The influence of the growth conditions on the structural and optical properties of hydrogenated amorphous silicon carbide thin films

Two series of hydrogenated amorphous silicon carbide (a-SiC:H) films have been prepared by using plasma-enhanced chemical-vapor deposition (PECVD) with the gas mixture of methane (CH4) and silane (SiH4). The influence of the r.f. power density on the structural and optical properties of the films has been investigated with the CH4 gas ratio in the total gas flow rate ranging from 50 to 90%. The r.f. power density is an important parameter which affects both the carbon content and the structures of the films. Under high r.f. power condition, the samples are Si-rich and the structure of them is described as a disordered amorphous silicon network in which hydrogen atoms are incorporated in the form of Si-CH2 and Si-CH3 entities and carbon atoms are in a sp(3) carbon-related configuration. The optical band gaps of these samples increase with the increase of the gas flow ratio. Under low r.f. power condition, the samples are carbon-rich and the structure of them is a mixed phase of amorphous Si and graphite-like C clusters. The optical band gap of the series samples decrease with the increase of the gas flow ratio. (C) 1999 Elsevier Science S.A. All rights reserved.