bluuebunny/crossref_metadata_2025 huggingface dataset:
Accurate determination of the two carriers steady-state mobility-lifetime products in hydrogenated amorphous silicon
Authors: Balberg I. , Weisz S. Z.
Published: July 2002

The photocarrier grating (PCG) technique is used for the first time in the high electric field regime. The results are shown to confirm previously unproven theoretical predictions for this regime. It is demonstrated that, by application of the PCG technique in the high-field regime, accurate values for the ratio of the two carriers mobility-lifetime products can be deduced. This is in contrast with the fact that their sum cannot be derived accurately from the measurement of photoconductivity because one cannot determine accurately the carrier generation rate. Combining the ratio, determined by the high field PCG, with the low-field data yields accurate values for the mobility-lifetime products of both carriers.
Yellow–green luminescence from isoelectronic nitrogen centers in GaP grown by molecular-beam epitaxy
Authors: Baillargeon J. N. , Cheng K. Y.
Published: July 2002

Molecular-beam-epitaxial growth of GaP incorporating isoelectronic N traps was achieved through coinjection of NH3 and PH3 which were dissociated into P2 and PN fluxes. The photoluminescence spectrum of a sample with a N concentration of ∼2×1019 cm−3 indicated that the dominant emission wavelength was at 5691 Å (2.18 eV), which is characteristic of the nearest-neighbor pair transition NN1. The spectrum of a sample containing ∼2×1020 cm−3 N atoms also displayed strong NN1 pair luminescence in addition to much stronger emission line at 5846 Å (2.121 eV), which is believed to be from a local mode outside the vibrational band. The peak intensity of this local mode was ∼25 times greater than the peak emission of the NN1 line from the lighter doped sample.
Poled polymers for optical testing of electrical circuits
Authors: Gauterin F. , Jäger D.
Published: July 2002

We report on experimental investigations of electro-optic polymers, carried out in connection with the development of a contactless measuring technique for electrical signals in printed circuit boards. We describe the preparation of the poled polymers and the measurement of the electro-optic properties. The polymer samples consist of poly methyl methacrylate doped with N,N-dihexyl-4-amino-4’-nitrostilbene (DHANS). For a sinusoidal electrical field with a frequency of 1.325 kHz applied to the polymer sample we observe a change of the refractive index linear in the electrical field, the poling field, and the DHANS concentration. Using a dc field, we obtain a considerably larger field-induced change of the refractive index which is quadratic in the field, linear in the DHANS concentration, and nearly independent of the poling field. For both cases a figure of merit is defined and experimentally determined. With the present experimental setup, a minimum detectable change of the refractive index requires an ac voltage amplitude of 85 V and a dc voltage of 20 V.
Grain size dependence of 1/f noise in Al-Cu thin-film interconnections
Authors: Schwarz J. A. , Patrinos A. J. , Bakshee I. S. , Salkov E. A. , Khizhnyak B. I.
Published: July 2002

1/f noise measurements have been performed on Al-Cu thin films, of varying grain size, which were also subjected to electromigration lifetime tests. The results indicate a strong grain size dependence of the 1/f noise magnitude in the films. Moreover there is a correlation between electromigration lifetimes and values of 1/f noise magnitude, suggesting that 1/f noise measurements could be used as a nondestructive alternative to traditional electromigration testing.
Estimation of the alloy scattering strength in Hg0.8Cd0.2Te from the magnetic field dependence of the longitudinal resistivity in the extreme quantum limit
Authors: Banerji Pallab , Sarkar C. K.
Published: July 2002

The magnetic field dependence of the longitudinal resistivity in Hg0.8Cd0.2Te at a lattice temperature of 4.2 K has been studied theoretically in the extreme quantum limit (EQL) considering the electron scattering by the acoustic phonons, the ionized impurities and the alloy disorder. The calculation includes band nonparabolicity, free carrier screening and nonequipartition of acoustic phonons. The theoretical longitudinal resistivity of Hg0.8Cd0.2Te in the EQL shows a magnetic field dependence as Bn where n=0.24. The alloy scattering strength is estimated by fitting the theoretical results with the experimental results of the longitudinal resistivity of Hg0.8Cd0.2Te in the EQL at 4.2 K, where Hg0.8Cd0.2Te behaves as a free electron gas and the Wigner crystallization is not observed. Its value is found to be exactly the difference in the band-gap energies of HgTe and CdTe in agreement with the other calculations.
Hydrostatic pressure studies of an asymmetrically doped resonant tunneling diode
Authors: Othaman Z. , Peck A. J. , Bending S. J. , Saunders G. A. , Rossmanith M. , Ploog K. , von Klitzing K.
Published: July 2002

A study has been made of the effect of hydrostatic pressure on an AlAs/GaAs/AlAs resonant tunneling diode in which the electrodes have been deliberately asymmetrically doped. In reverse bias, current is injected into the structure from a highly doped n+-GaAs electrode and in forward bias from a two-dimensional accumulation layer at the GaAs/AlAs interface. When large hydrostatic pressures are applied at 77 K, regions of negative differential resistance are induced in both bias directions. Current maxima with peak-to-valley ratios as large as 4 have been measured at 8 kbar. The intrinsic asymmetry of the structure aids in the identification of the origins of these features in terms of the X-point conduction-band minima of the device.
Rail electrodynamics in a plasma armature railgun
Authors: Rolader Glenn E. , Jamison Keith A. , Villecco Roger A. , Graham Floyd R.
Published: July 2002

