Characterization of the defect levels in copper indium diselenide

High-resolution photoluminescence (PL) measurements were carried out at 10 K to identify the energy levels associated with the various defect states dominating the semiconductor CuInSe₂ (CIS). PL measurements were taken on the bare surfaces of both thin film and single-crystal (polished and cleaved) samples and through a (Cd,Zn)S window layer deposited by thermal co-evaporation onto the CIS absorber surface. A complete energy band diagram is proposed which identifies the origin of the 12 intrinsic defect states expected in this material. The effects of surface and heat treatments, used in device fabrication processing, on the existence and generation of defect states (deep and shallow) are identified and correlated with the device performance. The inferior single-crystal device performance is correlated with presence of a high density of process-generated radiative surface recombination states and trap levels.