bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the cathode region of a free-burning high intensity argon arc
Authors: Hsu K. C. , Pfender E.
Published: February 2003

This paper is concerned with analytical/numerical studies of the cathode region of an atmospheric pressure, free-burning high intensity argon arc. The cathode region is divided into two model zones: the ionization zone and the space-charge zone. The former accounts for the generation of ions while the latter is responsible for the sheath formation. The governing equations for each zone are established by taking the dominant physical processes into account. Employing boundary conditions from the results of previous studies of the flow-affected region, one-dimensional solutions of the governing equations are obtained. The results indicate a net positive space charge in front of the cathode surface and the electron and ion fluxes are mainly driven by the potential gradient. A significant fraction of the total current is carried by positive ions which is important for establishing the energy balance at the cathode surface.
Theoretical study of the ultimate resolution in electron beam lithography by Monte Carlo simulation, including secondary electron generation: Energy dissipation profile in polymethylmethacrylate
Authors: Samoto Norihiko , Shimizu Ryuichi
Published: February 2003

A new Monte Carlo simulation including generation of secondary electrons has been performed to study ultimate resolution in electron beam lithography. With respect to the simulations of inelastic scattering process of the primary electrons we used Gryzinski’s excitation function for single electron excitation processes, generating secondary electrons, while the inelastic mean free path proposed by Seah and Dench for organic material and energy loss spectrum obtained by Ritsko were used for simulating the inelastic scattering processes of the secondaries. The calculations were made to obtain energy dissipation profile for 20-kV electrons, particularly, in the vicinity of the point of incidence on nanometer-scale in 3000-Å-thick films of polymethylmethacrylate (PMMA) on a silicon substrate. The result clearly indicates that the secondary electrons play a most important role in determining the energy dissipation profile in the vicinity of the point of incidence, being the significant source of broadening of the energy dissipation profile. The blurring due to secondary electrons at the surface of the PMMA resist is of the order of 10 nm.
Effect of Si and SiO2 thermal nitridation on impurity diffusion and oxidation induced stacking fault size in Si
Authors: Mizuo Shoichi , Kusaka Takahisa , Shintani Akira , Nanba Mitsuo , Higuchi Hisayuki
Published: February 2003

The effect of thermal nitridation on impurity diffusion and Oxidation induced Stacking Fault size in Si are clarified by selective nitridation. Enhanced B and P diffusion, retarded Sb diffusion, and growth of OSF’s are found in Si masked with SiO2 films. Retarded B and P diffusion, enhanced Sb diffusion and rapid OSF shrinkage are found in nonmasked Si that has undergone NH3 heat treatment. On the other hand, in N2 or N2+H2 (1:3) ambients, no significant ambient effect on impurity diffusion is found in Si masked with SiO2 films. However, retarded B and P diffusion and enhanced Sb diffusion are found in nonmasked Si with N2 ambient. The results are shown to be consistent with the model that shows that interstitials and vacancies effect thermal equilibrium.
Spin coated amorphous chalcogenide films: Thermal properties
Authors: Chern G. C. , Lauks I. , McGhie A. R.
Published: February 2003

The annealing behavior of spin coated thin films prepared from solutions of As2S3 dissolved in n-propylamine and n-butylamine has been investigated using IR, mass spectrometry, thermogravimetric analysis, and scanning calorimetry. As prepared films containing arsenic sulfide glass domains with surfaces reacted as alkyl ammonium salt undergo loss of amine and hydrogen sulfide during heating. H2S removal is believed to be accompanied by cross linking of glass domains resulting in a network glass containing only arsenic and sulfur.
Chemical equilibrium calculations of tungsten–halogen systems
Authors: Sell J. A.
Published: February 2003

The performance of the compound bromotrifluoromethane (CBrF3) as a tungsten–halogen bulb fill gas was evaluated theoretically by chemical equilibrium calculations. It was found to be an ideal fill gas in terms of maintaining clear bulb walls and redepositing evaporated tungsten on hot spots in the filament. The calculations were done at different CBrF3 and water concentrations. The compounds most responsible for tungsten transport were identified; fluorine compounds of tungsten dominate over bromine compounds. Finally, CBrF3 is compared to other possible fill gases such as CBr2F2, CBr3F, CBr4, and also HBr, since HBr is presently used commercially.
Interaction of Pd–Er alloys with silicon
Authors: Ottaviani G. , Tu K. N. , Thompson R. D. , Mayer J. W. , Lau S. S.
Published: February 2003

I n situ resistivity measurements together with MeV 4He+ backscattering, x-ray diffraction, barrier height measurements, and Auger electron spectroscopy combined with Ar sputtering have been used to investigate the interaction of silicon with alloys of rare-earth and near-noble metals with annealing at temperatures up to 650 °C. Alloys of Pd–Er with three different compositions have been prepared by dual electron-gun coevaporation on both n- and p-type silicon and Pd/Er bilayers have been deposited on SiO2. The results show that as-deposited these alloys are amorphous and the initial stages of the reaction with silicon upon annealing is controlled by the metal–metal interaction as well as the metal–silicon interaction. The Er-rich alloy (Pd15Er85) segregates Er to the silicon interface and forms Pd2Er5. The segregated Er reacts with silicon producing ErSi2. For the Pd-rich alloy (Pd65Er35) the excess Pd is segregated at the silicon surface forming Pd2Si. The near 50-50 alloy forms PdEr and a slightly higher temperature is necessary to promote the reaction with silicon to form the silicide of the excess component.
Laser-recrystallized polycrystalline silicon resistors for integrated circuit applications
Authors: Schaber H. , Cutter D. , Binder J. , Obermeier E.
Published: February 2003

