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.