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Release of water trapped in damaged fuel subsurface voids

Description: Uranium metal reacts actively with water to produce uranium oxide and hydrogen gas, and radiolysis of water also produces hydrogen in fuel containers. These fuel reactivities increase the potential for over pressurization and pyrophoric events during storage. Flow rate calculations were undertaken to examine the problem of the release of water trapped in subsurface voids during the vacuum drying for damaged fuel. To calculate the flow rates of the water vapor, five flow models are developed based on the kinetic theory of gases. The difference between the vapor pressure and the operating pressure provides the driving force for crevice water removal. Gas flow is divided into three types: viscous flow, molecular flow, and slip flow in the transition range. These calculations were focused on assessing that measured moisture release from the whole element drying studies currently in progress includes any water that may be trapped in subsurface voids.
Date: April 27, 1998
Creator: Huang, F.F.
Partner: UNT Libraries Government Documents Department

Hanford spent nuclear fuel cold vacuum drying proof of performance test procedure

Description: This document provides the test procedure for cold testing of the first article skids for the Cold Vacuum Drying (CVD) process at the Facility. The primary objective of this testing is to confirm design choices and provide data for the initial start-up parameters for the process. The current scope of testing in this document includes design verification, drying cycle determination equipment performance testing of the CVD process and MCC components, heat up and cool-down cycle determination, and thermal model validation.
Date: June 10, 1998
Creator: McCracken, K.J.
Partner: UNT Libraries Government Documents Department

Evaluation Of FWENC Process For Treatment Of MVST Sludges, Supernates, And Surrogates

Description: In 1998, the Foster Wheeler Environmental Corporation (FWENC) was awarded an 11-year contract to treat transuranic waste at the Oak Ridge National Laboratory, including Melton Valley Storage Tank (MVST) waste. Their baseline tank waste process consists of: (1) Separating the supernate from the sludge, (2) Washing the sludge with water and adding this wash water to the supernate, (3) Stabilizing the supernate/wash water or the washed sludge with additives if either are projected to fail Resource Conservation Recovery Act (RCRA) Toxic Characteristics Leaching Protocol (TCLP) criteria, and (4) Stabilizing both the washed sludge and supernate/wash water by vacuum evaporation. An ''Optimum'' treatment procedure consisted of adding a specified quantity of two stabilizers--ThioRed{reg_sign} and ET Soil Polymer{reg_sign}--and an ''Alternate'' treatment simply increased the amount of ThioRed{reg_sign} added. This report presents the results of a study funded by the Tanks Focus Area (TFA) to provide Oak Ridge Operations (ORO) with independent laboratory data on the performance of the baseline process for treating the sludges, including washing the sludge and treating the wash water (although supernates were not included in the wash water tests). Two surrogate and seven actual tank wastes were used in this evaluation. Surrogate work, as well as the initial work with actual tank sludge, was based on an existing sludge sample from Bethel Valley Evaporator Storage Tank (BVEST) W23. One surrogate was required to be based on a surrogate previously developed to mimic the weighted average chemical composition of the MVST-BVEST using a simple mix of reagent grade chemicals and water, called the ''Quick and Dirty'' surrogate (QnD). The composition of this surrogate was adjusted toward the measured composition of W23 samples. The other surrogate was prepared to be more representative of the W23 sludge sample by precipitation of a nitrate solution at high pH, separating the solution from ...
Date: January 30, 2003
Creator: Barton, JW
Partner: UNT Libraries Government Documents Department

Improving the figure of very good mirrors by deposition

Description: Mid-spatial frequency errors of near perfect mirrors can be reduced by deposition through a computer generated mask without degrading the superpolish. Experimental results are presented.
Date: June 1996
Creator: Sweatt, W. C.; Weed, J. W.; Farnsworth, A. V.; Warren, M. E.; Neumann, C. C.; Goeke, R. S. et al.
Partner: UNT Libraries Government Documents Department

