concentration is more pronounced at higher growth temperatures. In addition, the presence of TMGe yields more abrupt p+-n junctions, possibly suggesting the formation of more ‘‘defect-free’’ epitaxial growth of Ge from GeH4 and reduced boron diffusion into n-Ge layers.