Spectroscopic features of nonlinear AgGaSe2 crystals

• Large AgGaSe2 crystals of high optical quality were grown by the Bridgman technique.
• Annealing in Ag2Se lowers optical losses down to 0.03 cm−1 in the 0.9–12 µm range.
• Reversible photoinduced absorption is a result of change in the charge state of point defects.
• Low temperature photoluminescence is due to free excitons and native point defects.

When producing large AgGaSe2 single crystals of high optical quality, the shadow and light scattering techniques were found effective. Annealing in proper atmosphere allows one to affect the crystal composition and the state of submicron-sized inclusions and point defects. Stoichiometric crystals demonstrate mainly photoluminescence (PL) of free excitons. New PL bands, a 727/745 nm doublet and a 950 nm broad band, are associated with selenium vacancy, VSe, and cation antisite defect, GaAg, respectively. Using the thermoactivation spectroscopy, the traps of charge carriers were revealed in AgGaSe2: those with thermal activation energy ET>0.4 eV were found responsible for photoinduced absorption on the 0.1 cm−1 level.