CIS photovoltaic technology. Annual technical report, January 12, 1996--January 11, 1997

Description: Thin film photovoltaic modules based on Cu(In,Ga)Se{sub 2} have been shown to possess attributes that should enable them to compete effectively with silicon-based modules, and that should ultimately allow realization of a much lower $/Wp cost figure. These attributes are stability, high efficiency, and low materials cost. Energy Photovoltaics has explored novel CIGS formation recipes that can be implemented on a unique pilot line constructed to coat substrates 4300 cm{sup 2} in area. One particular feature of this line is the use of proprietary linear sources capable of downwards evaporation. After experimentation with several types of recipe, a so-called {open_quotes}hybrid{close_quotes} process was found to simultaneously yield the desired combination of properties, namely good adhesion, device efficiency, uniformity, and reproducibility. The steps involve precursor formation, compound formation, and termination. Diagnostic techniques used to study and improve the CIGS films included spatial mapping of thickness, composition (using Auger analysis), resistance, V{sub oc} and I{sub sc}. The last three items are determined by quick tests designed to provide rapid feedback on plate quality. Problem areas were broken down and isolated through use of techniques involving substitution of different pieces of equipment for certain processing steps. For example, pilot line precursors were selenized in both the pilot line and smaller scale R&D equipment.
Date: June 1, 1997
Creator: Delahoy, A.E.; Britt, J.S. & Kiss, Z.J.
Partner: UNT Libraries Government Documents Department

Integrated nonthermal treatment system study

Description: This report presents the results of a study of nonthermal treatment technologies. The study consisted of a systematic assessment of five nonthermal treatment alternatives. The treatment alternatives consist of widely varying technologies for safely destroying the hazardous organic components, reducing the volume, and preparing for final disposal of the contact-handled mixed low-level waste (MLLW) currently stored in the US Department of Energy complex. The alternatives considered were innovative nonthermal treatments for organic liquids and sludges, process residue, soil and debris. Vacuum desorption or various washing approaches are considered for treatment of soil, residue and debris. Organic destruction methods include mediated electrochemical oxidation, catalytic wet oxidation, and acid digestion. Other methods studied included stabilization technologies and mercury separation of treatment residues. This study is a companion to the integrated thermal treatment study which examined 19 alternatives for thermal treatment of MLLW waste. The quantities and physical and chemical compositions of the input waste are based on the inventory database developed by the US Department of Energy. The Integrated Nonthermal Treatment Systems (INTS) systems were evaluated using the same waste input (2,927 pounds per hour) as the Integrated Thermal Treatment Systems (ITTS). 48 refs., 68 figs., 37 tabs.
Date: January 1, 1997
Creator: Biagi, C.; Bahar, D.; Teheranian, B.; Vetromile, J.; Quapp, W.J.; Bechtold, T. et al.
Partner: UNT Libraries Government Documents Department

Spent nuclear fuel project cold vacuum drying facility safety equipment list

Description: This document provides the safety equipment list (SEL) for the Cold Vacuum Drying Facility (CVDF). The SEL was prepared in accordance with the procedure for safety structures, systems, and components (SSCs) in HNF-PRO-516, ''Safety Structures, Systems, and Components,'' Revision 0 and HNF-PRO-097, Engineering Design and Evaluation, Revision 0. The SEL was developed in conjunction with HNF-SO-SNF-SAR-O02, Safety Analysis Report for the Cold Vacuum Drying Facility, Phase 2, Supporting Installation of Processing Systems (Garvin 1998). The SEL identifies the SSCs and their safety functions, the design basis accidents for which they are required to perform, the design criteria, codes and standards, and quality assurance requirements that are required for establishing the safety design basis of the SSCs. This SEL has been developed for the CVDF Phase 2 Safety Analysis Report (SAR) and shall be updated, expanded, and revised in accordance with future phases of the CVDF SAR until the CVDF final SAR is approved.
Date: February 24, 1999
Creator: IRWIN, J.J.
Partner: UNT Libraries Government Documents Department

