Photoluminescence of epitaxial CuGaS2 on Si(111): model for intrinsic defect levels

Epitaxial thin films of the wide-band-gap chalcopyrite semiconductor CuGaS2 have directly been grown on single crystalline Si substrates of (111) orientation. The CuGaS2 films crystallize exclusively in the chalcopyrite structure of bulk CuGaS2 material without considerable strain. Photoluminescence (PL) measurements reveal excitonic emissions from 5 to 300 K and defect-related optical transitions at low temperatures. Based on the identification of two free-to-bound and the two related donor-acceptor transitions, we propose a model for intrinsic defect levels, which includes one shallow donor and two acceptor states.