bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of arsenic species and growth temperature on the properties of GaAs/(Al,Ga)As superlattices grown by molecular beam epitaxy
Authors: Sun Ya Li , Masselink W. T. , Fischer R. , Klein M. V. , Morkoc̢ H. , Bajaj K. K.
Published: February 2003

The interrelation between dimeric and tetrameric arsenic sources and high- (700 °C) and low- (600 °C) growth temperatures on the properties of GaAs/(Al,Ga)As superlattices has been investigated. Superlattices consisting of alternating 100-Å-thick layers of GaAs and (Al,Ga)As were grown by molecular beam epitaxy and characterized by low temperature photoluminescence and excitation spectra. At low growth temperatures, the quality of the superlattice can be improved substantially by using As2 instead of As4. At 700 °C the arsenic species do not have as much an effect on the overall quality, but varying the group V/III ratio changes the relative intensities of the observed multiple excitonic peaks. These peaks are separated from one another by less than 1 meV, indicating extremely sharp and high quality interfaces and making it possible for the first time to relate them to excitonic processes.
Gas source molecular beam epitaxy of GaxIn1−xPyAs1−y
Authors: Panish M. B. , Sumski S.
Published: February 2003

The use of P2 and As2 beams generated by several different beam sources for the growth of InP, GaAs, and GaxIn1−xPyAs1−y has been investigated. Accommodation coefficients for As2 and P2 were determined for heated GaAs and InP surfaces. It is demonstrated that a source utilizing decomposition of the hydrides over the range 200–2000 Torr and providing a leak of the resulting P2, As2, and H2 molecules into a molecular beam epitaxy (MBE) system can be used for the growth of GaxIn1−xPyAs1−y layers lattice matched to InP. Heterostructure lasers emitting at 1.5 μm with room temperature threshold current densities of 2000 A/cm2 and differential quantum efficiencies of 17%–19% were fabricated to demonstrate the quality of the epitaxy by this method. Initial studies of the cracking of AsH3 and PH3 at low pressures in contact with heated Ta suggest that Ta acts as a catalyst for the decomposition and that low pressure beam sources may also be useful for gas source MBE.
Contour maps of EL2 deep level in liquid-encapsulated Czochralski GaAs
Authors: Holmes D. E. , Chen R. T.
Published: February 2003

Contour maps of the EL2 deep level concentration across 3-in.-diam, semi-insulating 〈100〉 GaAs crystals grown by the liquid-encapsulated Czochralski technique were determined by optical profiling. The EL2 patterns at the seed end of the crystals are invariably fourfold symmetric, and correlate with the distribution of dislocations. EL2 distributions at the tail, on the other hand, are often less symmetrical. The contour maps are independent of the melt stoichiometry and relative direction of crystal and crucible rotation. The results indicate that whereas the average EL2 concentration along crystals is controlled by the melt stoichiometry, the 10%–20% concentration variations across crystals result from a second effect possibly related to dislocation climb or dislocation gettering. Implications of the observed EL2 distribution on the uniformity of electrical properties is also discussed.
Phase-resolved photoacoustic microscopy: Application to ferromagnetic layered samples
Authors: Cesar C. L. , Vargas H. , Pelzl J. , Miranda L. C. M.
Published: February 2003

The possibility of using the phase shift of the acoustic signal of different constituents as a new tool for a depth profile analysis of layered samples is discussed. This new method is experimentally demonstrated by measuring the phase variations of the photoacoustic detected ferromagnetic resonance of a sample consisting of an iron film bonded to a nickel film.
Crystallization behavior of evaporated Gd-Fe alloy films
Authors: Lee S. R. , Miller A. E.
Published: February 2003

The composition dependence of the as-deposited structure, the in situ crystallization sequences, and thermal stability were investigated for evaporated Gd-Fe alloy films. The composition dependence of the structural variations in the as-deposited alloy films, the glass forming range, and the crystal size variation in the microcrystalline regions are consistent with the predictions of a model using hard spheres of two different sizes. The in situ crystallization reaction of Gd-Fe alloy films was characterized by the three reaction stages. (1) α-Fe and α-Gd were precipitated by the primary crystallization. The growth of primary crystals is characterized by a continuous process. (2) Some intermetallic compounds were formed by a polymorphous reaction. The growth of these phases is characterized by a discontinuous process. (3) The equilibrium phases are formed by decomposition reaction which was not detected in this study. The Gd atom array in the amorphous structure is concluded to be similar to the Fe atoms array of tetrahedra connected at corners. The thermal stability of the amorphous structure is the highest and growth rate of the primary crystals is the lowest at around 33 at. % Gd which is the composition of the close packed cubic Laves phase.
Pressure dependence of oxygen-related defect levels in silicon
Authors: Keller W. W.
Published: February 2003

The activation energies of thermal donors and of the A center in silicon, the oxygen vacancy complex, are measured as a function of hydrostatic pressure by Hall effect and by deep level transient spectroscopy. The A center is classified as a deep level because the strong pressure dependence of its activation energy indicates a short-range potential. In contrast, thermal donors are true shallow levels associated with a long-range coulomb potential because of the low pressure dependence of their activation energy. Based on these results, an atomic model for thermal donors is suggested, consistent with results of investigations concerning pressure dependence of energy levels, formation kinetics, IR absorption, electrical activity, and electron paramagnetic resonance.
Effects of Cl+ and F+ implantation of oxidation-induced stacking faults in silicon
Authors: Xu J. Y. , Bronsveld P. M. , Boom G. , De Hosson J. Th. M.
Published: February 2003

