bluuebunny/crossref_metadata_2025 huggingface dataset:
Special Purpose Processors for Computing Materials Properties
Authors: Bakker A. F.
Published: March 2011

The need for computational power in the modeling of physical systems is rapidly increasing. Realistic simulations of materials often require complex interactions and large numbers of particles. For most scientists, full-time access to supercomputers is not possible, and even this might not be sufficient to solve their problems. As most of the calculations involved are straightforward and repetitive in nature, a possible solution is to design and build a processor for a specific application with a low cost/performance ratio. This approach is to be contrasted with the use of a general purpose computer, which is designed to treat a large class of problems and includes many expensive features (e.g. software) that are not utilized in the simulations. The architecture of a special purpose computer can be tailored to the problem; e.g., parallel and pipelined operations can be incorporated to obtain efficient computational throughput, and memory organization and instruction sets can be optimized for this purpose. A few of such algorithm oriented processors have been built in the last decade and have been utilized for certain specific jobs; for example: molecular dynamics simulations of systems of Lennard-Jones particles and Monte Carlo calculations of Ising models. An overview of some existing algorithm oriented processors and expectations for the future will be presented.
The Study of Surface Phonons by Electron Energy Loss Spectroscopy: Theory of the Excitation Cross Section
Authors: Mills D. L.
Published: March 2011

In the past few years, experimental developments in electron energy loss spectroscopy have allowed study of the dispersion relations of surface phonons, on clean and adsorbate covered surfaces. Also, theoretical analyses of the angle and energy variation of the excitation cross sections have been developed. These have guided the choice of scattering geometry, and also have assisted directly in the interpretation of the data. We review the recent work, with emphasis on the theoretical side.
Computer Simulation of Electron Microscope Images from Atomic Structure Models
Authors: Krakow William
Published: March 2011

It is generally the case that simple direct interpretation of high resolution electron microscope images is not possible due to the phase contrast imaging modes necessary to achieve atomic level spatial resolution. Therefore, an extensive number of computer programs have been developed to perform electron diffraction and image computations. Both single scattering or dynamical scattering processes can be simulated as well as any form of imaging mode currently available on most modern high performance transmission electron microscopes. Since one is interested in imperfections rather than perfect crystal structures, a large number of sampling points in real and reciprocal space are required. Often, large atom position arrays must be sampled requiring large mainframe computer memories and fast CPU's. High quality displays are also required for realistic image representations and even faster computational methods via television rate digital frame store devices. This paper will be centered about a number of materials areas requiring high resolution electron microscopy computer simulation from atomic structure models. These areas include: organometallic molecules, point defects, surface structure and reconstructions, amorphous thin films, quasi-crystals, semiconductor interfaces and grain boundary structure in metals.
Rate-Sensitivity of Mode I and Mode II Fracture of Concrete
Authors: Shah Surendra P. , John Reji
Published: March 2011

For rational and accurate analysis of concrete structures subjected to impact or impulsive loads the knowledge of crack propagation under such dynamic loads is essential. Cracks frequently propagate under mixed-mode (opening and sliding: mode I and mode II) conditions. The rate of loading effects on the mechanical properties have been attributed to the rate sensitivity of crack propagation. The strain-rate effects may be different in mode I and mode II fracture of concrete. Single edge notched beams were subjected to varying rates of loading, to establish the mode I Stress Intensity Factor, KIvs. Crack Velocity, V, relationship for mortar and concrete. Impact tests were conducted using a Modified Instrumented Charpy Impact Test System. The rate of crack growth was obtained using brittle ‘Krak Gages'.

Mode I test results lead to the following conclusions. (1) Slow (prepeak) crack growth for concrete is larger than that of mortar, at a given strain rate. (2) Pre-peak crack growth decreases with increase in strain-rate. This could be the reason for decrease in pre-peak non-linearity at higher strain rates. Hence LEFM approach may be valid at high rates of loading. (3) log KI- log V relationship is non-linear especially at the higher rates of loading.
Influence of the Crack Opening Rate on the Fracture Toughness of Plain Concrete
Authors: Rossi P. , Boulay C. , Acker P. , Malier Y.
Published: March 2011

Three D.C.B. tests (Double Cantilever Beam) under different loading histories have shown that the applied crack opening rates can have an effect on the KIC fracture toughness values computed on the basis of linear elastic behavior of concrete. This assumption can be well justified for a certain range of crack opening rates, outside of which viscous phenomena must be taken in account. The concepts of ductile and brittle fracture appear then as related to the crack opening rate.
Characterisation of Fly Ash Hydration Reactions from Microstructure
Authors: Mills R. H.
Published: March 2011

Reaction products of high lime fly ash (FA), mixed with distilled water and hydrated in contact with Portland cement (PC), and in hardened PC/FA pastes of various mix proportions, were examined by SEM and EDX. Structures contributing to early strength originated mainly through solution depositions of ettringite, and portlandite. Some evidence of ettringite instability suggested gypsum deficiency in PC/FA mixtures.
Modeling of Fly Ash Concrete Mixtures
Authors: White Elizabeth L. , Roy Della M.
Published: March 2011