[Dynamic study of small metallic clusters]; Estudio Dinamico de Pequenos Agregados Metalicos

Description: We present a brief introduction to computer simulation techniques (particularly to classical molecular dynamics) and their application to the study of the thermodynamic properties of a material system. The basic concepts are illustrated in the study of structural and energetic properties such as the liquid-solid transition and the fragmentation of small clusters of nickel. [Espanol] Presentamos una breve introducci{acute o}n de las t{acute e}cnicas de simulaci{acute o}n por ordenador (en particular de la Din{acute a}mica Molecular cl{acute a}sica) y de su aplicaci{acute o}n al estudio de las propiedades termodin{acute a}micas de un sistema material. Los conceptos b{acute a}sicos se ilustran en el estudio de las propieades estructurales y energ{acute e}ticas, as{acute i} como de la transici{acute o}n de fase s{acute o}lido-l{acute i}quido y de las fragmentaciones de peque{tilde n}os agregados de n{acute i}quel.
Date: December 31, 1995
Creator: Lopez, M.J. & Jellinek, J.
Partner: UNT Libraries Government Documents Department

Laser-ablation processes

Description: The various mechanisms by which ablation of materials can be induced with lasers are discussed in this paper. The various ablation processes and potential applications are reviewed from the threshold for ablation up to fluxes of about 10{sup 13} W/cm{sup 2}, with emphasis on three particular processes; namely, front-surface spallation, two-dimensional blowoff, and contained vaporization.
Date: January 1, 1992
Creator: Dingus, R.S.
Partner: UNT Libraries Government Documents Department

DOE Hydrogen Sorption Center of Excellence: Synthesis and Processing of Single-Walled Carbon Nanohorns for Hydrogen Storage and Catalyst Supports

Description: The objective of the project was to exploit the unique morphology, tunable porosity and excellent metal supportability of single-walled carbon nanohorns (SWNHs) to optimize hydrogen uptake and binding energy through an understanding of metal-carbon interactions and nanoscale confinement. SWNHs provided a unique material to understand these effects because they are carbon nanomaterials which are synthesized from the 'bottom-up' with well-defined, sub-nm pores and consist of single-layer graphene, rolled up into closed, conical, horn-shaped units which form ball-shaped aggregates of {approx}100-nm diameter. SWNHs were synthesized without metal catalysts by the high-temperature vaporization of solid carbon, so they can be used to explore metal-free hydrogen storage. However, SWNHs can also be decorated with metal nanoparticles or coatings in post-processing treatments to understand how metals augment hydrogen storage. The project first explored how the synthesis and processing of SWNHs could be modified to tailor pore sizes to optimal size ranges. Nanohorns were rapidly synthesized at 20g/hr rates by high-power laser vaporization enabling studies such as neutron scattering with gram quantities. Diagnostics of the synthesis process including high-speed videography, fast pyrometry of the graphite target, and differential mobility analysis monitoring of particle size distributions were applied in this project to provide in situ process control of SWNH morphology, and to understand the conditions for different pore sizes. We conclude that the high-temperature carbon-vaporization process to synthesize SWNHs is scalable, and can be performed by electric arc or other similar techniques as economically as carbon can be vaporized. However, the laser vaporization approach was utilized in this project to permit the precise tuning of the synthesis process through adjustment of the laser pulse width and repetition rate. A result of this processing control in the project was to eliminate the large (2-3 nm) internal pores of typical SWNHs which were found not to store hydrogen ...
Date: May 24, 2011
Creator: Geohegan, David B.; Hu, Hui; Yoon, Mina; Puretzky, Alex A.; Rouleau, Christopher M.; Thonnard, Norbert et al.
Partner: UNT Libraries Government Documents Department

Preparation and properties of evaporated CdTe films: Final subcontract report, 16 February 1985-31 March 1987

