bluuebunny/crossref_metadata_2025 huggingface dataset:
Viscosity Temperature Dependence and Crystallization of Heavy Metal Fluoride Classes
Authors: CrichtoN S. N. , Mossadegh R. , Moynihan C. T. , Gupta P. K. , Drexhage M. G.
Published: March 2011

The temperature dependence of the viscosity of heavy metal fluoride glasses is important for determining processing temperatures for procedures such as fiber drawing and in understanding crystallization behavior in these systems. Viscosity data in the glass transition region and in the liquid region have been measured by several different laboratories for ZBLA (58 ZrF4-33 BaF2-5 LaF3-4 AlF3) and ZBLAN viscosity-temperature curves for these two compositions are highly non-Arrhenius in nature, and cannot be described by the Fulcher equation; however the Cohen-Crest equation fits the data very well. On a reduced temperature scale (Tg/T), the viscosity curves nearly coincide, suggesting the possibility of a master viscosity equation for fluorozicronate glasses. Crystallization temperatures for these compositions have been measured by differential scanning calorimetry. On reheating, the first crystallization product for both compositions is a barium fluorozicronate phase. However, ZBLAN glass does not crystallize until a much lower viscosity is reached, compared to ZBLA. These results indicate that the devitrification behavior for ZBLAN is due to additional entropy of mixing from the addition of NaF.
Strength of Ge-Sb-Se Chalcogenide Glass Fibers
Authors: Swiler Daniel R. , Varshneya Arun K. , Prideaux Peter H.
Published: March 2011

Strength of Ge-Sb-Se UV-cured acrylate coated chalcogenide glass fibers was measured in various environments using specially designed fixtures for testing in tensile and bending modes. The data are analyzed using Weibull statistics. Humid or water immersion initially lowered the observed strength of these fibers, presumably due to corrosion by the moisture which penetrated the semi-porous coating. However, after the glass surface became wetted, there was no evidence of further strength degradation (over 1.5 months of immersion).
Optical Spectra of Silica Core Optical Fibers Exposed to Hydrogen
Authors: Lemaire P. J. , Decoteau M. D.
Published: March 2011

The reaction of H2 with undoped silica core fibers was evaluated by means of “in situ” spectral loss measurements. Drawing induced loss peaks at 0.63 μm decreased rapidly upon exposure to hydrogen. Simultaneous loss increases at 1.39 and 1.53 μm suggest that H2 reacts at nonbridging oxygens and oxygen vacancies created during the drawing process, forming SiOH and SiH. The 1.53 μm SiH peak slowly decayed after its initially rapid growth, indicating that SiH is not thermodynamically stable in silica. The concentration of drawing induced defects is estimated to be on the order of 100 ppb, based on the time required for H2 to diffuse to the fiber core. The appearance of peaks at 1.45 μm suggests that HF is formed by reaction of H2 in the fluorine doped cladding of the fibers.
Fluorine Doping of Pyrogenic Silica
Authors: Miller T. J. , Nicol D. A. , Pohl K. D. , Clark H. R.
Published: March 2011

The incorporation of atomic fluorine into flame synthesized silica boules has been investigated. Soot boules were doped with fluorine using three different methods: (A) in a low temperature process, using XeF2 as the fluorinating agent prior to consolidation, (B) utilizing SiF4 or SF6 in the reagent gas mix during the combustion synthesis and soot deposition step and (C) in situ treatment with SF6 during the dehydration/ consolidation step at elevated temperatures. All three methods produced uniformly down-doped glass after consolidation, although the maximum fluorine incorporation and level of down-doping for each method followed A <B <C. Fluorine incorporation mechanisms are proposed for each method.
Magnetic Specific Heat of Cd1−xMnxTe at Low Temperatures and High Magnetic Fields
Authors: Ching W. Y. , Huber D. L.
Published: March 2011

Theoretical predictions for the magnetic specific heat of Cd1−xMnxTe:x=0.20, 0.35, 0.50, and 0.65 are reported for B=0, 10T, and 100T. The analysis applies to the low-temperature regime, T≤10K, where the fundamental excitations are harmonic magnons. The calculations use values for the exchange interactions which were inferred from fits to the dynamic structure factor describing inelastic neutron scattering at low temperatures. For x=0.35, 0.50, and 0.65 the specific heat is only weakly affected by applied fields up to 10T. At the lowest concentration the application of a field of 10T leads to a significant reduction in the specific heat. Results are also presented for the distribution of magnon modes at various concentrations and fields.
Development of Electrostatic Levitator at JPL
Authors: Rhim Won-Kyu , Saffren Melvin M. , Elleman Daniel D.
Published: March 2011

We report preliminary results of the design and operation of electrostatic levitators we have developed at JPL. Discussion is focussed on the single-axis levitators for groundbased operation and for operation in the reduced gravity environment. Design principles and the performance of final products are described.
Air Jet Levitation Furnace System for Observing Glass Microspheres During Heating and Melting
Authors: Ethridge Edwin C. , Dunn Stanley L.
Published: March 2011

A collimated hole structure air jet levitation system has been developed which can be used to levitate hollow glass microspheres used in inertial confinement fusion studies. An ellipsoidal furnace has been added to the system to provide a heating source. A video camera and a 16 mm movie camera connected to a microsphere system provide real time observation as well as permanent documentation of the experiments. Microspheres have been levitated at temperatures over 1400°C for over 10 minutes at a time.
Present and Future Capabilities of Acoustic Levitation and Positioning Devices
Authors: Rey Charles A. , Whymark Roy R. , Danley Thomas J. , Merkley Dennis R.
Published: March 2011

