bluuebunny/crossref_metadata_2025_split huggingface dataset:
Large Area (100)CdTe and CdZnTe Layers on (100)GaAs Grown by Hot Wall Beam Epitaxy for Hgcdte Photovoltaic MWIR-Detectorarray Application
Authors: Humenberger J. , Gresslehner K.H. , Schirz W. , Lischka K. , Sitter H. 
Published: March 2011

ABSTRACTThe newly developed Hot Wall Beam Epitaxy was used for the growth of (100)CdTe and (100)Cd1-yZnyTe layers (y ∼ 0.04) on 1 inch (100)GaAs wafers. The structural properties of the epilayers were investigated by means of high resblution x-ray rocking curve measurements. The results demonstrate the high crystalline perfection of the layers. The CdTe and Cd1-yZnyTe/GaAs wafers were used as substrates for the growth of Hg1-xCdx Te by close space vapor phase epitaxy. The layers show excellent homogeneity. Across a 1 inch wafer the composition x varies by ±0.0026, and the width of the rocking curve (FWHM) by ±10arcsec. Values of the FWHM as low as 50arcsec for Hg1-xCdxTe (x = 0.32) on Cd1-yZnyTe/GaAs were obtained. Linear arrays of planar photovoltaic detectors were fabricated. Arrays of 32 elements show high uniformity of the cutoff wavelength and the responsivity. The variation of the cutoff wavelength is ±1.5% (±0.04μm) and the variation of the responsivity is ±3%.
Tem Assessment of Defects in (CdHg)Te Heterostructures
Authors: Lawson-Jack S.G. , Jones I.P. , Williams D.J. , Astles M.G. 
Published: March 2011

ABSTRACTTransmission electron microscopy has been used to assess the defect contents of the various layers and interfaces in (CdHg) Te heterostructures. Examination of cross sectional specimens of these materials suggests that the density of misfit dislocations at the interfaces is related to the layer thicknesses, and that the high density of dislocations which are generated at the GaAs/CdTe interface are effectively prevented from penetrating into the CdHgTe epilayer by a 3um thick buffer layer. The majority of the dislocations in the layers were found to have a Burgers vector b = a/2<110> and either lie approximately parallel or inclined at an angle of ∼ 60° to the interfacial plane.
Two-Layer LPE Hgcdte P-on-n 8-18μm Photodiodes
Authors: Krueger E. E. , Pultz G. N. , Norton P. W. , Mroczkowski J. A. , Weiler M. H. , Reine M. B. 
Published: March 2011

ABSTRACTThis paper reports recent results on two-layer P-on-n LPE HgCdTe heterojunction photodiodes with cutoff wavelengths beyond 19μm. These results demonstrate the potential of photovoltaic HgCdTe detectors to satisfy the detector requirements of advanced NASA satellite instruments out to wavelengths of 17μm.
Detection of Free Liquid in Cement-Solidified Radioactive Waste Drums Using Computed Tomography
Authors: Steude J.S. , Tonner P.D. 
Published: March 2011

ABSTRACTAcceptance criteria for disposal of radioactive waste drums require that the cement-solidified material in the drum contain minimal free liquid after the cement has hardened. Free liquid is to be avoided because it may corrode the drum, escape and cause environmental contamination. The DOE has requested that a nondestructive evaluation method be developed to detect free liquid in quantities in excess of 0.5% by volume. This corresponds to about 1 liter in a standard 208 liter (55 gallon) drum. In this study, the detection of volumes of free liquid in a 57 cm (2′) diameter cement-solidified drum is demonstrated using high-energy X-ray computed tomography (CT). It is shown that liquid concentrations of simulated radioactive waste inside glass tubes imbedded in cement can easily be detected, even for tubes with inner diameters less than 2 mm (0.08″). Furthermore, it is demonstrated that tubes containing water and liquid concentrations of simulated radioactive waste can be distinguished from tubes of the same size containing air. The CT images were obtained at a rate of about 6 minutes per slice on a commercially available CT system using a 9 MeV linear accelerator source.
Characterization of Stressed and Crosslinked Polymers by 13C-CP/MAS and NMR Imaging
Authors: Kuhn Winfried , Theis Isolde , Koeller Elmar 
Published: March 2011

