Effects of deviation from stoichiometry on excitons in CuInSe2 single crystals

Abstract High-quality CuInSe 2 (CIS) single crystals grown by the vertical Bridgman method were studied using photoluminescence (PL) and optical reflection. The Cu/In ratio of the crystals varied from 0.8 to 1.2. At 4.2 K free-exciton peaks A and B as well as a number of bound-exciton peaks were observed well resolved in the PL spectra. Deviations from Cu/In=1 result in shifts of the free-exciton peaks to lower energy and an increase in their full width at half maximum. The A–B separation energy was found to be strongly influenced by the Cu/In ratio and temperature suggesting that the valence band B is less sensitive to the tetragonal distortion in the lattice than the uppermost valence band A.