Thickness dependence of electron transport in pure a-Se photoconductive films

Abstract

Electron transport in vacuum-deposited a-Se films with thicknesses varying from 13 to 501 μm has been investigated by conventional time-of-flight (TOF) and interrupted field TOF experiments. To separate the influences of electric field and the thickness, all TOF experiments were performed at a constant electric field. It has been found that the electron mobility is relatively constant in thick films (L > 50 μm) and increases in thinner films (L < 50 μm) with decreasing thickness. On the other hand, the electron lifetime is relatively thickness independent in films with thickness L > 50 μm, but drops sharply in thin films when L < 50 μm. These observations can be explained based on the density of states model that includes three types of traps forming Gaussian-like distributions within the mobility gap as reported in Koughia et al. (J. Appl. Phys. 97, 033706 (2005)).