bluuebunny/crossref_metadata_2025 huggingface dataset:
Critical behavior of three-dimensional Ising model of spin glass (invited)
Authors: Ogielski Andrew T. , Morgenstern Ingo
Published: July 2002

First results of massive Monte Carlo simulations of the d=3 Ising spin glass with ± J bond distribution, performed on a fast special purpose computer, are discussed. Equilibrium static and dynamic correlation functions have been recorded for temperatures T/J=1.10 to 2.00. A qualitative change in the behavior of the system, and the best fits for the spin glass correlation length and relaxation time favor a continuous phase transition at Tc/J≊1.20±0.05. We find no evidence for the Tc=0 freezing picture.
Electrical characterization of GaAs/AlGaAs semiconductor-insulator-semiconductor capacitors and application to the measurement of the GaAs/AlGaAs band-gap discontinuity
Authors: Arnold D. , Ketterson A. , Henderson T. , Klem J. , Morkoç H.
Published: July 2002

Electrical measurements were made on n+GaAs-(Al,Ga)As-n−GaAs and p+GaAs-(Al,Ga)As-p−GaAs capacitors. Current conduction is due to thermionic emission at low bias voltages and high temperatures. At low temperatures and high fields Fowler-Nordheim tunneling contributes to the conduction process. An inverted n-type capacitor analogous to an inverted modulation doped structure shows electrical characteristics comparable to the ‘‘normal’’ structure grown under optimized conditions. Conduction- and valence-band discontinuities were calculated from measurements of thermionic emission barrier heights as a function of Al mole fraction in the (Al,Ga)As. A conduction-band discontinuity of 65% of the total band-gap discontinuity between GaAs and (Al,Ga)As, independent of Al mole fraction, was deduced. A classical theory for the capacitance voltage characteristics of p+GaAs-(Al,Ga)As-p−GaAs structures is presented.
Surface order and stoichiometry of sputter-cleaned and annealed CuInSe2
Authors: Corvini P. , Kahn A. , Wagner S.
Published: July 2002

CuInSe2 surfaces can be cleaned by bombardment with Ar ions at glancing incidence and with energies up to 1.5 keV without change in composition. At near-normal incidence a slight depletion of Cu is observed. The surface crystallinity can be partially restored by annealing to ∼550 °C, without preferential evaporation of an element. On Ar+-cleaned and annealed surfaces, single-crystal low-energy electron diffraction patterns of CuInSe2 have been produced for the first time.
Atomic structure model for Ga1−xInxAs solid solution
Authors: Fukui T.
Published: July 2002

A simple atomic structure model was proposed for Ga1−xInxAs solid solution. Distortion energy caused by the differences in Ga-As and In-As bond lengths was calculated using the valence-force-field approach. Calculated bond lengths for Ga1−xInxAs agree well with the extended x-ray absorption fine structure data. The calculated mixing enthalpy which corresponds to the excess energy caused by distortions agree with that from phase diagram.
Ohmic lines for one-dimensional in-line and two-dimensional cylindrical Josephson junctions
Authors: Helweg C. , Levring O. A. , Samuelsen M. R. , Olsen O. H.
Published: July 2002

Expressions for the ohmic lines in the IV characteristic for one-dimensional in-line geometry Josephson junctions as well as for two-dimensional cylindrical Josephson junctions are presented. The expressions are compared to numerical simulations of Josephson junctions using the fluxon model; the ohmic line in this model corresponds to a continuous generation at the boundaries of fluxons and antifluxons, being pairwise annihilated in the middle (due to damping). For large currents the results fit to the expressions. Further we find that the fluxon generation in most cases were simply periodic; however, depending on the initial conditions we find 1/2 and 1/3 harmonic generation.
Enhancement of photoacoustic signals from condensed materials in the presence of volatile liquids: Influence of optical absorption coefficient, particle size, length of the gas phase and chopping frequency
Authors: Somasundaram T. , Ganguly P.
Published: July 2002

The influence of the optical absorption coefficient, the particle size, the chopping frequency, and the length of the gas phase on the recently observed enhancement of photoacoustic signals in the presence of saturated vapors of ether has been investigated. Amorphous selenium has been used as the standard. The particle size plays a crucial role in understanding the enhancement as a function of optical absorption coefficient or chopping frequency. The enhancement is more when the optical absorption length is greater than particle size. The frequency dependence of the photoacoustic signal in the presence of ether is different from that in air when the thermal diffusion length of the solid is greater than the particle size. A qualitative interpretation of the results based on the ‘‘adsorbed’’ piston effect has been made.
Optimization of pulse energy from 4.3-μm CO2 lasers
Authors: Brimacombe R. K. , Reid J.
Published: July 2002

A detailed study of the output energy characteristics of the pulsed, optically pumped 4.3-μm CO2 laser is described. The predictions of a rate-equation model representing the laser dynamics are shown to be in good agreement with experiment over a wide range of operating conditions. The factors which control the performance of the laser are identified, and the optimum operating conditions for maximum output energy are discussed. Output energies of 15 mJ/pulse and peak powers of 100 kW/pulse have been obtained from an 88-cm-long by 11-cm2-aperture discharge. Scalability of the pulse energy to several hundred mJ using available pump pulse energies is shown to be feasible.
Influence of a magnetic field on the growth of instabilities in a helium glow discharge using Monte Carlo simulation of the cathode fall region
Authors: Razdan R. , Capjack C. E. , Seguin H. J. J.
Published: July 2002