The influence of grain boundaries on the electrical properties of laser-recrystallized polycrystalline silicon films, with a typical grain size 1×20 μm2 and doping concentration between 1016 and 1020 cm−3, has been investigated. Over a wide range of doping concentration, sheet resistance and its temperature dependence are found to be very close to the values expected for single crystal material. Deviations occur at low doping levels and are related to the average grain size perpendicular to the current flow. The standard deviation and laser power dependence of sheet resistance R⧠ are strongly correlated to the influence of grain boundaries, as measured by the deviation of R⧠ from the single crystal value. The main sources of resistor nonlinearity are substrate field effects and the dependence of grain boundary potential barriers on applied bias. At doping concentrations ≳1018 cm−3 very linear resistors are obtained reproducibly. Resistance ratios can be controlled to better than 1% and temperature coefficients ≲10−4/K can be achieved by proper choice of doping concentration.
Stress in polycrystalline and amorphous silicon thin films
Authors: Howe R. T. , Muller R. S.
Published: February 2003

Stress in polycrystalline and amorphous silicon thin films deposited on oxidized silicon wafers is determined from the lengthening of the undercut edge of a silicon stripe. The technique measures only compressive stresses, has a stress resolution of 108 dyn/cm2, and a spatial resolution on the wafer of 250 μm. Unannealed silicon thin films deposited on oxide are under high compressive stress (1010 dyn/cm2). This stress is reduced below the resolution by annealing at 1100 °C for 20 min in N2, except for the thinnest polycrystalline silicon films studied (230 nm thick).
Reduction of contact resistivity by As redistribution during Pd2Si formation
Authors: Ohdomari I. , Hori M. , Maeda T. , Ogura A. , Kawarada H. , Hamamoto T. , Sano K. , Tu K. N. , Wittmer M. , Kimura I. , Yoneda K.
Published: February 2003

We have investigated the redistribution of uniformly doped As atoms (ND=4.0×1019 cm−3) in Si during Pd2Si formation with neutron activation analysis and the influence of the redistribution on contact resistivity. Some of the uniformly doped As atoms are pushed ahead into Si near the silicide–silicon interface during Pd2Si formation at 250 °C. The amount of the redistributed As atoms increases with the thickness of Si consumed and reaches a peak concentration of 2.0×1020 cm−3. Contact resistivity is reduced from the initial values of 3.8×10−5−4.1×10−4 Ω cm2 before silicide formation, to a final value of 1.8×10−6 Ω cm2 after complete reaction. The electrically active As atoms is estimated to be 50% of the total redistributed.
Transient capacitance spectroscopy on large quantum well heterostructures
Authors: Martin P. A. , Meehan K. , Gavrilovic P. , Hess K. , Holonyak N. , Coleman J. J.
Published: February 2003

We report transient capacitance measurements on AlxGa1−xAs–GaAs–AlxGa1−xAs (x∼0.35) double heterojunctions with a large quantum well active region (Lz∼800 Å). It is suggested that the thin GaAs layer acts as a ‘‘giant’’ artificial deep level. It follows then that the band edge discontinuity ΔEc determines the electron emission rates (from the thin layer), thus making it possible for ΔEc to be determined by transient capacitance measurements.
The total anodization of copper films on platinum: Use as selective surface absorbers at high temperature
Authors: Milgram Alvin A.
Published: February 2003

A thin film of metallic copper deposited on an inert metallic conductor was totally anodized in a NaOH solution. The resulting anodic copper oxide film is shown to have excellent selective surface properties for use as a solar absorber at high temperatures.
The influence of growth conditions on sulfur incorporation in GaAs grown by molecular beam epitaxy
Authors: Andrews D. A. , Heckingbottom R. , Davies G. J.
Published: February 2003

An electrochemical sulfur cell has been used as a source of donors for molecular beam epitaxy grown GaAs. The galvanic cell is Pt/Ag/AgI/Ag2 S/Pt. The electrical and optical properties of the films grown in the substrate temperature range 550–590 °C are good. However, at substrate temperatures above 600 °C the incorporation rate of sulfur is much reduced. The reduction in the incorporation rate is explained on the basis of the competing reactions (1) the incorporation of sulfur into the GaAs matrix and (2) the formation of volatile Ga2S. A detailed discussion of the incorporation at elevated substrate temperatures and with varying As4/Ga ratio is presented. It is also demonstrated that if the substrate temperature is reproducibly known then the electrochemical cell can be used to introduce intricate doping profiles into epitaxial GaAs. A hyperabrupt varactor diode has been fabricated as an example.
Hole transport in pure and doped GaAs
Authors: Lee H. J. , Look D. C.
Published: February 2003

