EXCITONIC PHOTOLUMINESCENCE IN CUGAS2 CRYSTALS

The low-temperature photoluminescence (PL) spectra of CuGaS2 are investigated in this work. At 4.2 K, high-quality single crystals grown by both the iodine-transport and the melt-growth methods showed many sharp PL lines. Free-exciton (2.504 eV) and bound-exciton (2.501, 2.495, and 2.493 eV) lines are studied in detail with respect to transition energy, temperature, and excitation intensity. Phonon-assisted transitions have been observed in the low-energy regions of zero-phonon lines at 2.493, 2.404, and 2.397 eV. Most of them have been well interpreted on the basis of the phonon energies previously obtained by Raman measurements.