A model is developed to investigate rail electrodynamics in a plasma armature railgun. This model describes the rail motion in response to the transitory Lorentz force and the compressive restoration force from the material which is between the rails and the containment structure. In this model the distance between the rails is found to oscillate with a frequency of β. The magnetic field and the dynamic behavior of the rails induce local electric fields. We investigate the significance of these electric fields in the laboratory frame and in the projectile frame. In the lab frame, rail electrodynamics induces local electric fields which have maximums spaced behind the projectile at locations where βtp is an odd multiple of π, where tp is the time since the projectile has passed an axial location on the rails. When the projectile is accelerating, rail dynamics induce electric fields in the projectile frame which have maximums where βtp is an even multiple of π. As the projectile velocity increases, the locations of the peak voltages move farther behind the projectile. For the CHECMATE railgun, calculations indicate that the rail displacement is on the order of 2 mm, the rail velocity is on the order of 50 m/s, and the voltages induced in the projectile frame are on the order of 20–40 V.
The heat-of-mixing effect on ion-induced grain growth
Authors: Alexander Dale E. , Was Gary S. , Rehn L. E.
Published: July 2002

Irradiation experiments were conducted on multilayer (ML) and coevaporated (CO) thin films in order to examine the role that the heat-of-mixing (ΔHmix) has in ion-induced grain growth. Room-temperature irradiations using 1.7-MeV Xe ions were performed in the High Voltage Electron Microscope at Argonne National Laboratory. The ML films (Pt-Ti, Pt-V, Pt-Ni, Au-Co, and Ni-Al) spanned a large range of calculated ΔHmix values. Comparison of grain growth rates between ML and CO films of a given alloy confirmed a heat-of-mixing effect. With the exception of the Pt-V system, differences in grain growth rates between ML and CO films varied according to the sign of the calculated ΔHmix of the system. Substantial variations in growth rates among CO alloy films experiencing similar displacement damage demonstrated that a purely collisional approach is inadequate for describing ion-induced grain growth. Therefore consideration must also be given to material-specific properties, such as cohesive energy.
Global investigation of III-V semiconductor phase diagram by nonempirical method
Authors: Mohri T. , Nakamura K. , Ito T.
Published: July 2002

By combining electronic theory with the cluster variation method of statistical mechanics, five types of III⋅III-V and seven types of III-V⋅V pseudobinary phase diagrams are calculated. All the phase diagrams demonstrate phase separation and it is revealed that the phase separation is driven by elastic energy contribution. The asymmetry of the phase boundary can be systematically explained in terms of lattice constants of the constituent binary ordered compounds.
Deposition kinetics of platinum small ohmic contacts and Schottky diodes
Authors: Garrido C. , van den Bergh H.
Published: July 2002

A 351–363 nm wavelength argon laser is used to induce pyrolytic laser chemical vapor deposition of platinum, using platinum bishexafluoroacetylacetonate as a precursor. The deposit thicknesses and diameters are presented according to exposition time, precursor pressure, and laser spot diameter. Calculation of the temperature induced by the laser radiation exposition using a method developed by us allows us to study the kinetics of the deposition process which takes place either regimen controlled by the diffusion of the reactants or regimen controlled by the reaction kinetics, depending on the laser power density used. The process presents an apparent activation energy of about 6 kcal/mol. The deposits obtained present high purity and good electrical and morphological properties.
The electrical properties of a-Ge/a-SiOx superlattices
Authors: Williams G. V. M.
Published: July 2002

In-plane dc conductivity and ac perpendicular conductivity measurements have been performed on a-Ge/a-SiOx superlattices. The in-plane conductivity data are fitted to a four layer model for each period which allows the density of interface electronic defect states about the Fermi level to be estimated (4×1010 cm−2 per interface). The ac perpendicular conductivity data are successfully modeled and from the fitted parameters it is found that the perpendicular dc conductivity away from a Schottky metal/film region increases above that of a-SiOx when the a-SiOx layers are thinner than 7 nm.
Influence of sol-gel SiO2/TiO2 protective coatings on the optical and thermal properties of nickel-phosphorus selective surfaces
Authors: Papini Marie
Published: July 2002

A sol-gel coating was applied to an electroless acid-etched Ni-P spectrally selective surface in order to investigate its influence on the optical and thermal properties of the selective surface. The sol-gel process is a low-temperature preparation of glasses, which is of interest considering the lack of resistance of selective surfaces at the high temperatures generally needed to prepare glasses by the melting technique. The application of a glass coating on the Ni-P layer increases its oxidation resistance at high temperatures and improves the optical and thermal properties of this selective surface for heat treatments in air, up to 400 °C.
Two-photon photoeffect from resonant silver structures
Authors: Sabary F. , Dudek J. C. , Bergeret H.
Published: July 2002