We have used a two-band model (heavy and light holes) to calculate the transport properties of p-type GaAs. The scattering mechanisms included are acoustic-mode deformation potential, acoustic-mode piezoelectric potential, polar- and nonpolar-mode deformation potential, ionized impurity, and space charge. Interband scattering is included explicitly for the optical phonons and phenomenologically for the acoustic phonons. The intraband polar optical-mode scattering, for which a relaxation time cannot be defined, was calculated by using the numerical method of Fletcher and Butcher. The acoustic deformation-potential parameter and the coupling coefficient for interband scattering were calculated by fitting the theory to Hall-mobility data for both pure and doped samples. We have determined ionized-impurity and space-charge contributions for two of our samples, one doped with Cr and exhibiting an 0.33-eV activation energy (Cr4+/Cr3+), and the other heat-treated and exhibiting an 0.14-eV activation energy. The transport fit was carried out self-consistently with a statistical fit of the p vs T data, to determine the relevant donor and acceptor concentrations. Individual plots of the mobility contributions from the various scattering mechanisms are also presented. Finally, useful plots of the Hall mobility and Hall r factor, as functions of carrier density and compensation ratio, are provided to aid others in the analysis of their samples. An important conclusion of this study is that the light-hole band strongly influences the transport properties, even though its density of states is small compared to that of the heavy-hole band.
Space-charge waves in multilayered heterostructures
Authors: Datta S. , Gunshor R. L.
Published: February 2003

Space-charge waves in multilayered heterostructures are discussed using coupled Boltzmann equations. Acoustic plasma modes are investigated with practical examples. The formulation includes both degenerate and nondegenerate electron systems; exchange and correlation effects are incorporated using a local density approximation and are shown to affect the acoustic plasma mode significantly; lattice collisions are included using the relaxation time approximation.
Comparative study of surface acoustic wave and photocurrent spectroscopies in GaP
Authors: Fritz I. J.
Published: February 2003

Optical-excitation spectra of several GaP samples have been obtained using transverse acoustoelectric spectroscopy in the separated-medium surface-wave configuration. The results are compared with data obtained on the same samples using photocurrent spectroscopy of Au Schottky-barrier diode structures. Despite differences in the two measurement techniques, the observed spectral features are quite similar, and these features are in good agreement with photocurrent, photoconductivity, surface-wave and optical-absorption data in the literature. Both techniques are useful for probing the near-surface properties of semiconductors. However, the surface-wave technique, which is newer and less widely utilized, has an advantage in not requiring electrical contact to the sample. The surface-wave technique thus can provide quick, nondestructive characterization of photoexcitation processes in epitaxial layers and surface-modified regions of semiconductors.
Interpretation of dc characteristics of phosphorus-doped polycrystalline silicon films: Conduction across low-barrier grain boundaries
Authors: Loh Eugene
Published: February 2003

Current–voltage curves of phosphorus-doped polycrystalline silicon films of Lee and Cheng are reanalyzed with the same trapping model of thermionic and thermionic-field emission across symmetrical Schottky barriers between grains. The analysis yields unexpectedly low values of the effective number of grains Neff in the conducting path. Values of Neff/Ngeo decreases from 0.5 at 20 K to 0.1 at 300 K, where Ngeo =(film length)/(typical grain size). A dc conduction model is proposed. Carriers in phosphorus-doped polysilicon films travel extensively across low-barrier grain boundaries, where electrons from segregated phosphorus are abundant enough to fill most of the electron traps. The model can also explain an observed current–temperature relation i∝T3 at low bias voltages and yield values of barrier resistance comparable to reported data on polycrystalline silicon neutron-transmutation doped with phosphorus measured by a small-area traveling potential probe.
Degradation mechanism of Mo/GaAs0.6P0.4 Schottky barriers
Authors: Lou J. C. , Lin M. S. , Su W. H.
Published: February 2003

The electrical characteristics and interdiffusion in electron-beam evaporated Mo/GaAs0.6P0.4 Schottky barriers have been studied. The barrier height, ideality factor and deep trapping levels of these annealed or unannealed Mo/GaAs0.6P0.4 Schottky barriers are obtained by using the I–V, C–V, Rutherford backscattering spectroscopy (RBS), Auger electron spectroscopy (AES), and deep level transient spectroscopy (DLTS) analyses. A significant interdiffusion at the Mo/GaAs0.6P0.4 interface is demonstrated for 500 °C, 600 °C, annealed Schottky barriers. DLTS results show that there are two electron traps [Ec −(0.19±0.01) eV and Ec -(0.65±0.01) eV] and five hole traps [Ev +0.15 eV, Ev +(0.27±0.01) eV, Ev +(0.36±0.02) eV, Ev +(0.56±0.01) eV and Ev +0.84 eV] in existence at the metal-semiconductor interface or in the bulk of the degraded Schottky barriers. These traps enhance the generation-recombination effect and degrade the barrier height. RBS, AES, and DLTS results also indicate that the newly discovered hole trap Ev +0.84 eV, induced by Mo indiffusion, is believed to play a major role for Mo/GaAs0.6P0.4 Schottky barriers degradation.
Defect and impurity states in silicon nitride
Authors: Robertson J.
Published: February 2003

The electronic levels associated with silicon and nitrogen dangling bonds and Si-H, N-H, and Si-Si units within bulk Si3N4 have been calculated using the tight-binding and recursion methods. The Si dangling bond, the Si-H σ state and the Si-Si σ state all lie in the gap. The Si-Si σ state lies in midgap and could be a long-term hole trap. The Si dangling bond state lies just below the conduction band and could act as a very efficient electron trap.
Spinodal decomposition and magnetic properties of Fe–Cr–12Co permanent magnet alloys
Authors: Chin Tsung-Shune , Wu Tien-Shou , Chang C. Y.
Published: February 2003