Three implantation effects were investigated in floating-zone-grown silicon: (a) the effect of Cl+ implantation resulting in the shrinkage of oxidation-induced stacking faults; (b) the effect of F+ implantation giving rise to defaulting of the 1/3[111] Frank dislocations into 1/2[110] perfect dislocations due to the interaction with 1/6[112̄] Shockley partials; (c) the effect of a combined F+ and Cl+ implantation of dislocation motion. Notwithstanding the limited magnification of double-crystal x-ray topography it proves to be a valuable technique for determination of the effects of implantation, as removal of F; the oxidation layer is unnecessary for observation of the oxidation-induced stacking faults. Moreover, the role of the oxide layer in the Si-SiO2 interface can be followed more appropriately.
On the Hall effect observation of ∼0.07 eV deep acceptor in gallium arsenide
Authors: Pödör B.
Published: February 2003

Hall effect observation of an ∼0.07 eV deep acceptor in GaAs single crystals converted to p type by heat treatment is reported. The acceptor is thought to be identical with the center responsible for the 1.44-eV photoluminescence band usually seen in GaAs, and attributed recently to an intrinsic defect, namely gallium on arsenic site.
Deep levels in n-CdTe
Authors: Isett L. C. , Raychaudhuri Pranab K.
Published: February 2003

Deep-level transient spectroscopy (DLTS) was used to study electron traps in n-CdTe crystals. High-purity undoped and indium-doped samples were examined with Au Schottky barriers. Five levels were observed in CdTe:In, three of which are in good agreement with previously observed defect levels. The capture cross sections of these levels were measured. The energy levels relative to the conduction band were measured by isothermal DLTS. A single very deep level was observed in high-purity undoped CdTe. Modified CdTe surfaces were produced by brief (∼60 s) low-temperature (400 °C) annealing in air or argon. Schottky barriers made on these surfaces indicate a decrease in the near-surface carrier concentration. Changes in deep level concentrations were also observed. A very deep level (labeled IR5 in our study) (Ec =0.82 eV) is most changed by this process; annealing increases its concentration. It is suggested that IR5 is a native defect.
High power blue-green laser by hypocycloidal-pinch plasmas
Authors: Han K. S. , Nam S. H. , Lee J. H.
Published: February 2003

A high power blue-green laser has been pumped with an array of multiple-stage hypocycloidal-pinch plasmas. The maximum untuned laser power obtained with LD-490 dye exceeded 230 kW with a pulse width of 1.0 μs (FWHM). The characteristics of the new pumping source and optical coupling configuration indicate that the system can be developed for repetitive and high average power operation.
Discharge striations in rf excited waveguide lasers
Authors: He D. , Baker C. J. , Hall D. R.
Published: February 2003

The existence of transverse striations in radio-frequency discharge excited waveguide carbon dioxide lasers is reported. A simple model indicates how these effects can be explained in terms of internal space-charge fields. An additional effect of the space-charge regions on the discharge capacitance is described.
Measurements of laser shock pressure and estimate of energy lost at 1.05-μm wavelength
Authors: Cottet F. , Romain J. P. , Fabbro R. , Faral B.
Published: February 2003

Laser-driven shock pressures at 1.05-μm wavelength have been evaluated from measurements of shock transit time through aluminum foils by streak camera records of shock luminosity at the back face of the foil. An ablation pressure of 0.3 TPa is obtained for 1.2×1014 W/cm2 laser pulses focused on 300-μm spot diameter and 0.55 TPa for 3.5×1015 W/cm2 laser pulses focused on 60-μm spot diameter. These results, compared with theoretical values, show an important loss of energy, attributed to two-dimensional effects. The ratio of effective energy for compression to incident energy is estimated to be 12% for 1.2×1014 W/cm2 experiments and only 1% for 3.5×1015 W/cm2 experiments.
On the external magnetic field of two-dimensional semi-infinite plates: Single plates
Authors: Owen D. , Parris A.
Published: February 2003

A theory for determining the external magnetic field of single two-dimensional electromagnetic polepieces having different end shapes is developed. Four examples are considered, one of which is similar to a case studied previously by a different method and for which the results are in agreement. Methods for examining ‘‘flat-end’’ and ‘‘thin’’ polepieces are also discussed and applied to two cases.
KrF laser kinetics studies
Authors: Mandl A. , Klimek D. , Parks J. H.
Published: February 2003

A series of measurements characterizing an e beam pumped KrF* laser was carried out using a 200-nsec e-beam pulse having a rise time of 25 nsec at current densities up to 50 A/cm2. These pump conditions are relevent for inertial confinement fusion laser drivers. The measurements include fluorescence efficiency, sidelight suppression of the fluorescence during lasing, and laser energy output over a wide range of laser parameters including: total density 0.5–2.0 amagats, temperature 300–400 K, fluorine density 0.15%–0.5%, current density 38–50 A/cm2 and various mirror transmissions. This data was used to verify and refine a model of KrF* kinetics which was then used to estimate the performance of an angular multiplexed power amplifier suitable for laser fusion applications.
Quasistatic experiments to determine material constants for the piezoresistance foils used in shock wave experiments
Authors: Chen D. Y. , Gupta Y. M. , Miles M. H.
Published: February 2003