We report the two-photon photoelectric sensitivities of a granular silver film and a silver covered diffraction grating at the photon energy ℏω=3.5 eV of a frequency-tripled Nd:YAG laser when surface plasmons are excited. Values higher than 3×10−15 A cm2 W−2 have been obtained with both structures which correspond to a one-photon quantum yield of 1×10−5 under a 1-GW-cm−2 incident laser power density. These photoemitters could be used as high current density electron sources by illuminating them with picosecond or subpicosecond lasers in the 2–4-eV spectral range.
Field-dependent antiferro-ferromagnetic transition in Co/Ru superlattices (abstract)
Authors: Ounadjela K. , Suran G. , Muller D. , Arbaoui A. , Dinia A. , Panissod P.
Published: July 2002

Co/Ru hcp (0001) superlattices were grown by UHV evaporation onto mica substrates. We demonstrate the growth of epitaxially ordered Co/Ru superlattices–despite the large lattice mismatch (≂8%)–consisting of hcp (0001) Co and Ru sublayers initialized on 150-Å-thick single-crystalline Ru buffer layer by using RHEED and x-ray diffraction. The magnetic properties were studied by magnetization and ferromagnetic resonance (FMR) measurements. For uncoupled Co layers, the resultant anisotropy switch from planar to axial direction (perpendicular to the film plane) with decreasing Co sublayers thickness. For Co sublayer thickness smaller than a critical one tco≂14 Å, the magnetization is directed perpendicular to the film plane. For small Ru interlayer thickness, large antiferromagnetic exchange coupling between the Co sublayers is observed in agreement with precious results. For a certain range of Co and Ru thicknesses, superlattices with unique magnetic parameters are obtained. Indeed, in the absence of an applied field, the magnetization is oriented along the film normal while the adjacent Co layers are coupled antiferromagnetically. For this magnetic structure, the magnetization process exhibits a hysteresis and the FMR spectra an irreversible behavior when the applied field is along the film normal.

As shown by SQUID measurements, when the field is decreased from a quasi-saturated state, the layers are essentially coupled ferromagnetically, the antiferromagnetic state appearing following a spin-flip process (staircaselike on the magnetization curve) for a field smaller than a critical one. However, with increasing field, the antiferromagnetic state disappears by progressive steps suggesting that the spin reorientation process occurs by coherent rotation of the magnetization combined with spin-flip process. The occurrence of this effect is particularly spectacular on the FMR spectra. With decreasing field, a classical FMR absorption is observed due to the basical ferromagnetic state while with increasing field, this absorption is largely reduced or disappears completely due to the antiferromagnetic one. The magnitude of the hysteresis and its evolution with the direction of the applied field, the values of the critical field corresponding to the spin flip and to the field above which the magnetic state is reversible, are very well correlated on the FMR spectra and the magnetization curves.
Antiferromagnetic coupling and magnetoresistance enhancement in Co-Re metallic superlattices (abstract)
Authors: Freitas P. P. , From M. , Melo L. V. , Ferreira J. , Trindade I. , Monteiro P.
Published: July 2002

Co-Re metallic superlattices were prepared that show antiferromagnetic exchange coupling and enhanced saturation magnetoresistance for particular values of the Re spacer thickness. We report studies on films with the structure glass /150 Å Re/[13 ÅCo/tRe]16/50 Å Re, with tRe ranging from 3 to 40 Å. These structures were grown by magnetron sputtering in a system with a base pressure of 1×10−7 Torr with deposition rates of 0.3 and 0.4 Å/s for Co and Re, respectively. x-ray diffractograms indicate the structure to be highly textured with the c axis perpendicular to the sample plane. The superlattice structure was obtained from high-angle θ-2θ scans. First-, second-, and third-order satellites are observed on both sides of the central [002] peak. Periodicity and bilayer composition are obtained from comparison of the data with a theoretical calculation of the x-ray diffractogram. Thickness calibration was confirmed by Rutherford backscattering and profilometer data. In-plane magnetization and magnetoresistance data (Δρ/ρ) indicate that stronger antiferromagnetic coupling and highest Δρ/ρ occur for tRe≊6 Å. The saturation field (Hs) needed to align contiguous antiferromagnetically coupled Co layers is about 1 T. This corresponds to an exchange coupling between the Co layer J≊−1 erg/cm2. (Δρ/ρ) reaches 2% in samples deposited at 170 °C. This data confirms results obtained by Parkin et al.1 in Co-Ru and Co-Cr superlattices.
Predicted spin and orbital contributions to the magnetic structure of Co/2X superlattices (abstract)
Authors: Victora R. H. , MacLaren J. M.
Published: July 2002

The neighboring elements Rh, Ir, Pd, and Pt are used as bilayers in Co/2X superlattices in an effort to systematically examine properties advantageous to short wavelength MO recording. The calculations presented here use the local spin-density approximation to the potential within the layer Korringa–Kohn–Rostoker method. The set of coupled differential equations produced by the inclusion of the spin–orbit interaction is solved by the method of Boardman.1 Interfaces occur along the (111) plane of the fcc lattice. In all cases, the Co moment is found to be strongly enhanced relative to bulk and the bilayer element atoms are substantially polarized. However, in the case of the Rh and Ir bilayers, we predict antiferromagnetic coupling of the spin polarizations of neighboring layers within the bilayer. This probably explains the mysteriously low magnetization experimentally found in CoIr alloys. In contrast, Pd and Pt bilayers exhibit ferromagnetic coupling. The Pd spin polarization is approximately 30% larger than the Pt value; however, the orbital contributions exhibit the opposite trend with the value for Pt about 40% larger. This is in qualitative agreement with Kerr data which reflects the orbital polarization. Directing the Co/2Pd superlattice spin along the interface plane is found to decrease the orbital polarization. This may explain why our preliminary calculated results for anisotropy constant, like experiment, find an easy axis perpendicular to the interface plane.
Temperature-dependent magnetoresistance of Fe-Ni multilayers
Authors: Ehrlich A. C. , Gillespie D. J. , Tritt T. M. , Kim C. , Edelstein A. S. , Qadri S. B.
Published: July 2002

