bluuebunny/crossref_metadata_2025_split huggingface dataset:
Annealing Characteristics of Amorphous Silicon Alloy Solar Cells Irradiated with 1.00 MeV Protons
Authors: Abdulaziz Salman S. , Woodyard James R. 
Published: March 2011

ABSTRACTa-Si:H solar cells were irradiated with 1.00 MeV proton fluences in the range of 1.00E14 to 1.2 5E15 cm-2. Annealing of the short-circuit current density was studied at 0, 22, 50, 100 and 150 °C. Annealing times ranged from an hour to several days. The measurements confirmed that annealing occurs at O °C and the initial characteristics of the cells are restored by annealing at 200 °C. It is proposed that the degradation in the short-circuit current density with irradiation is due to carrier recombination through the fraction of D° states bounded by the guasi-Fermi energies. The time dependence of the rate of annealing in the short-circuit current density appears to be consistent with the interpretation that there is dispersive transport mechanism which leads to the annealing of the irradiation induced defects.
Highly Conductive Microcrystalline Silicon Layers for Tunnel Junctions in Stacked Amorphous Silicon based Solar Cells.
Authors: Prasad K. , Kroll U. , Finger F. , Shah A. , Dorter J-L. , Howling A. , Baumann J. , Schubert M. 
Published: March 2011

ABSTRACTWe have investigated the influence of substrate temperature on the optoelectronic and structural properties of heavily doped μc-Si:H, prepared with the Very High Frequency Glow Discharge process. At substrate temperatures as low as 160°C we obtain, for films with 0.5μm thickness, maximum conductivities of 100 S/cm and 20 S/cm for <n> and <p> material, respectively. Starting from these values the deposition parameters were optimised for ultrathin layers having thicknesses in the range of 100 to 500Å. We observe that boron doping plays a critical role in the crystallisation of ultrathin films. The thinnest layers investigated so far show conductivities of 0.2 S/cm at d=100Å for <n>, and 0.2 S/cm at d=250Å for <p> material. These properties make μc-Si:H films attractive candidates to form tunnel junctions in tandem solar cells.
Improvement of a-Si:H P-I-N Devices using Zinc Oxide based Back-Reflectors
Authors: Kothandaraman C. , Tonon T. , Huang C. , Delahoy A. E. 
Published: March 2011

ABSTRACTThe conversion efficiency of a-Si:H P-I-N photovoltaic devices was improved using aluminum doped zinc oxide thin films between the n-layer and the metal electrode. The improvement is due to the increase in the quantum efficiency, mainly in the wavelengths between 550 – 750 nm, and is attributed to the increased reflectivity of the zinc oxide/metal layer over the conventional metal electrode. The dependence of the enhancement, on the thickness of the zinc oxide layer and the back metal electrode was studied and the optimal configuration was identified as 800 angstroms of zinc oxide backed by a silver electrode. Photostability studies of devices containing these back-reflectors showed that their stability to light-soaking was comparable to conventional devices establishing the use of zinc oxide back-reflectors as a viable way of increasing the efficiency of a-Si:H devices without compromising their stability.
Amorphous Hydrogenated Silicon (a-Si:H) Photovoltaic Thin Films Deposited onto Ultra-Low Density Aerogels
Authors: Hotaling S. P. , Proni F. P. 
Published: March 2011

ABSTRACTAmorphous Hydrogenated Silicon (a-Si:H) photovoltaic thin films have been deposited onto ultra low density (ULD) silica aerogel substrates using plasma enhanced chemical vapor deposition (PECVD). The techniques and results of ULD aerogel fabrication, surface treatment, thin film deposition and photovoltaic (PV) characterization are discussed. DC photbcurrent and transient time of flight measurements were performed for the PV characterization, while ellipsometry, transmission optical spectrophotometry, scanning electron microscopy (SEM) and low magnification optical microscopy (×64) were used to obtain qualitative and quantitative surface morphology, microstructure and film thickness data. This research indicates that ULD aerogels may be used as substrates for dielectric and metallic thin films which have electrical, optical and mechanical properties comparable to films deposited onto conventional substrates such as glass, metals or plastics. These data taken together with the lightweight of the ULD aerogels may be of interest to the space based sensor community as a possible route to large, lightweight photonic sensors or PV arrays. These results thus indicate that ULD aerogels could be used as substrate materials for other thin films of interest to the PV community, for example, we have produced ultra lightweight reflective optics using this fusion of solgel and thin film technologies [1].
Ultra-High-Sensitive Image Pickup Tubes Using Avalanche Multiplication in a-Se.
Authors: Tsuji K. , Ohshima T. , Hirai T. , Gotoh N. , Tanioka K. , Shidara K. 
Published: March 2011