Experimental techniques and analysis to determine the complete set of linear piezoresistive and mechanical constants for foils used in piezoresistance measurements are presented. The plastic deformation contribution to resistance change is examined in detail. Material constants have been evaluated for manganin, ytterbium, and constantan. For the cold rolled manganin foils used in our work, plastic deformation makes negligible contribution to resistivity changes. The implications of the present results for shock wave studies are also presented.
Frequency characteristics of photoacoustic signals generated in liquids
Authors: Kitamori Takehiko , Fujii Masaaki , Sawada Tsuguo , Gohshi Yohichi
Published: February 2003

Photoacoustic signals generated in liquids are generally described with a wave equation of forced motion for which source terms are incident photoenergy. As a concrete example, the wave equation is applied to cylindrical cells, and photoacoustic signals are analyzed as a function of light modulation frequency using the assumption that the thermal diffusion length is negligibly smaller than the radius of the incident laser beam which has a Gaussian distribution. Experimental results show a monotonic decrease with increasing frequency under 10 kHz and resonance peaks beyond the 10-kHz region. These can be explained by theoretical analysis. The monotonic decrease is caused by decreased photoenergy with increasing light modulation frequency and number of the thermoelastic wave modes in the cell. The peak at 153 kHz is a resonance of the thermoelastic wave in the cell, while the other peaks correspond to structural resonance of the entire cell body and to the electrical resonance of the piezoelectric transducer.
Magnetic field fluctuations arising from thermal motion of electric charge in conductors
Authors: Varpula T. , Poutanen T.
Published: February 2003

A model is developed for the source of magnetic field fluctuations emanating from thermal agitation of electric charge in conductors. The calculation of the thermal magnetic noise with the model involves the solution of a general volume conductor forward problem. Frequency-dependent equations for this problem are derived from Maxwell’s equations. The model is applied to calculate the magnetic noise generated by infinite conducting slabs. A good agreement between theoretical predictions and experimental results were found. Thermal magnetic noise fields inside magnetically shielded rooms are estimated and noise in biomagnetic measurements is discussed.
Scattering losses in optic fiber materials. I. A new parametrization
Authors: Lines M. E.
Published: February 2003

Many different nonsilica-based fiber materials are presently being examined as possible candidates for use in extremely low loss fibers for infrared communications. One useful figure of merit in estimating fiber potential for low absorption is the total intrinsic scattering loss at the minimum dispersion wavelength. In this paper formulae for these losses, which include Rayleigh, Brillouin, and Raman mechanisms, are derived solely in terms of parameters which are either already known, or which can be reliably estimated, for essentially all of the materials in question. The basic techniques for calculating power losses due to intrinsic thermodynamic fluctuations are well established in principle. This paper first extends them for use with arbitrarily complex multicomponent mixtures and for the specific inclusion of Raman loss and then, via the use of the concept of bond polarizabililty, relates the various components (due respectively to density, composition, and lattice vibrational modulations of dielectric constant) in a new parametrization. Finally, using a three-parameter Sellmeier formalism to locate the wavelength of minimum dielectric dispersion, the various scattering losses at this wavelength are finally given in an explicit form for which all quantities involved are experimentally accessible and are included in their normally quoted experimental units. In the following companion paper these power loss formulae are used directly to obtain actual numerical estimates (in dB/km) for a wide selection of candidate materials.
Scattering losses in optic fiber materials. II. Numerical estimates
Authors: Lines M. E.
Published: February 2003

Applying the theoretical results outlined in the first paper of this series, numerical estimates have been obtained for density fluctuation, Raman, and concentration fluctuation scattering losses in a number of materials which are under consideration as candidates for ultralow loss fiber-optic applications. The materials include single-component oxide, halide, and chalcogenide glasses as well as a few multicomponent glasses and single component halide crystals. Attenuation estimates (in dB/km) are given both at the minimum dispersion wavelength and, whenever possible, at minimum total attenuation (including scattering and absorption mechanisms). Raman attenuation is found to be small in all cases, typically a few percent of the total at most, but concentration fluctuation attenuation is potentially dominant in some multicomponent samples. The broad conclusion is that a significant improvement over silicate glasses can only be obtained by use of halide glasses or by single crystal fibers. Ideal minimum values of ∼0.01 and ∼0.001 dB/km are indicated for vitreous BeF2 and ZnCl2, respectively, while values of the order 0.003–0.007 dB/km seem to be attainable using fluorozirconate glasses. Possible minimum attenuation as low as 10−4 dB/km is indicated for quasiperfect single crystal chloride fibers if they can be fabricated.
Determination of optical properties of fibrous thermal insulation
Authors: McKay N. L. , Timusk T. , Farnworth B.
Published: February 2003

