Photoluminescence in CuGaSe2

Abstract

The photoluminescence spectra of CuGaSe2 have been investigated at 76 K in the range 0.65 < λ < 1.1μ. The crystals were grown by iodine transport, and had p-type conductivity. The photoexcitation was provided by the single-line outputs of a CW Ar+ laser, and the luminescence spectra were analyzed using a 34 m grating monochromator.The luminescence observed consisted of a rather sharp structure near the energy gap, plus two broad peaks at considerably smaller energies. The broad peaks, centered around 1.52 and 1.30 eV respectively, are attributed to transitions involving deep localized states. The sharper structure near the energy gap is resolved into two peaks, one at 1.72 eV and another at 1.68 eV. This structure is explained by radiative recombination of free excitons (peak at 1.72 eV), and by recombination of free electrons with bound holes (peak at 1.68 eV).A thermal treatment done on the CuGaSe2 crystals changed both their electrical properties and their luminescence spectra. These changes produced by sample treatment, plus measurements of the excitation power dependence and the polarization of the luminescent radiation, are in agreement with the interpretation presented.