Description: Previous work on evaporated CdTe films for photovoltaics showed no clear path to successful p-type doping of CdTe during deposition. Post-deposition annealing of the films in various ambients thus was examined as a means of doping. Anneals were done in Te, Cd, P, and As vapors and in vacuum, air and Ar, all of which showed large effects on series resistance and diode parameters. With As, series resistance values of In/p-CdTe/graphite structures decreased markedly. This decrease was due to a decrease in grain boundary and/or back contact barrier height, and thus was due to large increases in mobility; the carrier density was not altered substantially. Although the series-resistance decreases were substantial, the diode characteristics became worse. The decreases were not observed when CdS/CdTe cells were fabricated on Te vapor-annealed films. Preparation of ZnO films by reactive evaporation yielded promising results. Deposition of p-ZnTe films by hot-wall vapor evaporation, using conventional techniques, yielded acceptable films without intentional doping.
Date: July 1, 1987
Creator: Bube, R H; Fahrenbruch, A L & Chien, K F
Partner: UNT Libraries Government Documents Department

Vacuum deposition system

Description: The Physics Section vacuum deposition system is available for several types of thin film techniques. This vacuum evaporation system operates in the high vacuum range. The evaporation source is a resistive heating element, either a boat or a filament design. Coating is then line of sight from the source. Substrates to be coated can have a maximum diameter of 17 inches. At this time the variations in the thickness of the coatings can be controlled, by monitor, to within about 100 angstroms. The system diagrams follow the Operation Procedures and the Sample Coating Procedures provided in this document. 3 figs.
Date: May 31, 1990
Creator: Austin, S. & Bark, D.
Partner: UNT Libraries Government Documents Department

Synthesis, evaluation and defect compensation of tetrahedral glasses as possible solar cell materials. Final report, February 1, 1979-April 30, 1980

Description: The work reported was directed towards evaluation of new amorphous compounds for application in solar cells. The ternary A/sup II/B/sup IV/C/sub 2//sup V/ chalcopyrite systems were selected because of their inexpensive constituent elements and tetrahedral geometry. Polycrystalline samples of the ternary arsenides with Cd and Zn as the group II element and Ge, Si, Sn as the group IV element were synthesized. Thin films were deposited by vacuum evaporation of the bulk ternary arsenides. The stoichiometries of the films were irreproducible and were usually deficient in the lower vapor pressure group IV element. Films made by evaporating polycrystalline ZnAs/sub 2/, which also has a tetrahedral bonding structure, had stoichiometries generally in the range from Zn/sub 3/As/sub 2/ to ZnAs/sub 2/. The former compound is formed by the decomposition of ZnAs/sub 2/ to Zn/sub 3/As/sub 2/ and As/sub 4/. The intermediate stoichiometries are thought to be mixtures of the decomposition products. Preliminary results from annealing of the films indicate that heat treatment produces the stoichiometries expected for one of the two forms of zinc arsenide. The as-deposited films are amorphous when the substrate temperature is kept below 100/sup 0/C. The a-ZnAs/sub x/ films were characterized. EDAX and Auger analysis showed that films were homogeneous in the plane of the substrate, but that some variation occurred in the depth profile of the films. This change in composition is consistent with the sample decomposition which occurs during the evaporation. The as-prepared films were p-type with room temperature resistivities on the order of 10/sup 2/-10/sup 4/..cap omega..-cm. Optical absorption measurements gave optical band gap values of 1.2 eV for a-Zn/sub 3/As/sub 2/ and 1.5 eV for a-ZnAs/sub 2/. The ZnAs/sub x/ films were photoconductive.
Date: April 1, 1980
Creator: Rauh, R.D.; Rose, T.L. & Scoville, A.N.
Partner: UNT Libraries Government Documents Department

Cadmium sulfide/copper ternary heterojunction cell research. Quarterly technical progress report, October 1, 1977-December 31, 1977