We present a method of obtaining optical parameters relevant to radiative heat transfer in polyester fiber insulations. The complex index of refraction of the bulk material for frequencies between 100 and 2000 cm−1 is derived from transmission measurements on thin films by an iterative procedure. Absorption and scattering functions for an isolated fiber are calculated from expressions analogous to those of Mie theory for spheres. Results for the extinction and absorption cross section compare well with measurements on the insulation material itself. The calculation also yields the scattering as a function of angle, which is highly anisotropic. A properly weighted average over angle together with the calculated absorption cross section gives the necessary parameters for a diffusion model of radiative heat transport. Approximate differential equations describing combined conductive and radiative heat flow are solved with these parameters, and the results compared with thermal measurements on a commercial polyester insulation. The excellent agreement between theory and experiment indicates that the diffusion model accurately describes radiative heat transport in these materials. Our method can be used to predict the effect of hypothetical alterations to the fibers.
A single-crystal silicon thin film formed by secondary recrystallization
Authors: Cline H. E.
Published: February 2003

Thin encapsulated silicon films were zone heated in the solid state just under the melting point with a quartz-iodine lamp over a range of speeds between 0.005 and 0.05 cm/sec. The recrystallized thin films were examined with electron channeling, transmission electron microscopy, scanning and optical microscopy. The recrystallized 1/2-μm- thick film was essentially a single crystal with large equiaxed subgrains oriented with the (100) nearly normal to the plane of the film and the 〈010〉 direction along the growth direction at growth velocities below 0.01 cm/sec. Misorientations between adjacent large 100-μm subgrains were of the order of 1°. The driving force of grain growth in the silicon thin film was determined to be the surface energy anisotropy of the silicon oxide interface from observations of grain boundary grooves that were pinned by a few micron-size included grains. Both the mechanism of recrystallization and the potential for producing silicon-on-insulator material by solid-state recrystallization are discussed.
Theoretical studies of the electric field distribution and open-circuit voltage of amorphous silicon-based alloy p-i-n solar cells
Authors: Hack M. , Shur M. S.
Published: February 2003

Using a computer model based on the solution of the complete set of transport equations we have investigated electric field profiles, carrier distributions and the open-circuit voltage of amorphous silicon-based alloy p-i-n solar cells illuminated through either the p+ or n+ layer. Our results indicate that even with a large difference in the electron and hole band mobilities there is no large difference (<50 mV) in the open-circuit voltage for the two cases. This difference is small because for optimized devices the open-circuit voltage is limited by the recombination current which is relatively insensitive to space charge and Dember effects. We also show that boron doping in the intrinsic layer can drastically alter the electric field profile in these devices, and can increase the open-circuit voltage of p-i-n solar cells with low built-in potentials.
10-nm resolution electron-beam lithography
Authors: Craighead H. G.
Published: February 2003

An analytical electron microscope has been used to fabricate a variety of ultrasmall structures and to test the size limits and some basic concepts of high-resolution electron-beam lithography. Arbitrarily shaped patterns on both thin film and bulk substrates have been written with dimensions of approximately 10 nm. A review of devices, structures, materials, and techniques is presented.
Applicability of the van der Pauw–Hall measurement technique to implanted samples
Authors: Iyer Suman B. , Nityananda Rajaram , Kumar Vikram
Published: February 2003

The application of the van der Pauw–Hall measurement technique to implanted samples in which the mobility varies with depth has still not been fully justified. A proof that the technique is in fact applicable in this situation is given.
Microstructural studies of CdTe and InSb films grown by molecular beam epitaxy
Authors: Wood S. , Greggi J. , Farrow R. F. C. , Takei W. J. , Shirland F. A. , Noreika A. J.
Published: February 2003

Epitaxial thin films of CdTe (1–5 μm) have been grown directly onto (001) InSb substrates or onto intermediate buffer layers of InSb (0.25–0.5 μm) by molecular beam expitaxy. Cross-sectional transmission electron microscopy and high-resolution transmission electron microscopy have been used to characterize the film and interfacial microstructures. Inferences about film quality were also compared with single-crystal x-ray rocking curve data and agreed well. Resulting microstructural features were correlated with various experimental growth parameters and substrate cleaning procedures. Results show that near-perfect CdTe films can be grown on InSb substrates, but film quality is critically dependent upon substrate cleaning. Other factors observed to influence defect formation in the films include growth rate, total growth time, or a change in growth rate during film growth. Extended defects which form include twins, line dislocations, or looplike defects. Lattice imaging has demonstrated the lattice matching across the InSb film/InSb substrate interface, despite the formation of In precipitates during the heat cleaning procedure.
Mechanical properties of thin alloy films: Ultramicrohardness and internal stress
Authors: Dirks A. G. , van den Broek J. J. , Wierenga P. E.
Published: February 2003

On a series of Ag-Al, Ag-Au, Ag-Cu, Au-Cu, and Au-Fe thin films, made by vapor deposition, both ultramicrohardness and internal stress were determined as a function of the chemical composition of the deposits. In order to interpret these results microstructural investigations were performed using x-ray diffraction and transmission electron microscopy, supplemented by electrical resistivity measurements. The observed data on hardness and internal stress can be well understood with the help of the metastable phase diagram of the alloy films. In the case of single-phase solid solutions, internal stresses are tensile. Compound formation, phase decomposition, or ordering are accompanied with dramatic changes of the internal stresses. With indentation experiments at very low loads the hardness-concentration dependences were observed in the case of films having a thickness of 1 μm only. Metallic films in general are characterized by a very high defect concentration. Moreover, a dramatic reduction of the average grain size was observed upon alloying. The resulting hardness increase may be understood in terms of a mechanism implying the blocking of the motions of dislocations.
Theoretical analysis of interacting dimers thermal desorption
Authors: Mola E. E.
Published: February 2003

