Defect levels and charge carrier photogeneration in amorphous selenium layers

Time-of-flight post-transit data that suggested positions in the band gap at similar toE(v) + 0.4 eV and similar toE(c) - 0.55 eV for the thermally accessible levels of the intrinsic negative-U centers of a-Se have been re-examined. The introduction into the Onsager formalism of a distribution of initial carrier separations in the photogeneration process, together with random internal field fluctuations, and of the ensuing processes of bimolecular recombination and deep trapping lead to a good description of experimentally observed photogeneration efficiency in a-Se. (C) 2003 Elsevier B.V. All rights reserved.