This report is concerned with the spinodal decomposition and magnetic properties of Fe–21∼30 Cr–12Co ternary alloys (by weight) as studied by transmission electron microscopy and magnetic measurements. Wavelength growth of the isothermally aged spinodal structure is found to be proportional to time1/3 for the later stage of aging at all aging temperatures, which suggests a coarsening process. Spinodal temperatures of these alloys are found to be higher than each of their Curie temperatures; nevertheless magnetic aging is effective in greatly improving the magnetic properties. Hence, a prerequisite of a higher Curie temperature in the magnetic aging theory is concluded to be unnecessary. Moreover, as the extrapolated onset spinodal wavelength, of 80–100 Å, is superparamagnetic in nature, this suggests a prerequisite for the magnetic aging theory. Before magnetic aging can be operative, the particle should grow to a certain critical size, determined by the aging temperature and the anisotropy energy at that temperature, in order to have thermally stable magnetization.
Corner clusters in thin soft magnetic layers: The corner cluster—a system of walls
Authors: van den Berg H. A. M.
Published: February 2003

The domain-wall cluster is a new concept revealing a large number of features about the domain structure and its conversions in thin soft magnetic layers, as used in field-access bubble devices and in integrated tape recorder heads. A wall cluster is a collection of domain walls having one intersection line, the so-called cluster knot, in common. This paper is confined to the relations in the mutual domain-wall positions in the corner clusters, characterized by a cluster knot that coincides with a corner of the geometry. A one-to-one relationship between the domain-wall positions and the magnetization distribution near the corner exist in a special class of corner clusters, the so-called completely uniform corner clusters. It is shown under which conditions this type of cluster might or have to occur. The other class of corner clusters contains rotation segments, defined as sectors in which the magnetization rotates circularly around the cluster knot. The circulation sense of the magnetization in the rotation segments of a specific cluster is the same for all segments. The magnetization distribution possible in this class of clusters systematically come up for review. Consequently, the paper offers a framework for the interpretation of the observations obtained in the Bitter, TEM and Kerr techniques.
Vibrational modes, elastic stiffness, and piezomagnetic strain of a magnetized rod
Authors: Lanotte L. , Luponio C. , Porreca F.
Published: February 2003

Vibrating-rod experiments on Ni samples, excited by dynamic magnetostriction, reveal three fundamental frequencies: two extensional modes and one shear mode. Both the c11, c12, c44 set of microscopic spring constants and the dz1, dz3, dr5, set of piezomagnetic strain constants can be directly evaluated. The frequency changes with a polarizing magnetic field (Δf effect) have been observed for all modes. Suitable elasticity tensors have been written and compared in order to explain the cij variations from the demagnetized state to saturation. The approach aids interpretation of the observed dij changes.
Photoluminescence measurements of Zn-doped Ga1−xAlxAs grown by metalorganic chemical vapor deposition
Authors: Xu Z. Y. , Kreismanis V. G. , Tang C. L.
Published: February 2003

We have investigated the photoluminescence properties of Zn-doped Ga1−xAlxAs grown by metalorganic chemical vapor deposition (MOCVD). The photoluminescence spectra exhibit weak bound-exciton lines, donor–acceptor pair transitions, free-to-bound excitons, and low energy broad bands. The Zn acceptor ionization energy is determined from the free-to-bound transitions as a function of aluminum concentration x up to 0.46. Two low energy bands have been observed in Zn-doped Ga1−xAlxAs. One is at ∼1.65 eV and is identified as due to the ZnGa–VAs complex. Another band has been observed at ∼1.81 eV from samples with x near or beyond the crossover. It is well separated from the band edge, but its origin is not yet well understood.
Optical and crystallographic properties and impurity incorporation of GaxIn1−xAs (0.44<x<0.49) grown by liquid phase epitaxy, vapor phase epitaxy, and metal organic chemical vapor deposition
Authors: Goetz K.-H. , Bimberg D. , Jürgensen H. , Selders J. , Solomonov A. V. , Glinskii G. F. , Razeghi M.
Published: February 2003

Optical, crystallographic, and transport properties of nominally undoped n-type and Zn doped p-type Gax In1−xAs /InP (0.44<x<0.49) grown by liquid phase epitaxy (LPE), vapor phase epitaxy (VPE), and metal organic chemical vapor deposition (MOCVD) have been studied and related to the different growth methods. Samples grown by LPE show in general much larger luminescence intensities than the VPE samples with similar impurity concentration and less structural and compositional inhomogeneities. Peaks related to free and bound excitons and to different impurities are found in the photoluminescence and absorption spectra of the undoped samples. The binding energy of the exciton is determined to be 2.1±0.1 meV, in agreement with hydrogenic theory. A longitudinal optical (LO) phonon energy of 32±0.5 meV is derived from LO-phonon replica of the exciton line. The dependence of the energy gap at T=2 K from the solid solution composition in the range xGa =45%–49% is determined yielding a bowing parameter of C=0.475 and a gap value of Eg =0.811 eV at optimum lattice match. Data on donor-acceptor pair transitions observed in the photoluminescence spectra are combined with secondary ion mass spectrometry data to identify for the first time different acceptors: C, Zn, and Si. Their binding energies are 13±1, 22±1, and 25±1 meV, respectively. C is the dominant acceptor in the MOCVD samples, but is hardly observable in the LPE and VPE samples. Si and Zn are present in LPE, VPE, and MOCVD samples. The Zn doped p-type samples show a broad donor-Zn-acceptor pair transition band accompanied by a weak LO-phonon replica and a very weak exciton line.
Production of O(1D) and O(3P) by vacuum ultraviolet photodissociation of molecular oxygen
Authors: Germany G. A. , Salamo G. J. , Anderson R. J.
Published: February 2003

