Anomalous DC dark conductivity behaviour in a-Se films

Thin films of amorphous selenium have been prepared by thermal evaporation. DC conductivity measurements were carried out on these films in the temperature range between 208 and 322 K. Above room temperature, the dark conductivity is thermally activated with activation energy E_σ = 1.05 ± 0.08 eV. For temperatures below 285 K, an increase in the dark current is observed, which is interpreted in terms of a shift of the Fermi level that makes more states available for a hopping process.