The hydrogenated amorphous silicon carbon alloys(a-SiC:H) have been prepared by mercury sensitized photo-CVD of silane-acetylene mixture. We have studied the electical and optical properties of a-SiC:H in the various conditions i.e., substrate temperature, total pressure, hydrogen dilution, and carbon incorporation. As substrate temperature increases, optical gap and activation energy decrease, but photoconductivity of the samples increases. As total pressure or carbon incorporation increases wider optical gap and lower photoconductivity are obtained. The optical gap of samples prepared in hydrogen dilution condition increases as dilution ratio increases, but the photoconductivity of samples increases slightly. IR absorption spectra show that electrical property of the samples is related to $Si-CH_3$ bonding. A photoconductivity of 9.65×$10^{-9}$ ($\Omega^{-1}cm^{-1}$) was obtained for undoped a-SiC:H with optical gap of about 2.0eV.
