Microscopic Origins of Metastable Effects in a-Si:H and Deep Defect Characterization in a-Si,Ge:H Alloys, Annual Subcontract Report, 1 February 1991 - 31 January 1992

Technical Report · Wed Jul 01 00:00:00 EDT 1992

DOI:https://doi.org/10.2172/7233282· OSTI ID:7233282

Cohen, J. D.

This report describes works to use transient photocapacitance and photocurrent measurements to determine the deep defect distribution and processes in low-band-gap a-Si,Ge:H alloys. Samples for these studies were produced by the photochemical vapor deposition (photo-CVD) growth method and were obtained through a collaboration with researchers at the University of Delaware. This report discusses how a detailed comparison between the photocapacitance and photocurrent spectra can be used to separately examine the majority and minority carrier processes. The results are as follows: (1) The midgap defect densities in the alloy regime near 1.3 eV can be as low as 5 {times} 10{sup 16} cm{sup {minus}3} in such photo-CVD samples. (2) There exists a second defect band roughly 0.4 eV below E{sub c} of a similar magnitude to the midgap defect density that exhibits significant lattice relaxation behavior in its electron trapping dynamics. (3) The hole {mu}{tau} products determined for the lowest defect sample are roughly 5 {times} 10{sup {minus}10} cm{sup 2}/V, comparable with the highest hole {mu}{tau} products reported in sandwich geometry measurements for alloys in this composition range. (4) The hole {mu}{tau} is found to be roughly inversely proportional to the midgap defect density for the samples studied. This is consistent with the fact that the effective minority carrier lifetime for such measurements is limited by the deep state trapping time.

• Research Organization: National Renewable Energy Laboratory (NREL), Golden, CO (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE)
• DOE Contract Number: AC36-08GO28308
• OSTI ID: 7233282
• Report Number(s): NREL/TP-451-4938; ON: DE92010588
• Country of Publication: United States
• Language: English

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14 SOLAR ENERGY
140501* -- Solar Energy Conversion-- Photovoltaic Conversion
360602 -- Other Materials-- Structure & Phase Studies
360606 -- Other Materials-- Physical Properties-- (1992-)
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AMORPHOUS STATE
CAPACITANCE
characterization
CHEMICAL COATING
CHEMICAL VAPOR DEPOSITION
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
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ELECTRIC CURRENTS
ELECTRICAL PROPERTIES
ELEMENTS
ENERGY LEVELS
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GERMANIUM ALLOYS
JUNCTIONS
MATERIALS
METASTABLE STATES
PHOTOCONDUCTIVITY
PHOTOCURRENTS
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PHOTOVOLTAIC CELLS
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