Photoinduced electron transfer involving localized electronic states

It is assumed that large numbers of localized states which exist within the band gap of thin or highly disordered surface films take part in the photoexcitation process. Model calculations have been performed which describe the photoexcitation of an electron into one such localized state and its subsequent escape from this state to yield a photocurrent. The Poole-Frenkel effect, which describes the lowering of the escape barrier due to a superimposed field, direct tunneling and phonon-assisted tunneling processes are considered. The effects of various parameters, such as the effective mass of the electron and the dielectric constant of the material, on the escape probability are studied. These results are compared to photo-electrochemical studies of ion implanted HfO₂ films.