Optical, electrical and structural properties of hydrogenated amorphous Si-C alloys deposited by different hydrocarbon gas mixtures

Abstract

Abstract The effects of rf power on the optical, electrical and structural properties of hydrogenated amorphous silicon-carbon (a-Sii1−xCx :H) films deposited by plasma-enhanced chemical vapour deposition from gas mixtures of silane (SiH4) + methane (CH4) and SiH4 + acetylene (C2H2) are reported. It was found that on increasing the rf power there is a marked increase in the carbon incorporation in CH4-based alloys grown in the low-power regime. a-Si1−xCx : H films with an optical energy gap from 1.9 to 2.2 eV were produced and the increasing C content did not affect the disorder and defect density. Furthermore these films can be obtained with a high deposition rate and good electronic properties. On the contrary, in C2H2-based alloys on increase in the rf power the optical gap and Urbach energy decrease while the photoconductivity increases. These behaviours can be attributed to decreases in both carbon and hydrogen incorporation. However, these alloys have, in the investigated range of the deposition par...