A Factor Analysis Model was applied to existing literature data on fly ash and cement properties to relate them to the strength and durability of the cured pozzolanic concrete products. A normal curve was fitted to each independent fly ash and cement property and to each dependent strength property. Functions of the moments, such as indicators of skewness and kurtosis of each property, were calculated and the significance of their departures from the expected values of a normal population was examined. About one-half of the properties were log-normally distributed; the remainder were normally distributed as given. A predictive model was proposed for compressive strength, using the percent sulfate as representative of Factor I, the cement quantity as representative of Factor II, and the percent Fe2O3 as representative of Factor III.
Short and Long-Term Leaching Behavior of a Low-Calcium Fly Ash and Cement-Stabilized Fly Ash
Authors: Malek R. I. A. , Licastro P. H. , Roy D. M.
Published: March 2011

Low-calcium fly ashes from eastern Pennsylvania power plants, stabilized with Portland cement, have a potential application as a pipeline bedding material. A typical fly ash, and a cement-stabilized material made with this fly ash, were subjected to extensive physical and chemical characterization. Two procedures were used to investigate whether leachates from the bedding materials were nonhazardous according to the criteria of the regulatory agencies. The first was the short-term EPA test, used to define a hazardous waste under the RCRA regulations, and the second was a long-term flow-through test developed at MRL/PSU. In the second test, driving pressure, flow rate and permeability were monitored during the experiment. Calculations showed that this flow-through technique simulates rain water percolation in a similar sized bed for about 25 years. The leaching fluids in both methods were deionized water (EPA procedure) and simulated rain water. Analyses for seventeen metals by DC plasma emission spectrometry and for seven anions by ion chromatography were performed. Concentrations of the leachates from the two procedures were well below the levels that define a hazardous waste. Considerable insight into the long term leaching mechanisms of various elements was obtained from the flow-through experiments.
Heteroepitaxy of Si, Ge, and GaAs Films on CaF2/Si Structures
Authors: Ishiwara H. , Asano T. , Lee H. C. , Kuriyama Y. , Seki K. , Furukawa S.
Published: March 2011

Recent progress in the research of heteroepitaxial growth of Si, Ge, and GaAs films on CaF2/Si structures is reviewed. Growth conditions and material properties of the Si/CaF2/Si structures are first discussed. It is shown that such growth techniques as the predeposition technique and the recrystallization method are useful to improve the crystalline quality of Si films on the CaF2/Si structures. Then, device application of the Si/CaF2/Si structure to field effect transistors with epitaxial MIS (metal-insulatorsemiconductor) gate electrodes is described. Finally, epitaxial growth of Ge and GaAs films on the CaF2/Si structure are discussed, in which such growth parameters as the substrate temperature and growth rate are optimized to obtain high-quality films with excellent crystallinity and smooth surface.
Electrical Properties and Structural Defects in Epitaxial CaF2 on Si
Authors: Schowalter L. J. , Fathauer R. W. , Ponce F. A. , Anderson G. , Hashimoto Shin
Published: March 2011

In this paper, a study is made of the electrical properties and of the types of structual defects which can occur in epitaxial CaF2 grown on Si(111) substrates by molecular beam epitaxy (MBE). High-resolution transmission electron microscopy (HRTEM) and high-energy (≥2 MeV) He+ ion channeling techniques are used to characterize defects in the epitaxial layer and at the CaF2 /Si interface while current-voltage (I–V) and capacitance-voltage (C–V)3 measurements are used to characterize the electrical properties. The HRTEM images show an atomically abrupt interface between the CaF2 and Si. The most common defect we have been able to identify is associated with an atomic step at the interface and is similar to a Shockley partial dislocation at a (111) twin interface in an fcc crystal structure. The ion channeling measurements also indicate the presence of defects at the CaF2 /Si interface. The apparent defect density measured by ion channeling decreases in the CaF layer as one moves away from the interface at a rate which depends on ihe final thickness of the epitaxial film. Ion channeling has also been used to measure strain and it is found that, while thin layers of epitaxial CaF2 on Si(111) have large strain, the strain becomes vanishingly small as the layers exceed 200 nm in thickness. This result can be adequately explained using an equilibrium model for the introduction of strain relieving misfit dislocations and indicates that epitaxial fluoride layers may be useful as thermal mismatch buffers in heteroepitaxial structures. In C–V measurements of epitaxial CaF2 layers on Si(111) which have been fabricated into metal-insulator-semiconductor structures, the capacitance is observed to remain constant over a large variation in applied voltage. This constant capacitance region can be explained as due to a high density of interface states in the band gap. In addition, I–V measurements indicate that, at low fields, the CaF2 resistivity exceeds 1014 Ω-cm. At high fields, the CaF2 starts to conduct in a manner which we speculate is due to defects at the CaF2/Si interface. The field at which this conduction takes place has been ovserved to exceed 1 MV/cm for a 42-nm-thick CaF2 film with the device geometry used for this work.
MOCVD Growth of III-V Compounds on Si Using Strained Superlattices
Authors: Sakai Shiro , Soga Tetsuo , Takeyasu Masanari , Umeno Masayoshi
Published: March 2011

GaAs and GaAsP with the entire compositional range are grow on Si using an intermediate layer of GaAsP strained superlattices to relax the lattice mismatch. The orientation of the overgrown GaAs layer is found to be determined by the direction of the off-angle of the Si (100) surface. The grown layers are characterized by photoluminescence, x-ray diffraction, electro reflectance and DLTS. GaAs/GaAlAs double heterostructure lasers and GaAsP visible LED's are fabricated on Si substrates. The structural and electronic properties of the grown layers and the device performances are reported in this paper.
GaAs/AlGaAs Diode Lasers on Monolithic GaAs/Si Substrates
Authors: Windhorn T. H. , Turner G. W. , Metze G. M.
Published: March 2011