First-order thermal desorption of interacting dimers is investigated using the lattice gas model. Dimers are assumed to interact if they occupy only nearest-neighbor lattice sites. A single type of site is used. By choosing an appropriate sublattice, able to describe first-order desorption of interacting dimers, the grand partition function is derived using the Bethe approximation. The rate of thermal desorption is written using absolute rate theory. The calculated thermal desorption spectra show two peaks, although a single binding state was considered.
The effect of pressure on the semiconductor-to-metal transition temperature in tin and in dilute Sn–Ge alloys
Authors: Vnuk F. , De Monte A. , Smith R. W.
Published: February 2003

The pressure/temperature characteristics of the grey (semiconductor) tin→white (metal) tin transition in pure tin and dilute Sn–Ge alloys has been examined by following electrical resistance changes in strip specimens. It is shown that grey tin→white tin phase boundary has a slope of −48.4±6 K/kbar, in good agreement with thermodynamic predictions.
Phase transformations in ion-mixed metastable (GaSb)1−x(Ge2)x semiconducting alloys
Authors: Cadien K. C. , Muddle B. C. , Greene J. E.
Published: February 2003

Low energy (75–175 eV) Ar+ ion bombardment during film deposition has been used to produce well-mixed amorphous GaSb/Ge mixtures which, when annealed, transform first to single phase polycrystalline metastable (GaSb)1−x(Ge2)x alloys before eventually transforming to the equilibrium two-phase state. At 500 °C, for example, the annealing time ta required for the amorphous to crystalline metastable (ACM) transformation was ∼10 min, while ta for the crystalline metastable to equilibrium (CME) transformation was >6 h. The exothermic enthalpy of crystallization and the onset temperature of the ACM transition were determined as a function of alloy composition using differential thermal analysis. The thermodynamic data was then used to calculate the surface energy per unit area σ of the amorphous/metastable-crystal interface. σ was found to exhibit a minimum between x=0.3 and 0.4. The driving energy for the transition from the crystalline metastable state to the equilibrium two-phase state was of the order of 0.12 kJ cm−3 while the activation barrier was ∼19 kJ cm−3. Thus, the metastable alloys, which had average grain sizes of 100–200 nm and a lattice constant which varied linearly with x, exhibited good thermal and temporal stability.
Platinum silicide contacts to silicon by lift-off
Authors: Cohen S. S. , Bower D. H. , Brown D. M. , Norton J. F.
Published: February 2003

Thin layers of platinum silicide, interposed between heavily doped silicon junctions and a thick overlying interconnect metallization, assure that good ohmic contact characteristics prevail. In conventional processes the thin PtSi film is formed by reacting a thin (200–500 Å) sputtered Pt film with the underlying silicon substrate. The unreacted platinum that is found on the surrounding field oxide area is then etched in aqua regia. This self-aligned process may pose some problems with regard to the integrity of the Pt/Si contact and the device yield. For these reasons we have studied an alternative Pt deposition-patterning scheme that promises to alleviate the seriousness of these problems. PtSi contacts have been fabricated by means of a new photoresist lift-off technique. The aim of the present study is to contrast this new lift-off process for the formation of PtSi contacts to Si with the conventional self-aligned technique. Our results indicate that the new process is preferred although it gives rise to somewhat higher values for the contact resistance.
Impact ionization induced minority carrier injection by avalanching p-n junctions
Authors: Childs P. A. , Eccleston W.
Published: February 2003

Excess minority carriers, generated in the substrate of metal oxide semiconductor transistors operating in saturation, are known to present reliability problems in dynamic memory circuits such as random access memories and charge coupled devices. It has been shown that the minority carriers result from light emission associated with the avalanche multiplication region close to the drain. In this paper we report evidence of a new minority carrier injection process which only occurs in p-n junctions having very low breakdown voltages (≲9 V). The avalanching emitter-base junctions of bipolar transistors were used as the injection sources and injection efficiencies (defined as the ratio of the minority carrier current to the multiplication current) as high as 5×10−3 were recorded. A model of the injection process based on impact ionization within the neutral regions is proposed. A Monte Carlo simulation of avalanche breakdown is used to demonstrate the feasibility of the model.
Properties of hydrogenated amorphous silicon prepared by chemical vapor deposition
Authors: Ellis F. B. , Gordon R. G. , Paul W. , Yacobi B. G.
Published: February 2003

