Temperature and field dependent effective hole mobility and impact ionization at extremely high fields in amorphous selenium

Abstract

An analytical model for the electric field and temperature dependent effective drift mobility of holes in amorphous selenium (a-Se) has been developed by considering density of states distribution near the valence band, field enhancement release rate from the shallow traps, and carrier heating. The models for the field-dependent microscopic mobility and momentum relaxation mean free path considering carrier heating are also proposed. The models are fitted with the published experimental results on effective hole mobility and impact ionization with wide variations of applied electric fields and temperatures. The fittings of the model with the published experimental data on the effective hole mobility reveal that, while the effective hole drift mobility increases with increasing temperature and field, the microscopic mobility and momentum relaxation mean free path in a-Se decreases with increasing electric field. A better fitting considering thermally activated tunneling for the field-enhancement release rate indicates that the shallow hole traps in a-Se are neutral defects.