Determination of semiconductor band gap state parameters from photoconductivity measurements. II. Experimental results

In this paper we apply various photoconductivity techniques to study different types of semiconductors. These methods are the modulated photocurrent, the steady-state photocarrier grating, and the steady-state photoconductivity techniques, and they are used to investigate a chromium-doped gallium arsenide crystal and different hydrogenated amorphous silicon thin films. First, we briefly recall what information on the material transport parameters can be extracted from the results of these various techniques. Second, we experimentally put into evidence the links existing between these apparently very dissimilar techniques by applying them first to a GaAs:Cr crystal and finally to three hydrogenated amorphous silicon samples prepared under different conditions. For this latter material, we show that the density of states distribution, the electron capture cross sections of the states---even that of the valence band tail---and the electron extended-states mobility can be obtained from the comparison of the results of these techniques. We conclude by showing that, by introducing these parameters into a numerical simulation, we can reproduce the behaviors experimentally observed for all the photoconductivity techniques.