The techniques of acoustic positioning without the use of resonant cavities have been explored and developed over a number of years and the currently available capabilities are reviewed. The performance and characteristics of these nonresonant acoustic systems are described in regard to containerless processing with emphasis on the low-g environment. This includes manipulation and mixing of liquid drops, super-cooling phenomena, heating to temperatures of 1600°C or higher, rapid cooling solidification, and surface shape control. Some possible applications are measurements of physical properties of substances at high temperatures or of highly reactive specimens, and the formation of unique glasses and alloys of new compositions.
Mass Transfer in Closed Ampoule Vapor Crystal Growth
Authors: Rosenberger Franz
Published: March 2011

EXPANDED ABSTRACT

Closed ampoule vapor transport techniques are widely employed for the preparation of single crystals [1–5]. The experimental simplicity of these techniques makes them also attractive for fundamental crystal growth transport studies in reduced gravity environments. However, the underlying transport processes are complex and difficult to quantify.
Studies on Aqueous Two Phase Polymer Systems Useful for Partitioning of Biological Materials
Authors: Brooks Donald E. , Bamberger Stephan
Published: March 2011

The two phase systems that result when aqueous solutions of dextran and poly(ethylene glycol) (PEG) are mixed above a critical concentration of a few percent provide a useful medium for the separation of biological cell subpopulations via partition between the top, PEG-rich phase and the liquid-liquid phase boundary. Interfacial tensions of such systems have been measured by the rotating drop technique and found to range between 10−1 and 102 μN m−1 . The tension was found to depend on the length of the tie line describing the system on a phase diagram, via a power law relationship which differed depending on the concentration of Na phosphate buffer present. The electrokinetic properties of drops of one phase suspended in the other were studied for a variety of systems. It was found that the droplet electrophoretic mobility increased monotonically with phosphate concentration and drop diameter but exhibited the opposite sign from that anticipated from phosphate partition measurements. It was possible to take advantage of these electrokinetic properties and dramatically enhance the speed of phase separation through application of relatively small electric fields.
Directional Solidification and Characterization of Hg1−xCdxTe Alloys
Authors: Lehoczky S. L. , Szofran F. R.
Published: March 2011

A series of Hg1−xCdxTe alloy crystals was grown by high-temperature-gradient directional solidification at furnace translation rates ranging from 0.068 to 1.12 μm/s. For several ingots, the measured longitudinal compositional profiles were fitted to theoretical profiles to estimate the magnitude of D, the liquid HgTe-CdTe interdiffusion coefficient. The best-fit value of D was about 5.5 × 105 cm2/s. The majority of the ingots showed significant radial compositional variations along the growth axis. These variations are attributed, at least in part, to fluid flows ahead of the growth interface. The results are discussed in terms of the heat transfer characteristics of the alloy/ampule/ furnace system and the effects of these characteristics on the shape and stability of the growth interface in a 1-g environment.
Growth of Single Crystals of Mercuric Iodide (HgI2) in Spacelab III1,2
Authors: Van Den Berg Lodewijk , Schnepple Wayne F.
Published: March 2011

Continued development of a system designed to grow crystals by physical vapor transport in the environment of Spacelab III will be described, with special emphasis on simulation of expected space conditions, adjustment of crystal growth parameters, and on board observation and control of the experiment by crew members and ground personnel.

A critical factor in the use of mercuric iodide for semiconductor detectors of x-rays and gamma-rays is the crystalline quality of the material. The twofold purpose of the Spacelab III experiment is therefore to grow single crystals with superior electronic properties as an indirect result of the greatly reduced gravity field during the growth, and to obtain data which will lead to improved understanding of the vapor transport mechanism

The experiments planned to evaluate the space crystals, including gamma-ray diffractometry and measurements of stoichiometry, lattice dimensions, mechanical strength, luminescense, and detector performance will be discussed.
Studies of Liquid Metal Surfaces Using Auger Spectroscopy
Authors: Hardy Stephen , Fine Joseph
Published: March 2011

The surface composition of liquid gallium-tin alloys has been studied in an Auger electron spectrometer (AES) as a function of bulk composition and temperature. The sessile drop samples were cleaned by argon ion bombardment sputtering of the liquid. This technique produced surfaces that were entirely free of impurities within the sensitivity of AES and remained so for many days. Tin was found to be strongly adsorbed at the liquid-vacuum interface. Surface concentrations based on Auger measurements are in reasonably good agreement with values calculated from surface tension measurements interpreted in terms of a monolayer depth distribution model for the adsorbed tin.
Ground Based Studies for the Space Processing of Lead-Tin-Telluride
Authors: Crouch Roger K. , Fripp A. L. , Debnam W. J. , Clark I. O. , Carlson F. M.
Published: March 2011

This paper summarizes the results of a series of studies dealing with crystal growth from the melt and in particular, the growth of the narrow bandgap semiconductor PbSnTe by the Bridgman technique. Theoretical calculations have shown that for low Prandtl number fluids such as semiconductors, convection has no effect on the temperature field in the melt but has a significant effect on the compositional field. They also show that convective flow will exist in a Bridgman growth system on Earth, even in the “thermally stable” configuration. Measurements of the specific heat have been made up to temperatures of 722° C. The thermal diffusivity has been measured up to 1010° C which includes values for the melt. The interdiffusion coefficients for PbTe and SnTe in the melt have been determined. A technique has been developed and tested which provides a vacuum tight quartz ampoule with electrical feedthroughs for interface demarcation studies during the Bridgman growth. Analysis of crystals grown has indicated that the PbSnTe system is solutally unstable and the distribution of SnTe in the crystal, after an anomalous first to freeze region, follows that predicted by Pfann for convection controlled growth. Studies of the amount of supercooling in PbSnTe indicates that this may explain an anomalous composition distribution in the first to freeze region of an unseeded growth.
Brazing Under Microgravity in a Resistance Heated Furnace
Authors: Key Frieler , Roland Stickler , Eberhard Siegfried
Published: March 2011

