The modulated photocurrent technique: a powerful tool to investigate band gap states in silicon based thin films

Abstract

The Modulated PhotoCurrent (MPC) technique is a very simple experiment that provides insight into localized gap states in semiconductors. It is particularly well suited to disordered silicon based thin films. We here give a review of the technique, emphasizing the effect of experimental parameters (frequency, temperature, dc generation rate) and the reconstruction of the density of states (DOS) in the two regimes: the widely used high frequency regime and the recently developed low frequency regime. We discuss the effect of different trap species and propose a new way to determine capture cross sections from the matching of the reconstructed DOS in both regimes. Illustrations are given theoretically with the help of a numerical modelling, and experimentally from data obtained on polymorphous silicon-germanium alloys. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)