Hydrogenated amorphous silicon‐carbon alloys (a‐SiC:H) with band gaps around 1.9 eV have been prepared using trisilylmethane (TSM) as the carbon source by plasma‐enhanced chemical vapor deposition. Compared toa‐SiC:H alloys prepared from the conventional CH4/SiH4mixture, the TSM‐based films show sharper optical‐absorption edge, weaker defect‐related optical absorption, lower methyl group concentration, longer ambipolar diffusion length, and higher photoconductivity.