Optical spectroscopy of excitonic states in CuInSe2

Optical properties of structurally perfect CuInSe2 single crystals were stu died in the temperature range of 4.2-300 K with the use of photoluminescenc e, optical absorption, optical reflection, and wavelength-modulated optical reflection (WMOR). The intense lines of free excitons A (similar to 1.0414 eV) and B (similar to 1.0449 eV) with a half-width of similar to 0.7 meV a t 4.2 K are found to be related to two extrema of valence band split by a c rystal field. The excitons emission line C (similar to 1.2779 eV) in WMOR s pectra are related to a lower valence band split-off by spin-orbit interact ion. Within the context of the quasi-cubic Hopfield model, the parameters o f valence band splitting Delta(CF) = 5.2 meV and Delta(SO) = 234.7 meV defi ned by the crystal and spin-orbit interaction, respectively, are calculated . In the region of the fundamental absorption edge, the lines of bound exci tons are found with a half-width similar to 0.3 meV that is indicative of a high quality of grown CuInSe2 crystals. (C) 2000 MAIK "Nauka/Interperiodic a".