Characterization of bulk Cu0.85In1.05Se2 by photoluminescence and cathodoluminescence

Melt grown crystals in the CuInSe system show the phenomenon of phase segregation into a nearly stoichiometric CuInSe2 compound with chalcopyrite structure and a strongly copper deficient compound with an ordered defect chalcopyrite (ODC) structure. The photoluminescence of such a two phase Bridgman-grown CuInSe crystal with the selected composition Cu0.85In1.05Se2 has two broad emission bands: a transition A around 0.93 eV and a transition B around 1.10 eV, the latter being above the bandgap energy of CuInSe2. Both transitions A and B exhibit donor-acceptor pair type recombination behaviour. Spatially resolved cathodoluminescence shows that the two emission energies come from different regions of the crystal and have the form of micrometer-sized stripes. We conclude that the two transitions A and B originate from the two different phases which penetrate the crystal in growth direction as micrometer-sized lamellae [M. Hornung et al., J. Crystal Growth 154 (1995) 315]. From the emission energies, transition A at 0.93 eV can be attributed to the CuInSe2 compound whereas transition B at 1.10 eV belongs to the ODC phase.