ABSTRACTExtremely high-sensitive image pickup tubes with sensitivities 1000 times higher than those of conventional tubes are fabricated using the avalanche phenomenon in a-Se as photoconductive targets. The excess avalanche noise of a video signal is found to be much less than that expected, based on the carrier ionization rates. The frequency spectra of the noise currents of both the pickup tubes and sandwich-type photocells are examined. The results are compared with those of a simulation, and it is found that the excess noise can be reduced by the charge-storage operation of imaging devices.
Characteristics of a-Si Pixel Arrays for Radiation Imaging
Authors: Fujieda I. , Nelson S. , Street R. A. , Weisfield R. L. 
Published: March 2011

ABSTRACTTwo-dimensional a-Si photodiode arrays with the a-Si TFT readout scheme were fabricated. Some performance characteristics were investigated for detecting visible light, X-ray and γ ray. Arrays of 64×40 1mm2-pixels have good uniformity with ± 1 % in linearity variation, ± 10 % dark current variation and ± 5 % sensitivity variation. The cross-talk between adjacent pixels was found to be negligible so that the intrinsic spatial resolution was determined entirely by the pixel size. Due to the high resistivity of a-Si photodiodes and TFTs, charges generated by pulsed light illumination were retained in photodiodes for a long period of time. This enables the accumulation-mode operation for detecting low-intensity light, where only one image is obtained over a long integration time. An encapsulated Co-57 source (3 μ.Ci) was successfully imaged with 5 sec integration. Alternatively, the array can be operated by the cine-mode for detecting high-intensity light, where a number of images are obtained successively.
Defect Equilibration and Metastability in Low-Spin-Density a-Si:H
Authors: McMahon T. J. 
Published: March 2011

ABSTRACTTo first order, the relaxation kinetics of thermally generated defects with spin observed in two differently prepared, 60-μm-thick undoped hydrogenated amorphous silicon (a-Si:H) films are consistent with a two-level system having a formation energy of 0.35 eV and an anneal barrier of 2.1 eV. However, closer examination of how relaxation depends on thermal treatments reveals the complexity that might be expected from a disordered material. For example, the stabilization of many spins quenched in from 260°C can be increased by annealing at an intermediate temperature: It appears that, some 260°C defects equilibrating further at 205°C will relax and become more locked-in configurationally than defects simply equilibrated at 260°C. Crossover of annealing data is the result. Crossover cannot be explained with two-level system approaches. Models in which a spin can be stabilized with alternate structural configurations must be invoked.
Comments on the Determination of Defect Density in a-Si:H Alloys by Integrating the Sub-Bandgap Optical Absorption Coefficient
Authors: Li Y.-M. , Paul W. 
Published: March 2011

ABSTRACTThe validity of determining the defect density in a-Si:H and its alloys by integrating the sub-bandgap optical absorption coefficient is examined. It is shown that a formula derived for estimating Si-H bond density has been incorrectly applied to defect related absorption. In addition, the complex defect absorption processes have been oversimplified, by assumption, to the case of a single type of transition. Further, in practice, the defect absorption spectrum can not be unambiguously obtained at energies near and above the low end of the optical absorption edge. It is concluded that die integration method for quantitative defect density determination should be viewed at best as an empirical practice with considerable arbitrariness.
Defect States in Hydrogenated Amorphous Silicon-Sulphur Alloys by ESR and PAS
Authors: Han Gaorong , Qiao Jianmin , Du Piyi , Jiang Zhonghua , Ding Zishang 
Published: March 2011

ABSTRACTWe have presented ESR and PAS measurements for a series of a-SiS:H and a-Si: H films deposited by glow discharge at different parameters. The spin density in a-SiS:H alloys measured by ESR is essentially independent of the sulphur content, while the density of defects measured by PAS increases significantly with the increasing of sulphur content. The ESR signals in a-SiS:H alloys strongly depend on both annealing and illumination. The spin density increases up to 540°C and then decreases with raising annealing temperature for a-SiS:H and a-Si:H alloys. The results suggest that some new defects such as molecular hydrogen and microvoids are appeared when addition of sulphur to a-Si:H films.
Nuclear Spin-Lattice Relaxation Via Paramagnetic Centers in Amorphous Hydrogenated Silicon (a-Si:H)
Authors: Cheung Man Ken , Petrich Mark A. 
Published: March 2011