ABSTRACTAging of polymers and elastomers is a time dependent alteration of the chemical composition and physical properties depending on the aging conditions. Chemical reactions and hence changes in the chemical composition result in many cases from influence by oxygen or solvents and treatment of the bulk material at high temperatures. Aging of the materials by mechanical strain as well as in an oxidative manner can alter the ratio of amorphous to crystalline portions in the polymer, break chemical bondings and hence can alter the physical behavior of the materials.
Characterization of Biomaterials with NMR
Authors: Garrido Leoncio , Pfleiderer Bettina , Ackerman Jerome L. , Moore John 
Published: March 2011

ABSTRACTSilicone based biomaterials are characterized with NMR. Bulk spin-lattice (T1) and spin-spin (T2) relaxation times are measured in polydimethylsiloxane (PDMS) model networks and various types of implants. The T2 results seem to indicate that crosslink densities of these biomaterials are lower than those of the PDMS model networks studied. 1H chemical shift NMR imaging techniques are developed to investigate the aging (e.g., migration of free polymer, rupture due to mechanical stress, etc.) of biomaterials in vivo.
A Study of Changes in Poly(Methyl Methacrylate) (pMMA) Resulting from the Adsorption of Methanol using NMR Imaging
Authors: Schuff Norbert , Hornung Phillip A. , Williams Evan H. 
Published: March 2011

ABSTRACTThe understanding of the adsorption of solvents into materials is of great interest in different fields of material science. NMR imaging techniques can be used to follow the process of solvent adsorption by obtaining spatial and chemical information in a nondestructive way. We report here a study of the uptake of methanol (a non-solvent) into poly(methyl methacrylate) beads produced by suspension polymerization and into compression mouldings. In both cases, the uptake is far faster than the rate of diffusion measured elsewhere. We also illustrate the nonreversible nature of this uptake with respect to temperature cycling.
Oxygen-17 and Proton Mr Microscopy in Materials Analysis
Authors: Mateescu G.D. , Kinsey R.A. , Yvars G.M. 
Published: March 2011

ABSTRACTPreliminary results of two applications of 17O/lH NMR microimaging (MRμI) are described. In the first case, it is shown that oxygen-17 MRμI presents a unique advantage in situations where a strong proton background hinders the analysis of water ingress in polymeric materials. This is illustrated with 17O-enriched water diffusion into an agar gel from a central well. While proton imaging cannot readily distinguish between exogenous and endogenous water, 17O imaging makes a clear differentiation, due to the fact that the natural abundance gel has virtually no 17O background. In the second case, proton MRμI was used to analyze the structure and performance of commercial time-release pellets (ProMacR) containing an active ingredient (surfactant) dispersed into an inert matrix. This was done after leaching the detergent with natural abundance water or after drying the leached sample and refilling the pores with water. Pores ranging in size from 25 to 325 μm diameter are clearly visualized. The 1H images have been quantitated with commercial image analysis software in terms of the total porosity and the individual pore characteristics. Two types of water can be separately imaged: “bound” water with restricted mobility (interacting with the polymer matrix), and “free” water (in large pools). The majority of water is in the bound state. It is possible to evaluate the control-release performance of the product from the size of the pores, the uniformity of dispersion and the time course of detergent-water exchange.
NMR Imaging of Industrial Flow Processes
Authors: Sinton S. W. , Iwamiya J. H. , Chow A. W. 
Published: March 2011

ABSTRACTThe application of nuclear magnetic resonance flow imaging to the study of Poiseuille flows of solid/liquid suspensions is described. The basic imaging method is presented along with results on suspensions with solid particle loading levels up to 52 vol. % and viscosities up to 7kPoise. The most concentrated suspensions are non-Newtonian, and the NMR flow data show evidence for deviations from a simple parabolic velocity profile in straight pipes. Cross-sectional intensity images derived from the flow image data on concentrated suspensions are non-uniform. Possible explanations for these results are discussed in terms of current rheological understanding of suspension flow and relaxation weighting phenomena in the NMR imaging experiments.
Coupled Effects of Light and Temperature on Degradation of a-Si:H
Authors: Benatar Lisa E. , Grimbergen Michael , Redfeeld David , Bube Richard H. 
Published: March 2011