Vacuum brazing under 1-g and microgravity (carried out on TEXUS II in preparation of an experiment for FSLP) conditions revealed the effect of various parameters (e.g. thermal history, hydrostatic pressure, buoyancy forces) on the microstructure of the joint and the gap filling phenomena.

The following results will be presented:

(a) Design of brazing specimens

(b) Variations of microstructure depending on gap width, gravity, and thermal history

(c) Flow patterns of molten braze as revealed by radioactive tracer experiments

(d) Evaluation of Plateau-type simulation experiments
Solidification Studies of Nb-Ge Alloys at Large Degrees of Supercooling
Authors: Lacy L. L. , Robinson M.B. , Rathz T.J. , Evans N. D. , Bayuzick R. J.
Published: March 2011

A 32 meter evacuated drop tube has been used to investigate the solidification of Nb-Ge alloys after deep undercooling. Samples have been supercooled as much as 500°K below the liquidus by using free-fall conditions to eliminate crucible induced nucleation. Final microstructures are dependent on the quenching rates at the bottom of the drop tube with a striking extension of the β phase solubility limit at the higher quenching rates.
Application of Microgravity and Containerless Environments to the Investigation of Fusion Target Fabrication Technology
Authors: Lee Mark C. , Kendall James M. , Elleman Daniel D. , Rhim Won-Kyu , Helizon Roger S. , Youngberg Charles L. , Feng I-An , Wang Taylor G.
Published: March 2011

During the past few years we have been studying several of the physical processes relevant to the production of spherical shells for inertial confinement fusion targets, both in a microgravity environment and in a containerless environment. The work has led to the development of several experimental facilities. Those which are most unique are described here, and fall into three categories as follows: 1. Ones which provide an induced low- or microgravity containerless environment, such as a vertical drag-free wind tunnel, two differing low-pressure and/or high-temperature drop towers for processing metallic or metallic-glass specimens, and a neutral buoyancy tank, 2. Ones providing containerless processing capability, such as a focusing radiator and an electrostatic levitator and 3. Ones providing extended microgravity and containerless capabilities, such as the KC-135 aircraft and the Space Processing Application Rockets. The physical processes which we have been studying include, but are not limited to, those which establish the shell sphericity, concentricity, surface topology, material properties, coatings, heating and cooling requirements and the effects of gravity on fusion pellet fabrication processes.
High Quality CdTe Growth by Gradient Freeze Method
Authors: Tanaka A. , Masa Y. , Seto S. , Kawasaki T.
Published: March 2011

The vertical Bridgman method, a gradient freeze technique, is feasible for the growth of high quality, large CdTe crystals. The equi-composition contour of Zn in doped crystals has been used to reveal the solid-liquid interface shape in the growth process. A slow cooling rate is necessary to obtain a convex interface shape. A low temperature gradient at the solid-liquid interface, down to 2 °C/cm, and Zn doping are found to be effective to reduce the etch pit density to 5×103/cm2 (minimum) to 104/cm2 (average). The crystallographic quality has been evaluated by means of X-ray diffraction, X-ray topography, etch pit delineation with the Nakagawa etchant, infrared measurements, photoluminescence and Hall effect measurements. CdTe crystals are found to be free from subgrain structure, Te precipitates and deep levels, and have high electron mobility.
Controtle Substitutional Doping of Cdte Thin Films and Cd 1-xMn xTe-CdTe Superlattices
Authors: Bicknell R. N. , Giles N. C. , Schetzina J. F.
Published: March 2011

We report the successful substitutional doping of CdTe epilayers grown by a new technique: photoassisted molecular beam epitaxy, in which the substrate is illuminated during the film deposition process. This new technique was found to produce dramatic changes in the electrical transport properties of the epilayers. In particular, highly conducting n-type and p-type CdTe films have been grown using In and Sb as n-type and p-type dopants,respectively. Photoassisted MBE has also recently been employed to produce for the first time highly conducting CdMnTe epilayers and Cd 1-xMnxTe-CdTe superlattices.
Tailored Microstructures for Infrared Detection
Authors: Chen Quark Y. , Bates C. W.
Published: March 2011

Using the effective medium approximation[1–4] and the theory of photoemission from small particles,[5] we look into the design-rules of infrared materials based upon the metalsemiconductor random heterostructures with Ag particles embedded in the semiconductor. It is found that semiconductor host matrices with higher dielectric constants show better optical absorption in the infrared and that optical properties are closely related to microstructural parameters such as volume fraction of metal particles, percentage of aggregation and particle size. Cu, Ag and Au particles all show similar characteristics. We synthesized materials with small silver particles embedded in Si. Their microstructures are analysized using X-ray diffraction, electron microscopy and sputter Auger profiling. Finally, we present the optical properties of these materials and make comparisons with our theoretical results.
Laser Annealing of Narrow Gap HgTe-Based Alloys
Authors: Kremer R. E. , Moore F. G. , Tamjidi M. R. , Tang Y.
Published: March 2011

