Study of hydrogenated amorphous silicon films prepared at intermediate frequencies

Hydrogenated amorphous silicon films were prepared in an intermediate-frequency regime, between radio frequency and very high frequency, at 30MHz. The films have optimized deposition rates of about 9 Å s and a minimum dihydride contribution of 22%. The films were characterized by the dark conductivity, the photoconductivity, the bandgap, the bonded hydrogen content and the light-induced degradation of the photoconductivity. Optical emission spectroscopy served as the plasma diagnostic tool to compare quantitatively the relative abundance of the different emissive species present in the plasma. The surface was studied through X-ray photoelectron spectroscopy. Light-induced degradation studies of the photoconductivity and short-circuit current density provided some important information about defect creation in the high-substrate-temperature regime. Annealing recovery of the degraded photoconductivity and Fourier transform infrared spectroscopy studies also provided useful information regarding the hydrogen bonding configuration and hydrogen content for the amorphous silicon films under consideration. Possible mechanisms for the growth of such films are explored but the results presented here indicate the possibility of a preferred growth mechanism that takes into account the role of atomic hydrogen present in the plasma to explain the high deposition rates obtained for intermediate-and very-high-frequency conditions.