ABSTRACTThe effects of excitation rate and temperature on the kinetics and steady-state behavior of metastable defect formation in hydrogenated amorphous silicon (a-Si:H) have been studied. The dependences on temperature of the lifetime, τ, and stretching parameter, β, from a stretched exponential description of the kinetics were measured for one sample. We do not see a linear dependence of β on temperature over die entire temperature range studied (270K–370K), and τ increases monotonically with decreasing temperature. Steady-state results show defect density to be dependent on bodi temperature and excitation rate over the ranges measured (from 395K to 470K and from 6 × 1020 to 2 × 1022 s-l cm-3). The gradual change in temperature dependence is explained by a distribution of barrier heights between the ground and metastable states.
An Alternative Model for the Kinetics of Light-Induced Defects in A-Si:H
Authors: Santos Paulo V. , Jackson W. B. , Street R. A. 
Published: March 2011

ABSTRACTThe kinetics of light-induced defect generation in a-Si:H was investigated over a wide range of illumination intensities and temperatures. The defect density around 1016cm-3 exhibits a power-law time dependence Ns ∼ G2εfε with ε = 0.2 to 0.3, where G is the photo-carrier generation rate. A model for the kinetics of defect generation is proposed based on the existence of an exponential distribution of defect formation energies in the amorphous network, associated with the valence band tail states. The model reproduces the observed time dependence of the defect density with an exponent e determined by the exponential width of the valence band tail. The temperature dependence of the defect generation rate is well-reproduced by the model, which provides a connection between the Stabler-Wronski effect and the weak-bond model.
Optically Addressable Input Circuit for Two-Dimensional Image Sensing
Authors: Hack M. , Lewis A. G. , Bruce R. H. , Lujan R. 
Published: March 2011

ABSTRACTUsing the combination of a novel amorphous silicon (a-Si) photosensing element and four a-Si thin-film transistors (TFTs) we have developed a circuit which has been incorporated into a two-dimensional image sensor to provide gain at the pixel level. Our circuit only requires two global connections and the complete array is fully process compatible with standard a-Si TFT fabrication procedures. This contrasts with conventional a-Si imaging arrays which have no gain at the pixel level, require an additional global power line, and necessitate a separate sensor deposition.
Vibrational Spectra of a-Si:H Obtained by Pds
Authors: Lotter E. , Schubert M. B. , Heintze M. , Bauer G. H. 
Published: March 2011

ABSTRACTIn the energy range below mid-gap, absorption spectra obtained by photothermal deflection spectroscopy (PDS) show much higher values than data evaluated from photo-current measurements. This difference can now be explained as an additional absorption arising from combined vibrational excitation of molecular hydrogen and Si-H stretching modes, which can occur when the H2 molecule is deformed in a collision with Si-H. Down to lower energies, our samples absorb even stronger than in mid-gap. Extension of spectral scans down to photon energies of 0.4 eV shows that this results from absorption of the high energy wings of the collision induced H2 absorption, which is superimposed by the first overtone of the Si-H and Si-H2 stretching modes. The analysis of the H2 absorption profile and strength on samples as grown and annealed gives evidence that molecular hydrogen is enclosed in small cavities and polarized by anisotropic environment in as-grown material while it is concentrated in larger voids under high pressure after annealing above 350°C.
Hydrogen Density of States Model for Amorphous Silicon and Alloys
Authors: Street R. A. 
Published: March 2011

ABSTRACTIt is proposed that hydrogen reactions near the growing surface control the structure of plasma-deposited amorphous silicon and its alloys. The model explains how the plasma influences the dangling bond density and silicon weak bond distribution, which are the main parameters influencing the electronic properties. The hydrogen interactions account for the dependence of the electronic structure on growth conditions, the transition to microcrystalline growth in hydrogen-rich plasmas, and the different electronic properties of a-Si:H alloys. The proposed growth mechanisms are closely related to the metastability phenomena which occur in bulk a-Si:H films.
Auger and EELS Study of a-Si1−x Cx:H Alloys
Authors: Seta M.De , Narducci P. , Evangelisti F. 
Published: March 2011

ABSTRACTIt is shown that Auger and electron energy loss spectroscopies can provide a well defined picture of the local bonding and structure of a-Si1−x Cx:H alloys. The samples were found macroscopically homogeneous but microscopically heterogeneous on a scale of few Angstroms. A simple model where the tetrahedral network is chemically ordered at low x values and carbon tends to segregate in C-C microclusters at high x values seems to reproduce the data very well. By fitting the C and Si Auger spectra it was possible to have a quantitative determination of the percentage of different configurations.
A New Self-Aligned A-SI TFT Using Ion Doping and Chromium Silicide Formation
Authors: Nishida S. , Uchida H. , Kaneko S. 
Published: March 2011

