The hetero-structured SiCX films have been deposited by hot-wire CVD using SiH3CH3 as the carbon source gas. Although the carbon source gas ratio and filament temperature in the deposition using SiH3CH3 were smaller than those using C2H6, the carbon content in the sample deposited using SiH3CH3 was similar to that deposited using C2H6. The optical energy gap in the sample deposited using SiH3CH3 was larger than that deposited using C2H6. The sample deposited using SiH3CH3 under optimized condition showed a wide optical energy gap of 1.99 eV and a large dark conductivity of 15.1 S/cm. The p-type sample deposited using SiH3CH3 under the optimized condition has been used as a window layer material in p-i-n a-S:H based solar cells. (C) 2007 Elsevier B.V. All rights reserved.