Description: CuInSe/sub 2/ film preparation and characterization and CuInSe/sub 2//CdS conceptual model development are reported. Theoretical analysis has shown the dependence of CuInSe/sub 2/ film stoichiometry on the separation between the elemental source positions. Chemical analysis by scanning electron microprobe quantometer has revealed the stoichiometry variation to be less than a few percent across the 2 inch by 2 inch film. To reduce the stoichiometric variation across the film width, the film deposition system was modified to include a high temperature vapor homogenizer chamber. The three major carrier transport mechanisms across junction governing the I/V characteristics of the CuInSe/sub 2//CdS cell are: 1) the Shockley diffusion mechanism, 2) recombination in the space charge region, and 3) recombination through interface states. Mechanism 1 is not expected in thin film heterojunctions. The diode I/V characteristics for interface state recombination has a diode ideality factor A equal to one, whereas CuInSe/sub 2//CdS cells reported to date have a diode A factor of two, indicating space charge recombination. Changing the doping concentration of the CuInSe/sub 2/ would be a way of controlling recombination level involvement. This would lead to ideal A values and hence improved open circuit voltages.
Date: January 1, 1978
Creator: Mickelsen, R.; Selikson, B. & Chen, W.
Partner: UNT Libraries Government Documents Department

Pilot test of a vacuum extraction system for environmental remediation of chlorinated solvents at the Savannah River Site

Description: Vacuum extraction is an environmental restoration technique that is currently being applied to the remediation of soils and shallow segments that are contaminated with volatile constituents. In 1987, a h study was performed to evaluate the performance and potential applicability of this technology at the Savannah River Site (SRS). Vacuum extraction is useful when volatile constituents are present in the vadose zone. The technology has been used to remediate a number of sites across the country, including leading underground storage tanks, spill sites, landfill, and production facilities. The primary objective of the pilot study was to test the performance of the technology under the conditions specific to many of the potential areas of application at SRS. There is only a limited body of literature documenting field studiesin similar environments with in sands and clayey zones and a relatively thick vadose zone. Careful studies of this type are needed to develop full scale designs at SRS. The vacuum extraction pilot study at SRS was performed by a mm consisting of technical representatives of the Environmental Sciences Section in the Savannah River Laboratory (SRL), the Raw Materials Engineering and Technology Section of SRS, and TerraVac Inc., a subcontractor with experience in this field.
Date: December 29, 1991
Creator: Looney, B.B.; Pickett, J.B. (Westinghouse Savannah River Co., Aiken, SC (United States)) & Malot, J.J. (Terra Vac Inc., San Juan (Puerto Rico))
Partner: UNT Libraries Government Documents Department

Improved amorphous Si solar cells. Quarterly progress report No. 5, February 1-April 30, 1981

Description: Both n and p-type a-Si:H films with very high conductivities have been grown by diluting SiH/sub 4/ in Ar or H/sub 2/. These films have Fermi levels close to the conduction and valence bands (0.03 eV). The use of these heavily doped films as p/sup +/ and n/sup +/ junction layers in a p/sup +/in/sup +/ cell should increase the diffusion voltage of the diode, thereby increasing both J/sub sc/ and V/sub oc/. The analysis of conductivity and thermoelectric power on films of diverse thickness have revealed no systematic changes. However, the drift mobility shows a systematic increase with thickness. The analysis of cells by studying quantum efficiency vs. applied voltage has revealed the electron (..mu.. tau) product is limiting transport in nip cells and not the hole (..mu.. tau) product. Analysis reveals that typically (..mu.. tau)/sub eta/ = 10/sup -9/ cm/sup 2//V. A new device design, Tandem parallel-connected cells, has been evolved to improve the current collection in a-Si cells. This design may help increase J/sub sc/ to 15 to 16 mA/cm/sup 2/ in a-Si:H.
Date: November 1, 1981
Creator: Dalal, V.
Partner: UNT Libraries Government Documents Department