A pulsed fluorine excimer laser operating at 1576 Å wavelength, 10 ns pulse width, 10 Hz repetition rate, and ∼0.2 MW average output power is used to photodissociate ground state molecular oxygen, O2(X3∑−g). The dissociation products, O(1D) and O(3P), are produced with unit quantum efficiency and ∼0.4 eV translation energy. Time-resolved techniques are used to monitor the O(1D2)→O(3P2) radiative transition over the O2 pressure range 10–400 mTorr. The O(1D)–O2 quenching rate constant is determined to be (3.7±0.3)×10−11 cm3 s−1. The O(1D)/O2 dissociation fraction is estimated to be 0.4% to ∼50% corresponding to O(1D) densities as high as 3×1015 cm−3.
Reactively rf magnetron sputtered AlN films as gate dielectric
Authors: Fathimulla Ayub , Lakhani Amir A.
Published: February 2003

AlN films were deposited on silicon (100, 111), fused quartz and GaAs (100) by sputtering in an Ar:N2 gas mixture. We report on the physical and chemical analysis of the films with the aid of scanning electron microscopy, x-ray diffraction, and Auger electron spectroscopy. The films were found to be transparent with a c-axis orientation. Their bulk resistivity was 1015 Ω-cm. Quasistatic C-V analysis of Al/AlN/Si gave a flat-band voltage of 0.85 V, density of fixed charge of 6×1010 cm−2 and a density of fast interface charge of 1.5×1011 cm−2 eV−1 at midgap. These films were formed at 250 °C and offer an attractive fabrication alternative for gate dielectric.
Analysis of space charge in photonic tubes
Authors: Kalibjian R. , Peterson G. G.
Published: February 2003

Temporal resolution in fast photonic tubes, e.g., streak tubes, frame tubes, and photodiodes, is enhanced by using a high electric field at the photocathode. However, at relatively high irradiance, the tube performance is degraded in both temporal and spatial resolution. It is generally assumed that the degradation is due to space charge. It is well known that space charge depresses the electric field in the immediate region of the cathode. For zero initial-energy electrons, the electric field at the photocathode decreases with increasing space charge and becomes zero when the full space-charge-limit current is extracted from the cathode; however, photoelectrons from real cathodes have finite energy distributions that can change the polarity of the cathode field from accelerating to retarding at high irradiance. By utilizing appropriate photoelectron energy distribution functions, we will first calculate the electric field at the cathode-grid region for high irradiance and then examine the perturbing effects upon the resolution in the photonic tube.
Ion implantation of Si and Be in Al0.48In0.52As
Authors: Choudhury A. N. M. Masum , Rowe W. , Tabatabaie-Alavi K. , Fonstad C. G. , Alavi K. , Cho A. Y.
Published: February 2003

Electrical characterization of (Al,In)As ion implanted with Be and Si following low and high dose multiple energy implant schedules, and annealed between 740 and 815 °C with a pyrolytic silicon dioxide cap is reported. Only very low activation of Be is achieved (<3%). Silicon activation is considerably higher (>40%) and increases with increasing anneal temperature. However, a high concentration n-type surface layer is found on samples annealed at 815 °C. This surface layer is not found on similarly annealed samples which were not implanted, or which were implanted with phosphorus.
Diffusion of boron into polycrystalline silicon from a single crystal source
Authors: Rausch W. A. , Lever R. F. , Kastl R. H.
Published: February 2003

Boron was outdiffused at 900 °C from single crystal silicon into undoped chemical vapor deposited polycrystalline silicon. Boron concentration profiles measured by secondary ion mass spectrometry showed preferential segregation into the polysilicon with a segregation coefficient of 0.7. Pileup of boron at grain boundaries due to migration of boron ions in the interface field during the diffusion process can account for some of the observed segregation.
Electron microscope studies of a Ge–GaAs superlattice grown by molecular beam epitaxy
Authors: Kuan T. S. , Chang C.-A.
Published: February 2003

A Ge–GaAs superlattice with individual layer thicknesses of 10 nm (Ge layers) and 8 nm (GaAs layers) grown on a (100) oriented GaAs substrate at 400 °C by molecular beam epitaxy was examined by transmission electron microscopy. Cross-sectional lattice images of the superlattice revealed no lattice irregularities in both GaAs and Ge layers and perfect lattice match at the Ge–GaAs interfaces. However, bright field and dark field images of the same superlattice indicated the presence of planar defects in the GaAs layers but not in the Ge layers. These planar defects, whose nature does not involve perturbations of the crystal lattice other than elastic strain fields, are most likely antiphase boundaries, which are generated during the growth of the GaAs layers by the coalescence of GaAs domains independently grown on the Ge surface. The generation of antiphase boundaries in GaAs layers might be responsible for the segregated Ge and GaAs columnar structure previously observed in Ge–GaAs superlattices with individual layer thicknesses of only a few monolayers.
Detection of minority traps by simultaneous measurement of thermoluminescence and thermally stimulated conductivity
Authors: Mathur V. K. , Brown Matt D.
Published: February 2003