We have used a cw CO2 laser to study the effects of rapidly annealing HgTe-based alloys. Both as-grown and thermally annealed samples of HgCdTe, HgMnTe, HgZnTe, and HgMgTe have been examined for mercury loss and surface damage using energy-dispersive x-ray analysis and optical reflectivity measurements. Small, but systematic differences were found between the asgrown and the thermally annealed samples and among the various materials studied. No degradation of the material at all was observed when the samples were cooled to 77 K and exposed to the laser.
Study of HgTe-cdTe Multilayer Structures by Transmission Electron Microscopy
Authors: Otsuka N. , Ihm Y. E. , Harris K. A. , Cook J. W. , Schetzina J. F.
Published: March 2011

A transmission electron microscope study of HqTe-CdTe multilayer structures grown by molecular beam epitaxy (MBE) on (100) Cd Zn Te is presented. Both cross-sectional and plain-view observations show highly reaular structures of superlattices and tunnel structures. Dislocation densities estimated by Plan-view observations are of the order of 104 cm−2 in these multilayer structures. A quantitative characterization of interface sharpness of superlattices has been carried out by intensity analysis of satellite spots in electron diffraction patterns. It is shown that interfaces in these superlattices are hichly abrupt with a width of one or two monolayers. These observations suggest the effectiveness of the use of lattice-matched substrates to qrow high quality HgTe-CdTe multilayer structures.
Hgl−xCdxTe Near Surface Characterization using Computer Aided Rutherford Backscattering Spectrometry
Authors: Kao T.-M. , Sigmon T. W.
Published: March 2011

In this work, we report the use of Rutherford backscattering(RBS) measurements and computer simulations to provide accurate stoichiometry information and semi-quantitative defect densities for the near surface region of Hg1−xCdxTe (MCT). The accuracy of the Hg1−xCdx Te x-values determined by our method is found to be comparable to other commonly used methods, such as FTIR or the electron microprobe. The data obtained as structural defects from RBS channeling measurements are in basic agreement with other techniques, such as chemical etching. The sensitivity of the channeling measurement to uniformly distributed dislocations is found to be about 107−108 cm−2, however, for dislocations forming subgrains, the detectable level of dislocation comes to 105 – 106 cm−2. The depth profiles of lattice disorder resulting from ion implantation into MCT are also extracted from RBS channeling measurements using these simulation programs. These profiles are found to closely match the calculated profiles for the displaced atoms calculated using an implantation modeling program (TRIM). We also report on the use of channeling-in-grazing-angle-out technique for evaluating the stoichiometry of the first few monolayers of the MCT surface.
Interdiffused Multilayer Processing (IMP) in Alloy Growth
Authors: Mullin J B , Giess J , Irvine S J C , Gough J S , Royle A
Published: March 2011

The Interdiffused Multilayer Processing (IMP) technique has been developed as a way of growing uniform layers of cadmium mercury telluride (CMT). The principle of the technique is discussed in the context of an interdiffusion coefficient so as to assess the potential applicability of the technique to the growth of other II–VI or III–V alloys. The development of IMP for the growth of CMT layers, together with the properties of the layers and their suitability for use in the fabrication of IR detectors, are reviewed.
Molecular Beam Epitaxial Growth of Cdl-xznxTe Matched to HgCdTe Alloys
Authors: Magnea N. , Dal'bo F. , Pautrat J. L. , Million A. , Cioccio L. Di , Feuillet G.
Published: March 2011

CD1−xZnxTe alloys of various composition have been grown by the Molecular Beam Epitaxy Technique and characterized by Transmission Electron Microscopy. C(V) measurements and photoluminescence spectroscopy techniques. The quality of the thick layers is comparable to that of bulk material. Thin strained layers have also been grown whose interfaces are structurally good. The recombination within a CdTe well confined between Cd1−xZnxTe barriers is dominated by intrinsic processes.
CdTe Films Grown on InSb Substrates by Organometallic Epitaxy
Authors: Bhat I. B. , Taskar N. R. , Ayers J. , Patel K. , Ghandhi S. K.
Published: March 2011

Cadmium telluride layers were grown on InSb substrates by organometallic vapor phase epitaxy and examined using secondary ion mass spectrometry (SIMS), photoluminescence (Pb) and double crystal x-ray diffraction (DCD). The substrate temperature and the nature of the surface prior to growth are shown to be the most important parameters which influence the quality of CdTe layers. Growth on diethyltelluride (DETe) stabilized InSb substrates resulted in CdTe growth with a misorientation of about 4 minutes of arc with respect to the substrates. On the other hand, the grown layers followed the orientation of the substrates when a dimethylcadmium (DMCd) stabilized InSb was used. Growth at 350°C resulted in the smallest x-ray rocking curve (DCRC) full width at half maximum (FWHM) of about 20 arc seconds.
Plasma-Assisted Epitaxial Growth of Compound Semiconductors for Infrared Application
Authors: Matsushita K. , Hariu T. , Fang S. F. , Shida K. , Gao Q. Z.
Published: March 2011