A Monte Carlo simulation technique has been used to model the cathode fall region of a glow discharge under the influence of a nonuniform electric field and a transverse magnetic field. It has been shown experimentally that a magnetic field can serve as an effective means for reducing the growth of discharge instabilities. The stabilization mechanism involves the dispersion of localized charged particle perturbations over the discharge area in a time less than that required for an instability to fully develop. The results of this paper provide a deeper insight into the magnetic stabilization technique, which has the potential of increasing the power output of a wide variety of gas lasers.
A wedge cell characterization method for the bistable cholesteric twist cell
Authors: Heffner W. R. , Berreman D. W. , Butler G. , Marcus M.
Published: July 2002

The bistable cholesteric twist cell (BCTC) described here is a liquid-crystal device which can be in either of two stable laminar configurations while a particular holding voltage is applied. The major shortcoming of previous implementations of this device was the narrow thickness tolerance required for proper bistable operation. In order to ascertain the effect which material parameters might have on increasing this thickness tolerance an adequate method is needed for characterizing the behavior of the cell. In this paper we describe a wedge cell method for characterizing the behavior of a given BCTC system. The characterization can be conveniently done within a single cell. The data obtained include both the thickness to pitch range for pratical bistable operation and the switching properties. All of these features can be interpreted in terms of static free energy curves calculated for the system. We have also used this wedge cell method to determine the effect of the bend to splay elastic constant ratio on the thickness range of bistable operation in the BCTC. The range is observed to increase with increasing ratio of bend to splay elastic constant. A material has been identified with a bistable thickness range in excess of 10%.
Photoluminescence determination of the nonuniformity of Fe, Zn, and other centers in undoped semi-insulating liquid-encapsulated Czochralski GaAs
Authors: Yu P. W. , Theis W. M. , Ford W.
Published: July 2002

2-K photoluminescence was used to determine the amount of nonuniformity present in undoped semi-insulating GaAs bulk substrate materials grown by the liquid-encapsulated Czochralski method. The relative photoluminescence intensities of the intracenter (5T2−5E) transition of the Fe2+ state, the near-band-edge transitions, and the Zn peaks, measured across the wafer diameter, show almost the same ‘‘W’’ pattern. The deep-center bands at 0.63 and 0.77 eV were also measured. Possible mechanisms of the photoluminescence intensity variation are discussed. In the materials used, a predominant shallow acceptor was observed to be Zn.
Thermal behavior of thick vacuum evaporated polycrystalline silicon layer
Authors: Ota Yusuke , Clapper Raymond A. , Schimmel Donald G.
Published: July 2002

Thick polycrystalline silicon layers (≥1 mm) were deposited on SiO2-coated single-crystalline Si wafers at a wide range of temperatures by vacuum evaporation. The crystalline structure and thermal behavior of the layers were strongly dependent on the deposition temperature. These characteristics were also reflected in the mechanical strength and warpage of the polycrystalline silicon-coated single-crystalline Si system. A careful investigation was made to understand the thermal characteristics of the vacuum-evaporated polycrystalline silicon layers for possible semiconductor device application such as dielectrically isolated integrated circuits.
Optimization and preservation of deep-level transient spectroscopy signal response
Authors: Thomas H.
Published: July 2002

Variations in the classical deep-level transient spectroscopy experimental procedures lead to degradation of signal-to-noise and signal resolution, and result in nonexponential transients. Simple analyses illustrate the implications of these errors, and by example, the zero-bias trap filling pulse condition is shown to give rise to a constant series capacitance.
Strain-induced level in copper-doped silicon
Authors: Tōyama Naotake , Otsuji Taiichi
Published: July 2002

It has been found that in copper-doped silicon, both the concentration and the degeneracy ratio of the deep acceptor level lying at 0.16 eV from the conduction band edge vary having a maximum and minimum value with increase in copper-doping level. Since the variations of these deep-level parameters correspond very well to that of the silicon crystal lattice strain due to numerous copper precipitates, we can infer that the acceptor level is a strain-induced level which is introduced by copper diffusion.
Improved performance of InSe-based photoelectrochemical cells by means of a selective (photo)electrochemical etching
Authors: Tenne R. , Theys B. , Rioux J. , Levy-Clement C.
Published: July 2002

It is shown that the performance of photoelectrochemical cells based on the lamellar material InSe can be considerably improved by means of a selective (photo)electrochemical etching. Whereas the cleavage Van de Waals plane (⊥ to c axis) shows little improvement, the photcurrent in the ∥ face (parallel to the c axis) is doubled (30 mA cm−2 under AM1 illumination). For n-type InSe a reverse bias (+1.5 V versus standard calomel electrode SCE) was employed during the photoetching, p-InSe electrodes were electrochemically etched by applying a forward bias (+1.5 V). In both cases, surface holes carry out the selective corrosion of the semiconductor surface which is another manifestation for the asymmetry played by holes and electrons on semiconductor surfaces. It is hoped that this finding will pave the way for the construction of high-efficiency solar cells based on a thin film made of lamellar materials.
Flaw states in processed GaAs, detected by photoconductive and photo field-effect techniques
Authors: Leigh W. B. , Blakemore J. S. , Koyama R. Y.
Published: July 2002

