The influence of electrode shape and hydrogen dilution of SiH4 on the optical properties of glow-discharge hydrogenated amorphous silicon

Abstract We have investigated the influence of the shape of the r.f. electrode and the influence of hydrogen dilution of SiH4 on the optical properties of glow-discharge hydrogenated amorphous silicon, deposited at 100 and 250°C. Three r.f. electrodes were used one ring-shaped electrode and two circular flat-plate electrodes with different diameters. We conclude that by using the largest electrode, material with the lowest band-gap (E0 = 1·61 ev) is obtained. Fourier-transform infrared spectroscopy measurements suggest that the decrease of E0 with electrode size is not caused by a decrease in the total hydrogen content, but by a redistribution of H from clustered Si-H bonds at the surface of internal voids to isolated Si-H bonds. We suppose that this is due to a reduction in the void fraction. When we dilute SiH4 with H2 we find a pronounced decrease in the amount of SiH2 polymers, an increase of the refractive index and a decrease of the optical bandgap. This is also interpreted as being caused by a redu...