Effect of low-level boron doping and its implication to the nature of gap states in hydrogenated amorphous silicon

Abstract
Large simultaneous changes in ambipolar diffusion length (Ld) and photoconductivity (σph) were observed with boron doping below 1 ppm. The results can be explained satisfactorily by postulating that electrons and holes interchange their roles as majority or minority carriers at ∼0.4 ppm. The μτ products for both carriers are determined as a function of doping. The light intensity dependences of Ld and σph present new evidence for the existence of the hole trapping centers in a-Si:H and show that doping enhances the sensitizing effect due to these centers.