AMORPHOUS-SILICON FOR PHOTOVOLTAICS PRODUCED BY NEW MICROWAVE PLASMA-DEPOSITION TECHNIQUES

Amorphous hydrogenated silicon (a-Si:H) has been prepared by microwave (2. 45 GHz) plasmas in Ar-SiH//4 mixtures using two different deposition systems, a large-volume microwave plasma (LMP) apparatus, and a Surfatron system. Films of a-Si:H are characterized structurally (primarily by scanning electron microscopy), and by Fourier transform ir spectroscopy, as well as according to their electro-optical properties (dark and photoconductivity, I-V characteristics of Schotky-barrier diodes). Although microwave plasmas are thought to differ significantly from conventional lower frequency plasmas, results of the present characterizations show no evidence of this. Deposition in the Surfatron system gives rise to device-grade a-Si:H, as demonstrated by Schottky cell efficiencies exceeding 3%. We have been unable to duplicate this in the LMP system in spite of nominally identical fabrication conditions. Finally, an ageing effect of Au/a-Si:H/Sb-Cr Schottky diodes is described, unlike any reported hitherto.