The spectral dependence of extrinsic photoresponse is reported for measurements at 8 K on ‘‘fat-gate’’ metal-semiconductor field-effect transistors (MESFETs) made by silicon implantation into undoped semi-insulating GaAs, and for similarly implanted conductive layer samples. The interest, for the field-effect transistors (FETs), lies in any evidence concerning deep-level flaw contributions to a space charge at the channel–substrate interface. A large photosensitivity seen in the 1.0–1.5-eV range was identified as associated with photoionization of EL2 midgap donors, from its spectrum and photobleaching characteristics. Peaks of photoresponse were noted also at 0.54, 0.66, 0.79, and 0.89 eV. The 0.89-eV peak can be photobleached, and is attributed to EL2+ photoneutralization at sites in the interface region. The same region is postulated for the sites causing the 0.54-eV response, postanneal complexes dervied from the ‘‘U band’’ of implant damage states. The origins are as yet undetermined for the 0.79-eV and the (very weak) 0.66-eV response regions.
Analysis of stress in chemical vapor deposition tungsten silicide film
Authors: Shioya Yoshimi , Itoh Takahiro , Inoue Shin-ichi , Maeda Mamoru
Published: July 2002

Stress in chemical vapor deposition (CVD) tungsten silicide film was studied by changing the flow ratio of SiH4 and WF6, deposition temperature, and annealing temperature. It was revealed that the stress is tensile on the order of 109 dyn/cm2. Stress is not significantly influenced by the flow rate of SiH4, but it is greatly influenced by the composition ratio of Si and W. As the film becomes Si rich, the stress is reduced remarkably, and after annealing its value peaks at 500 °C. This behavior was analyzed using an x-ray diffractometer and secondary ion mass spectrometry (SIMS). Annealing behavior of the stress can not be explained solely by the Nakjima–Kinoshita model which indicates that increase of tensile stress is caused by grain size increase, but it can be fully explained by adding to the model an expression which takes the grain structure and orientation into account. A tensile stress increase accompanies reaction between the tungsten silicide film and Si substrate at a high temperature of 1100 °C.
Relationship between changes in compositional short-range order and field-induced anisotropy in amorphous Co58.3Fe4.7Ni10Si11B16 alloy
Authors: Yokota R. , Miyazaki M. , Komatsu T. , Matusita K.
Published: July 2002

Relationship between the changes in compositional short-range order (CSRO) and field-induced anisotropy (Ku) was studied in the amorphous zero-magnetostrictive alloy of composition Co58.3Fe4.7Ni10Si11B16, which has an appropriate Curie temperature (Tc) and high-crystallization temperature. Resistivity measurements after quenching from preannealing temperature (TQ) show that the reversible CSRO can be separated from the nonreversible topological short-range order. Resistivity change (Δρ/ρ) and Ku change (ΔKu) were measured isothermally at 250 °C (<Tc) and also isochronally in the sample quenched from TQ. It was found that [d/Δρ/ρ)/dt]/[d(ΔKu )/dt] is constant and the higher TQ is, the larger both d(Δρ/ρ)/dt and d(ΔKu )/dt are. The approximate theory of the kinetics of both CSRO and Ku were given and it can explain the observed changes in Δρ/ρ and ΔKu. By assuming that the tail of the distribution of sizes of the interstitial sites in the soft-sphere dense random-packing model can act as a vacancylike defect, the formation mechanism of ΔKu which can explain the observed experimental facts was proposed.
Fourfold to threefold transition in diamondlike amorphous carbon films: A study of optical and electrical properties
Authors: Savvides N.
Published: July 2002

Hard, diamond-like amorphous carbon films (a-C) were prepared as a function of sputtering power density by employing dc planar magnetron sputtering of a graphite target in pure argon. Films deposited at 300 K and at increasing sputtering power density in the range 0.25–25 W cm−2 show a transition of optical and electrical properties, with the room temperature electrical conductivity increasing from 5×10−4 to 5 Ω−1 cm−1 and the optical gap decreasing from 0.74 to 0.40 eV. The imaginary part ε2 of the complex dielectric function is determined in the photon energy range 0.5–7 eV and shows a clear dependence on sputtering power density. The ε2 spectra for a a-C films possess features typical of amorphous semiconductors. neff, the effective number of valence electrons per carbon atom taking part in optical transitions, is determined via a sum rule operation on ε2. Comparisons of neff for each a-C film with that for crystalline graphite allow the average coordination of the carbon atom to be determined. We observe a systematic four-fold to three-fold transition, with the ratio of carbon atoms having four-fold sp3 configuration (diamond-like) to carbon atoms with three-fold sp2 configuration (graphite) varying from 3:1 to 1:1.
Intrinsic carrier concentrations and effective masses in Hg1−xCdxTe
Authors: Madarasz Frank L. , Szmulowicz Frank , McBath John R.
Published: July 2002

Intrinsic carrier concentrations are calculated for the semiconductor alloy Hg1−xCdxTe. Unlike previous calculations we make no approximations to the band structure, and hence to the density of states, beyond those inherent in the Kane k ⋅ p theory. Our results are compared with the recent calculation of Hansen and Schmit. Close agreement is found in the low compositional x range. However, significant differences, up to 50%, were found for higher alloy compositions. The reasons for the disagreement between the two calculations are discussed.
Acceptor associates and bound excitons in GaAs:Cu
Authors: Wang Z. G. , Gislason H. P. , Monemar B.
Published: July 2002

