Density of states of a-Se near the valence band

Abstract The density of states (DOS) distribution in the vicinity of the valence band mobility edge in vacuum coated a-Se films has been constructed by studying the dependence of the shape of time-of-flight (TOF) transient photocurrent on the electric field and temperature, and also the dependence of the drift mobility on the temperature and field. We provide not only new experimental TOF data, but also re-examine previous TOF data, and show that, analogous to electron transport in a-Si:H, the DOS near Ev is a featureless, monotonically decreasing distribution in energy up to Ev + 0.4 eV, without the 0.28 eV peak near the valence band which was thought to control the hole drift mobility. Such a DOS was able to account for hole TOF data reported previously by several authors.