Microscopic Origins of Metastable Effects in a-Si:H and Deep Defect Characterization in a-Si,Ge:H Alloys, Annual Subcontract Report, 1 February 1992 - 31 January 1993

Technical Report · Sun Aug 01 00:00:00 EDT 1993

DOI:https://doi.org/10.2172/10180625· OSTI ID:10180625

Cohen, J. David

This report describes work to evaluate low-mobility-gap a-Si,Ge:H alloy films. Results are based on junction capacitance techniques of admittance spectroscopy, transient photocapacitance (and photocurrent), and drive-level capacitance profiling. Eight a-Si,Ge:H alloy samples grown by photo-CVD encompassed the range of optical gaps from 1.3 to 1.6 eV, and corresponding Ge fractions from about 20 to 60 at%. We employed junction capacitance techniques to determine deep defect energies and densities, Urbach band-tail energies, and {mu}{tau} products for holes. Electron microprobe analysis provided accurate Ge fractions for our samples, thus enabling us to establish clear trends in measured electronic properties vs Ge fraction. We concluded that these photo-CVD samples exhibited equal or superior properties in terms of band-tail widths, and stable defect densities compared to any reported results on a-Si,Ge:H samples grown by glow discharge. By assigning defect energy levels from analysis of transient subband-gap photocapacitance and photocurrent spectra, we found clear evidence for two distinct defect subbands, one at roughly midgap and the other in the upper half of the gap. The trapping lifetime related {mu}{tau} products for holes decreased in direct proportion to the density of mid-gap defects in these samples. This appears to be the case regardless of whether we are dealing with stable defects or defects created by light-soaking.

• 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: 10180625
• Report Number(s): NREL/TP-451-5737; ON: DE93018205
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140501
360606
426000
alloys
amorphous silicon
AMORPHOUS STATE
CAPACITANCE
characterization
CHEMICAL VAPOR DEPOSITION
COMPONENTS
ELECTRON DEVICES AND CIRCUITS
CRYSTAL DEFECTS
ELECTRICAL PROPERTIES
ENERGY GAP
FILMS
germanium
GERMANIUM ALLOYS
HOLES
HYDROGEN ADDITIONS
JUNCTIONS
OPTICAL PROPERTIES
PHOTOCHEMICAL REACTIONS
PHOTOVOLTAIC CONVERSION
photovoltaics
PHYSICAL PROPERTIES
PROGRESS REPORT
SCHOTTKY BARRIER DIODES
SILICON ALLOYS
solar cells