Hydrogenated amorphous silicon (a-Si:H) films were prepared by chemical vapor deposition (CVD) from mixtures of silane, disilane, trisilane, and higher polysilanes in hydrogen carrier gas at 1 atm total pressure, at substrate temperatures from 420–530 °C. Experimental parameters are explained and properties as a function of these parameters are shown. The measurements include hydrogen content (by IR), optical, electrical, and photovoltaic properties of the material. In most respects, the CVD material closely resembles the a-Si:H usually prepared by glow discharge. The following differences have been noted: (1) the CVD a-Si:H shows no IR absorption at 840–850 cm−1, which is consistent with the expected better thermal stability of the CVD material because of the much higher substrate temperatures in the CVD process than in the glow discharge process. (2) The band gap of CVD a-Si:H is lower by about 0.1 eV than glow discharge a-Si:H of the same hydrogen content. Thus, the band gap of CVD a-Si:H is better matched to the solar spectrum than is glow discharge a-Si:H. (3) All three IR absorption bands due to hydrogen are about 20% narrower in the CVD a-Si:H, suggesting a simpler structure. (4) The temperature dependence of the dark conductivity of CVD a-Si:H fits a curve for a single activation energy, in contrast to the more complicated temperature dependence often found in glow discharge a-Si:H, in which two different activation energies are seen at high and low temperatures. This suggests that the conduction mechanism is also simpler in the CVD a-Si:H. (5) The growth rates of good-quality CVD films are much higher (up to about 100 Å/s) than are typical of the glow discharge method.
Quantum size effect in the transport of electrons in semiconductor quantum well structures
Authors: Ogale S. B. , Madhukar A.
Published: February 2003

In this paper we present the results of calculations for the low temperature mobility of electrons confined in isolated quantum well structures, when the scattering is dominated by ionized impurities. The effect of the variation in quantum well thickness on the electron mobility is studied, with particular emphasis on the quantum size effect regime. Explicit results are presented for AlxGa1−xAs/GaAs(100) quantum wells for x=0.3, both for uniform and modulation doping schemes. The present results for the quantum size effect regime differ significantly from those reported recently for a nondegenerate confined electron gas at a single heterojunction interface. The reasons for these differences are discussed.
Magnetoresistive switching of small permalloy sandwich structures
Authors: Berchier Jean-Luc , Solt Katalin , Zajc Tomislav
Published: February 2003

The magnetoresistive (MR) switching behavior of small permalloy/silicon monoxide/permalloy sandwich elements is investigated. A comparison with single layer elements shows that the best MR-switching results are found for the sandwich structures with the smallest dimensions (10×100 μm). A theoretical calculation based on the magnetostatic coupling between the two permalloy layers of the sandwich and on inhomogeneous demagnetizing fields shows good agreement with the experimental results. The formation of magnetic domain configurations other than those found in small single layer elements is illustrated using a ferrofluid observation technique.
Photoluminescence and thermoluminescence of Ti centers in LiF (TLD-100)
Authors: Delgado L. , Delgado A.
Published: February 2003

The influence of thermal treatments (quenching and annealing) on the optical absorption and luminescence (emission and excitation) spectra of the Ti-related 200-nm absorption band is studied. Correlations between thermoluminescence (TL) and photoluminescence (PL) emission spectra at different temperatures support the identification of the 200-nm Ti-related centers as the luminescence centers of the dosimetric glow peak 5 (205 °C). The results are discussed with reference to a recently suggested TL model involving correlated trapping-recombination centers in which thermal release of fluorine atoms in interstitial position yields impurity light emission.
Control of lateral epitaxial chemical vapor deposition of silicon over insulators
Authors: Bradbury D. R. , Kamins T. I. , Tsao C.-W.
Published: February 2003

Single-crystal silicon films have been grown over SiO2-covered regions of a single-crystal silicon wafer by lateral epitaxial chemical vapor deposition (CVD). Nucleation of polycrystalline silicon on the SiO2 is suppressed by adding HCl to the SiH4 deposition gas. Sequential variation of the HCl partial pressure during different stages of the deposition process controls the relative deposition rates of the [100] and [110] planes and, consequently, the shape of the laterally advancing growth fronts, allowing the fronts from opposite sides of the SiO2 region to join uniformly. A plane surface is obtained by increasing the HCl partial pressure after coalescence. A standard silicon CVD epitaxial reactor is used for the deposition.
Effect of spatial averaging on the compositional analysis of crystals by absorption spectroscopy
Authors: Forman Richard A. , Bell Michael I. , Mayo Santos , Kahn Arnold H.
Published: February 2003

Calculations of optical absorption based on a model of a single crystal containing spatially periodic compositional variations are presented. These variations can contribute a significant soure of systematic error in the analysis of composition by optical or surface techniques. The model is most appropriate for melt-grown crystals and in particular for striated semiconductor crystals, and the surface concentration profile which it predicts is confined by comparison with a published x-ray topographic study of silicon. Implications of the results for optical absorption studies of impurities in silicon crystals are discussed and it is shown that significant measurement errors may occur.
High deposition rate preparation of amorphous silicon solar cells by rf glow discharge decomposition of disilane
Authors: Kenne Jean , Ohashi Yutaka , Matsushita Tsutomu , Konagai Makoto , Takahashi Kiyoshi
Published: February 2003