Preparation and properties of evaporated CdTe films compared with single crystal CdTe. Progress report No. 2, February 1-April 30, 1981

Description: The design, construction and testing of the hot-wall vacuum evaporation system is proceeding on schedule. The vacuum system, a Varian 3118 diffusion pump system, has been installed and tested. A calculation of the optimum possible efficiency for an n-p CdTe homojunction indicates a value of 14%. A complete background is given on the growth of over fifty CdTe single crystals at Stanford, the last four of which were grown as part of this program. Use of crystal regrowth and vibration during growth both increase crystal quality. Higher electrical activity of phosphorus acceptors in CdTe is achieved when 0.1% excess Te is used in place of 0.5% excess Te. Careful characterization of boules grown for this program are underway, using Hall effect or capacitance-voltage data on selected samples. Initial investigation of the properties of grain boundaries in p-type CdTe : P crystals indicates a grain boundary height of 0.44 eV unaffected by illumination. These results suggest that grain boundaries are more strongly pinned in p-type than in n-type CdTe.
Date: January 1, 1981
Creator: Bube, R H
Partner: UNT Libraries Government Documents Department

Preparation and properties of evaporated CdTe films compared with single-crystal CdTe. Progress report No. 5, November 1, 1981-January 31, 1982

Description: The hot-wall vacuum evaporator system has been put into use with successful deposition of seven thin films of n-type CdTe on glass. Microprobe analysis indicated that the films were stoichiometric CdTe. Optical transmission showed a well-defined absorption edge. Film resistivities on glass were reduced from 1.7 x 10/sup 8/ ohm-cm, to 6 x 10/sup 4/ ohm-cm by In doping; film resistivities under AM1.5 illumination are 2.0 x 10/sup 4/ and 5 x 10/sup 2/ ohm-cm, respectively compared to the dark values given above. Temperature dependence of the dark conductivity of the undoped CdTe film indicates an activation energy of 0.79 eV; in the light the activation energy was reduced to 0.1 eV. The high dark resistivity and activation energy indicate high intergrain potential barriers, which could produce the high resistivities observed even with fairly high free electron densities in the grains. Comparison will be sought between these results and those found for films deposited epitaxially on single crystal substrates. A detailed summary of absorption constant vs wavelength data for CdTe has been assembled for both single crystal and thin film materials. The absorption constant for thin film material appears to vary from 2 x 10/sup 4/ cm/sup -1/ at 8000A to 10/sup 5/ cm/sup -1/ at 5000A; single crystal values may be slightly higher. EBIC and light scanning techniques are being developed for characterizing grain boundary effects in bicrystals, and to evaluate the effects of passivation techniques. Defect densities at a grain boundary in a p-type bicrystal were found to range from 2 x 10/sup 12/ to 8 x 10/sup 12/ cm/sup -2/eV/sup -1/, using data derived from the J-V dependence of the grain boundary.
Date: January 1, 1982
Creator: Bube, R H
Partner: UNT Libraries Government Documents Department

Cadmium sulfide/copper ternary heterojunction cell research. Final report, April 1, 1980-August 25, 1982