The effect of several parameters in the diffusion conditions for copper into GaAs on the 1.36-eV photoluminescence (PL) band and the C0 (1.5026 eV) and F0 (1.4832 eV) bound excitons (BE) has been investigated using photoluminescence techniques. Also, the different behavior of the corresponding centers under heat treatment and cool down after diffusion is reported. The results are discussed in relation to the vast literature on the GaAs:Cu, which is confusing on the relation between the 1.36-eV PL band, C0 and F0 bound excitons and the well-known 0.156- and 0.45-eV acceptors. Here it is concluded that there exists no simple relation between the C0 BE and the 1.36-eV PL band nor is the F0 BE related to any other Cu-related PL band in our samples. Models for the identities of these centers are suggested on the basis of the new experimental data presented in this paper.
Two-dimensional electron gas in In0.53Ga0.47As/InP heterojunctions grown by atmospheric pressure metalorganic chemical-vapor deposition
Authors: Zhu L. D. , Sulewski P. E. , Chan K. T. , Muro K. , Ballantyne J. M. , Sievers A. J.
Published: July 2002

High-quality modulation doped In0.53Ga0.47As/InP heterostructures have been grown by atmospheric pressure metalorganic chemical-vapor deposition (MOCVD) using solid trimethylindium source. The two-dimensional nature of electrons bound in the In0.53Ga0.47As/InP heterojunctions is proved by a Shubnikov-de Haas effect experiment. Electron Hall mobilities as high as 12000, 83000, 98000, and 92000 cm2/V s at 300, 77, 40, and 4.2 K are obtained, respectively. The electron effective mass is measured to be m*CR =0.043 m0 by cyclotron resonance experiments on the samples with two-dimensional electron sheet concentrations of (3.0–3.7)×1011/cm2. From far-infrared impurity absorption data the ionization energy of the residual donors in the MOCVD-grown In0.53Ga0.47As is determined to be 2.95 meV.
Nonalloyed ohmic contacts to Si-implanted GaAs activated using SiOxNy capped infrared rapid thermal annealing
Authors: Kuzuhara M. , Nozaki T. , Kohzu H.
Published: July 2002

SiOxNy capped infrared rapid thermal annealing was investigated for activating high dose (>7×1013 cm−2) Si implants in GaAs. The SiOxNy encapsulation resulted in enhancement in electrical activation. An electron concentration as high as 9×1018 cm−3 was obtained by 1120 °C, 5-sec annealing using an SiOxNy encapsulant with 1.75 refractive index. Nonalloyed ohmic contacts were formed by depositing AuGe-Ni on a heavily doped n-type layer activated by this technique, where a 9×10−5 Ω cm2 specific contact resistance was obtained. Furthermore, low-temperature (300 °C) alloying significantly improved a specific contact resistance to as low as 6×10−6 Ω cm2 while keeping a smooth morphology. These techniques, including low-temperature alloying, are promising for GaAs and its heterostructure device applications.
Phase transformations of alloys on a reactive substrate: Interaction of binary alloys of transition and rare-earth metals with silicon
Authors: Thompson R. D. , Tu K. N. , Ottaviani G.
Published: July 2002

Transition and rare-earth metals have been found to interact with single-crystal Si in a way that allows a division into three distinct classes: near noble, refractory, and rare earth. Recently, attention has turned to the reaction of their binary alloys with Si. In this paper we will try to demonstrate that by regarding the alloy-Si reaction as a phase transformation of alloys under the influence of a reactive substrate, we can undertake a systematic approach for the study of this kind of phase transformations involving ternary elements. In essence we show that the kinetic path taken by the alloy-Si interaction can be understood and anticipated from the reaction characteristics of the proper metal/Si bilayers and the reaction in the alloy itself. Results will be shown for Er-Pt, and Gd-Ti alloys on Si which confirm this systematic approach, which is also supported by previously published data.
Fitting of data to a Frenkel-effect model of conduction in insulators
Authors: Comizzoli R. B.
Published: July 2002

In some published work, the omission of the voltage from the preexponential factor in the current expression derived from the Frenkel effect has resulted in error in constants calculated from the data. This is illustrated with an example from the literature in which the data fit a Schottky model much more closely than the Frenkel model.
Calculation of the image potential in multiple layered structures
Authors: O’Neill A. G.
Published: July 2002

Calculations of the image potential of a point charge in three-layer systems reported previously in the literature are cumbersome. A much simpler method is presented here, by treating the system like a classical optical system where rays of light are replaced by rays of electric flux.
Response of lithographic mask structures of intense repetitively pulsed x rays: Thermal stress analysis
Authors: Ballantyne A. , Hyman H. , Dym C. L. , Southworth R.
Published: July 2002

This paper examines the effects of thermal loading and time history upon the thermal stresses developed in lithographic mask structures as would be expected under irradiation by intense soft x rays. The objective of this work was to examine the phenomenology of the interaction and to evaluate the limits placed upon mask dosage. The mechanics of mask failure are examined in terms of single pulse and cumulative, or fatigue, effects. A number of prototypical mask structures are investigated, which show that the application of intense pulsed sources to x-ray lithography does not reduce the potential utility of the techique. However, it is shown that the estimated damage thresholds do impact the operating conditions chosen for optimal production rates and mask lifetime.
Optical properties of AgGa1−xInxSe2 thin films
Authors: Kim Wha-Tek , Hahn Suk-Ryong , Jeong Hae-Mun , Yun Chang-Sun
Published: July 2002

