Dependence of the phototransport properties on the position of the Fermi level in polycrystalline CuInS₂ films

We report a simultaneous study of the phototransport properties of both the majority and minority carriers in polycrystalline CuInS₂ layers. This is done for n-type as well as p-type layers. The dependencies of these properties and their light intensity exponents on the position of the Fermi level yield a picture of the recombination levels and the recombination kinetics in these layers. We show that the simplest model which is consistent with the data is that of a symmetric two-level system. One level is associated with donorlike recombination centers lying around 0.35 eV below the conduction band edge, and the other level is associated with acceptorlike recombination centers lying around 0.35 eV above the valence band edge. This interpretation of the results is shown to be consistent with the luminescence and transport data reported previously on single crystals of CuInS₂.