Optoelectronic properties, structure and composition of a-SiC:H films grown in undiluted and H-2 diluted silane-methane plasma

a-SiC:H films with energy gap in the range 2.00-2.65 eV have been grown by plasma enhanced chemical vapor deposition in undiluted and H-2 diluted SiH4 + CH4 gas mixtures, by making use of optimized deposition conditions, A complete picture of structural, compositional, optoelectronic, and defective properties for high quality films has been drawn for the first time, We show that the addition of H-2 to the gas mixture leads to a different chemical composition of the deposited films; in particular, carbon incorporation is enhanced and a carbon fraction in the solid matrix up to C/(C + Si)approximate to 0.45 can be obtained. These films have a higher mass density, a reduced microvoid and carbon cluster concentration, a better structural connectivity, and improved optoelectronic properties. For samples with optical gap below 2.4 eV, the reduced defect concentration of H-2 diluted films results in an increase of the photoconductivity gain and the steady-state (eta mu tau)(ss) values up to two orders of magnitude. (C) 1997 American Institute of Physics.