The variation of optical properties with the relative composition of AgGa1−xInxSe2 thin films prepared by the flash evaporation method (FEM) and the electron-beam evaporation method (EBEM) has been investigated. Single-crystalline films with (112) surfaces and polycrystalline thin films were grown, respectively, by FEM and EBEM with the former having the chalcopyrite structure. The energy gap for AgGa1−xInxSe2 thin films decreased with increasing X composition and a discontinuity near X=0.6 was observed for the crystalline thin films but not in the amorphous thin films. Also, the energy gap and the photoconductivity peak energy of these films decreased with increasing ambient temperature. The temperature coefficient of the energy gap is −(4–9)×10−6 eV/K (50–100 K) and −(2–7)×10−5 eV/K (100–300 K), and that of the photoconductivity peak energy is −(2.7–6.6)×10−5 eV/K (50–100 K) and −(4.3–7.8)×10−4 eV/K (100–300 K).
An improved method of light-beam-induced current characterization of grain boundaries
Authors: Sawyer W. D.
Published: July 2002

An improved light-beam-induced current apparatus was used to evaluate grain-boundary activity in a polycrystalline solar cell. The grain-boundary recombination velocity and the diffusion length in the neighboring grains were obtained by processing of the grain-boundary profiles. The technique was applied using various wavelengths in the 550–950 nm range to check the consistency of the method and to examine the depth profile of the parameters measured. The results show that the diffusion length measurement is independent of the wavelength, and that the measured grain-boundary recombination velocity increases with the wavelength. The method was also used to evaluate hydrogen passivation of the grain boundary examined.
Weakly coupled two-dimensional correlations in finite-level epitaxy and chemisorption
Authors: Pimbley J. M. , Lu T.-M.
Published: July 2002

We formulate a two-dimensional ordering model for a finite-level system of adatoms on a crystalline surface. The placement of steps in the two surface directions obeys Markovian disorder. Steps in the two directions are weakly correlated due to the restriction that the system occupies only a finite number of levels in the vertical dimension. In particular, we derive the surface atom pair correlation function and the diffracted intensity for the two-level system and obtain a closed-form solution. We discuss the effect of the weak correlation of the two surface directions. This is perhaps the simplest two-dimensional model that can describe the molecular-beam epitaxy measurements of Si/Si(111) reported by Gronwald and Henzler [Surf. Sci. 117, 180 (1982)]. The results of our calculation are also compared to our previous one-dimensional and fully correlated two-dimensional model calculations.
Growth and characterization of InxGa1−xAs/InyGa1−yAs strained-layer superlattice on InP substrate
Authors: Quillec M. , Marzin J. Y. , Primot J. , Le Roux G. , Benchimol J. L. , Burgeat J.
Published: July 2002

The InxGa1−xAs/InyGa1−yAs strained-layer superlattices can be grown lattice matched to an InP substrate if proper compositions and thicknesses are chosen. Such structures were grown by molecular-beam epitaxy. The wavelength range covered by this material is from 1.65 μm to beyond 2 μm. Structural (double x-ray diffraction) and optical (absorption) characterizations were performed and quantitatively interpreted; they show the excellent properties of these structures.
Transient response of nonlinear optical interactions in semiconductor superlattices
Authors: Chang Yia-Chung
Published: July 2002

Transient behaviors of the optical bistability and degenerate four-wave mixing in semiconductor superlattices due to two different mechanisms, the band nonparabolicity and photoexcited plasma, are studied theoretically. For the optical bistability, the switching time and switching power are estimated for a number of semiconductor superlattices.
Implications of light-induced defects on the performance of amorphous silicon alloy p-i-n solar cells
Authors: Hack M. , Shur M.
Published: July 2002

We present results of computer simulations of the performance of amorphous silicon alloy p-i-n solar cells upon prolonged light exposure, for a range of device thicknesses for illumination through both the n+ and p+ layer. Our model realistically describes the dominant loss mechanisms in these devices, which are shown to be bulk recombination. We show how an understanding of the light-induced degradation can lead to designing cells with improved stability by suitable modifications to the optical absorption characteristics of the intrinsic layer near to where light enters the device. Finally, by relating defect creation to the minority-carrier diffusion length, we have calculated solar cell performance versus time in the absence of annealing for a range of device thicknesses for global AM1.5 illumination through both the n+ and p+ layers.
Reply to ‘‘Comment on ‘Recent results on hydrogen passivation of silicon sheet solar cells’ ’’ [J. Appl. Phys. 5
7, 5523 (1985)]
Authors: Tsuo Y. Simon , Milstein Joseph B.
Published: July 2002

We discuss the differences between essentially single-crystal dendritic web and polycrystalline edge-defined film-fed growth (EFG) silicon ribbons. We conclude that a single mechanism does not adequately explain the hydrogen passivation data for these two cases.
Al-Ti and Al-Ti-Si thin alloy films
Authors: Dirks Albertus G. , Tien Tien , Towner Janet M.
Published: July 2002

The microstructure and properties of thin films depend strongly upon the alloy composition. A study was made of the metallurgical aspects of homogeneous Al alloy films, particularly the binary Al-Ti and the ternary Al-Ti-Si systems. The films were deposited by either multiple source e−-beam evaporation or magnetron sputtering from alloy targets. Electrical resistivity, ultramicrohardness, grain size morphology, second phase formation, and electromigration have been studied as a function of the alloy composition and its heat treatment. The relationship between the microstructure and these properties will be discussed.
III-V compound thin layer characterization by a chemical bevel angle Auger technique
Authors: Bresse J. F.
Published: July 2002