One approach to the development of optical interconnects between Si systems utilizes diode lasers fabricated in III-V epitaxial layers grown on Si wafers. We have fabricated double-heterostructure lasers in GaAs/AlGaAs layers grown on a Ge-coated Si substrate, and both asymmetric largeoptical- cavity (LOC) lasers and graded-index, separate-confinement heterostructure (GRIN-SCH) lasers in such layers grown directly on a Si substrate. The GaAs/AlGaAs layers were grown by molecular beam epitaxy on (100) p-Si substrates. Si and Be were used as the n- and p-type dopants, respectively. Oxide-defined stripe-geometry devices, 300 μm long, were fabricated using standard AuSn and CrAu metallizations for the n- and ptype contacts, respectively. The laser facets were formed by ion-beamassisted etching. The double-heterostructure devices (8 μm stripe width), in which the active region contained about 10 mole percent AlAs, were evaluated using pulsed bias at 77 K. They produced power outputs up to 3.3 mW per facet and exhibited thresholds as low as 170 mA. The LOC devices (4 μm stripe width), which had a GaAs active region, were characterized using pulsed bias at 300 K. These devices produced power outputs up to 27 mW per facet. The lowest threshold was 775 mA. The GRIN-SCH devices (4 μm stripe width), which incorporated a 70 Å GaAs quantum well active layer, were also characterized using pulsed bias at 300 K. These devices were not operated at power outputs above −5 mW. Their lowest threshold was 220 mA.
Epitaxial Crystallization of Ge on Si Using Evaporation and Recrystallization Techniques
Authors: Lee El Hang , Awal M. Abdul , Celler G. K. , Pfeiffer L. , Sheng T. T.
Published: March 2011

Germanium films have been epitaxially crystallized on silicon substrates using the electron-beam evaporation technique and the laser! strip-heater recrystallization technique. Epitaxy was achieved either directly on Si surfaces or laterally on oxide/nitride-coated Si wafers. Evaporated Ge epi-layers were mirror-smooth and were found to be in excellent crystal quality. The recrystallized Ge on Si were also found to be good crystal, but showed somewhat roughened surface morphology. In both cases, the Ge near the Ge/Si interface is heavily replete with misfit dislocations arising from 4% lattice mismatch between Ge and Si. The recrystallized Ge on insulator (GOI) showed no mismatch dislocations at the Ge/insulator interface but developed voids arising from Ge dewetting from the insulator surface. Twins have been observed to be the most prominent defects in recrystallized Ge, whether seeded or unseeded. The objective of this study is to achieve quality Ge layers that can be used as intermediate template to accomodate GaAs on Si.
Initial Stages of Epitaxial Growth of GaAs on (100) Silicon
Authors: Biegelsen D. K. , Ponce F. A. , Smith A. J. , Tramontana J. C.
Published: March 2011

Direct observations of early stages of growth of GaAs on (100)Si are presented. Cross sectional TEM and plan view SEM images show three dimensional island growth, for growth above 300°C. Island size, island spacing, surface morphology and stacking fault defect spacing all decrease with substrate temperaturefor fixed Ga and As2 fluxes. Below 300C, 7nm thick films are uniform. Diffusion-controlled growth kinetics are inferred.
Observation of GaAs/Si Epitaxial Interfaces by Atomic Resolution Electron Microscopy
Authors: Otsuka N. , Choi C. , Nakamura Y. , Nagakura S. , Fischer R. , Peng C. K. , Morkoc H.
Published: March 2011

Recent studies have shown that high quality GaAs films can be grown by MBE on Si substrates whose surfaces are slightly tilted from the (100) plane. In order to investigate the effect of the tilting of substrate surfaces on the formation of threading dislocations, the GaAs/Si epitaxial interfaces have been observed with a 1 MB ultra-high vacuum, high voltage electron microscope. Two types of misfit dislocations, one with Burgers vectors parallel to the interface and the other with Burgers vectors inclined from the interface, were found in these epitaxial interfaces. The observation of crosssectional samples perpendicular to each other has shown that the tilting of the substrate surface directly influences the generation of these two types of misfit dislocations. The mechanism of the reduction of threading dislocations by the tilting of the substrate surface is discussed based on these observations.
Preferential Sputtering Effects in Elemental Depth Profiling of Tellurium-Based Alloy Thin Films
Authors: Ross R. C. , Jones G. L. , Chao S. S. , deNeufville J. P. , Bjornard E. J. , Tyler J. E.
Published: March 2011

The compositions of sputtered amorphous thin films of Se50Te50, Ge50Te50, and (Te90Ge5 In5)100-x 0 x=0-25 have been measured by electron microprobe x-ray analyzer (EMP) and Auger electron spectroscopy (AES) with sputter depth profiling. Preferential removal of certain elements from the surface region during sputtering is shown to significantly alter the AES-determined surface composition. The effects of sputtering ion mass (He1, Ar1, Xe1), Ar+ energy (1.5 and 4.0 keV), and target temperature (-100 and 25°C) were investigated. The degree of preferential sputtering is found to be controlled predominantly by differences in surface binding energy of the elements with secondary contributions in the case of 0 due to bombarding atom to target atom collisional energy transfer processes.
Strain Effects on Sensitization Development in 304 Stainless Steel as Measured by EPR and Stem/Eds Methods
Authors: Charlot L. A. , Arey B. W. , Bruemmer S. M.
Published: March 2011