The optical and electrical properties of hydrogenated amorphous silicon films produced by rf glow discharge decomposition of disilane diluted in helium (Si2H6/He=1/9) have been studied while systematically varying the film deposition rate. The properties and composition of the films were monitored by measuring the optical band gap, IR vibrational spectrum, dark conductivity, and the photoconductivity as a function of the deposition rate. The photoluminescence of the high deposition rate films gave a peak at 1.33 eV. These films, whose properties are rather similar to those of the conventional a-Si:H films prepared from monosilane, have been used to fabricate nip-type a-Si:H solar cells. At a deposition rate of 11 Å/sec, a conversion efficiency of 6.86% was obtained. This high efficiency shows that disilane is applicable for mass production fabrication of a-Si:H solar cells.
Surface segregation of Ag in CdTe induced by photon absorption
Authors: Tregilgas J. H. , Gnade B. E.
Published: February 2003

The first observation of a new impurity segregation or gettering phenomenon has been demonstrated in CdTe using radioactive Ag. Noble metal dopant impurities have been found to segregate to the surface region of CdTe during exposure to ambient light. This phenomenon occurs while the sample is held at room temperature and is not induced by localized heating or surface chemical reactions. Experimental results suggest that a redistribution of excess carriers produced by photon absorption near the CdTe surface may be responsible for the behavior.
Amorphous Ta-Ag films and β-Ta films
Authors: Hauser J. J.
Published: February 2003

Amorphous TaxAg1−x films (0.25≤X≤0.90) were obtained by getter-sputtering powder targets at 77 K. These films crystallize around 750 °C. The similarity between the crystallization and the superconducting transition temperature of these films and of β-Ta films suggest that the short-range order in amorphous Ta-Ag films (and possibly in amorphous Ta) is closer to the β-Ta structure than to the bcc structure of bulk Ta.
Impurity-band conduction in natural pyrrhotite
Authors: Sakkopoulos S. , Vitoratos E. , Argyreas T.
Published: February 2003

The resistivity and Hall effect curves versus 1/T for natural single crystals of pyrrhotite are compared to the analogous curves of heavily doped Ge and Si samples, where impurity-band conduction takes place. The existence of characteristic ‘‘knees’’ in the resistivity, corresponding to maxima of the Hall effect for these materials, indicates an impurity-band conduction in pyrrhotite. This can explain the sign reversal of the Hall coefficient for conduction perpendicular to c axis. Moreover, the high concentration of impurities and defects in natural pyrrhotite, as it is revealed from spectroscopic and chemical analyses, support the suggestion that an impurity-band conduction occurs in this mineral.
Electrical and optical properties of Si- and Sn-doped InxGa1−xAs (x≂0.53) grown by molecular beam epitaxy
Authors: Kubiak R. A. , Harris J. J. , Dawson P.
Published: February 2003

This communication reports the majority-carrier properties and room-temperature photoluminescence of InxGa1−xAs (x≂0.53) doped with Si and Sn, grown on InP substrates by molecular beam epitaxy. The peak doping levels attainable with Si and Sn are established, and comparison is made with dopant behavior in GaAs. The effects of Si-doping level on photoluminescent yield are reported.
Ion implantation and diffusion of Zn in GaAs
Authors: van Gurp G. J. , van Ommen A. H. , Boudewijn P. R. , Oosthoek D. P. , Willemsen M. F. C.
Published: February 2003

Zn implantation (dose 5×1015 cm−2) and subsequent diffusion were carried out on GaAs wafers and on liquid-phase epitaxial GaAs layers. A silicon nitride cap was deposited by chemical vapor deposition (CVD) or by sputtering either before or after implantation. Profiles were determined with Secondary Ion Mass Spectrometry and Differential Hall Effect measurements and damage was studied with Rutherford Backscattering Spectrometry. Annealing gave rise to Zn segregation at the surface or just below it and at a depth past the implantation maximum. The diffusion was much deeper and the damage recovery was much less with implantation through a nitride layer than with implantation directly into GaAs. This is explained in terms of recoil implantation of Si and N and of a smaller Ga vacancy concentration so that less trapping of interstitial Zn by such vacancies takes place. Surface segregation of Zn and differences in diffusion depth between samples with sputtered and CVD silicon nitride caps are ascribed to the effects of stress. Except in a surface layer, complete electrical activation and ideal Hall mobility values were found after annealing at 700 °C.
Study of manganese accumulation in ion implanted GaAs influenced by Fermi energy and annealing technique
Authors: Kanber H. , Feng M. , Whelan J. M.
Published: February 2003

The redistribution of Mn during post-implantation annealing in bulk semi-insulating GaAs and GaAs vapor phase epitaxial buffer layers is studied by secondary ion mass spectrometry for Si, Se, and Cd implanted materials annealed capless in an As4-H2 atmosphere. The secondary ion mass spectrometry chemical profiles are correlated to the electrical profiles of the implanted layers and agree with the stages of approach toward equilibrium during annealing. We have developed a model for Mn diffusing by an interstitial-substitutional mechanism and one that agrees with the relative amount and type of implantation damage due to stoichiometric disturbances generated during the implantation process. Mn accumulation caused by differences between donor and acceptor implants, the effects of annealing temperature, time, and atmosphere are discussed. The implant fluences used in this investigation are appropriate for GaAs field-effect transistor device applications.
Neutron transmutation doping of gallium phosphide
Authors: Huber A. , Kuchar F. , Casta J.
Published: February 2003

