Photo-induced changes in the properties of undoped and boron-doped a-Si:H films

Light-induced effects on the dark conductivity, photoconductivity, spectral responses and band gap of hydrogenated amorphous silicon thin films have been studied. The a-Si:H films were prepared by the r.f. glow-discharge decomposition of silane gas in a capacitatively coupled plasma-reactor system. Undoped a-Si:H films were prepared from a mixture of silane and hydrogen with the proportion of hydrogen varying from 0 to 80%. It was found that the magnitude of light-induced effects decreased with an increase in hydrogen concentration, which may be due to the removal of weak bonds contributing to the Staebler-Wronski effect. The effect of boron doping on light-induced effects has also been studied. For nearly compensated films at low boron concentrations the light-induced effects are small. As the boron doping is increased, the dark conductivity increases on light exposure and reaches a maximum which is the reverse of the normal Staebler–Wronski effect. It has been suggested that this effect is due to an increase in effective boron doping on exposure to light.