GaSb, InSb and InAs epitaxial layers with mirror surface were grown on GaSb, GaAs, InP, Si and sapphire substrates at relatively low temperatures by plasma-assisted epitaxy (PAE) in hydrogen plasma. Carrier concentrations and Hall mobilities of undoped PAE layers at room temperature are p=6×O16 cm−3; μp=750cm2/Vs, n=1×1016cm−3; μn=39,000cm2/Vs and n=7×1017 cm−3; μn=21,000cm2/Vs for GaSb on GaAs, InSb on GaAs and InAs on InP, respectively. As the first application of PAE layers to optoelectronic devices, p-GaSb/n-GaAs heterojunction photodiodes have been demonstrated to result in remarkable reduction of dark current with photoresponse in the wavelength region between 0.85 and 1.7μm for the light incident from GaAs.
Defects in Mg-Doped InP and GaInAs Grown by Omvpe
Authors: Bacher Fred R. , Cholan H. , Leigh Wallace B.
Published: March 2011

We report on the defects present in doped InP and GaInAs grown by organometallic vapor phase epitaxy (OMVPE). The material was grown in an atmospheric pressure system using group III trimethyl sources, arsine and phosphine. Bis(cyclopentadienyl) magnesium (Cp2Mg) was present as a p-type source of magnesium. Defects in as-grown material were characterized using photoluminescence (PL), Hall-effect, and deep level transient spectroscopy (DLTS). Various levels of Mg doping were investigated, ranging from 5 × 1015 to 1 × 1019 cm−3. Radiative defects were observed at 77 K corresponding to PL emission from conduction band/shallow donor to acceptor levels including emission at 1.37 eV identified as the shallow hydrogenic acceptor, and emission lines at 1.3 eV and 1.0 eV in heavily doped material. Corresponding hole traps in InP:Mg were observed by DLTS having thermal activation energies of 0.20 and 0.40 eV, the 0.40 eV trap being the dominant defect in p-type InP. In GaInAs grown near lattice-matched to InP, radiative emission is also observed from deep centers 100 meV from band edge emission. This emission is observed to be related to lattice-mismatch of the ternary with the InP, and is found to be accentuated and broadened in GaInAs doped with Mg.
Epitaxy in the Presence of Very Large Misfit: High Resolution TEM Study of Al/Si, Ag/Si, Al/CaF2/Si and Ag/CaF2/Si
Authors: LeGoues F. K , Liehr M. , Renier M.
Published: March 2011

We summarize high resolution transmission electron microscopy studies of interfaces with 33% misfit. We explain the existence of epitaxial interfaces for this systems by a geometrical argument similar to the 0-lattice models used to study high angle grain boundaries. Differences between systems very similar in structures are explained. We use the thus found epitaxial interfaces to build multilayered structures of the type metal/insulator/semiconductor.
The Initial Stages of Silicide Epitaxy - Nucleation and Morphology
Authors: Nemanich R. J. , Doland C. M. , Ponce F. A.
Published: March 2011

The initial stages of epitaxial silicide formation are described in terms of the nucleation properties. The reaction process is divided into the stages of interdiffusion, nucleation, and growth and coalescence. The aspects of the nucleation from the interdiffused regions are described. Results are presented for Pd and Pt deposited on clean Si surfaces. The initial thickness where silicide compound formation is observed is related to he critical cluster size of the nucleation model. The epitaxial morphology can be strongly influenced by heterogeneous nucleation involving the substrate interface, and this effect is demonstrated by reaction with metal overlayers less than the critical thickness.
Study of Epitaxial Growth of Au on Ni(110) by Scanning Tunneling Microscopy
Authors: Kuk Y. , Silverman P. J. , Buck T. M.
Published: March 2011

The structure of the Au segregated Ni(110)-0.8%Au surface has been studied by scanning tunneling microscopy. The segregated Au layer forms a (7×4) structure with a c(2×4) subunit. At various coverages of Au overlayer, commensurate and incommensurate Au structures were observed. At a coverage of I monolayer, islands and facets assciated with incommensurate Au atoms were observed.
Photoemission Studies of the Initial Adsorption and Growth of Ag on Ge(111)
Authors: Wachs A. L. , Miller T. , Shapiro A. P. , Chiang T. -C.
Published: March 2011

We present electron diffraction, and high-resolution angle-resolved and angle-integrated photoemission studies of the initial phases of adsorption and growth of Ag on Ge(111). The results provide information on the structural properties of the Ge(111)-c(2×8) substrate surface, show Ag grows upon it almost laminarly at room temperature, and unambiguously demonstrate the presence of a small amount of Ge segregating on top of the growing Ag overlayer. The origins and behavior of these segregated atoms are discussed. Ag films more than a few monolayers thick exhibit quantum well states which are observed to evolve as a function of film thickness.
Nucleation of Gaas on Vicinal Si(100) Surfaces
Authors: Hull R. , Fischer-Colbrie A. , Rosner S. J. , Koch S. M. , Harris J. S.
Published: March 2011

We investigate the nucleation of epitaxial GaAs grown on vicinal Si(100) surfaces by Molecular Beam Epitaxy. We find that the vicinal surface structure is highly sensitive to the surface cleaning process, and that in-situ desorption of a volatile surface oxide at 900°C appears to result in significant step mobility, resulting in the formation of low angle surface facets. Nucleation of GaAs then occurs on these facets, raising the possibilty of influencing the heteroepitaxial nucleation and growth processes by influencing the substrate surface “template” at the surface cleaning stage.
Gas Phase Reactions in Horizontal MOCVD Reactors
Authors: Tanaka Hitoshi , Komeno J.
Published: March 2011

We have applied kinetic simulation to MOCVD chemistry in a horizontal MOCVD reactor. Both chemical reactions and material diffusion are considered. For trimethylgallium decomposition, concentrations of chemical species reach their steady state values which differ largely from the equilibrium values.
Antiphase Domain Structures of CdTe on Sapphire Substrates
Authors: Maruyama Kenji , Yoshikawa Mitsuo , Takigawa Hiroshi
Published: March 2011