Description: The properties of polycrystalline, thin-film CuInSe/sub 2//CdS and CuInSe/sub 2//Zn/sub x/Cd/sub 1-x/S solar cells prepared by vacuum-evaporation techniques onto metallized-alumina substrates are described. An efficiency of 10.6% for a 1 cm/sup 2/ area cell and 8.3% for an 8 cm/sup 2/ cell when tested under simulated AM1 illumination is reported. The mixed-sulfide cells are described as exhibiting increased open-circuit voltages, slightly higher short-circuit currents, and improved efficiencies. Mixed-sulfide film preparation by evaporation of CdS and ZnS powders from a single source and from two sources is discussed with preference given to the later technique. Selenide-film preparation in a planetary or rotating substrate vacuum-deposition apparatus is described. A 1 cm/sup 2/ area cell without AR-coating produced by the planetary approach is reported to demonstrate a 7.5% efficiency. The results of cell heat-treatment studies showing a strong environmental dependence are presented and indicate the desirability of an oxygen-containing atmosphere. An automatic, computer-controlled, cell-measurement system for I-V, C-V, and spectral-response analysis is described. The results of the cell-analysis and cell-modeling studies on both the plain CdS and mixed Zn/sub x/Cd/sub 1-x/S thin-film devices are presented. Finally, data obtained from constant illumination and elevated temperature life-tests on the thin-film cells showing little degradation after 9300 hours is reported.
Date: August 1, 1982
Creator: Mickelsen, R. A. & Chen, W. S.
Partner: UNT Libraries Government Documents Department

Thin-film cadmium sulfide/mixed copper ternary heterojunction solar cells. Technical progress report, September 30, 1977-September 30, 1978

Description: The objective of the work reported is to fabricate efficient thin-film photovoltaic cells in which one of the semiconductors is cadmium sulfide and the other is an alloy of two or more copper ternary chalcopyrite semiconductors of the type CuInS/sub 2/, CuInSe/sub 2/, etc. The alloys are chosen to provide perfect lattice matching with CdS. By recourse to pentenary alloys of the type Cu/sub x/Ag/sub 1-x/InS/sub 2//sub z/Se/sub 2//sub (1-z)/ it is possible within certain constraints to adjust energy gap and lattice constant independently. A goal of the program is to identify alloys of this type having perfect lattice matching with respect to CdS and energy gap of approximately 1.5 eV and to fabricate solar cells with this material as one of the constituents. Materials synthesis for use in sputter targets and thin film preparation are discussed. Films were prepared by r-f sputtering, vacuum evaporation, neutral argon beam sputtering, and spray pyrolysis. Also discussed are attendance of meetings, presentations of papers and publications, planned activity for the next period. Contract activities are summarized from the time of initiation. (LEW)
Date: January 1, 1978
Creator: Loferski, J. J.; Shewchun, J.; Roessler, B.; Vitale, G.; Gorska, M.; Piekoszewski, J. et al.
Partner: UNT Libraries Government Documents Department

Preparation and properties of evaporated CdTe films compared with single-crystal CdTe. Progress report no. 6, February 1, 1982-April 30, 1982

Description: Films of n-type CdTe:In have been deposited by hot-wall vacuum evaporation (HWVE) on 7059 glass substrates, BaF/sub 2/ single crystal substrates, metal (Pt, Cr, Mo, Al) coated glass substrates, and single crystal p-type CdTe substrates. Films deposited on 7059 glass show typically a dark resistivity of 2 x 10/sup 5/ ohm-cm and a light resistivity of 3 x 10/sup 2/ ohm-cm. With increasing In source temperature, the resistivity decreases, but actually increases slightly again if the T/sub In/ is raised above 600/sup 0/C. Photoexcitation increases the electron density but does not affect the electron mobility. It appears that the grains are depleted in the dark. Films deposited on BaF/sup 2/ show dark resistivity of about 5 ohm-cm and light resistivity of about 2 ohm-cm, corresponding to electron densities of about 3 x 10/sup 16/ cm/sup -3/ and electron mobilities of about 30 cm/sup 2//V-sec. For doping levels abpove 10/sup 16/ cm/sup -3/ photoexcitation increases the mobility, but not the electron density; it appears that the grains are not depleted in the dark in this case. Cr coated 7059 glass makes an ohmic contact to n-type CdTe films. A Schottky diode formed with a 100A thick Au layer showed V/sub oc/ = 0.46 V, J/sub sc/ = 9 mA/cm/sup 2/ and a solar efficiency of about 2%. An n/p homojunction device was made by HWVE deposition of a 1.5 ..mu..m thick n-type CdTe layer on a p-type CdTe single crystal substrate. Values of V/sub oc/ = 0.73 V and J/sub sc/ = 0.24 mA/cm/sup 2/ were obtained. Grain boundary investigations showed the additive quality of two independent grain boundaries when measured in series, and tested the effects of passivation by Au, Cu, Li and H/sub 2/ in p-type CdTe grain boundaries, and In in n-type CdTe grain boundaries. Marked decreases in ...
Date: January 1, 1982
Creator: Bube, R H
Partner: UNT Libraries Government Documents Department

