Role of carbon content in tuning the physical quantities of a-Si1-xCx:H alloys deposited by PECVD

Silicon rich hydrogenated amorphous silicon-carbon alloy films were deposited by plasma enhanced chemical vapour deposition in low power regime from silane methane mixtures diluted in helium by varying the methane fraction between 0.4 and 0.8. Films with carbon content ranging from 0.06 to 0.28 were obtained with a deposition rate of about 0.1 nm/s. The influence of carbon incorporation on the optical properties as well as disorder and defect density of the films has been investigated. The increase in carbon content leads to a decrease of the refractive index and an increase of the optical gap and disorder in the films. The defect density also increases with increasing carbon content, however lower values than those of films deposited by undiluted silane methane mixtures have been obtained for a carbon content greater than 0.1. Finally, the enhancement of carbon content causes the shift of peak position as well as the increase in the intensity and the width of the photoluminescence spectra. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim