BAND-EDGE PHOTOLUMINESCENCE AT ROOM-TEMPERATURE FROM ZNGEP2 AND AGGASE2

Photoluminescence near the band edge has been observed at room tempera ture from bulk single crystals of ZnGeP2 and AgGaSe2. Both of these ma terials are ternary chalcopyrite semiconductors, but they have quite d ifferent edge-related emission behavior. The emission from ZnGeP2 is o bserved to peak near 2.35 eV and is dominated by transitions from the upper Gamma(7) conduction band to the upper Gamma(6) valence band. The lack of emission at 1.99 eV from the lowest Gamma(6) conduction band in ZnGeP2 indicates a Gamma(6) conduction-band-energy minimum at the h igh-symmetry point T (T-1+T-2 band), rather than at Gamma (k=0). In co ntrast, AgGaSe2 is a direct band-gap semiconductor and ex hibits k=0 r adiative recombination at 1.793 eV. Based on the power dependence of t he PL emission intensity, this 1.793 eV band is shown to be excitonic in nature, thus giving a room-temperature band-gap energy near 1.814 e V for AgGaSe2.