Temperature-dependent longitudinal and transverse magnetoresistance measurements have been carried out on a series of five Fe-Ni multilayer thin films. The samples were prepared by sputtering onto glass substrates that were nominally at room temperature and proved to be highly textured with the (111) direction perpendicular to the substrate. The multilayer wavelength ranged from 21 to 155 Å with each sublayer composed of an equal number of monolayers of Fe and Ni. For the larger-wavelength films the magnetoresistance data shows a preferred direction of in-plane magnetization associated with the film growth parameters. With the field perpendicular to the plane the data shows the characteristic break at the applied magnetic field required for saturation. This saturation field is not temperature dependent and does not vary much or in any systematic manner with wavelength. Above the saturation field the magnetoresistance varies linearly with applied field with a slope, dR/dH, that varies systematically with temperature but very little with wavelength. For the smaller-wavelength samples where both the Fe and Ni are in the fcc crystal structure there is evidence in both the magnetization and dR/dH for a more complicated magnetic structure than either the long-wavelength films or bulk materials. In particular there is evidence for atomic scale magnetic anisotropy that differs from the film average.
Electrical resistivity of Co-Ni-Pd and Co-Pd alloys
Authors: Jen S. U. , Chen T. P. , Chang S. A.
Published: July 2002

Three series of ferromagnetic alloys have been made: Co100−xPdx, Co25Ni75−yPdy and Co5−zNizPd95. The electrical resistivity ρ of these alloys was measured from 4 to 300 K. Their high field (H≳2 T) susceptibility χHF was obtained with superconducting quantum interference device measurements at 5 K. Comparing the residual resistivity ρ0 of Co-Ni and Co-Pd, it is found that the spin-up resistivity ρ↑ of Co-Ni follows the Nordheim’s rule, while that of Co-Pd peaks at x=85. This indicates the spin-up d band of Co-Pd is not full for all the x values. Also, χHF data reveal the same tendency of the spin-up band. Based on the deviation from Matthiessen’s rule of the two-current model, we estimate α=ρ0↓ /ρ0↑≂2 for the dilute PdCo alloy, where ρ0=ρ0↓ ρ0↑/(ρ0↑+ρ0↓ ), from the residual resistivity of the ternary Co5−zNizPd95 alloy and from the temperature dependence of ρ(T) of the binary Co5Pd95 alloy
Deep-level transient spectroscopy on p-type silicon crystals containing tungsten impurities
Authors: Ando Toshio , Isomae Seiichi , Munakata Chusuke , Abe Takao
Published: July 2002

Tungsten deep levels are investigated to clarify energies, which are inconsistent among current research. Hole traps located at 0.41 eV above the top of the valence band are determined to be due to tungsten impurities. The concentration of hole traps is almost one-third of that of the tungsten impurities in the substrates. Similar hole traps are also found in different silicon substrates in which tungsten impurities are thermally diffused from the surface. These facts indicate that the hole traps are truly due to tungsten impurities.
On the rectifying ability of a p-type semi-insulating junction
Authors: Solomon P. M. , Weiser K.
Published: July 2002

The system consisting of an unintentionally doped GaAs epitaxial layer on a semi-insulating (SI) GaAs substrate forms a starting point for the GaAs integrated circuit technology. It is also the genesis of problems for GaAs field-effect transistors (FETs) in the form of back gating. Potentials applied to a point on the surface may propagate several millimeters to modulate the conduction of an FET built into the layer. In addition, the conductivity of the epilayer may be efficiently modulated by a potential applied to the back of the SI substrate. Well-developed p-channel FET characteristics have been observed in an epilayer on top of a 0.4-mm-thick SI substrate using the back of the substrate as a gate. Numerical simulations revealed that under some circumstances potentials may propagate across the substrate with little attenuation, giving a degree of modulation in agreement with experiment. Conditions for current transport then corresponded closely to those in a rectifying p-n junction. The parameter space was fully explored numerically and using an analytical model, and a simple set of conditions for rectification were developed.
A model for steady-state breakdown plasmas in microwave transmit-receive tubes
Authors: Hamnén H. , Anderson D. , Lisak M.
Published: July 2002

A model is proposed for the consistent description of the steady-state interaction between a high-power microwave and a breakdown plasma in transmit-receive (TR) tubes often used as switches in radar microwave systems. The electron-density equilibrium in the TR tube is established as a balance between the ionization produced by the wave and various electron-loss processes. In the currently proposed model, it is shown that diffusive losses of electrons in the direction of wave propagation is the most important loss process. An approximate analytical solution is derived from the model and compared with the numerically obtained full solution. Finally, the predictions obtained from the model concerning the scaling of absorbed and reflected microwave power are shown to be in good agreement with experimental results.
Modeling of the optical recording process on chromium films
Authors: Agranovsky M. L. , Korol’kov V. P. , Rubenchik A. M.
Published: July 2002

