Impact ionization and mobilities of charge carriers at high electric fields in amorphous selenium

The behaviour of electron and hole quantum efficiencies as well as mobilities are investigated experimentally at high electric fields. The shape of transient small charge drift current as well as the field dependence of contributions of ionized electrons and holes to the quantum efficiency indicate impact interband ionization by holes at E > 8 × 107 V/m. At fields about 2 × 107 V/m the field dependence of electron and hole mobilities turnes from the power law, typical to stochastic transport, to a more pronounced dependence. The hole mobility at E ≈ 108 V/m loses its activated behaviour and saturates at the value of μp ≈ 10−4 m2/Vs.