On thermal quenching of the photoconductivity in hydrogenated amorphous silicon

Abstract

Thermal quenching (TQ) of the photoconductivity [sgrave]_p is the decrease in [sgrave]_p with increasing temperature. We present an explanation for TQ of [sgrave]_p usually observed above 100 K in undoped and weakly doped hydrogenated amorphous silicon (a-Si:H). With computer simulations employing the theory of Simmons and Taylor, we show that TQ is caused by the natural density of gap states of a-Si: H. The onset of thermal quenching occurs at the temperature T_TQ where the trapped hole density in the valence band tail has decreased to twice the density N_D of dangling bonds. We elucidate the experimental observation that T_TQ shifts to lower temperatures as the Fermi level shifts toward the valence band or as N_D is increased and explain the reported superlinear dependence of the inverse photoconductivity [sgrave]_p ⁻¹ on N_D . We test and discuss the validity of the Simmons-Taylor theory by comparing the simulated and experimental temperature dependences of the Rose exponent γ, which relates the photoconductivity and the generation rate.