Light-induced metastable state in doping-modulated amorphous silicon superlattices

Abstract

Photo-induced decrease in conductance after long light exposure has been observed for hydrogenated amorphous silicon (a-Si:H) npnp . doping-modulated superlattices showing large persistent photoconductivity (PPC). The initial increase in PPC is taken over by the decrease even to the negative PPC after long illumination. This light-induced, metastable conductance can be recovered completely by 160°C annealing, which is independent of exposure time. In particular, the metastable defects created in the p-layers are found to be annealed out at 100°C. The subband gap light exposure on the a-Si:H npnp. multilayers showing n-type conduction gives rise to the increase of conductance. On the contrary, the conductance of the multilayers having p-channel conduction decreases by IR exposure. These results strongly suggest the creation and annealing of dangling bonds by light-soaking and annealing in doping-modulated superlattices.