ABSTRACTA new self-aligned a-Si TFT has been developed. Ion doping and chromium silicide (CrSix) formation technique was used to fabricate source and drain, which are self-aligned to the gate electrode, instead of using the previously reported lift-off process. The fabricated TFT mobility is about 0.5cm2/V' sec and threshold voltage is about 3V. The ON/OFF ratio is over 106. The actions of as short as 2μm channel TFT have been confirmed, using a large area TFT process. These results show that this technique can be applicable to manufacturing high quality TFT-LCDs in a large area.
High Temperature off Current in a-Si TFTS - Effect of Process and Structure
Authors: Possin George E. 
Published: March 2011

ABSTRACTThe OFF current in a-Si TFTs is an important parameter, especially for applications such as active matrix liquid crystal displays. In some demanding applications operation at 70°C or higher is required. This paper reports studies of the OFF current limiting mechanisms at room temperature and above. It is shown that the limiting mechanisms are hole injection from the drain junction at room temperature and electron conduction at higher temperatures. The importance of silicon thickness and interface state density at the passivation interface is stressed.
Effects of Temperature and Electrical Stress on the Characteristics of Amorphous Silicon Thin-Film Transistors
Authors: Park Jin S. , Oh Chang H. , Choi Hong S. , Han Min K. , Choi Yearn I. , Han Chul H. 
Published: March 2011

ABSTRACTThe experimental and analytical results regarding to the effects of temperature and electrical stress on the characteristics of amorphous silicon thin-film transistors (a-Si TFT's) have been presented. The variations in the device parameters of a-Si TFT, such as threshold voltage and field-effect mobility, have been examined under various operating temperatures and electrical stress conditions. The hysteresis in the transfer characteristics and the trapped charges at the a-Si/silicon nitride interface were measured at the operating temperature ranges. From the experimental results, it has been found out that the increase of the interface charge trapping may be responsible for the degradation in the a-Si TFT characteristics. Also, an analytical formulation, employing the interface charge trapping, is presented to clarify the instability phenomena and verified successfully with the experimental results.
Temperature Dependence of a-Si:H Nip Diodes
Authors: van Berkel C. , Powell M. J. , French I. D. 
Published: March 2011

ABSTRACTWe analyse the temperature dependence of the forward characteristics of a-Si:H nip diodes, which are characterised by a well defined exponential region at low bias and space charge limited current at higher bias. At each bias, the temperature dependence of the diodes shows a well defined activation energy and a linear dependence on bias exists for both the activation energy and exponential prefactor. We describe these phenomena with a first order temperature expansion of the diode quality factor n and present a physical interpretation in terms of electron and hole recombination in the i-layer.
Studies of MOS and Heterojunction Devices Using Doped μc-Si and a-Si
Authors: Lee D. R. , Bjorkman C. H. , Wang C. , Lucovsky G. 
Published: March 2011

ABSTRACTCurrent-voltage voltage characteristics of heterojunctions formed by remote plasma enhanced chemical vapor deposition (PECVD) of heavily doped μc-Si onto doped c-Si have been studied, as well as capacitance-voltage characteristics of MOS capacitor structures using heavily doped remote PECVD μc-Si and a-Si films as gate electrodes on thermally oxidized crystalline Si. Shifts in the flat-band voltages of MOS devices using the μc-Si and a-Si as gate electrodes relative to that of a reference Al/SiO2/c-Si structure are measured and explained in terms of a band structure model for the μc-Si and a-Si. Rectification and a photovoltaic effect observed in the pn heterojunctions are also explained in context of the same model.
Bias Stress Induced Instabilities in Amorphous Silicon Nitride / Crystalline Silicon and Amorphous Silicon Nitride / Amorphous Silicon Structures
Authors: Kanicki J. , Godet C. , Gelatos A. V. 
Published: March 2011

