A model of the avalanche carrier multiplication in amorphous materials is s
uggested. The model is based on the concept of sub-gap impact ionization co
ntrolled by thermally assisted dissociation of generated geminate pairs of
carriers. The obtained results explain an experimentally observed positive
temperature dependence of the avalanche multiplication factor in amorphous
selenium. (C) 2000 Elsevier Science B.V. All rights reserved.