Antiphase domain (APD) structures have been discovered in CdTe layers grown on (0001) sapphire substrates by MOCVD. To explain APD formation, an obstruction model based on a surface-reaction mechanism has been proposed. The proportion of one-phase domains to the total area varies with the [DETe]/[DMCd] ratio (VI/II ratio). A single-domain CdTe layer can be obtained at a VI/II ratio of 5. The APD structure shows a strong correlation with the crystallinity measured by X-ray. For a single-domain CdTe epilayer, theFWHM of the X-ray rocking curve shows 114 arc seconds and the EPD is 6×10 cm−2
Charge Carrier Recombination in Doped a-Si:H Studied by Contactless Photoconductivity Measurements
Authors: Werner A. , Kunst M.
Published: March 2011

Transient photoconductivity measurements in a-Si:H at different n- and p-doping level point to decay kinetics which strongly depend on the doping level and excitation densities. In undoped a-Si:H excess charge carriers decay mainly by a transition between electrons and holes at their respective mobility edges. The generation of hole traps by n-doping quenches this decay channel and transitions between localized states in the bandgap play an important role in charge carrier kinetics. In p-doped material the availability of a large density of mobile holes and positively charged recombination centers increases the electron decay drastically.
Hydrogen Content and the Optical Bandgap in Amorphous Silicon
Authors: Maessen K. M. H. , Pruppers M. J. M. , Bezemer J. , Habraken F. H. P. M. , van der Weg W. F.
Published: March 2011

The dependence of the optical bandgap on the hydrogen concentration is measured for amorphous silicon films prepared under different glow-discharge conditions. A deviation from the usually accepted linear dependence is found for hydrogen concentrations above 12 at.‰ We find that in this concentration region an increase of hydrogen incorporated as SiH2 is responsible for this behaviour.
Exafs Study of a-Si1−xGex:H, a-Si1−x Cx:H and a-Si1−xNx:H at the Si K-Edge
Authors: Filipponi A. , Fiorini P. , Evangelisti F. , Mobilio S.
Published: March 2011

The structure of three series of hydrogenated amorphous Si-based alloys was studied by EXAFS at the Si K-edge. Average bond-lengths and first shell compositions were determined. It is shown that the two atomic species are randomly distributed in a-Si1−xGex:H whereas a chemical ordered composition is favored in a-Si1−xNx:H
Comparative Study of Structure and Hydrogen Incorporation in Glow Discharge a-Si:C:H and a-Si:N:H Alloys
Authors: Beyer W. , Wagner H. , Mell H.
Published: March 2011

Plasma-deposited a-Si:C:H and a-Si:N:H alloys both show a rapidly rising hydrogen incorporation with increasing carbon or nitrogen content. For hydrogen concentrations exceeding ∼ 20 at.%, the host material starts to lose its connectiveness leading to the formation of a void structure as evidenced by hydrogen evolution and infrared absorption. Raising the substrate temperature leads to a reduction of the hydrogen concentration, to an increase of the Si-C and Si-N bond concentration and to a more compact naterial. However, for a-Si:C:H films it leads also to graphitic carbon bonds. The widening of the optical bandgap of a-Si:C:H films up to about 50 at.% of carbon is almost entirely due to the increased hydrogen incorporation whereas for a-Si:N:H films both hydrogen and nitrogen incorporation plays a role.
Substitutional and Interstitial Doping of Amorphous Silicon Nitride
Authors: Spear W. E. , Dunnett B. , Lecomber P. G.
Published: March 2011

Doped films of amorphous silicon nitride have been prepared by the glow discharge technique over a wide range of ammonia/silane mixtures. P- and B-doped specimens were produced by admixing phosphine or diborane during deposition. Interstitial doping was attempted by Na-ion implantation, and by in-diffusion of evaporated Li. For values of the ammonia/silane volume ratio R < 10−2, the optical gap remains unchanged and all the above dopants raise the room temperature conductivity to σRT ≅ 10−2(Ω cm)−1. With increasing R the efficiency of P, B and Na doping decreases rapidly. However, incorporation of Li continues to significantly increase σRT at higher R where the optical gap approaches 5eV. Near-stoichiometric, transparent specimens have been prepared with σRT increased by up to 14 orders of magnitude by Li doping. A discussion of the doping results is given.
Metal / Hydrogenated Amorphous Silicon Interfaces
Authors: Kanicki Jerzy
Published: March 2011

The contact properties between different metals and hydrogenated amorphous silicon, prepared by various deposition techniques in different laboratories, are reviewed. From these studies the appropriate metallizations have been established for the achievement of Schottky diode, quasi-ohmic or ohmic contact to undoped and doped films. The various characteristic parameters describing Schottky barrier interfaces such as ideality factor, current saturation, contact resistance and barrier height are discussed. The dependence of Schottky barrier height upon the metal work function, measuring and annealing temperature, and optical band-gap are also reported. The minority-carrier injection and series resistance effects on the contact properties of a-Si:H diodes are described. All the results are interpreted in terms of a self-consistent model that exhibits an electrode-limited to bulk-limited transition.
Dynamic Characteristics of Amorphous Silicon Thin Film Transistors
Authors: van Berkel C. , Hughes J. R. , Powell M. J.
Published: March 2011