Preparation and properties of evaporated CdTe films compared with single-crystal CdTe. Progress report No. 8, August 1-October 31, 1982

Description: The goal of the research is to develop efficient thin-film CdTe solar cells using the method of hot-wall vacuum evaporation for CdTe film deposition. A series of undoped CdTe film depositions was performed. Ampoules with small apertures were designed for Zone 3 and Zone 4 of the furnace (dopant zone, and Cd or Te zone) to allow the temperatures of these zones to be raised near that of the substrate and thus prevent deposition of Te in these zones during a deposition run. Weighing these ampoules also provides a convenient test of material evaporated. The first set of depositions with As impurity to produce p-type CdTe:As films was carried out. No large effect of As doping was observed in these early runs, but some system improvements have been made for the future. A CdTe homojunction with a 0.15 ..mu..m n-type CdTe:In layer on a p-type CdTe:P single crystal substrate has been analyzed. Modelling of the spectral response of the quantum efficiency suggests the presence of a thin inactive layer at the surface, possibly a depletion layer in the n-type film. Large values of the diode factor A indicate non-simple homojunction structures. A light spot scanning apparatus has been constructed using a He-Ne laser and a 4 ..mu..m optical fiber. This apparatus will be used to measure the recombination characteristics of grain boundaries covered by transparent Schottky barriers. The electrical conductivity of p-type CdTe films prepared by close-spaced vapor transport is markedly increased by heat treatment in H/sub 2/. Some recovery of the film resistivity is seen after 1 week in air.
Date: January 1, 1982
Creator: Bube, R Hl
Partner: UNT Libraries Government Documents Department

Preparation and properties of evaporated CdTe films compared with single crystal CdTe. Progress report No. 4, August 1-October 31, 1981

Description: The hot-wall vacuum evaporation system is nearly complete and the first films are expected in early December. CdTe homojunction cells were theoretically modelled and to some extent tested experimentally using the n-type CdTe film on p-type CdTe crystal homojunction cells previously deposited at Linz. Modelling emphasizes the known importance of surface recombination velocity for such homojunction cells. The n-type layer on the experimental cell was thinned by etching from 5 micrometers to 1.5 micrometers, with a corresponding increase in short-circuit current from 0.1 to 1 mA/cm/sup 2/. This behavior is as theoretically expected; to obtain a short-circuit current of 11 mA/cm/sup 2/, as required for a 10% cell, requires a thickness of about 0.2 micrometers for a surface recombination velocity of 10/sup 6/ cm/sec and other realistic cell parameters. By doping experiments on single crystal CdTe, it has been shown that the hole density does decrease when the P dopant density is decreased below a critical value in CdTe:P crystals, thus eliminating the possibility that the major acceptors in the P-doped crystals were not P impurity. Attempts to heavily dope CdTe with As were less successful, but this may be due to the use of elemental As as the dopant in this case rather than a compound of the dopant. Cs was shown to be an effective dopant of CdTe and resistivities as low as 0.3 ohm-cm corresponding to hole densities in the low 10/sup 17/ cm/sup -3/ range were obtained. An apparent correlation between the low-temperature barrier height associated with a grain boundary in CdTe and the angle of mismatch between the two grains has been observed. Improved capacitance of grain boundary measurements should yield defect densities.
Date: unknown
Creator: Bube, R H
Partner: UNT Libraries Government Documents Department