ABSTRACTThis is the first NMR study of a-Si:H which measures the 29Si spin-lattice relaxation time, T1. Measurements of T1 are useful in learning about the silicon network structure and the localized states within the mobility gap. Dangling-bonds are randomly distributed in device quality materials but are inhomogeneously distributed in nondevice quality materials. There are two simultaneously occurring dangling-bond spin-lattice relaxation mechanisms: one is through the spin-orbit coupling modulated by thermal excitation of “two-level systems”, and the other is through hopping conduction between localized states near the Fermi level.
Problems in Large Size Amorphous Silicon Plate Manufacturing
Authors: Schmttt J. P. M. 
Published: March 2011

ABSTRACTThe growing aSi:H based component industry needs large PECVD machines for high throughput coating of flat substrates up to 1 meter in size. Deposition uniformity can be affected by gas depletion in diffusion and laminar gas flow geometries. Deposition rate is shown to be in conflict with large size uniformity. Main uniformity problems are found to originate from uneven RF voltage distribution, the effect is shown to be amplified near plasma equilibrium transitions. Contamination, a key factor for production quality, is controlled by the hot pressurized plasma box by both reducing unwanted background gas near UHV level and by allowing systematic fast plasma cleaning without machine corrosion or post contamination. Powder formation and dynamic is discussed based on several novel experiments and powder formation threshold is shown to be pushed away if the plasma is made intermittent.
Characterization of Electron Cyclotron Resonance Plasma-Deposited Hydrogenated Amorphous Silicon and Related Alloy Films
Authors: Essick J. M. , Pool F. S. , Shing Y. H. , Holboke M. J. 
Published: March 2011

ABSTRACTWe characterized a-Si:H films deposited by the electron cyclotron resonance (ECR) microwave plasma-enhanced CVD technique with the purpose of comparing ECR film quality widi that of films deposited by the rf plasma-enhanced CVD method. These ECR films were deposited in the 1–10 mT pressure region under a variety of growth conditions. Our investigations reveal the following typical properties for intrinsic ECR-deposited a-Si:H: (1) high photosensitivity as indicated by a light-to-dark DC conductivity ratio of up to 2×106, (2) a Tauc gap in the range of 1.75–1.85 eV, (3) an Urbach slope of 45–60 meV as determined by CPM and (4) an integrated deep defect density of 0.5–2×1016 cm-3 with Ec - Ef = 0.74–0.87 eV as determined by drive level profiling and junction capacitance vs. temperature scans. Variations of these quantities with deposition temperature, hydrogen dilution and magnetic field profile are discussed. Our results indicate that ECR-deposited a-Si:H is of comparable quality to a-Si:H deposited by the rf plasma glow discharge technique. ECR deposition conditions for a highly conductive type of a-Si:H film also are discussed. This material, while only slightly photosensitive and possessing an Urbach slope of over 100 meV, has a light DC conductivity of 3×10-4 (Ωcm)-1. Boron doping of this material produces a conductivity of 5×10-2 (Ωcm)-1.
Growth and Characterization of Hydrogenated Amorphous Silicon using Liquid Organic Sources
Authors: Gaughan K. , Hershgold S. , Viner J. M. , Taylor P. C. 
Published: March 2011

ABSTRACTThe uses of liquid sources such as tertiarybutylphosphine (TBP) for n-type doping in hydrogenated amorphous silicon (a-Si:H) and ditertiarybutylsilane (DTBS) and n-butylsilane (NBS) for hydrogenated amorphous silicon-carbon alloys (a-SiC:H) are described. A rf glow discharge process is employed to produce the doped a-Si:H and a-SiC:H thin films. Tertiarybutylphosphine (TBP) may ultimately be preferred over phosphine because TBP is less toxic, less pyrophoric and safer to implement. The gross doping properties of a-Si:H doped with TBP are the same as those obtained with phosphine, but there are some differences. N-butylsilane (NBS) and DTBS have been used to produce wide band gap (E04 3 ≈ eV) a-SiC:H.
Measurement of Intrinsic Stress in a-Si:H thin films Deposited in a Remote Hydrogen Plasma Reactor
Authors: Stevens K. S. , Johnson N. M. 
Published: March 2011

ABSTRACTThe effects of deposition conditions on the intrinsic stress in a-Si:H films deposited in a remote hydrogen plasma reactor are reported. The intrinsic stress is calculated from the change in substrate curvature induced by the a-Si:H film, as measured by the optical lever technique, and the results are compared with those for rf glow discharge deposited a-Si:H films.
Study of Oxidation Properties of Amorphous Si:B Films
Authors: Yang G.-R. , Nason T. C. , Wu Y.-J. , Tong B. Y. , Wong S. K. 
Published: March 2011