The effect of uniaxial straining during isothermal heat treatment of a Type 304 stainless alloy has been examined using scanning transmission electron microscopy/energy dispersive x-ray spectroscopy (STEM/EDS) and electrochemical potentiokinetic reactivation (EPR) methods. Solution-annealed, flat tensile specimens were deformed at 600°C at various strain rates up to 6%/h. EPR and STEM/EDS results show an acceleration in sensitization development with increasing deformation. STEM/EDS measurement suggest that simultaneous straining affects both the kinetics of sensitization and the chromium concentrations established at grain boundaries.
Charge Collection Microscopy of Single Crystal and Polycrystalline GaAs
Authors: Paz O. , Borrego J. M.
Published: March 2011

This study demonstrates a new technique of measuring transport properties of minority carriers by varying the generation rate of the electron-beam induced carriers and measuring the amount of collected charge per incident electron. The technique is suitable. for measurements of very short diffusion length in bulk GaAs material and for measurements in polycrystalline, CVD grown GaAs layers containing grains that are smaller than the diffusion length.

The diffusion length in single crystal GaAs measured at several values of electron-beam energy was.32μm. For l-2μm polycrystalline grains it was found that the diffusion length in the bulk of the. grain can remain high (8μm) but high recombination levels (up to 2 × 106 cm sec−1) prevail at the grain boundaries.
Fourier Transform Photoluminescence Analysis of Trace Impurities and Defects in Silicon
Authors: Duncan W. M. , Eastwood M. L. , Tsai H-L.
Published: March 2011

In this paper we describe Fourier transform Photoluminescence (FTPL) spectroscopy and report the first application of this technique to the analysis of semiconductor silicon. Two applications of FTPL spectroscopy to silicon are discussed. The first application is to quantitative trace analysis of the Ill-V impurities B,P, As and Al in silicon. Both high purity and compensated silicon have been studied and PL features correlated to the concentrations of the individual impurity species present. The capability of analysing B, P, As and Al at part per trillion atomic concentrations in silicon is demonstrated. In the second part of this paper, application of FTPL to the analysis of thermally induced microdefects in silicon is discussed. Defect band intensities are shown to be proportional to the concentration of interstitial oxygen precipitated in the case of plate precipitate morphology. In these two applications, FTPL is shown to uniquely provide both residual impurity and microdefect information of as grown and processed silicon.
Super Sims for Ultrasensitive Impurity Analysis
Authors: Anthony J. M. , Donahue D. J. , Jull A. J. T.
Published: March 2011

The technique of accelerator mass spectrometry has been used extensively in recent years as a method for detecting low levels (< 1 part per trillion atomic) of radioactive isotopes in solid materials. The technique consists of a Secondary Ion Mass Spectrometer (SIMS) system in which the conventional mass spectrometer has been replaced by a particle accelerator. We have applied this method to the study of stable elements, primarily semiconductor dopants, using the Univ. of Arizona tandem accelerator mass spectrometer. The use of tandem accelerators allows molecular interferences to be removed due to dissociation of the molecules. Particle energies of several MeV are produced, and energy spectroscopy removes the background due to scattered particles, detector noise, etc. to provide positive particle identification. The current detection limits (-10 parts per billion atomic) are primarily due to ion source contamination and their origin is discussed. Removal of this contamination will allow parts per trillion level detection of stable elements.
Optical Current DLTS with a Bipolar Rectangular Weighting Function for High-Resistivity Neutron Transmutation Doped Silicon
Authors: Tokuda Yutaka , Usami Akira
Published: March 2011

Defects in high-resistivity neutron transmutation doped (NTD) silicon without annealing were characterized by optical current DLTS with a bipolar rectangular weighting function using a GaAs LED. The DLTS method with a bipolar rectangular weighting function was also described. Two clear peaks labeled A and B were observed in addition to unresolved peaks due to overlaps of DLTS signals of several defects. The thermal emission activation energies of defects A and B were 0.15 and 0.50 eV, respectively. The DLTS signals of these defects were broader than the calculated ones. This indicates the clustered nature of defects produced by fast neutron irradiation. However, the fact that the characteristic peaks were observed suggests that the material state of high-resistivity NTD silicon is crystalline but not amorphous.
Materials Analysis with X-Ray Rocking Curves
Authors: Paine Bruce M.
Published: March 2011

We review the technique of x-ray double crystal diffractometry as applied to measurement of microscopic profiles of strain in semiconductor materials. The first step in this technique is the extraction of average strains and layer thicknesses directly from the x-ray rocking curves. Profiles of strains with depth are then found by iterative fitting of the experimental rocking curves with trial distributions, incorporated into a theoretical model for the diffraction. The kinematic approximation is accurate for thicknesses up to 1μm in most semiconductors. For greater thicknesses, the more precise dynamical model must be applied.
Studies of Defects and Limits of Solid Solubility in SPE Grown in and Sb Implanted Silicon
Authors: Narayan J. , Holland O. W.
Published: March 2011