A method for characterization of III-V compound microstructures by line scan Auger measurements using chemical beveling is presented. A theoretical model is developed to obtain layer thickness, interface width, and apparent atomic concentrations from experimental profiles. Interface widths less than 2 nm have been measured by this method for an InP/In0.73Ga0.27As0.62P0.38/InP structure, significantly lower than the reported value using the sputter Auger depth profiling. The thickness of the quaternary layer (in the 5–10 nm range) has been measured with a 10% accuracy.
Transient diffusion doping in Si
Authors: Davies D. Eirug , Ludington C. E.
Published: July 2002

Short-term diffusion cycles ∼10 s are shown to be suitable for shallow junction formation in silicon. Phosphorus diffused from a surface film source can produce shallow 1000–2000 Å layers that have surface doping ≳1020 cm−3. No diffusion enhancement, such as is often associated with similar cycle implantation annealing, has been encountered and layer depths follow the customary square root of time dependence.
Calculation of the infrared reflection spectra of inhomogeneously doped silicon semiconductor layers at an arbitrary angle of incidence
Authors: Hild Erzsébet , Evans Myron Wyn
Published: July 2002

A method is developed, based on the optical admittance, to calculate reflectance and transmittance at arbitrary angle of incidence of stratified media with arbitrary refractive index profiles. For n-type silicon samples, calculated and measured IR spectra are shown. In the case of a lightly doped epitaxial layer on heavily doped substrate, measurement in π polarization at the Brewster angle of the layer produces a spectrum which is free of the interference waves due to the layer and gives direct information about the profile beneath the layer. Such spectra could be used for the characterization of the transition layer between the epitaxial layer and the substrate.
Activation of free-charge carriers in Be-implanted GaAs annealed at low temperatures
Authors: Liou L. L. , Spitzer W. G. , Fredrickson J. E. , Kwun Sook-Il
Published: July 2002

Free-charge carriers in both room- and low-temperature Be-implanted GaAs were generated by annealing at 400, 450, and 475 °C and were observed by using both infrared reflection and electrical measurements. Annealing at 400 °C for 2 h removes homogeneously most of the damage-related changes in the refractive index. Longer annealing (∼50 h) or shorter term annealing at higher temperature produces free carriers. A computer model including plasma effects was used to fit the reflection curves. In general the infrared analysis results and the electric data were in reasonable agreement. Results for the room-temperature-implanted samples show the free-carrier density profile, approximated by joined half-Gaussians, to be (i) a standard deviation for the deeper half-Gaussian (σh≤0.1 μm), which is about the same or smaller than that observed by secondary ion mass spectrometry measurements (∼0.13 μm) for the Be profile, and (ii) a peak position 1.2 μm, which is deeper than the Be ion peak at 0.95 μm. Both peak positions remain essentially unchanged during the anneals. Activation of carriers at these low temperatures is not seen in either Si- or Zn-implanted GaAs. The Zn-implanted material has a weak effect at 500 °C, while the Si-implanted material has none up to 550 °C. The free-carrier profile is considered as the combination of the concentration distributions of dopant ions, Ga vacancies, and possible compensating damage-related states. The discussion centers on the detailed results for the Be case.
Ar ion laser-assisted chemical etching of molybdenum foils in air
Authors: Koren G.
Published: July 2002

Ar ion laser-assisted chemical etching of Mo foils in air is reported. Etching occurred due to local heating by the focused laser beam which induced the Mo oxidation to form the volatile MoO3 at the elevated sample temperature. Holes and slots with slightly tapered walls and a minimum hole diameter of less than 10 μm could be etched in 25-, 50-, and 150-μm-thick foils. The hole diameters increased with increasing laser power and at any given laser power they decreased with increasing sample thickness. Etch-rate measurements as a function of the laser power were performed with static and scanned samples. Threshold powers for etching through the Mo foils were found. They increased with increasing sample thickness. Above these thresholds the etch rates increased rapidly with increasing laser power and rates as high as dz/dt=50 μm/s in the static mode and dV/dt=20×50×300 μm3/s in the scanning mode were obtained in a 50-μm-thick Mo foil under 10-W laser irradiation. Average sample temperatures as functions of the laser power in the scanning mode of operation where thermal equilibrium exists were measured by the use of optical pyrometry. A model which relates the laser power to the etch rate and temperature of the sample is presented and tested for agreement with the experimental results.
An analysis of majority-carrier three-layer bulk semiconductor unipolar diodes
Authors: Chilana G. S. , Gupta R. S. , Srivastava G. P.
Published: July 2002

Bulk unipolar diodes are majority-carrier three-layer (n-p-n) semiconductor diodes in which the current flows due to the thermionic emission of majority carriers over a barrier formed in the bulk of the material. Expressions for the barrier height of two typical bulk unipolar diodes, namely a bulk barrier diode (n++p+n) and a p-plane barrier diode (n+p++n), are derived. The functional dependence of the barrier height on various technological parameters is discussed. The two diodes are quite similar in their structure and characteristics. However, the p-plane barrier diode is more suitable as a majority-carrier diode. The variation of ideality factor and the saturation current of these diodes is shown to be very similar to the metal semiconductor diode.
Preparation and electrical properties of polymeric copper phthalocyanine thin films by plasma polymerization
Authors: Osada Yoshihito , Mizumoto Akira
Published: July 2002

