Influence of irradiation of Cu(In,Ga)Se2 thin films by 10 MeV electrons on photoluminescence spectra

Abstract

Thin films of Cu(In,Ga)Se2 on Mo coated glass substrates were studied by photoluminescence (PL) technique before and after irradiation in liquid nitrogen bath with a dose of 1.8 x 1015 cm−2 of 10 MeV electrons to determine the nature of radiation defects in Cu(In,Ga)Se2. The PL spectra before irradiation contain a broad dominant band at 1 eV, consisting of 3 peaks P1, P2 and P3, and two low intensity bands P4 at 0.86 eV and P5 at 0.77 eV. Because of their strong j-shift the P1, P2 and P3 were assigned to the free-to-bound (FB) recombination of free electrons and holes localised at 3 different acceptors whose energy levels are affected by potential fluctuations of the valence band. The P4 and P5 bands were also assigned to the FB recombinations of free electrons but with deeper acceptors. Irradiation reduced the PL intensity of the dominant 3 bands P1, P2 and P3. We assign such a reduction to the formation of nonradiative defects acting as deep traps. Irradiation did not change the j-shift of the P3 band (12 meV/d) suggesting that the acceptor, associated with P3, was not affected by irradiation. However, irradiation reduced the P2 j-shift from 13.8 meV/d to 4 meV/d demonstrating a significant reduction of the compensation level associated with this acceptor. Warming to the room temperature doubled the intensity of the dominant band probably due to annealing of some radiation induced defects. It increased the P2 j-shift to 10 meV/d demonstrating rising compensation level associated with this acceptor.