The problem of the thermochemical modification of chromium films is studied. The oxidation of the thin film on the glass wafer produced by local heating using laser radiation is considered. The temperature distribution is calculated. The width of recording trace is defined. The results of the experimental studies are presented and compared with the theoretical calculations. The effects of the parameter variations on the recording trace width are studied. The optimal conditions for optical recordings is defined.
Theoretical analysis of power generation in gasdynamic lasers
Authors: Mathiazhagan C. , Reddy K. P. J. , Reddy N. M.
Published: July 2002

The power generation in a gasdynamic laser (GDL) has been theoretically studied. Quasi-one-dimensional unsteady flow equations are numerically solved simultaneously with the rate equation for the laser intensity inside the laser cavity. Steady-state coupled solutions for the field variables and the laser intensity inside the GDL cavity are obtained by a time-dependent numerical technique. The laser intensity variations along the axis of the flow (across the laser cavity) are computed for different laser gas mixture compositions and reservoir conditions. The analysis predicts a sharp spike in the laser intensity at the leading edge of the laser cavity followed by a sharp fall from which it recovers to a uniform constant value for the lower H2O concentrations. It is shown that the H2O concentration above 2% in the CO2-N2-H2O gas mixture is detrimental to the power generation.
An asymptotic treatment of the Elenbaas–Heller equation for a radiating wall-stabilized high-pressure gas-discharge arc
Authors: Kuiken H. K.
Published: July 2002

An asymptotic analysis of the Elenbaas–Heller equation for a radiating wall-stabilized high-pressure gas-discharge arc is given. This analysis applies when the operating temperatures within the arc are lower than the ionization temperature by an order of magnitude. It is shown that for arcs that are radiating highly efficiently a further asymptotic treatment can be given. It is shown under what conditions, governed by a dimensionless parameter M, this limiting case prevails. Comparison with earlier results put forward by Zollweg [J. Appl. Phys. 49, 1077 (1978)] shows satisfactory agreement.
Interaction of CO2 laser pulses of microsecond duration with Al2O3 ceramic substrates
Authors: Beyer H. , Ross W. , Rudolph R. , Michaelis A. , Uhlenbusch J. , Viöl W.
Published: July 2002

The working efficiency and other properties of laser-induced surface plasmas have been compared for the case where two kinds of CO2 laser pulse interact with alumina substrates. Pulses of several times 10-μs duration are able to drill hole patterns while producing negligible mechanical stresses in the material. However, because of the formation of a laser-induced plasma which shields the material against the incoming laser beam, the drilling efficiency is rather low. A simple vaporization model shows that 30%–100% of the laser-pulse energy is used for material processing. There is in addition a threshold energy of about 50 mJ, below which no material processing occurs. Plasma diagnosis verifies characteristic times of absorptive modulation in the range of 5–10 μs. Therefore, laser pulses of high repetition rate (≳10 kHz) and of a pulse duration below 5 μs have been used in order to overcome the above-mentioned disadvantages. An important role with respect to the shielding effect is played by the electron density inside the laser-induced plasmas, because the absorption coefficient of the laser light in these surface plasmas is proportional to the square of the electron density. The spatial and temporal distribution of the electron density during material processing is therefore continuously monitored by a beam-deflection technique.
Beam divergence from sharp emitters in a general longitudinal magnetic field
Authors: Lau Y. Y. , Colombant D. G. , Pilloff Mark D.
Published: July 2002

We calculate the trajectories of electrons emitted from a sharp protrusion with corners, where the electric field is intense and the radius of curvature tends to zero. The calculations include the effects of a longitudinal magnetic field but ignore the space-charge effects. We find that the arbitrarily large electric field at a mathematically sharp corner does not necessarily impart to the electrons an excessive amount of transverse momentum, whether or not the external magnetic field is present. Scaling laws are derived for the beam’s transverse displacement in terms of macroscopic quantities, such as anode-cathode voltage drop, gap separation, magnetic field, and the protrusion dimensions. The implication of these findings on the electron sources generated from microtips is addressed.
Electrical characters of oxygen defects in silicon subjected to intrinsic gettering treatment
Authors: Li Jianming
Published: July 2002

The influence of oxygen defects on the resistivity and mobility of silicon wafers is discussed. Grinding processes were performed on the surfaces of samples in order to obtain the information on interior defects of the samples. Spreading resistivity and Hall measurements prove that SiOx complexes alone result in resistivity increase and mobility decrease. Deep level transient spectroscopy experiments prove that SiOx complexes alone are electrically active. A mechanism of carrier scattering by electrically active SiOx complex is proposed to explain the changes of resistivity and mobility.
Propagation of shear horizontal surface acoustic waves parallel to the grooves of a random grating
Authors: Maradudin A. A. , Huang Xuemei , Mayer A. P.
Published: July 2002