Transmission electron microscopy (plan-view as well as cross-section) and high-resolution Rutherford backscattering and channeling techniques have been combined to investigate residual defects and substitutional concentrations of In and Sb in <100> and <111> orientations of ion implanted silicon layers after solid-phase-epitaxial (SPE) growth at 475–600°C. The maximum concentrations of Sb and In in substitutional sites were found to be, respectively, 1.3 × 1021 and 5.0 × 1019 cm−3 , exceeding the respective retrograde maxima by factors of 18 and 60. These results provide direct evidence of solute trapping and metastable alloying under solid-phase growth conditions. Accumulation of solute at the crystalline-amorphous interface was observed only for indium above a certain interfacial concentration. At still higher interfacial concentrations, the planar interface was observed to become unstable and SPE growth was retarded.
Structure and Properties Changes During Ion Bombardment of Crystalline Fe75B25
Authors: Berkowitz A.E. , Johnston W.G. , Mogro-Campero A. , Walter J.L. , Bakhru H.
Published: March 2011

Ribbons of Fe75B25, prepared by quenching from the melt, were mostly amorpbous. After annealing at 773 K, the ribbons were entirely crystalline, with the phases Fe3B, Fe2B and α - Fe. Annealed ribbons were bombarded at RT with 4 MeV argon ions, at a damage rate of 7 × 10−4 dpa sec−1 near the surface. The Fe3B was completely converted to an amorphous form at 0.15 dpa, the lowest damage level at which amorphization of a metal alloy has been reported. The Fe2B disappeared by about 1.5 dpa. The α -Fe disappeared between 17 and 50 dpa, apparently by ion beam mixing rather than direct amorphization. Amorphous films also were prepared by sputtering at low power level, and crystallized at 773 K, which also caused sintering. Bombardment with argon ions produced major changes in resistivity and magnetic coercive force at the same low damage levels that caused amorphization of Fe3B Hc of the bombarded film was the same as in an as-quencheo amorpous ribbon. The relatively high resistivity of as sputtered amorphous film was apparently due to the porosity in the columnar cell walls. With present technology, it should be possible to produce amorphous films or structures of Fe3B at rates approaching 50 m2 hr−1.
Mossbauer Spectroscopy Study of the Amorphization of Tellurium by Ion Implantation
Authors: Langouche G. , Dezsi I. , Van Rossum M. , De Potter M. , De Bruyn J. , Schroyen D. , Coussement R.
Published: March 2011

125Te was implanted into Te single crystals, held at different temperatures, and studied by Mössbauer Spectroscopy. It is shown that amorphization of the target occurs during implantation at liquid nitrogen temperature. The role of the target temperature in the Naguib and Kelly criterion for amorphization is discussed.
Transmission Electron Microscopy and Resistivity Measurements on Pd1−x Six Alloys Prepared by Ion Implantation.
Authors: Traverse A. , Ruault M.O. , Mendoza-Zelis L. , Schack M. , Bernas H. , Chaumont J. , Dumoulin L.
Published: March 2011

After 6K implantation of Si in Pd films, resistivity measurements (previously reported (1)) had provided preliminary evidence that an amorphous state had been reached for a composition Pd.80 SiO 20· This result has been recently confirmed by transmission electron microscopy (TEM) observations : diffuse diffraction rings appear in the implanted part of the Pd film. New experiments are reported : - resistivity dose dependence (and temperature dependence) of a 300K Si implanted Pd film ; - in situ TEM experiments to follow the amorphization process during implantation.
Ion Mixing and Demixing in The Au-Si System
Authors: Liu Bai-Xin , Wieluński Leszek S. , Nicolet Marc-A. , Lau S. S.
Published: March 2011

After a relatively low dose Xe+ irradiation (∼ 2 × 1015 Xe/cm2), an initially discrete multilayered film of average composition Au7Si3 transforms to a uniform layer and forms a metastable phase. This is the well known ion mixing process. The same samples were subjected to higher dose irradiation (> 4 × 1015 Xe/cm2). It was found that the Si migrates to the sample surface and forms a nonuniform depth profile in BS spectra. At the same time, the metastable phase dissociates into Au and Si phases. As this process is opposite to that of ion mixing, we suggest to name this process ion demixing. These observations demonstrate that ion mixing and ion demixing can both occur in the same system, if it is properly chosen. Possible mechanism responsible for these processes are discussed.
Ion Beam Mixing of Ceramic Alloys - Preparation Andmechanical Properties
Authors: Lewis M. B. , McHargue C. J.
Published: March 2011

Techniques used to produce unique states of pure metals mixed into ceramic materials are presented. The samples were prepared by irradiating a 1-MeV Fe+ beam on A12O3 crystal surfaces over which a thin chromium or zirconium film had been evaporated. The limitations of using noble gas ion beams are noted. Micro Knoop hardness tests performed near the surfaces of the samples indicated a significant increase in the hardness of most samples prepared by ion beam mixing.
The Dangling Bond in Undoped Amorphous Hydrogenated Silicon: Trap or Recombination Center?
Authors: Parker M. A. , Conrad K. A. , Schiff E. A.
Published: March 2011

The role of the neutral dangling bond defect upon photocarrier processes in undoped amorphous hydrogenated silicon (a-Si:H) is discussed. The evidence that the dangling bond is a simple recombination center is reviewed, and it is shown that this model does not account for photocurrent response time measurements. Experimental data pertinent to the role of electrical contacts upon response time measurements are presented, and it is concluded that contact effects do not account for response-time measurements. The possibility that the dangling bond is primarily an electron trap is discussed.
Analytical Determination of Generation-Recombination Rate In Amorphous Silicon
Authors: Furlan Jože , Amon Slavko
Published: March 2011