In this paper we report on the dynamic characteristics of amorphous silicon thin film transistors in the time interval between ips to 1s after gate switch-on. The experimental results show a continuous change in the threshold voltage in this t'me regime. A model based on carrier thermalisation to the deep states including the spatial dependence of the thermalisation process in the band-banding region is presented to account for these results. The effect responsible for the observed time dependence of the threshold voltage is shown to be the trapping of charge in deep states in the bulk amorphous silicon away from the interface with the gate dielectric.
Properties of a-SiGe and Application to Stacked Solar Cell
Authors: Itozaki H. , Fujita N.
Published: March 2011

Deposition technique of a-SiGe:H and its application to a stacked solar sell were investigated. Properties of a-SiGe:H were improved by a glow discharge method with a negatively biased substrate, and a mercury sensitized photo CVD under lower pressure. An a-SiGe:H single junction solar cell was improved by slight boron doping to an i layer and insertion of a buffer layer into a p/i interface. A conversion efficiency of more than 10 % was obtained by a triple stacked solar cell on a alass substrate.
Characterization of Heavily Boron-Doped a-Si:H Films Deposited at Low Substrate Temperatures
Authors: Jang Jin , Kim Sung Chul , Lee Dae Bong , Lee Choochon
Published: March 2011

The electrical and optical properties of heavily boron-doped hydrogenated amorphous silicon (a-Si:H) films deposited at 100°C with a gas phase doping concentration between B2H6/SiH4=0.001 and 0.1 have been investigated. The absorption edge exhibits the characteristic Urbach form and the width of exponential absorption tail, Eo, increases with increasing doping concentration. The optical gap has a linear relationship with the Eo and it is expected to be 2.20 eV when the Eo is zero. Thus, the disorder determines the optical gap directly whether the sample is doped or undoped, the hydrogen and boron in the film change the disorder. The conversion efficiency of n-i-p cell is improved by 15% if the p-layer is deposited at 100°C after preparing the n- and i-layers ∼250°C.
Changes of Drift Mobility in a-Si:H with Light Exposure and Doping
Authors: Takada J. , Fritzsche H.
Published: March 2011

Measurements of the drift mobility μ of photo-excited electrons in n-type hydrogenated amorphous silicon (a-Si:H) as a function of light intensity are reported. The value of μ increases as the quasi Fermi level is moved closer to the transport states in accordance with the multiple trapping theory. The drift mobility decreases with increasing doping as well as with an increase in the concentration of metastable dangling bonds defects by strong light exposures. This decrease in μ between 300 and 360K can be explained by a corresponding decrease in the microscopic mobility, by an increase in the density of tail states within 0.35eV below the electron mobility edge, or by a combination of both these effects.
Light Induced Change in a-Si:H p-i-n Solar Cells Under Various Light Soaking Conditions
Authors: Sakai H. , Ihara T. , Nabeta O. , Yoshida T. , Maruyama K. , Ichikawa Y. , Uchida Y.
Published: March 2011

Lihgt-induced change in photovoltaic performance of p-i-n solar cell was studied. The behavior of degradation of the solar cell strongly depends on the intensity and the spectrum of illumination light. The results of these light soaking tests are presented and discussed. On the basis of these results, the superiority of double-stacked a-Si/a-Si tandem solar cells is discussed.
Heterojunction Bipolar Transistors (HBT) with a-Si:H or μc-Si Emitter
Authors: Symonsj J. , Nijs J. , Vanhellemontk J. , Baerth K. , Michielg H. , Willekew G. , Vandervors W. , Mertens R.
Published: March 2011

In this paper phosphorous doped amorphous and microcrystalline silicon are used as emitter material for npn bipolar transistors. A heterojunction is formed between emitter and base, resulting in a higher current gain β for the same base parameters in comparison with conventional transistors. Because the amorphous silicon results in a too high emitterresistance, a compromise solution is microcrystalline silicon (μc-Si). HREM-micrographs give credit to the true heterojunction concept and show epitaxial reorganization, especially after annealing of the amorphous silicon.
The Properties of Microcrystalline and Amorphous Silicon Electron Blocking Layers in a-Si Alloy Photoreceptors
Authors: Johncock A. G. , Hudgens S. J. , Guha S.
Published: March 2011

Positive charging amorphous silicon alloy photoreceptors require intentionally fabricated electron blocking layers at the photoreceptor/substrate interface. Thin insulating films and lightly boron doped (300ppm) a-Si alloy layers have been previously employed either singly or in multilayers as back blocking layers. We report here, for the first time, the use of thin (≈300Å) heavily doped microcrystalline (≈10 Ω−1 cm−1) Si back blocking layers [1], with enhanced photoreceptor performance. Investigation of the temperature and electric field dependence of the dark decay of photoreceptors with amorphous or microcrystalline silicon back blocking layers as a function of blocking layer thickness and boron doping is interpreted within a comprehensive model of blocking layer operation.
Application of a Low Frequency Technique to the Study of Amorphous Materials.
Authors: Pickup C. , Cochrane R. W. , Brebner J. L. , Perluzzo G.
Published: March 2011

The extension of a recently reported application of a dielectric spectroscopic technique on c-GaAs will be shown in the case of a-Si:H. This technique is based upon the application of a small signal a.c. voltage at several fixed frequencies using a Frequency Response Analyzer.

The technique is particularly useful for applications to material study where more traditional methods (i.e. DLTS) fail to apply. Thus we can probe the nature of bulk transport processes in the most resistive of materials and also study the interface between the contact and the substrate. It therefore becomes relatively simple to distinguish Schottky or blocking contacts from Ohmic or quasi-Ohmic contacts.

