Amorphous hydrogenated carbon-silicon (a-Si_XC_Y:H) films were produced by plasma enhanced chemical vapor deposition (PECVD) in the audio-frequency (at) three-electrode reactor using tetramethylsilane as a source compound. The negative amplitude of af voltage, V_(-), measured on a small electrode, on which the films were deposited, was the only operational parameter of the deposition process. Investigations of electrical conductivity, optical absorption and internal photoemission were carried out for the films deposited at various V_(-). It was found that these films are composed of amorphous insulator (a-I) and amorphous semiconductor (a-S) fractions with different electronic structures. A basic band structure model for the a-I and a-S forms was proposed.