Characterization of a-SiGe: H films prepared by rf glow discharge

Abstract

Hydrogenated amorphous silicon-germanium alloy films have been prepared by rf glow discharge decomposition of a mixture of silane, germane and hydrogen varying the germane concentration in the gas mixture and the substrate temperature. The opto-electronic properties of a-SiGe: H films deteriorate sharply as the germane concentration is increased in the source gas mixture. This deterioration is attributed to an increase in defect density with Ge incorporation. The substrate temperature, T_s, was varied in the range 100-350°C. Due to the healing effect on the amorphous network at higher temperature, the opto-electronic properties of a-SiGe: H films improve up to T_s not, vert, similar 250° C. At higher T_s, the properties deteriorate due to the breaking of weak Ge--H bonds. Infrared vibrational spectra show formation of polyhydrides and higher Ge concentration at lower T_s. The increase in density of states with higher Ge content is shown by ESR data.