A general expression for generation-recombination rate in a-Si based on classical SRH theory including different electron and hole capture cross-sections for donor-like and acceptor-like centers inside the mobility gap is derived. Applying appropriate approximations and two-exponential model for localized states distribution two methods of analytical solution are presented and discussed.
Increased Conductivity in P-Type Hydrogenated Amorphous Silicon
Authors: Pankove Jacques I. , Dresner Joseph
Published: March 2011

The low conductivity of B-doped a-Si:H is usually attributed to the fact that only a small fraction of the boron is tetrahedrally coordinated. In the presence of hydrogen, that small fraction can be inactivated via the acceptor-neutralization process that was described for the case of B-doped crystalline Si. When a B-doped sample of a-Si:H was annealed to drive away hydrogen near the boron atoms, the conductivity increases by a factor of 600.
Although a-Si:H can be doped either n-type or p-type, the doping efficiency is orders of magnitude poorer than in crystalline Si. In fact the doping efficiency of boron is one order of magnitude lower than that of phosphorus. Several models account for the low doping efficiency of a-Si:H, the most plausible being the location of B in a trigonal site, i.e. surrounded by three Si-atoms as shown in Fig. 1. Such a center is neutral and cannot act as an acceptor.
The present work is an offshoot of our study of the hydrogenation of dangling bonds in crystalline Si (1). The awareness that H ties to a Si dangling bond more strongly than another Si-atom led us to passivate the numerous dangling bonds on the surface a Si-crystal. Then, we passivated dangling bonds in grain boundaries and in dislocations and we showed that ion implantation damage also could be neutralized by atomic hydrogen thus removing non-radiative recombination centers and allowing the luminescent transitions to become more efficient.
Capacitance Studies of Metastable Defect Creation in Hydrogenated Amorphous Silicon
Authors: Cohen J. D. , Mahavadi K. , Zellama K. , Harbison J. P. , Delahoy A. E.
Published: March 2011

We have studied the light induced instability problem in hydrogenated amorphous silicon using junction capacitance techniques. These techniques are used to examine specific changes in the density of gap states, and occupation of gap states, for undoped a-Si:H samples after light saturation and for a series of partial anneal “states” which culminate in the original dark annealed state (state A). We find that the observed changes in the metastable occupied and unoccupied defects contradict the Si-Si bond breaking model and indicate at least two defect creation processes. In several samples we also find clear evidence that the metastable defect distribution near midgap has a slightly different energy distribution than the stable deep state (dangling bond) distribution. At the same time, these results seem to be qualitatively consistent with many aspects of recent ESR and optical absorption studies of metastable defect creation. We discuss these findings in terms of alternative possible microscopic models for metastable effects in a-Si:H.
Time Dependence of the Metastable, Optically-Induced Esr in a-Si:H
Authors: Lee C. , Ohlsen W. D. , Taylor P. C.
Published: March 2011

The occurrence of optically-induced, metastable changes in the paramagnetism in films of a-Si:H is well known. The effect was first observed with white light in powdered samples, but recent experiments with both white and monochromatic light incident on films on substrates have observed a similar effect. This optically-induced ESR appears to be stable at temperatures < 400 K. Typical inducing curves for samples with initial dark spin densities ns > 1016 spins/cm3 approach a power law behavior (ns ∼ t1 / 3) at long times. However, when the dark spin density is less than 1016 spins/cm3, the samples exhibit an inducing curve (on a log-log scale) with a continuously decreasing slope. The curve does not exhibit a unique power law behavior over an extended range of time and is at all times < t1 / 3.
Microcrystallinity in α-Si, Ge:H, F Alloys
Authors: Shen D. S. , Kolodzey J. , Slobodin D. , Conde J. P. , Lane C. , Campbell I. H. , Fauchet P. M. , Wagner S.
Published: March 2011

Microcrystalline inclusions in hydrogenated and fluorinated amorphous silicongermanium alloys, α-Si, Ge:H, F, were studied. Microcrystals grown during RF or DC glow discharge deposition from SiF4, GeF4 and H2 consist of either pure Si or Ge. Microcrystals produced by thermal annealing of initially amorphous alloys are either microcrystalline Ge or microcrystalline Si-Ge alloys depending on the annealing temperature. Values for the grain size were calculated from X-ray diffraction (XRD) and Raman spectra. The grain size of the “grown” microcrystal ranges from 8 to 60 nm. These grown grains exhibit preferential orientation of the (220) planes parallel to the substrate surface. Microcrystals produced by high-temperature anneal are randomly oriented. Scanning electron micrographs of as-grown samples show protruding platelets several 100 nm long and several 10 nm wide. Fractured cross sections exhibit columnar structure.
Deuteron Magnetic Resonance in a-Si and a-SiGe Produced from Fluorides
Authors: Bork V. P. , Fedders P. A. , Norberg R. E. , Leopold D. J. , Mackenzie K. D. , Paul W.
Published: March 2011

Deuteron magnetic resonance line shapes and spin lattice relaxation times are presented for a-Si:D, F and a-SiGe:D, F. These parameters differ from those for typical a-Si:D, H samples, but in some respects are similar to those for an annealed a-Si:D, H sample. The a-SiGe:D, F spectra display an unusually large broad central weakly bound D resonance component and a barely-resolved Ge-D quadrupolar doublet. Comparisons indicate substantial differences in void morphology between the a-Si:D, F and a-SiGe:D, F.
Characterization of a-Si:H Near a-Sinx:H/a-Si:H Interface by Photoluminescence Spectra
Authors: Yoshimura Tetsuzo , Hiranaka Kouichi , Yamaguchi Tadahisa , Yanagisawa Shintaro , Asama Kunihiko
Published: March 2011

