Hydrogenated amorphous $Si_{1-x}C_{x}$ films were prepared by PECVD from a mixture of $C_{3}H_{8}$ and $SiH_4$. The optical properties and chemical bond structure of $a-Si_{1-x}C_{x}:H$ have been studied with using the deposition parameters such as substrate temperature($T_{s}$), r.f.power and propane fraction (Q) in gas mixture. The optical band gap increase monotonically with decreasing $T_{s}$, and also r.f.power and propane fraction Q.
From the result of the IR spectra analysis for $a-Si_{1-x}C_{x}:H$, a wider band gap is mainly due to Si-C and C-H bond in the deposit. Comparing $C_{3}H_{8}-SiH_{4}$ with $CH_{4}-SiH_{4}$, the $C_{3}H_{8}$-based $a-Si_{1-x}C_x:H$ films have wider optical band gap than the $CH_{4}$-based $a-Si_{1-x}C_{x}:H$ films. This result is attributed to the difference of decomposition between $C_{3}H_{8}$ and $CH_{4}$.
