OPTICAL-PROPERTIES OF EXCITONS IN GATE

We present photoluminescence and transmission measurements of vapor-grown GaTe crystals. The ground-state IS triplet and singlet excitonic peaks are well resolved in the optical photoluminescence spectra from high-quality crystals, the triplet state lying approximately 1. 6 meV lower in energy than the singlet state. The emission intensity ratio of these two peaks is close to the 3:1 ratio of their spin multiplicities. The IS singlet-state emission is strongly polarized perpendicular to the crystal b axis, whereas the emission from the triplet state is partially polarized along the crystal b axis. Transmission spectra also indicate that the absorption corresponding to the n = 1 exciton is made up of two peaks, of which the higher-energy one is observed only for light polarized perpendicular to the b axis. Two small peaks on the lower-energy side of the photoluminescence triplet peak are believed to correspond to IS singlet and triplet excitons bound to a strain-induced defect center.