Generally, thermoluminescence (TL) and thermally stimulated conductivity (TSC) measurements are carried out to detect majority traps. It is pointed out in this communication that a careful analysis of the ratio R(=σTSC/ITL) and ITL, where σTSC is the thermally stimulated conductivity and ITL is the intensity of thermoluminescence, has the potential of revealing information about the hole emission and hole traps. These two cases can be differentiated by comparing the initial rise of the temperature derivative of 1/R, i.e., (d/dT)(1/R) and ITL. It is also possible to estimate the activation energy of shallow hole traps.
Possible application of nuclear resonance fluorescence to study surface effects
Authors: Wielopolski L. , Vartsky D. , Cohn S. H.
Published: February 2003

Observations were made of the differences between the iron nuclear resonance fluorescence yield from a gaseous 56MnCl2 source in a clear fused quartz vial and a source in a clear fused silica (Suprasil) vial. The nuclear resonance fluorescence may be applied to study surface effects in materials undergoing radiation damage.
Flux trapping in Josephson tunnel junctions
Authors: Uchida N. , Enpuku K. , Matsugaki Y. , Tomita S. , Irie F. , Yoshida K.
Published: February 2003

Effects of flux trapping in the electrodes of Josephson tunnel junctions on junction characteristics are studied experimentally in the case of the field-cooling process. The suppression of the critical current and the increase of the quasiparticle current of the junction due to the trapped flux are measured. From the increase of the quasiparticle current, the amount of the flux trapped in junction electrodes is evaluated. The obtained amount of the trapped flux is discussed quantitatively on the basis of the pinning theory of nonideal type-II superconductors, which gives the parameter of the electrodes characterizing the flux trapping. The relation between the amount of the suppression of the critical current and that of the trapped flux estimated from the quasiparticle current is studied quantitatively. It is shown that each trapped flux quantum suppresses the critical current of the junction by the ratio of about π(6λL)2/A, where λL is the London penetration depth and A is the junction area.
Low temperature photoluminescence of n-type GaInAsP layers grown on InP by liquid phase epitaxy
Authors: Beaumont B. , Nataf G. , Guillaume J. C. , Vèrié C.
Published: February 2003

Layers of the quaternary alloy GaxIn1−xAsyP1−y (x∼0.1, y∼0.3) were grown on InP (100) substrates by super-cooling liquid phase epitaxy. Tellurium was used for n-type doping in the range 8×1017–5×1019 cm−3. A good homogeneity of the composition of the layers was obtained at the surface. No microprecipitates of tellurium were detected by scanning electron microscope. Systematic studies of luminescence at low temperature were used to characterize the samples, with a particular attention focused on the degeneracy of the conduction band. Calculations of the line shapes were performed based on a recombination mechanism involving acceptor-like states of the valence band and conduction band filling effects. Good agreement was obtained between calculated and experimental line shapes. The Fermi level in quaternary alloys is found to be lower than predicted by theoretical calculations using band structure properties developed in the past for definite III-V compounds such as GaAs and InP. It is suggested that this could be related with disorder electronic effects.
Computer-aided study of hot wall epitaxy system using a Monte-Carlo technique
Authors: Ramachandran V. , Vaya P. R.
Published: February 2003

Theoretical analysis of PbTe molecular flow in hot wall epitaxy system has been made using a Monte-Carlo approach for free molecular flow. Variation in transmission probabilities with the dimensions of the wall have been obtained. These results are applied to get epitaxial growth conditions for PbTe on KCl substrates. It has been observed that at condensation energy Ec=1.6 eV, the substrate temperature range obtained using the present analysis agrees well with the experimental observations.
Single crystal magnets
Authors: Ikuta N. , Okada M. , Homma M. , Minowa T.
Published: February 2003

Single crystals of the Fe–Cr–Co alloys without and with 3% Mo were prepared by a recrystallization process. The microstructures and the magnetic properties of 〈100〉, 〈110〉, and 〈111〉 single crystals were investigated after the heat treatment in the ridge region of the miscibility gap. The magnetic properties of the Fe–22 Cr–17 Co ridge single crystals were not affected very much by the crystal orientation. However, the Fe–23 Cr–20 Co–3 Mo alloys show the crystal orientation dependence of the magnetic properties. The single crystal alloys are aged in a magnetic field, the direction of which is varied around 〈100〉 axes. The magnetic properties are measured parallel to the applied field directions and are summarized in view of deviated angle from a 〈100〉 axis. The greater the deviation of the applied field direction from a 〈100〉 axis, the poorer are the magnetic properties of the Mo single crystal alloy. The best magnetic properties are achieved with Fe–22 Cr–18.5 Co–3 Mo 〈100〉 ridge single crystal as Br=1.58 T (15.8 kG), bHc=72.8 kA/m (910 Oe), and (BH)max=91.2 kJ/m3 (11.4 MGOe), which is the highest energy product reported for the Fe–Cr–Co magnet family.
Marker experiments for diffusion in the silicide during oxidation of PdSi, Pd2Si, CoSi2, and NiSi2 films on 〈Si〉
Authors: Bartur M. , Nicolet M-A.
Published: February 2003