Polymeric copper phthalocyanine (CuPc) thin films (600–3000 Å thick) were prepared for the first time by glow-discharge plasma polymerization. The film largely maintained the original structure of CuPc. The films obtained were interposed between aluminum and ITO electrodes (Al/polymeric CuPc/ITO) and the electrical properties of the sandwich cells have been studied. These cells were found to exhibit good rectification, photovoltaic, photoreduction, and electrochromic characteristics.
Variation of the nucleated products in ultrathin films of Ti-Co on Si substrates with processing changes
Authors: Yang Hwa-yueh , Bene R. W.
Published: July 2002

The purpose of this study is to investigate solid-state nucleation and growth in Ti/Co/Si and Co/Ti/Si thin-film ternary systems, and to compare results under a variety of preparation conditions. The deposition methods used were rf sputtering and e-beam evaporation. The nucleated compounds are determined by transmission electron microscopy and diffraction. CoTi2 is the first nucleated compound in the Ti/Co/Si ternary systems prepared by e-beam evaporation irrespective of substrate temperature, thickness, or other factors. This is in contrast to the films produced by rf sputtering where this phase was not observed. Experimental findings also show that in thin-film ternary systems, the first-phase nucleation temperature and subsequent compounds could be altered as the intermediate metal layer becomes less than 20 Å. This is an indication that interference between interfaces begins to play a significant role at about this thickness, so that the reaction paths and the first nucleated phases are determined not only by internal binary kinetics, but also by intermediate transition metal layer restrictions in the interfacial region. In addition, a phase previously reported on Ti/Si system was also found in the Ti/Co/Si and Co/Ti/Si systems, and is labeled the (TiSi)N (metastable) phase. This phase occurs in the form of coherent precipitates of a nonequilibrium metastable structure.
A theoretical model of a photoelectrochemical solar cell
Authors: Chandra S. , Singh S. L. , Khare Neeraj
Published: July 2002

A Schottky barrier theoretical model for explaining the J-V characteristic of a photoelectrochemical solar cell (PESC) has been developed considering the effect of dark current, space-charge recombination, surface states, and detailed charge transfer kinetics at the interface. Both isoenergetic charge transfer and inelastic charge transfers (via surface states) at the interface have been considered and their relative importance are discussed. The theory has been applied to explain the (a) J-V characteristic for n-GaAs/Se2−, Se2−2 junction and (b) Fermi-level pinning observed in GaAs PESC. The inelastic charge transfer via surfaces states has been shown to play an important role in deciding these characteristics.
Photoluminescence study of interface defects in high-quality GaAs-GaAlAs superlattices
Authors: Deveaud B. , Regreny A. , Emery J-Y. , Chomette A.
Published: July 2002

Using luminescence and luminescence excitation spectroscopy, we have studied a series of very high-quality molecular beam epitaxy grown multiple quantum well and superlattice structures. Reduction of the linewidth and appearance of a splitting of the exciton peaks is observed when the growth process is optimized. This behavior is explained by the enlargement of the growth islands at the GaAs/GaAlAs interfaces. The splitting, observed both in luminescence and in luminescence excitation, is explained by the occurrence of very large, only one monolayer high, interface growth defects. Introduction of larger wells in our structures (+3a/2 or +5a/2) brings a clear confirmation of this attribution. The observed splittings are in good agreement with calculated values.
On the motion of dust particles in a gas
Authors: Simons S.
Published: July 2002

It is pointed out that the use of the usual equations relating to particle motion in a gas in the presence of diffusion and drift can lead to certain paradoxes. Modified equations are derived which resolve these paradoxes and which (among other things) lead to a modification in the form of the equilibrium distribution for particles in a gravitational field. This modification becomes of importance when the particle sedimentation velocity approaches its thermal velocity.
Anisotropic optical scatter from moisture patches in thin films deposited obliquely
Authors: Gledhill R. F. , Hodgkinson I. J. , Wilson P. W.
Published: July 2002

Moisture adsorption patches in magnesium-fluoride spacer layers of metal-dielectric-metal interference filters deposited obliquely are known to possess elliptical symmetry. The spatial distribution of light scattered from these patches at normal incidence is shown to exhibit the same elliptical symmetry with the major and minor axes interchanged.
Third harmonic generation of p-polarized laser radiation in an inhomogeneous laser-produced plasma
Authors: Salimullah Md. , Amin Md. Ruhul
Published: July 2002

In this paper, we have made a theoretical investigation of third harmonic generation from intense p-polarized laser radiation in an inhomogeneous laser-produced plasma. The fluid equations have been employed to obtain the nonlinear response of the plasma electrons. The power conversion efficiency of the generated third harmonic wave depends drastically on the scale length of the plasma inhomogeneity and the angle of incidence of the laser radiation with the density gradient of the plasma.
Contribution of small dislocation loops to the precursor decay of a longitudinal plane pulse
Authors: Duan Z. P. , Markenscoff X. , Ni L.
Published: July 2002

