Numerical simulation of the steady state photoconductivity in hydrogenated amorphous silicon including localized state electron hopping

Numerical simulation of the steady state photoconductivity in hydrogenated amorphous silicon over a wide temperature range (25–500 K) is extended, to include previously neglected carrier transitions between localized states. In addition to free carrier capture (emission) transitions into (from) localized states, we include the process of electron hopping in conduction band tail states. Exponential distributions are assumed for both conduction and valence band tail states, while the dangling bond defect distribution is calculated in accordance with the defect pool model. Localized to extended state transitions follow the Simmons and Taylor statistics, and localized to localized state transitions involve electron hopping between nearest neighbour sites. Comparison with simulations in the absence of electron hopping reveals a smooth transition around 110 K, between regions of (high temperature) extended state conduction and (low temperature) hopping conduction. A hopping transport energy level is identified as the peak of the energy distribution of the hopping photocarriers, and shows a temperature dependence in agreement with existing theoretical work.