The doping of GaP with Ge using nuclear transmutation is reported. Electrical and optical measurements were used to characterize the neutron-irradiated samples. After annealing at 800 °C for 2 h, essentially all the Ge atoms are located on lattice sites where they act as single donors. This is most likely the Ga site. Higher temperatures are needed to anneal all the defects induced during irradiation and decay of the activated nuclei.
Deep levels related to Co in InP
Authors: Rojo P. , Leyral P. , Nouailhat A. , Guillot G. , Lambert B. , Deveaud B. , Coquille R.
Published: February 2003

Electrical and optical junction space-charge spectroscopies, photoluminescence, and electron paramagnetic resonance are used to investigate the charge states of Co present in n-type InP and to characterize the deep levels occuring in such Co doped materials. Electron paramagnetic resonance and photoluminescence results indicate unambiguously that the Co2+ charge state is present in n-type material substitutional to indium. Only one deep level at EV +0.24 eV is detected with a concentration similar to Co doping. The (EV +0.24 eV) level is identified with the (Co2+→Co3++eCB) charge state change mainly on the analysis of its optical cross sections σ0n (hν) and σ0p (hν). Optical transitions are well interpreted as transitions from the Co2+ ground state (4A2) to the Γ point minimum of the conduction band for σ0n (hν) and from the valence band to the Co2+ ground (4A2) and excited state (4T2) for σ0p (hν). The value of the ionization energy for Co2+ in InP (1.16 eV) is shown to agree quite well the value predicted by the trends of the ionization energies of 2+ charge states of transition metals in III-V semiconductors.
Semi-insulating GaAs examined using a three-band model
Authors: Lee H. J. , Park Y. S.
Published: February 2003

Electrical transport parameters were calculated at 296 K as a function of Fermi energy around n- and p-type conversion points using a three-band model comprising the Γ1 C and the heavy and light hole bands. This study indicates that all of the recently reported semi-insulating GaAs are n type (negative Hall coefficient), and futhermore the electrical transport phenomena can be explained only in terms of electrons and the contribution of the holes can be neglected. The resultant calculations can be used in assessing the semi-insulating GaAs crystals in a routine way only by measuring the electrical conductivity and Hall coefficient at one temperature, 296 K.
Simple theory of buried channel acoustic charge transport in GaAs
Authors: Hoskins Michael J. , Hunsinger Bill J.
Published: February 2003

A theory is developed which describes the fundamental charge transfer characteristics of basic buried channel GaAs structures which are illuminated by large amplitude surface acoustic waves. Several approximations which simplify the analysis are shown to be valid in this channel structure. The theoretical approach treats carrier diffusion as a perturbation on the diffusionless two-dimensional electrostatic problem. Simple closed form expressions are obtained for packet charge density and boundary shape in terms of the channel parameters. It is shown that four sets of numerically generated and normalized curves are sufficient for the determination of the transport characteristics of a wide range of channel potential geometries. The dependence of diffusion induced transfer inefficiency on charge load and wave potential is investigated. The results indicate that high speed acoustic charge transport is capable of supporting typical buried channel charge loads at very high transfer efficiency.
Diffusion-limited saturation current of a finite p-n junction
Authors: Holloway H. , Brailsford A. D.
Published: February 2003

We present a quantitative analysis of the diffusion-limited saturation current of a finite planar p-n junction. In addition to the current that is given by Shockley’s analysis for a junction with infinite extent, there is a contribution from the periphery of the device. In many cases of practical interest the net effect may be approximated by considering the junction area to be supplemented by a border with width equal to one half the minority-carrier diffusion length of the surrounding semiconductor. This simple result may be modified by the effects of finite specimen thickness, reduction of the junction dimensions to values less than the diffusion length, and the proximity of other p-n junctions. Our analysis includes the effects of these parameters.
Built-in voltage of a silicon p-n junction having a heavily doped region
Authors: Sinha Amitabha
Published: February 2003

An analysis of the built-in voltage of a silicon p–n junction has been done, taking into account the band-gap narrowing effects in the heavily doped region. It has been observed that much lower values of built-in voltage are obtained when heavy doping effects are considered. Also, the magnitude of built-in voltage decreases when the temperature of the p–n junction is increased.
Reply to ‘‘Comment on ‘Current limits in linear accelerators’ ’’
Authors: Reiser M.
Published: February 2003

The relativistic effect mentioned by Winterberg [J. Appl. Phys. 55, f6 (1984)] is negligible for the proton and ion linacs (γ<2) discussed in my paper [J. Appl. Phys. 52, 555 (1981)].
Upstream boundary conditions for channel model representation of arcs in gas flow
Authors: Lowke J. J. , Kovitya P. , Ahmed S. S. , Benenson D. M.
Published: February 2003

It is shown that the equations used in the channel model representation of an arc in an axial gas flow define the upstream values of arc temperature and area where the plasma velocity is zero. Arc temperature and area are determined by the plasma material functions and the axial gradient of the plasma velocity at the stagnation point. The relations apply for either the stagnation point in a double flow nozzle or for the point immediately adjacent to the upstream electrode in a single flow system where there is also a stagnation point. It is predicted that arc temperatures and current densities will generally be larger for arcs in sulfur hexafluoride compared with nitrogen.