Donor-acceptor pairs and excitons recombinations in AgGaS2

Silver thiogallate (AgGaS2) is a ternary semiconductor which crystallizes in the chalcopyrite structure. Silver thiogallate has been widely used in different applications for its interesting physical properties: wide transparency range (from 0.5 to 12 μm), high non-linear optical coefficient combined with good mechanical properties. The direct band gap in this compound is of about 2.7 eV and emissions due to free and bound excitons had been observed. Photoluminescence spectrum is also characterized by a wide emission band centred at 496 nm (2.50 eV) due to donor-acceptor pairs recombination (DAP). We performed photoluminescence (PL) measurements exciting with the third harmonic (3.5 eV) of a Nd:YAG laser from room temperature down to 10 K at different excitation power. In this work, we report the dependence of the photoluminescence features of AgGaS2 on the excitation power at various temperatures: ionization energy of defects are estimated on the basis DAP theoretical model and of thermal quenching of the photoluminescence; evidences of non-radiative processes competitive to DAP is also presented