Abstract The effects of discharge parameters on the properties of hydrogenated silicon–carbon films deposited by PECVD system have been investigated. Hydrogenated microcrystalline silicon–carbon films have been grown at low RF power. The increase in RF power from 5 to 25 W leads to a decrease of the crystallinity degree and an enhancement of the carbon content from 0.025 to 0.10. The optical energy gap can be tuned in the 1.86–1.96 eV range and the dark conductivity decreases by about three orders of magnitude. In the investigated pressure range (1.7–2.9 Torr) microcrystalline samples show approximately the same optical and electrical properties. Microcrystalline films with high dark conductivity present an n-type character and the micro-mono crystalline silicon heterostuctures fabricated with these materials reveal a rectifying behaviour of the junctions.