The influence of the a-SiNx:H composition on the near-interface properties of the a-SiNx:H/a-Si:H layered structure was studied by photoluminescence measurements and the results were compared with a-Si TFT characteristics. It was found that the cw photoluminescence spectra of a-Si:H near the interface tend to shift to the low-energy side with an increase in nitrogen content of the a-SiNx:H layer. Time-resolved photoluminescence measurement revealed that the low-energy shift of the cw photoluminescence band is attributed to an enhancement of an additional broad band, which is caused by deep states, appearing in the low-energy side of the band arising from the transition between band tail electrons and holes. A decrease in field effect mobility in TFTs with an a-SiNx:H gate-insulator was observed when the nitrogen content of the a-SiNx:H increases, and correlated well with the low-energy shift of the cw photoluminescence band. These results suggest that the deep states in a-Si:H near the interface tend to increase with the nitrogen content of the a-SiNx:H. The origin of the states is believed to be a lattice strain induced in the a-Si:H layer.
Origin of Persistent Photoconductivity in Modulation Doped Amorphous Silicon Multilayers
Authors: Agarwal S. C. , Guha S.
Published: March 2011

We show that persistent photoconductivity (PPC) observed in npn … multilayers of hydrogenated amorphous silicon (a-Si:H) and compensated thin a-Si:H films have a common origin. It is caused by special centers lying in the upper half of the mobility gap. The centers are not related to the presence of argon during deposition. Similarities of PPC between the layered and compensated films are shown. We also find that PPC in compensated samples, is not entirely a surface effect. Experiments are suggested to decide whether these centers are P-B complexes or can arise from the presence of boron alone.
a-Si Basis Heterojunction Stacked Solar Cells
Authors: Hamakawa Y. , Matsumoto Y. , Zhang-Yang Xu , Okuyama M. , Takakura H. , Okamoto H.
Published: March 2011

A systematic study has been made on a-Si basis heterojunction tandem structure solar cells. Design rule and optimizations of cell parameters on two and three stacked heterojunction solar cells are discussed on various material bottom junctions stacked with a-Si. A series of experimental trials has been made on some candidate materials. Technical data on cell fabrication processes, device performance are presented. In the -present stage of experiments, 13.3% efficiency on a-Si/poly-Si two terminals tandem solar cell and also on a-Si//poly- CdS/CdTe four terminals cell have been obtained. Some key technologies for future low cost massproduction processes such as growth of polycrystalline thin film for bottom cell are also discussed.
Asymmetries in Amorphous Silicon Devices
Authors: Smith Z E. , Wagner S.
Published: March 2011

The consequences of the asymmetries in the density of electronic states of hydrogenated amorphous silicon on the behavior of electronic devices are discussed. Asymmetries in the relative widths of valence and conduction bandtails, the position of the dangling-bond states within the gap, and the occupation statistics of non-correlated defects are shown to affect the performance of p-i-n solar cells, and explain their superior performance and stability when compared with such devices illuminated through the n-layer (n-i-p). The device-modeling concepts which emerge help explain the differences between cell degradation via light exposure under various bias conditions, and cell degradation by dark forward bias.
Wavelength Dependence of the Turn-Off Character in a-Si:H Solar Cells
Authors: Oqinghai Mia , Guang Gao , Baocheng Cao , Guocai Dai
Published: March 2011

The turn-off character in a-Si:H solar cells has been studied by rectangular monochromatic light pulses. It is found that the turn-off time increases obviously with the decrease of the excitation light wavelengths when the turn-off steady photovoltages are the same. This phenomenon can be explained by the wavelength dependence of the photocapacitance and the time constant products RC in the a-Si:H solar cells.
Amorphous Silicon Alloy Technology For Active Matrix Displays
Authors: Yaniv Z. , Cannella V. , Baron Y. , Lien A. , McGill J.
Published: March 2011

Thin film semiconductor devices have been investigated over the past twenty years for application in large area flat panel displays. The development of thin film transistors and diodes based on amorphous silicon (a-Si) alloy materials has made the application of these devices, to display technologies, very attractive. More recently, manufacturing techniques to produce high quality large area films of amorphous silicon alloys have been demonstrated for photovoltaic applications.

Most of the current research and development effort on active matrix liquid crystal displays (LCDs) has concentrated on a-Si alloy TFTs. The success of TFT based displays for large area flat panel displays has been limited so far, mainly due to the difficulty of obtaining a high quality gate dielectric by plasma deposition and due to the presence of crossing conductors on the same substrate, both increasing the probability of defects in the display. When a two terminal sandwich device is used, on the other hand, no gate dielectric is required, hence, a higher yield can be expected. Metal-insulator-metal and hydrogenated amorphous silicon alloy devices have been proposed for incorporation in LCDs. Performance requirements for a useful active matrix switching element and a comparison among the different a-Si alloy thin film devices used for this purpose will be reviewed.
Tellurium Alloys for Reversible Optical Data Storage
Authors: Young R. T. , Strand D. , Gonzalez-Hernandez J. , Ovshinsky S. R.
Published: March 2011

