Temporal and spatial distribution of minority carriers in semiconductors generated by modulated inhomogeneous illumination

Abstract

The distribution of minority carriers is derived which results from inhomogeneous illumination modulated at arbitrary frequency in a semiconductor sample with surfaces characterized by their surface recombination velocity. Results for a point source are discussed in detail. They are compared with experimental results from photoluminescence and light beam induced currents in solar cells. The method to determine the diffusion length in solar cells from the dependence of the short circuit current on the penetration depth of the light is discussed for arbitrary frequencies and inhomogeneous illumination in the vicinity of grain boundaries in polycrystalline materials. An unexpected phenomenon is found experimentally and is explained theoretically which demonstrates the complex nature of the carrier concentration by an interference effect of carriers with different phases. When a light beam, modulated at high frequencies, is scanned over the surface towards a grain boundary or an edge of the sample the amplitude of excess carriers is observed to increase although the recombination probability is increasing too.