Differences in the properties of amorphous hydrogenated silicon-carbide layers prepared with either methane or silylmethanes

Using a standard rf glow discharge deposition, we compare the properties of amorphous silicon-carbide (a-SiC:H) films prepared with different carbon sources, namely methane and di-, tri-, and tetrasilylmethane (DSM, TSM, and TetraSM). The optical bandgap E_G was varied between 1.8 eV and 2.4 eV. While we do not find significant differences in the optoelectronic properties of the differently prepared films there exist clear differences in the bonding structure as estimated by Fourier transform infrared spectroscopy: in one class, the methane based layers, hydrogen and carbon are mainly incorporated through CH₃ groups. In the other class, the silylmethane (SM) based layers, carbon is mainly bound in two configurations, i.e. in a silicon environment with tetrahedral coordination, and through CH groups incorporated in the SiC network. The consequences for the SiC stretching mode absorption of the two kinds of materials are discussed