The precursor decay relation in plate impact experiments by a longitudinal wave is studied on the basis of the elastodynamics of dislocations. The material is modeled as an elastic continuum containing a distribution of dislocation loops. The waves radiated from the dislocations as they are hit by the incident wave result in the decay of the latter at the wave front. The response of the instruments is considered finite, so that the decay is calculated at a time Δt behind the front. The loops are assumed small, i.e., of radius α0∼0 (c1Δt) so that the wavelets emanated from the whole loop have the time to contribute to the decay. The loops are assumed to lie on a plane which makes an angle with the direction of propagation of the incident front and they are set in motion of uniform radial expansion by the incident front. The fundamental solution from each loop is obtained asymptotically and the precursor decay is obtained by superposition of all the loops that had the time to contribute. The obtained precursor decay relation is a modified Orowan’s relation since it is of the same form as that obtained by using Orowan’s formula but with a correction factor which depends on the dislocation velocity and configuration (curvature and orientation).
Nonlinear optical studies and CO2 laser-induced melting of Zn-doped GaAs
Authors: James R. B. , Christie W. H. , Eby R. E. , Mills B. E. , Darken L. S.
Published: July 2002

The absorption of CO2 laser radiation in p-type GaAs is dominated by direct free-hole transitions between states in the heavy- and light-hole bands. For laser intensities on the order of 10 MW/cm2, we report that the absorption associated with these transitions in moderately Zn-doped GaAs (∼1017 cm−3) begins to saturate in a manner predicted by an inhomogeneously broadened two-level model. At higher laser intensities surface melting occurs initially at localized sites in moderately doped material and more uniformly in heavily Zn-doped samples (≳1018 cm−3). As the energy density of the CO2 laser radiation is progressively increased further, the surface topography of the samples shows signs of ripple patterns, high local stress, vaporization of material, and exfoliation of solid GaAs fragments. Electron-induced x-ray emission data taken on the laser-melted samples show that there is a loss of As, compared to Ga, from the surface during the high-temperature cycling. By irradiating the samples in air, argon, and vacuum, we find that the vaporization rates are directly influenced by the ambient environment, particularly by the interaction of oxygen with the molten GaAs. Secondary ion mass spectrometry measurements are used to study the diffusion of oxygen from the native oxide and the incorporation of oxygen in the near-surface region of the GaAs samples that have been melted by a CO2 laser pulse. We find that oxygen incorporation does occur, and that the amount and depth of the oxygen incorporation depends on the laser energy density, number of laser shots, and ambient environment. For samples that are irradiated in argon or vacuum, we find that removal of the native oxide can be accomplished with CO2 laser pulses. Similar measurements are performed on Si-implanted GaAs, and results are reported for the redistribution of the implanted silicon atoms, the deviations from stoichiometry, and the incorporation of oxygen in the resolidified layer.
Highly conductive poly(phenylene sulfide) prepared by high-energy ion irradiation
Authors: Bartko John , Hall Barbara O. , Schoch Karl F.
Published: July 2002

Ion irradiation of poly(phenylene sulfide) (PPS) films with various ions produces highly conductive films. Using 5.6-MeV fluorine ions, the conductivity of irradiated films at a dose of 1×1016 ions/cm2 is comparable to chemically doped films (0.77 S/cm), and higher conductivities should be possible with higher doses. Iodine ions of 50 MeV produced films with similar conductivities at a dose of 1×1014 ions/cm2: the highest conductivity reported for an organic material irradiated by such a low dose. Films irradiated with 0.32-MeV lithium ions did not change their conductivity up to 1×1015 ions/cm2. We attribute the higher conductivities obtained in our iodine irradiated films to the substantially higher electronic energy deposition associated with 50-MeV I ions. The Li-implanted films showed no substantial change in conductivity probably because their energy deposition rates are too low.
Suppression of higher-order thickness modes in magnetostatic forward volume wave delay lines
Authors: Bajpai S. N.
Published: July 2002

This paper presents a theoretical study of suppression of undesired higher-order thickness modes excited in magnetostatic forward volume delay lines. This can be done by using the exciting and receiving transducers deposited directly on the top of an yttrium iron garnet film. Though this geometry has been used before, this paper describes more detailed investigation. Numerical results obtained are quite useful and encouraging. The magnetostatic volume wave delay lines have potential applications in microwave signal processing with larger operating bandwidth directly at microwave frequencies.
Amorphous and crystalline properties of thin films of NdFe(B)
Authors: Gasgnier M. , Colliex C. , Manoubi T.
Published: July 2002

NdFe(B) thin films are deposited onto glass substrates by means of a tungsten crucible. The as-deposited films are studied by the Lorentz microscopy method in order to observe the different magnetic domains. STEM analysis (EELS method) permits us to obtain the characteristic absorption edges of Fe and Nd (but not of boron). The crystallization behavior, inside the electron microscope, by means of the electron beam, allows us to observe the formation of the α-Fe, A-Nd2O3, and NdFeO3 phases. The different stages of appearances of these structures are discussed.
Magnetic and magneto-optic properties of amorphous Gd-FeAu films
Authors: Hansen P. , Hartmann M.
Published: July 2002

Amorphous rare-earth transition metal alloys of composition (Gd1−xFex)1−yAuy with x=0.74, 0.77, and 0≤y≤0.40 were prepared by evaporation onto rotating glass substrates. The magnetic and magneto-optic properties have been investigated in the temperature range 4.2≤T≤TC revealing a decrease of the compensation and Curie temperature, the uniaxial anisotropy, and the Faraday and Kerr rotation with increasing gold content. The temperature behavior can be interpreted in terms of a mean-field analysis indicating a pronounced influence of the gold on the iron moment and the exchange constants. The temperature dependence of the Faraday rotation can be described in terms of the sublattice magnetizations inferred from the fit of the mean-field theory to the measured saturation magnetization.