Inert markers (evaporated tungsten and ion implanted Xenon) were used to investigate the mass transport through a silicide layer on a 〈Si〉 substrate during thermal oxidation at 700–900 °C. The SiO2 growth from PdSi, Pd2Si, CoSi2, and NiSi2 films on 〈Si〉 is a process limited by the diffusion of the oxidant from the ambient gas to the silicide/oxide interface. Possible diffusion processes through the silicide that supply Si to the growing SiO2 layer, but keep the silicide stoichiometry intact, are discussed. Backscattering spectrometry is used to monitor the marker position in the silicide layer. We find that the diffusing species during oxidation correlate with the moving species during silicide formation.
Theoretical analysis of solar cells based on graded band-gap structures
Authors: Sassi G.
Published: February 2003

The performance of p–n graded energy gap solar cells has been calculated for Ga1−fAlfAs structures present in either the front region, the base, or both. The graded gap structure in the base is assumed to exist with a high energy gap gradient next to the junction or with a low one along a large portion of the base itself. All the possible configurations in which the builtin fields aid the minority carrier collection are analyzed with a practical theoretical model. The results indicate that the best cell has a high energy gap gradient in the front region and a low energy gap gradient in a large region of the base. This is due to an inverse window effect occurring in the base if the energy gap variation in it is too high. The optimum junction depths for the various configurations are determined as well, and it is shown how the value of these depths is not a critical parameter, as it can vary widely with little influence on the conversion efficiency of the devices. Finally, the results are analyzed versus the surface recombination velocity S and it appears that these graded energy gap structures are suitable only for S≫104 cm/sec.
Silicon–oxygen complexes containing three oxygen atoms as the dominant thermal donor species in heat-treated oxygen-containing silicon
Authors: Oehrlein G. S.
Published: February 2003

A kinetic study of thermal donor formation in 450 °C heat-treated modern silicon crystals has been performed and it is concluded that SiO3 complexes are the dominant thermal donor species (for heat-treatment times of up to about 100 h), rather than SiO4 complexes. Clusters containing a number of oxygen atoms other than three or four seem to be also electrically active.
Deep level transient spectroscopy evaluation of nonexponential transients in semiconductor alloys
Authors: Omling P. , Samuelson L. , Grimmeiss H. G.
Published: February 2003

Evaluation of data obtained from deep level transient spectroscopy (DLTS) is often based on the assumption that the transients are exponential. The applicability of DLTS to the study of deep energy levels in semiconductor alloys has therefore been questioned since thermal transients are often nonexponential in these materials. In this paper we present calculated DLTS spectra in a simple model for broadened defect levels. The calculated spectra are compared with experimental data for a deep electron trap in GaAs1−xPx . The main result is that, within the model, DLTS-deduced activation energies and thermal emission rates are, indeed, relevant even when the transients are strongly nonexponential as a result of alloy broadening. A method of estimating the corrected concentration of deep levels and the distribution in binding energies is also presented.
Theory of hot electron emission from silicon into silicon dioxide
Authors: Tang J. Y. , Hess Karl
Published: February 2003

We present Monte Carlo simulations of the hot electron emission from silicon into the oxide of metal oxide silicon transistors. The calculations include the pseudopotential band structure and quantum effects such as collision broadening due to the electron–phonon interaction. As a result, we present a set of transport parameters which well describes all hot electron effects in silicon (including saturation velocity and impact ionization). We also show that the collision broadening effect leads to an effective barrier lowering and may require that voltages be scaled down far below the interface barrier height of ∼3.1 V in order to avoid hot electron emission.
Photoeffects in cadmium sulfide and sulfoselenide powders: A reexamination by microwave photoconductivity
Authors: Klosterboer D. H. , Meissner W. L. , Sahyun M. R. V.
Published: February 2003

Cu doped CdS powders in electrophotographic devices have been characterized using the flash microwave photoconductivity method. The signals representative of these materials exhibited minima, as well as maxima, in microwave absorption, hence conductivity; the former were identified with the slow thermalization of deep trapped electrons, which allowed the trapping characteristics of the samples to be inferred. Correlation of the microwave photoconductivity results with electrophotographic measurement elucidated the role of the trapping states in interfering with electrophotographic response. From temperature and wavelength dependence of the photoconductivity it was inferred that (except at low temperatures) the conduction band is not populated directly on light absorption, even of band-gap wavelengths. A kinetic analysis revealed that the observed decay of the photoconductivity was controlled by hole trapping at the Cu(I) centers in the powder; thus the experimental data could be used to reveal a two-stage mechanism for hole trapping, and some features of the potential surface associated therewith are inferred.
Electrical switching in silver chloride
Authors: Friedenberg A. , Shapira Y.
Published: February 2003

Observation of threshold switching is reported in AgCl. Subsequent to a forming process, switches are developed from AgCl samples of various crystalline structures. The switching dynamics as well as the relevant electrical properties are characterized. During the forming process Ag dendrites are believed to form by electrolytic process. The principal ON state current channel bridges the dendrites via a thermal or an electronic mechanism.
Techniques for improving the Si–SiO2 interface characterization
Authors: Sher A. , Hoffman H. J. , Su Pin , Tsuo Y. H.
Published: February 2003

