Identifying Electronic Properties Relevant to Improving Stability in a-Si:H- Based Cells and Overall Performance in a-Si,Ge:H-Based Cells

Research output: NRELSubcontract Report


The work carried out by the University of Oregon under this subcontract focused on the characterization and evaluation of low-gap (a-Si,Ge:H) alloy materials and on issues related to overall stability in the mid-gap (a-SiH) materials. First, researchers characterized an extensive series of Uni-Solar a-Si,Ge:H samples using drive-level capacitance profiling and the analysis of sub-band-gapphotocapacitance and photocurrent spectra. Thus, several bands of deep defect transitions were identified. Researchers were able to verify that charged defects are responsible for the different observed defect bands in device-quality a-Si,Ge:H alloy material. Second, they reported results of their measurements on a-Si,Ge:H alloy 'cathodic' samples produced at Harvard University; these sampleswere found to exhibit significantly lower defect densities in the high Ge composition range (>50at.% Ge) than alloy samples produced either by conventional glow discharge of photo-chemical vapor deposition. Third, they performed voltage pulse stimulated capacitance transient measurements on a-Si:H/a-Si,Ge:H heterostructure samples to look for carrier trapping states that might be associated withthis interface; they found there was a clear signature of trapped hole emission extending over long times associated specifically with the interface itself in concentrations of roughly 1011 cm -2. Fourth, researchers reported the results on several hot-wire a-Si:H samples produced with varying hydrogen levels. Their studies indicate that hot-wire-produced a-Si:H, with H levels between 2-5at.%,should lead to mid-gap devices with superior properties. Finally, they discussed some results on glow-discharge material, as well electron-cyclotron-resonance-deposited a-Si:H grown under hydrogen dilution conditions, and confirmed that, in terms of deep-defect creation, such films exhibited improved stability compared to conventional glow-discharge material.
Original languageAmerican English
Number of pages68
StatePublished - 1998

Bibliographical note

Work performed by Department of Physics and Materials Science Institute; University of Oregon; Eugene, Oregon

NREL Publication Number

  • NREL/SR-520-25802


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