ABSTRACTThe effects of positive and negative bias stress on hydrogenated amorphous silicon nitride / crystalline silicon and hydrogenated amorphous silicon nitride / hydrogenated amorphous silicon (a-Si:H) structures are investigated as a function of stress time, stress temperature and stress bias. It is shown that in both structures bias stress induces a parallel shift of the C-V (capacitance-voltage) characteristics. For a given stress bias the direction of the C-V shift depends on the sign of the applied stress voltage, while the magnitude of the C-V shift depends on stress time and temperature. In addition, it is shown that positive bias stress slightly increases the number of localized states in the a-Si:H mobility gap, but negative bias stress does not. These results lead us to conclude that the C-V shift is not induced by dangling bond defects in a-Si:H but rather by carrier trapping in the insulator.
Critical Assessment of Sub-Bandgap Primary Photocurrent in a-Si:H Based Solar Cells.
Authors: Zhou T. X. , Hegedus S. S. , Fortmann C. M. 
Published: March 2011

ABSTRACTThe sub-bandgap primary photocurrent and the solar cell performance of a-Si:H p-i-n devices have been studied before and after light induced degradation. The results indicate significant discrepancy between the two methods when used to estimate the degree of degradation and the defect density in the i-layers. A preliminary explanation is proposed.
Simulation of Amorphous Silicon Hydride Solar Cells Using a Personal Computer
Authors: Shapiro Finley R. 
Published: March 2011

ABSTRACTThe simulation of a-Si:H solar cells has the potential to make a major contribution to the development of improved devices. However, to achieve this potential, simulations must run quickly on personal computers. This will require simplified approaches which are justified by the correspondence of their results to more elaborate but slower running simulations.
Role of Sio at TCO/P Interface on the Electrical Properties of the P/I Junction
Authors: Carvalho C. , De Nijs J. M. M. , Martins R. , Guimarāes L. 
Published: March 2011

ABSTRACTThe reduction of the ITO (Indium Tin Oxide) by the deposition of an a-Si:C:H p layer by means of a Plasma Enhanced Chemical Vapour Deposition (PECVD), is considerably diminished if a thin silicon monoxide layer (estimated to be between 5–50Å thick) is applied as a diffusion barrier. The amount of reduced indium diminishes (its concentration is two times lower), while the amount of silicon oxide is less although silicon monoxide was added on purpose. The influence of the silicon monoxide layer on the electrical properties of the p/i junction is shown by its J-V characteristics (in the dark and under illumination). We can see that with a suitable silicon monoxide thickness we can improve the short circuit current density (Jsc) and the rectifying ratio.
Electron Transport in a-Si:H at Low Temperatures
Authors: Nebel C. E. , Kocka J. 
Published: March 2011

ABSTRACTTime-of-flight and charge collection experiments performed on a-Si:H p-i-n structures in the temperature range 40–300K reveal electron drift mobilities which continuously decrease with decreasing temperature and electric field. At 40K, fields ≥ 2×105 V/cm are necessary to collect almost all carriers. A discussion of the data on the basis of a nearest neighbour hopping model shows the significant influence of the applied field on the hopping down process of electrons. Field-induced re-emission of deep trapped carriers back into shallow tail states establishes a narrow band of energy levels where electrons accumulate and propagate. The band width and energy position of the accumulation levels in the tail depends strongly on the applied field and the distribution of localized states. With increasing electric field, it shifts up in energy closer towards the conduction band edge and changes the hopping mobility for orders of magnitude. The calculated and experimental data are in reasonable agreement with the model of a hybrid distribution of localized states.
States in the Gap of Improved a-Ge:H Studied by Photomodulation Spectroscopy
Authors: Chen L. , Tauc J. , Pang D. , Turner W. A. , Paul W. 
Published: March 2011

ABSTRACTThe photomodulation spectra of a-Ge:H of average photoelectronic quality(ημπ = 1 × 10-10cm2/V) and of improved quality (ημπ = 3 × 10-7cm2/V), produced under different plasma conditions in an r.f. diode reactor by glow discharge, were measured at 80K and are analyzed in analogy with earlier studies of a-Si:H. The spectra of the poorer material are dominated by transitions between dangling bond states and the conduction and valence bands. By contrast, the spectra of the better material require contributions of transitions from the band tail states, indicating that the reduced defect density has resulted in pump-beam induced quasi-Fermi levels reaching near the conduction and valence band edges. A very acceptable fit between plausible density-of-states distributions and the experimental spectra has been found.