Determination of semiconductor band gap state parameters from photoconductivity measurements. I. Theoretical developments

C. LONGEAUD; J. A. SCHMIDT; J. P. KLEIDER

PHYSICAL REVIEW B - CONDENSED MATTER AND MATERIALS PHYSICS

The American Physical Society

Lugar: Ridge; Año: 2006 vol. 73 p. 23531601 - 23561620

0163-1829

In this paper we examine and cross-check the information that can be extracted from different photoconductivity experiments. First, taking account of localized states in the band gap of a semiconductor, we give an analytical expression for the coefficient g that relates the dc photoconductivity s to the generation rate G by g= dln(s)/dln(G). We demonstrate that in the very simple case when all the gap states have the same capture cross-section, it is possible to perform a density of states spectroscopy from the variation of g with temperature and/or generation rate. We also propose a simplified expression for g in the case when different species of states are present within the gap of the semiconductor. Second, we put into evidence the links existing between three techniques apparently very different: the dc photoconductivity, the steady-state photocarrier grating and the modulated photocurrent techniques. The links between the results of these three techniques are explained and illustrated by means of numerical simulations. Finally, we show that the density of states distribution, the capture cross-sections of the states and, to a smaller extent, the extended states mobility of photoconductive semiconductors can be obtained from the comparison of the results of these techniques.