In a companion paper [P. Su, A. Sher, Y. H. Tsuo, J. A. Moriarty, and W. E. Miller, Appl. Phys. Lett. 36, 991 (1980)], an improved characterization of the Si–SiO2 interface in metal-insulator-semiconductor-capacitor (MIS-C) structures was reported. In this paper, details of the refined experimental methods that lead to those results are presented, and a more extensive interpretation offered. The well-established quasistatic and conductance methods are improved by using (i) effectively thin composite insulators, (ii) low carrier concentration substrates, and most importantly (iii) low-level illumination at a wavelength that creates electron-hole pairs. Items (i) and (ii) extend the dynamic range of the interface-state density measurement to four decades. Item (iii) decreases the response time of the slow states (for n-type samples, those in the lower part of the band gap); thus, the quasistatic condition is well satisfied and the conductance method can be used on all the states throughout the band gap. Without illumination, the quasistatic condition is not satisfied, even for ramp rates on the low side of those used previously. The major consequences of not satisfying the quasistatic condition are that the deduced variation in surface potential is too large, the interface-state density is underestimated, and the positive-fixed-charge density is overestimated. The sample investigated had a 250-Å, thermally grown oxide prepared in dry oxygen. It was never exposed to H2 or H2O at an elevated temperature. We speculate that this processing produces an abrupt Si–SiO2 interface. The composite gate insulator was completed by having an e-gun deposited 250 Å of LaF3. The resulting interface, subjected to the improved experimental method, yields a wealth of distinctive structure rather than the often-reported featureless U-shaped interface-state density.
A new transient capacitance technique for the determination of interface traps in metal-oxide-semiconductor transistors
Authors: Vitanov P. , Eisele I.
Published: February 2003

A new method for determining the interface trap distribution is described. The measurements are performed on n-channel metal-oxide-semiconductor field-effect transistors and yield the densities of interface traps near the minority carrier band (0.04<Et−Ec<0.3). The technique reveals trap densities as low as 2×108 cm−2 eV−1. The sensitivity is high enough to still detect capacitance changes of the order of 0.01 pF out of the noise. The method is applicable to samples with nonuniform doping concentrations.
Electric field induced effects at the Si–SiO2 interface: Theory and experiment
Authors: Ancona M. G.
Published: February 2003

In a previous paper the fully macroscopic description of semiconductors was employed to demonstrate on theoretical grounds that the surface charge density at a semiconductor interface, as measured statically, depends not only on surface potential but also on surface electric field. In the present work, further theoretical discussion of this effect is given and, most importantly, experimental evidence demonstrating its existence and significance at Si–SiO2 interfaces is obtained. In particular, it appears necessary to describe certain features of the admittance of a metal-oxide-semiconductor capacitor in inversion not explained by conventional theory. The coefficient quantifying these electric field effects, which we determine for particular samples, represents an additional independent parameter by which interfaces may be characterized. The importance of the effect in the interface description leads to a clearer macroscopic understanding of the meaning of the ‘‘interface state density’’ (Dit) which is commonly determined from macroscopic (electrical) experiments. And, in connection with the underlying microscopic picture, its significance may provide experimental support for the microscopic bond strain model for the origin of interface states.
Energy concepts of insulator–semiconductor interface traps
Authors: Engström Olof , Alm Anders
Published: February 2003

A general statistical language developed for impurities and defects in semiconductors has been applied to the interpretation of experimental results from different methods of investigations of insulator–semiconductor interface traps. Interface state energy distributions obtained from traditional capacitance–voltage methods or ‘‘Scanned Light Pulse Technique’’ are interpreted in a Gibbs free energy scale. On the other hand, distributions obtained from Deep Level Transient Spectroscopy (DLTS) are put on an enthalpy scale. The difference between the two parameters depends on the entropy properties of the trap centers. Carrier capture data taken from DLTS are demonstrated to be influenced by the ‘‘entropy factor’’ of the interface trap resulting in discrepancies of capture cross sections of up to two orders of magnitude. It is further pointed out that the energy resolution of experimental energy state distributions is fairly rough for different methods ranging up to 0.1 eV for CV technique at room temperature.
Physical and electrochemichromic properties of rf sputtered tungsten oxide films
Authors: Miyake K. , Kaneko H. , Suedomi N. , Nishimoto S.
Published: February 2003

The physical and electrochemichromic properties of rf sputtered tungsten oxide films from a compressed powder WO3 target have been investigated. This report mainly concerns the dependence of the properties on the total pressure of the sputtering atmosphere. The oxide films, 5000–5300 Å thick, were deposited on substrates maintained at 200 °C under total pressures of 5×10−3–8×10−2 Torr in an atmosphere of Ar gas or Ar–5% O2 mixture. The physical and electrochromic properties of the oxide films prepared are dependent on the total pressure during deposition. The electrical resistivity ranges from 4.75×107 to 3.33×1011 Ω cm depending on the pressure. From x-ray analysis, the films prepared under pressures of 5×10−3–1.5×10−2 Torr were found to be crystalline and assigned a composition of WO2.83. The films prepared under pressures of 1.8×10−2–8×10−2 Torr were found to be amorphous. Electrochemical coloration of these oxide films was observed using an asymmetric cell, and the coloration characteristics of the oxide films were found to be dependent on the electrical resistivity and structure of the films. The amorphous films with high resistivity have good electrochromic properties, but the crystalline films with low resistivity are hardly colored. The optical band gap, refractive index, and density of the oxide films are described.