Doping dependence of the low-temperature photoconductivity in hydrogenated amorphous silicon

Abstract

The effect of doping on the steady-state photoconductivity σ_p of hydrogenated amorphous silicon (a-Si:H) down to temperatures of 4·2 K has been studied. Phosphorus doping up to 10⁻² PH₃/SiH₄ does not essentially change σ_p/eG, the photoconductivity normalized by the photocharge generation rate eG either at low T where σ_p/eG is constant, or between 30K < T < 50K where it rises with T. Boron doping on the other hand causes σ_p/eG at low T to decrease significantly and to rise with T at a higher temperature. This effect of boron doping is not related to the defect density or to the sign of the charge carriers. We tentatively attribute this effect to a heterogeneous morphology that is associated with boron doping.