Transient hole currents in hydrogenated amorphous silicon at low temperatures and high fields

Abstract

Low-temperature high-field properties of hole transport have been investigated by transient photoconductivity experiments on undoped hydrogenated amorphous silicon. The hole μτproduct at 80K is roughly 7 × 10⁻¹⁰ cm ² V⁻¹ and the hole mobility 9 × 10⁻³ cm ² V⁻¹ s⁻¹ or greater at about 10⁵Vcm⁻¹. The dispersion parameter α_D calculated from the slope of the post-transit decay increases from 0 at F< 10⁵Vcm⁻¹ to about 0·4 for F = 2.5 × 10⁵ Vcm⁻¹. The data are discussed in terms of field-stimulated hopping in the valence-band tail and an analytic interpretation of the characteristic current decay is introduced. The data demon-strate the large influence of the field on hole propagation at low temperatures.