An elastic medium that occupies the region x3≳ζ(x1), where the surface-profile function ζ(x1) is assumed to be a stationary, stochastic process, is studied. The displacement field u(x;t) in this region is assumed to satisfy stress-free boundary conditions on the surface x3=ζ(x1). First the boundary conditions satisfied by the mean displacement field 〈u(x;t)〉 on the plane x3=0 are obtained, where the angle brackets 〈 〉 denote an average over the ensemble of realizations of ζ(x1). The results are then used to obtain the dispersion relation for surface acoustic waves of shear horizontal polarization propagating in the x2 direction, i.e., parallel to the grooves of the random grating defined by the surface-profile function ζ(x1). It is found that the surface acoustic waves of this polarization, which cannot exist on a planar, stress-free surface of an elastic medium, are trapped by the random roughness, but are bound to the surface for only a finite range of values of the wave number k2 characterizing their propagation in the x2 direction. The attenuation of these roughness-trapped surface acoustic waves is also determined.
Detection of hydrogen from the photodissociative splitting of water through hydrogen-oxygen separation over a thin Pd film
Authors: Dannetun H. , Lundström I. , Petersson L.-G.
Published: July 2002

The photodissociative splitting of water has been studied in gas phase on a plane solid surface. A hydrogen sensitive Pd-metal-oxide-semiconductor (MOS) structure was coated with 1–2 nm TiOx and exposed to water vapor and ultraviolet light. A natural separation of the produced hydrogen and oxygen occurs over the Pd film of the structure and the produced hydrogen is monitored by the electric behavior of the MOS device. The results suggest that suitably treated thin Pd membranes may be of interest for studying the continuous photodissociation of water.
Percolation in implanted Si film
Authors: Hiraiwa Atsushi , Kobayashi Takashi
Published: July 2002

The conductivity degradation of implanted Si film has been characterized by nuclear-deposited energy independently of implant conditions. The conductivity decreases as a result of the carrier density change for the nuclear-deposited energy En ≤ 1 × 1023 eV/cm3, and becomes zero with mobility for En = 2.5 × 1024 eV/cm3. These results have been investigated by the percolation theory with the assistance of the Kinchin–Pease theory. The decrease in carrier density is a result of carrier trapping by vacancy-related defects. The mobility becomes zero when the nondamaged Si cluster is localized by a heavy implantation. The calculation using the site percolation is in good agreement with the experiments, where 0.428 is assumed as the percolation threshold, and 2 as the conductivity exponent. The Si displacement energy obtained is 25 eV by comparing the theory with the experiments. The experimental results suggest that microscopically conductive domains exist even in films that are macroscopically insulating.
Analysis and modeling of quantum waveguide structures and devices
Authors: Weisshaar Andreas , Lary Jenifer , Goodnick Stephen M. , Tripathi Vijai K.
Published: July 2002

A complete description of the numerical analysis of quantum waveguide structures and devices is given. Modal expansions of the wave function together with a mode-matching technique are utilized to calculate the generalized scattering matrices (GSMs) of junctions or discontinuities and uniform waveguide sections. The different GSMs are combined via an extended generalized scattering-matrix technique to obtain the scattering parameters of composite quantum waveguide structures. Results for cascaded right-angle bends and periodic multiwaveguide structures in a split-gate configuration are presented. A sharp transition to a plateau of zero conductance is observed for the double-bend configuration. For the periodic multiwaveguide structures, strong resonant behavior similar to that in resonant tunneling diodes is found. Calculated current-voltage characteristics for the special case of a double constriction are shown, exhibiting a region of negative-differential resistance (NDR) for temperatures up to approximately 10 K with a peak-to-valley ratio of about 2.5:1 at zero temperature. Using a simple design procedure, the temperature range with achievable NDR is extended to up to approximately 60 K with a peak-to-valley ratio of over 80:1 at zero temperature.
Specific resistivity of ohmic contacts to n-type direct band-gap III-V compound semiconductors
Authors: Cho S. M. , Lee J. D. , Lee H. H.
Published: July 2002

Contact resistivity curves are given in terms of intrinsic barrier height and doping level for ohmic contacts to n-type direct band-gap III-V semiconductor compounds, including AlxGa1−xAs. The results are based on a rigorous treatment of carrier transport across the metal-semiconductor interface. They show that the resistivity behaves quite differently from what might be expected from the usual notion of the effects of doping and barrier height on the resistivity. As such, the results can be used as a useful guide in attempts to lower the contact resistivity.
The effect of hydrogen treatment on damaged and undamaged metal-insulator-semiconductor solar cells
Authors: Babsail Laila S. , Morrison S. Roy
Published: July 2002

A metal-insulator-semiconductor structure was used to study the effect of hydrogen plasma treatment of solar cells. Cells were fabricated on single-crystal p-type silicon and treated in hydrogen plasma for different exposure times. This causes a noticeable drop in the photocurrent and density of charge carriers with exposure time. This in turn leads to a drop in the solar cell efficiency. Other cells were fabricated on damaged p-type silicon, where dislocations were created by lapping the silicon surface. Such a procedure simulates controllably the effect of dislocations and grain boundaries. The damaged silicon was then exposed to hydrogen plasma and an overall improvement in the performance of the solar cell was found. However over-exposure led to degradation as with single-crystal material. It is concluded that hydrogen plasma exposure has both beneficial and degrading effects. It improves solar cell characteristics when they have been degraded by dislocations, but it degrades cells by interacting with accepters in the p-silicon. Further studies are needed to attain the best compromise and to optimize solar cells made from low quality silicon.
Rapid thermal processing of zirconia thin films produced by the sol-gel method
Authors: Pascual R. , Sayer M. , Kumar C. V. R. Vasant , Zou Lichun
Published: July 2002

