Role of Zn Impurities in CuGaS2 at Relatively Low Concentrations Revealed by Photoluminescence Measurements

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Abstract
Photoluminescence spectra were studied for Zn-doped CuGaS2 crystals prepared by the iodine transport method from sources satisfying the (CuGaS2)1-x –(2ZnS) x (x=0.00025, 0.0005) relation. These crystals showed three donor-acceptor pair emissions. Analyses of the time-resolved spectra during decays of these emissions indicated the existence of several isolated levels, i.e., a common shallower level of ∼70 meV and three deeper levels of ∼120, ∼155 and ∼204 meV. Considering the possible defect formations in the crystals under the present preparation condition, the origin assignments of these levels were made as follows. The level of ∼70 meV and that of ∼120 meV are due to ZnCu donors and ZnGa acceptors, respectively. One of the levels of ∼155 and ∼204 meV is due to ZnCu–VGa acceptors and the other is due to VGa acceptors.