Typical capacitance and dielectric loss data will be presented as a function of frequency. Arrhenius plots obtained from the temperature dependence of the above parameters will show that activated processes have been observed and may be related to specific defect centres.
A Study of the State Distribution in Various a-Si:H Materials by a New Capacitance Method
Authors: Balberg I.
Published: March 2011

A new method for the determination of the deep states density in amorphous semiconductors is presented. The method is based on the carriersemission- time dependence of the capacitance-voltage characteristics of Schottky barriers. The applicability of the method for the study of hydrogenated amorphous silicon materials is demonstrated. The pitfalls associated with trying to deduce the density of states from a single capacitance-voltage characteristic are also discussed.
Real Structure and Internal Friction of Boron Doped with Zirconium
Authors: Darsavelidze G. Sh. , Tsagareishvili G. V. , Antadze M. E. , Tsagareishvili O. A. , Khvedelidze A. G. , Tavadze F. N.
Published: March 2011

The nature of interaction of point and linear defects in semiconductor boron doped with zirconium (∼ 1.5% at.) has been studied using electron microscope and internal friction methods. It was shown that doping with zirconium promoted the multiplication of polysynthetic twins and stacking faults. A computer simulated analysis of diffraction patterns was performed in terms of trigonal presentation. At the frequency of free torsional vibrations of ∼ 1Hz a high level of internal friction with maxima at 250, 300–320 and 380–420°C was revealed. It is supposed that the maxima are respectively due to: the twin-boundary motion accompanied by breaking of intericosahedral bonds (a); the process of ordering-disordering of atoms in the impurity atmospheres under the continuous change of the temperature and elastic fields of moving twinning dislocations in the {100} system (b); the impurity controlled twin-boundary motion in the {511} system.
Electron Deformation Density Distribution in α-Boron
Authors: Will G. , Kiefer B. , Morosin B. , Slack G. A.
Published: March 2011

The bonding features of α-boron were studied using electron density analysis procedures. Deformation density maps and valence density were calculated and the structure analysed by so-called multipole refinements, yielding R - 0.0119. The refinement model correctly describes the bonding and results in a difference density distribution free from any meaningful residual peaks.
Electron Transport in Boron-Rich Borides
Authors: Golikova O. A.
Published: March 2011

Boron-rich borides represent a class of unique semiconductors. They combine the physico-chemical properties of refractory crystals with the electrical, optical, thermal properties typical for amorphous semiconductors [ 1–3 ].
Epitaxy of SiC Films on Sapphire by Laser CVD
Authors: Nakamatsu Hirohide , Kawai Shichio
Published: March 2011

ArF excimer laser CVD was performed in a very-low pressure reactor. C2H2 and Si2H6 were used as source gases and carrier gases were not used. Epitaxial 3C-type SiC(111) grew parallel to α-Al2O3 (0001) substrate. It had a twin structure. Mismatch between the lattice parameters was estimated to be 12%. The epitaxial growth occurred down to 980°C and the films about 0.5μm in thickness grew at 1150°C for 30 minutes. Unirradiated films were polycrystalline or spontaneously peeling-off epitaxial films, while irradiated ones were strongly adherent epitaxial films.
Inversion-Type Mos Field Effect Transistors Using CVD Grown Cubic SiC on Si
Authors: Shibahara K. , Takeuchi T. , Saitoh T. , Nishino S. , Matsunami H.
Published: March 2011

Inversion-type n-channel MOSFET's of cubic-SiC were successfully fabricated. MOSFET's were fabricated on an antiphase-domains free layer grown on Si(100) by carbonization and subsequent chemical vapor deposition. Ion implantation technique was used to form source and drain of MOSFET's. A gate oxide of SiO2 was formed by thermal oxidation of SiC. Inversion mode operation was confirmed for the first time. Annealing temperature dependence of electrical characteristics of P+ and N2+ implanted layer and characteristics of p-n junction diodes fabricated using ion implantation technique were also investigated.
Anomalous Seebeck Coefficient in Boron Carbides
Authors: Aselage T. L , Emin D. , Wood C. , Mackinnon I. , Howard I.
Published: March 2011

Boron carbides exhibit an anomalously large Seebeck coefficient with a temperature coefficient that is characteristic of polaronic hopping between inequivalent sites. The inequivalence in the sites is associated with disorder in the solid. The temperature dependence of the Seebeck coefficient for materials prepared by different techniques provides insight into the nature of the disorder.
Single Crystal Epitaxial Growth of β-SiC for Device and Integrated Circuit Applications
Authors: Parsons J. D.
Published: March 2011

Beta SiC is an important semiconductor whose development has been slowed by synthesis difficulties. The physical and electronic properties which make β-SiC desirable for high speed and high power electronics are discussed, with special emphasis on field effect transistor (FET) applications. A history of synthesis efforts is presented to illuminate the obstacles encountered in the growth of semiconductor device quality P-SiC. A new approach to single crystal epitaxy of β-SiC, using TiC as a substrate, is described. The properties of TiC which make it a uniquely suitable substrate for β-SiC epitaxial growth are discussed, and procedures used to prepare TiC surfaces for β-SiC epitaxy are described. The growth process employed at our laboratory, chemical vapor deposition (CVD), is described, and experimental observations of the effects of the CVD growth environment on β-SiC epitaxial growth are presented. Based on these observations, we propose to synthesize β-SiC in a singlesource reaction, using molecules which decompose directly to SiC units. This contrasts with current approaches, which introduce Si and C separately, in molecules which must decompose and subsequently react to form SiC.