The kinetics of the amorphous-to-tetragonal transformation has been studied in sol-gel-derived thin films of zirconia deposited on alumina substrates. A rapid-thermal-annealing system was used which allowed good control of processing parameters such as temperature and heating rates. The effect of these two parameters on the transformation kinetics was studied and the experimental results were analyzed in terms of conventional nucleation and growth models. The use of two-step thermal processing cycles shows potential for the modification of the microstructural features of crystallized films and for a reduction in processing times.
Finite element analysis of nonlinear, coupled thermal-electric problems: The memory switch
Authors: Robertson Struan R. , Liao Kuen-Liang
Published: July 2002

The finite element method is applied to heat conduction problems where the heat generation is due to electric current flowing through the body. The electric and temperature fields are, in general, coupled. The electric field causes Joule heating and both the electric and thermal properties are temperature dependent. The time scale for changes in the electric field is short compared to that for the temperature field. Therefore, the electric field is assumed to be quasistatic and the temperature field transient. The formulation is applied to memory switching devices which rely on Joule heating to cause a thermally induced transition from a state of low, to one of high electric conductivity.
Deep defect states in hydrogenated amorphous silicon studied by a constant photocurrent method
Authors: Sakata I. , Yamanaka M. , Numase S. , Hayashi Y.
Published: July 2002

Experimental studies by means of a constant photocurrent method (CPM) have been carried out on the deep defect states in undoped hydrogenated amorphous silicon (a-Si:H). Assuming Gaussian energy distributions, two types of defect states (ST1 and ST2) have been found from careful analysis of CPM spectra; one of these states (ST1) is a neutral Si dangling-bond (Si D0) state, and the other (ST2) is a negatively charged dangling-bond-like defect state located in the lower gap. ST2 lies deeper in energy by 0.1 eV, and has a narrower full width at half-maximum (FWHM) when compared with ST1. Possible candidates for ST2 have been discussed by referring to the previous models of defects in a-Si:H. The FWHM of ST1 (the Si D0 state) does not always depend on the overall structural disorder estimated from Raman spectra. The energy position of the Si D0 state measured from the valence-band edge is almost independent of the optical band gap. Long exposure to light increases the density of ST1 (the Si D0 state) and decreases that of ST2, which suggests that defect conversion proceeds during the illumination.
Variational bound principle for surface wave scattering
Authors: Hahn Y. , Robinson H.
Published: July 2002

The use of a variational bound principle to determine surface wave solutions will be examined. It will be demonstrated that the variational solution for the surface wave velocity in a semi-infinite substrate is bounded from below and that the value of this bound coincides with the exact solution in the simple case of the substrate only. In the presence of an overlay, the variational solution for the surface wave velocity still maintains the boundedness property, but the solution has changed to reflect the perturbing effect of the overlay. Improved reflection coefficients and velocity shifts are calculated, including the second-order effects of evanescent waves. The variational bound approach provides a simple but powerful alternative to other conventional methods in which each Floquet component of the solution is treated separately. Bulk wave coupling requires a separate treatment as the bound principle is violated in this case.
Numerical investigations of the electromigration boundary value problem
Authors: Clement J. J. , Lloyd J. R.
Published: July 2002

The electromigration diffusion boundary value problem with the perfectly blocking diffusion barrier is numerically investigated. Three possible boundary conditions are identified as physically meaningful and the solutions compared at the blocking barrier. It is seen that the solution of M. Shatzkes and J. R. Lloyd [J. Appl. Phys. 59, 3890 (1986)] is a good approximation for the time to failure if the critical vacancy concentration for failure is not too near a steady-state value. A dimensionless parameter is introduced which may be useful in estimating ultimate electromigration performance.
Current-frequency characteristics of submicrometer GaAs Schottky barrier diodes with femtofarad capacitance
Authors: Roeser H. P. , Titz R. U. , Schwaab G. W. , Kimmitt M. F.
Published: July 2002

At room temperature different GaAs Schottky barrier diodes with submicrometer structure and ∼fF capacitance C have been investigated in a heterodyne receiver. Using microwave sources and submillimeter lasers as the local oscillator (LO) they show that the number of electrons Ne passing through the Schottky contact each LO cycle is constant and is a characteristic value for each diode type. This is expressed by the experimentally derived equation for the optimum current I=Ne eν (e is the electronic charge and ν the frequency of the radiation). The required optimum LO voltage amplitude VLO is independent of operating frequency and fulfills the equation VLO=(Ne e)/2C.
Hole capture at the DX(Si) and DX(Te) defects in AlxGa1−xAs
Authors: Dobaczewski L. , Kaczor P. , Żytkiewicz Z. R. , Missous M. , Saleemi F. , Dawson P. , Peaker A. R.
Published: July 2002

Results of measurements of the hole recombination process at DX centers related to group-IV (silicon) and group-VI (tellurium) donor elements in AlxGa1−xAs are presented. For the DX(Si) and DX(Te) defects the values of hole capture cross section σh=2×10−13 and σh=10−13 cm2 were found, respectively. In both cases no systematic change of σh with temperature was observed. The results show that the DX center in the ground state is negatively charged as a consequence of its negative-U two-electron character.
Theory of localized phonon modes and their effects on electron tunneling in double-barrier structures
Authors: Turley P. J. , Teitsworth S. W.
Published: July 2002

