Experimental evidence for long-range potential fluctuations in a-Se films

Transient photocurrents are used to study the energy distribution of deep localized states in amorphous selenium films. The distribution of traps, as resolved from the post-transit time-of-flight photocurrent transients, reveals an apparent temperature dependence at temperatures less than 0°C. However, no such temperature dependence of the trap-energy distribution was observed if this distribution is obtained from photocurrent transients measured in a gap-cell sample. We argue that this difference can be explained by the occurrence of long-range random potential fluctuations restricting access of carriers to some deep traps at lower temperatures.