ABSTRACTThin films of an amorphous silicon-boron alloy with boron content 1–50 at.% have been deposited by low pressure chemical vapor deposition (LPCVD). The boron content and film thickness of the samples were controlled by regulating the ratio of diborane and silane gases during the deposition. It was observed that the crystallization of the amorphous alloy took place at higher temperatures as boron concentration was increased. After a thermal oxidation was performed, the stoichiometry of die resulting oxide layers on various samples was determined by the secondary ion mass spectrometry and Auger depth profile methods. While the threshold temperature for thermal oxidation was determined to be inversely proportional to the boron concentration, the oxidation rate showed a dramatic increase with boron content. In particular, an alloy containing 30% boron was readily oxidized at 500°C. Mechanisms for the enhancement of oxidation consistent with stoichiometric and spectroscopic properties of the oxide layers are discussed.
An Investigation of the Influence of Plasma Characteristics on the Electronic and Optical Properties of Device Quality a-Si:H Grown by Electron Cyclotron Resonance Plasma Deposition
Authors: Knox Ralph D. , Dalal V. L. , Moradi B. 
Published: March 2011

ABSTRACTThe electronic and optical properties of device quality hydrogenated amorphous silicon (a-Si:H) films grown by electron cyclotron resonance (ECR) plasma deposition were studied together with in-situ plasma characteristics. Hydrogen and helium plasmas, excited by 50–250 watts of 2.45 GHz microwave power under ECR conditions, were used to decompose silane at 6 to 20 mtorr pressures during the deposition of a-Si:H films at a 297 C substrate temperature. Both the electron temperature and density, and ion flux are measured near the deposition surface using plane and cylindrical Langmuir probes. An attempt is made to correlate these plasma properties with the light and dark photoconductivity, optical gap, refractive index, and subband gap photoconductivity.
The Influence of Nitrogen Content on the Properties of Sputtered a-Si56Ge44:N:H Films
Authors: Drusedau T. 
Published: March 2011

ABSTRACTNitrogen related absorption bands of the IR spectra are used to determine the content of nitrogen and N—H bonds in a—Si56 Ge44 films. A preferential attachment of nitrogen to silicon is observed. Nitrogen incorporation enhances the normalized photoconductivity to 5 · 107 cm2/V at maximum. This is related to N—H complexes acting as donors. A correlation between optical gap and single oscillator energy is reported.
Hydrogen Stability in Hydrogenated Amorphous Silicon-Based Alloys
Authors: Beyer W. , Herion J. , Wagner H. , Zastrow U. 
Published: March 2011

ABSTRACTThe thermal stability of hydrogen in amorphous silicon-based alloy films was studied by deuterium/hydrogen interdiffusion and hydrogen effusion experiments. Depending on the film structure, hydrogen stability is limited by hydrogen surface desorption or hydrogen diffusion. The hydrogen surface desorption energy is found to decrease with rising germanium content and to increase with rising nitrogen and carbon content. At T = 400°C, hydrogen diffusion is found to proceed in the germanium subnetwork for a-SiGe alloys and in the silicon subnetwork for a-SiN and a-SiC alloys.
The Investigation of Fluorine Effects on Charge Trapping and Interface State Generation in Mos Structures
Authors: Xie Dunxian D. , Lin Ta-Cheng , Young Donald R. 
Published: March 2011

ABSTRACTThe bulk and interface charge trapping phenomena of fluorinated oxides have been studied by various electronic measurements. Fluorine is introduced into dry oxides by low energy (25kev) implantation followed by a 1000°C N2 ambient anneal to remove physical damage. Both the flat band and the mid gap voltage shifts of such MOS devices are measured during avalanche electron injection. We have developed techniques to separate effects due to interface state generation from bulk trapping effects. The bulk electron traps in the fluorinated oxides have a different cross section from the known water-related traps in conventional oxides. The generation of fast and slow interface states for different dosages of fluorine implantation is discussed based on Q-V and C-V measurements. The fast interface donor states, generated during avalanche injection, are charged at flat band but discharged at mid gap and beyond. An optimum dosage of fluorine implantation is found to suppress the so called turn-around effect during avalanche injection due to the formation of slow donor states. Finally, injection under high temperature (120°C-150°C) anneals out most of these donor states.
Interface Effects on Photocarrier Transport in a-Si:H
Authors: Persans P. D. , Arnzen D. , Possin G. , D'Anna L. , Zhao X. S. , Breton K. 
Published: March 2011