The role of localized phonon modes in phonon-assisted tunneling in GaAs/AlAs double-barrier resonant tunneling structures is considered for a range of temperatures and magnetic fields. Phonon modes are calculated using a dielectric continuum model and electron-phonon Hamiltonians are presented for the most important modes. Formulas for phonon-assisted tunneling currents are derived that express the inherently three-dimensional process in a simple one-dimensional form. It is found that the excess current due to phonon-assisted tunneling in typical structures is caused primarily by two types of localized modes: confined modes in the well and symmetric interface modes, with interface modes dominating in structures with narrow wells. Current peaks broaden with increasing temperature, and for temperatures ≳20 K the resolution of features due to distinct phonon types is very difficult. The application of a magnetic field parallel to the current flow leads to a complex spectrum of sharp current peaks corresponding to various inter-Landau-level transitions which occur during phonon-assisted tunneling.
Determination of insulator/semiconductor interface trap density by correlation deep level transient spectroscopy method
Authors: Li Xin , Tansley T. L.
Published: July 2002

The correlation deep level transient spectroscopy (DLTS) method is developed for insulator/semiconductor interface studies. Trap transient modeling indicates that the energy range in which the trap transients can contribute to the DLTS signals of the correlation method is about 12 kT, and is much wider than that of the boxcar method (several kT). Moreover, large voltage pulse for saturation will cause the capacitance transient to shift away from the ideal exponential due to the sum of the various emission rates. Hence, the equations for determination of interface trap density suitable for the boxcar method is invalid for the correlation method. For this reason, an equation for determining the interface trap density suitable for the correlation method is derived. The interface trap density determined by this method agrees well with other methods.
Model studies of long Josephson junction arrays coupled to a high-Q resonator
Authors: Filatrella G. , Rotoli G. , Gro/nbech-Jensen N. , Parmentier R. D. , Pedersen N. F.
Published: July 2002

Series-biased arrays of long Josephson junction fluxon oscillators can be phase locked by mutual coupling to a high-Q, linear distributed resonator. A simplified model of such a device, consisting of junctions described by the particle-map perturbation theory approach which are capacitively coupled to a lumped, linear tank circuit, reproduce the essential experimental observations at a very low computational cost. A more sophisticated model, consisting of partial differential equation descriptions of the junctions, again mutually coupled to a linear tank, substantially confirm the predictions of the simplified model. In the particle-map model, the locking range in junction bias current increases linearly with the coupling capacitance; in the partial differential equation (p.d.e.) model, this holds up to a certain maximum value of the capacitance, after which a saturation of the locking range is observed. In both models, for a given spread of junction lengths, the existence of a minimum value of the capacitance for locking to a tank with a given resonant frequency is evidenced.
Two photon optical nonlinearities in a resonant quantum well system
Authors: Rosencher E.
Published: July 2002

Resonant optical transitions in asymmetric quantum wells yield huge second order optical nonlinearities but also strong absorption. It is shown that, under these specific conditions where the conversion length may be far smaller than the coherence length, the second harmonic generation equations can be put into a simple dimensionless form. The influence of the quantum well parameters on the optical nonlinearities may thus be easily studied. It is shown that, by optimizing these parameters, second harmonic generation efficiency as large as 20% may be obtained for moderate pump power (≊15 MW/cm2, i.e., before saturation) without any phase match procedure.
Misfit dislocation distributions in capped (buried) strained semiconductor layers
Authors: Gosling T. J. , Bullough R. , Jain S. C. , Willis J. R.
Published: July 2002

An elastic continuum model is used to investigate distributions of misfit dislocations in a capped layer structure. Effects of the free surface at the top of the cap and of interactions between dislocations have been rigorously incorporated, making the study applicable to structures with caps of arbitrary thickness and to the process of strain relaxation in layers already containing misfit dislocations. Two dislocation types are considered in detail: single dislocations (singles) residing at the lower interface, between the strained layer and the substrate, and dislocation dipoles, i.e., pairs of parallel dislocations with opposite Burgers vectors, one at the lower interface and the other at the upper interface, between the strained layer and the cap. Although singles cause unwanted long-range distortion in the cap, which is not caused by dipoles, dipoles give rise to increased localised distortion, due to the presence of the additional dislocation, at the upper interface. Hence singles and dipoles compete as misfit dislocation types in capped layers, with the dominant type being determined by the parameters of the layer structure. It is demonstrated that interactions between dislocations are crucial, and that experimental observations cannot be explained by consideration of an isolated single or dipole. Interactions between singles in an array at the lower interface result in a buildup of strain energy in the cap. The rapidity of this buildup with dislocation density demands a transition from relaxation by singles to relaxation by arrays of dipoles; such a transition would not be predicted by a consideration of isolated singles or dipoles. Energy evaluations are performed to incorporate such interactions between dislocations while providing a sequential view of strain relaxation, with singles and dipoles entering the structure one at a time. It is thus demonstrated that a mixture of singles and dipoles is expected in many capped layers of practical interest. An example calculation predicts a mixture that is consistent with experimental observation.