CHARACTERIZATION OF A-SIGE-H FILMS PREPARED BY RF GLOW-DISCHARGE

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-degrees-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) approximately 250-degrees-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.