ABSTRACTWe discuss the absorption-length and film thickness dependence of photoconductivity in amorphous silicon using measurements of the ambipolar diffusion length and the Debye screening length.
Steady State Photocarrier Charge Collection in a-Si:H for Electrons and Holes
Authors: Abel C.-D. , Paes H. R. , Bauer G. H. 
Published: March 2011

AbstractCarrier transport in amorphous silicon pin-diodes has been analyzed by steady state photocarrier charge collection applying strongly absorbed light. For low intensities at room temperature electron charge collection is limited by recombination in the generation region. For increasing intensity ø and/or decreasing temperature charge collection becomes nonlinear in ø and shows S-like characteristics versus voltage.We present a model for this behaviour, including space charge limitation which e.g. for holes in a-Si:H limits charge collection even at room temperature due to low extended state mobility of holes and dark Fermi level position above midgap.
Thermal Quenching of Photoconductivity and the Sign of Photocarriers in Doped a-Si:H
Authors: Yoon B.-G. , Fritzsche H. , Tran M. Q. , Chi D.-Z. 
Published: March 2011

ABSTRACTThermal quenching (TQ) of photoconductivity σp occurs when the demarkation level of minority carriers passes through recombination centers having small capture cross section for majority carriers compared to other centers present but normal cross section for minority carriers. The photoconductivity becomes superlinear with light intensity at the temperature of maximum TQ. We discovered TQ not only in n-type but also p-type a-Si:H. This cannot happen with the same centers unless the sign of the majority carriers changes. We present evidence that in p-type and undoped films majority carriers are electrons at T below TQ and holes above TQ. The nature of these special centers will be discussed.
Elastic Moduli of H2O: Liquid, Ice VI and Ice VII
Authors: Grimsditch M. , Rahman A. , Poliant A. 
Published: March 2011

ABSTRACTThe results of a Brillouin scattering study of the room temperature phases of H2;O (liquid, ice VI and ice VII) up to 30 GPa are presented. Longitudinal elastic moduli thus obtained are compared with values of the bulk modulus obtained from density measurements [1] and with both static and molecular dynamics calculations of the bulk modulus using potentials which have been proposed in studies of the liquid state. The calculations indicate that the potentials are not capable of describing the high pressure region of ice VII.
Raman Spectra of Fluids in Elastohydrodynamic Contacts
Authors: Gardiner D.J. , Baird E. , Gorvin A.C. , Marshall W.E. , Dare-Edwards M.P. 
Published: March 2011

ABSTRACTInitial results of a novel Raman spectroscopic method for studying fluid lubricant characteristics in a simulated elastohydrodynamic contact are reported. The method uses a Raman microscope which allows spectra to be obtained from a small volume (∼ 0.1 nl) of lubricant entrapped in the elastic deformation formed when a loaded glass plate falls onto a lubricated steel ball. The work described here was undertaken to obtain direct pressure measurements from an entrapped fluid at equilibrium after the initial impact. Our results indicate that pressures in twofold excess of the maximum Hertzian pressure can be generated in ball-plate entrapments of the polyphenyl ether 5P4E. In addition 5P4E has been studied as a pure liquid and as a solution in CCl4 using a diamond anvil cell (DAC). Preliminary results on 2,4-dicyclohexyl-2-methylpentane studied using a DAC and a hydrostatic equilibrium cell are also described.
The Collapse or Ballooning Pressure of Thick-Walled Pressure Vessels
Authors: Crossland B. 
Published: March 2011

ABSTRACTDiscussion of the proposed extension of the ASME pressure vessel code to cover operating pressures up to 1.4 GPa (200000 lbf/in2 ) has generated the proposal that two criteria should be used, of which one would be the collapse or ballooning pressure not the bursting pressure. The present paper examines this proposal in relation to extensive data on the collapse and bursting of thick-walled vessels available to the author.It is concluded that the collapse pressure is only readily calculable for materials which approach the behaviour of an elastic/perfectly plastic material. It also appears for materials with significant strain hardening characteristics, such as mild steel, that the collapse pressure considerably underestimates the bursting pressure, whereas for a material which behaves as an elastic/perfectly plastic material the collapse pressure is nearly coincident with the bursting pressure. Consequently if the collapse pressure was adopted and if the factor of safety against collapse was adequate for one material it might be more or less than adequate for another material, which would appear to be unacceptable.