MEASUREMENT OF THE DENSITY OF GAP STATES IN AMORPHOUS SEMICONDUCTORS BY INFRARED STIMULATED CURRENTS

Abstract

A new method of measuring the density of gap states in amorphous semiconductors by employing a two-beam photoconductivity experiment is reported. In the two-beam experiment, an intensive bandgap pump light is used to create non-equilibrium carriers and most of these carriers are trapped in the gap states. Then, at a latter time td after turning off the pump light, these trapped carriers are re-excited by an infrared probe light A photoconductivity overshoot, which depends on the delay time and temperature, is observed in the onset process of IR excited photoconductivity. The results are discussed using the multiple trapping theory. The distribution of the density of gap states is deduced from the experiment.