Identifying Electronic Properties Relevant to Improving Stability in a-Si:H-Based Cells and Overall Performance in a-Si,Ge:H-Based Cells: Annual Subcontract Report, 18 April 1994 - 17 April 1995

This report describes work performed by the University of Oregon focusing on the characterization and evaluation of amorphous semiconductor materials produced by novel deposition conditions and/or methods. The results are based on a variety of junction capacitance techniques: admittance spectroscopy, transient photocapacitance (and photocurrent), and drive-level capacitance profiling. Thesemethods allow the determination of deep defect densities and their energy distributions, Urbach bandtail energies, and, in some cases, ..mu..tau.. products for hole transport. During this phase, we completed out several tasks: (1) We carried out measurements on a-Si,Ge:H alloy samples produced at Harvard University by a cathodic glow discharge process. Measurement indicated a smaller value of (..mu..tau..)h for these samples than would have been expected given their lower defect densities. (2) We characterized several hot-wire a-Si:H samples produced with varying hydrogen levels. Our studies indicated that hot-wire-produced a-Si:H, with H levels between 2 5 at.% should lead to mid-gap devices with superior properties. (3) We reported some results on a-Si:H glow discharge material grownunder hydrogen dilution conditions. Preliminary studies point to film strain as playing a primary role for the observed differences in behavior.