Tellurium-based chalcogenide alloys, which are used for electronic switch materials, also have the appropriate optical and thermal properties for reversible optical data recording. One of the major concerns encountered with this type of phase change material is that there can be two contradictory characteristics of the material, i.e., the amorphous phase thermal stability and the crystallization rate are involved. We have demonstrated, in this paper, that this problem can be solved. We report that certain transition metal elements added to Te alloy films can substantially improve the rate of crystallization without any reduction of the amorphous phase stability.
The Optical Properties and Stability of GE and Sn-Doped TEOx Films
Authors: Lee W -Y , Davis C. R. , Lim G. , Coufal H. , Sequeda F.
Published: March 2011

The optical properties and the thermal stability of Ge and Sn doped TeOx films prepared by coevaporating TeO2, Te, Ge and Sn are reported. These films are amorphous as-deposited and crystalline Te appears after annealing at, e.g., 100 to 250°C. As expected, the addition of Ge and Sn increases the absorption of the TeOx films at the wavelength of interest (e.g., 830 nm). However, the thermal stability of (TeO1.1)1-xGex (x=0 to ~0.7) films is found to decrease with increasing x initially, starting to increase with increasing x only after x reaches a value between 0.3 and 0.4. These results differ from those reported previously for Ge and Sn-doped TeOx films and from those observed for Te-Ge alloy films. Interpretations of these results based on a solid state reaction between TeO2 and Ge or Sn during deposition are presented and discussed.
Tem Characterization of Solid-Phase Epitaxy in Amorphized Polysilicon
Authors: Chang P.-H. , Sundaresan R.
Published: March 2011

Solid Phase Epitaxy (SPE) of amorphous silicon thin films can be employed to build novel device structures for VLSI applications. One way of achieving SPE is to use a room temperature silicon implant to amorphize a polysilicon layer followed by a thermal treatment to promote epitaxial growth. Both vertical SPE, in which the epitaxial film is grown directly on silicon substrate, and lateral SPE, in which the epitaxial growth is extended over a thin layer of oxide using the vertical SPE region as a seed, have been realized using this approach. This paper presents results obtained by cross-sectional TEM analysis of the epitaxial films, with particular emphasis on the effects of implant schedule and annealing conditions on the epitaxial regrowth.
Effect of Preanneal Heat Treatment on Oxygen Precipitation in Epitaxial Silicon
Authors: Wijaranakula W. , Burke P. , Forbes L. , Matlock J.H.
Published: March 2011

Substrate wafers used for fabrication of P/P+ epitaxial silicon wafers were preanneal heat treated at 650°C in nitrogen ambients prior to the epitaxial deposition process for various periods up to 300 minutes. Subsequently, epitaxial wafers were subjected to CMOS simulation heat treatments. Postepitaxial nucleation heat treatment at 750°C in nitrogen ambient was also done on some epitaxial wafers. The results shows that preanneal heat treatment can preserve precipitate nuclei from dissolution during the epitaxial deposition process and lead to a high bulk defect density. These results also indicate the effect of the thermal history and spatial location in the grown crystal on the bulk defect formation.
Algorithms for Use in Modeling Diffusions on Personal Computers
Authors: Chan Archie Y.C.
Published: March 2011

The capability of IBM PC to model the dopant redistribution of ion-implanted impurities in silicon was demonstrated and its performance compared with that of mainframe computers.TURBO PASCAL was found to be a preferable programming language due to its relatively high speed and good ability of graphics handling. The operation speed of PC was about 4 to 6 times slower than that of an IBM 3031/VM370/MVS mainframe system.
Electrical Properties of Polycrystalline-Silicon Thin Films for VLSI
Authors: Kamins T I
Published: March 2011

The electrical properties of polycrystalline silicon differ from those of single-crystal silicon because of the effect of grain boundaries. At low and moderate dopant concentrations, dopant segregation to and carrier trapping at grain boundaries reduces the conductivity of polysilicon markedly compared to that of similarly doped single-crystal silicon. Because the properties of moderately doped polysilicon are limited by grain boundaries, modifying the carrier traps at the grain boundaries by introducing hydrogen to saturate dangling bonds improves the conductivity of polysilicon and allows fabrication of moderate-quality transistors with their active regions in the polycrystalline films. Removing the grain boundaries by melting and recrystallization allows fabrication of high-quality transistors. When polysilicon is used as an interconnecting layer in integrated circuits, its limited conductivity can degrade circuit performance. At high dopant concentrations, the active carrier concentration is limited by the solid solubility of the dopant species in crystalline silicon. The current through oxide grown on polysilicon can be markedly higher than that on oxide of similar thickness grown on singlecrystal silicon because the rough surface of a polysilicon film enhances the local electric field in oxide thermally grown on it. Consequently, the structure must be controlled to obtain reproducible conduction through the oxide. The differences in the behavior of polysilicon and single-crystal silicon and the limited electrical conductivity in polysilicon are having a greater impact on integrated circuits as the feature size decreases and the number of devices on a chip increases in the VLSI era.
Effects of Rapid Thermal Processing on Thermal Oxides of Silicon
Authors: Lee S.K. , Shih D.K. , Kwong D.L. , Alvi N.S. , Wu N.R. , Lee H.S.
Published: March 2011

The effects of rapid thermal processing (RTP) on the electrical properties of thin gate oxides in MOS devices have been studied. MOS capacitors have been analyzed by capacitance-voltage (C-V), current-voltage (I-V), and constant current stress techniques. MOSFET degradation due to hot carrier injection has also been investigated. No significant RTP-induced degradation was detected in any category of the device properties considered here. An abnormal trapping behavior was observed on the wafer annealed at 1100°C for 5 seconds.