THE THEORY OF THE PHOTOCONDUCTANCE UNDER THE PRESENCE OF A SMALL PHOTOCARRIER GRATING

Recently, responding to the need for the determination of the minority-carrier diffusion length in noncrystalline materials and devices, Ritter, Zeldov, and Weiser suggested a new photocarrier grating technique that became very popular among researchers of these materials. In this paper we present the first closed-form solutions for the photoconductance of the corresponding physical system. This system consists of a photoconductor that is subjected to both a uniform illumination and a periodically varying illumination of much lower intensity. The present analysis, which considers the effect of trapping, enables the evaluation of the conditions under which the experimental results can be uniquely translated into the value of the ambipolar diffusion length and thus into the mobility-lifetime (μτ) product of the minority carriers. In particular it is shown that the larger the shallow trapping the more justified the above translation.