Space-charge-limited currents at low temperatures in hydrogenated amorphous silicon

Abstract

Transient and steady-state space-charge-limited currents (SCLCs) have been measured in intrinsic hydrogenated amorphous silicon (a-Si: H) n⁺-i-n⁺ and p⁺-i-p⁺ configurations of various thicknesses in the low-temperature regime T < 100 K. Transient measurements of the field dependence of the electron mobility and its dispersion are compared with d.c. SCLC results made on the same samples. At fields above 10⁵Vcm⁻¹, the increase in conductivity is dominated by the increase in carrier mobility. A simple model is presented to show that a strongly field-dependent mobility prevents the build-up of inhomogeneous carrier and field distributions in the bulk of a-Si: H in the SCLC regime. The field enhancement explains the similarity of transport properties measured for intrinsic a-Si: H in the SCLC regime and for doped a-Si:H in the SCLC-free case.