Low-temperature photoluminescence study of GaS0.5Se0.5 layered crystals

Photoluminescence (PL) spectra of GaS0.5Se0.5 layered single crystals have been studied in the wavelength range of 565-860 nm and in the temperature r ange of 15-170 K. Two PL bands centered at 585 nm (2.120 eV) and 640 nm (1. 938 eV) were observed at T = 15 K. Variations of both bands were studied as a function of excitation laser intensity in the range from 10(-3) to 15.9 W cm(-2). These bands are attributed to recombination of charge carriers th rough donor-acceptor pairs located in the band gap. Radiative transitions f rom shallow donor levels located at 0.029 and 0.040 eV below the bottom of the conduction band to deep acceptor levels located 0.185 and 0.356 eV abov e the top of the valence band are suggested to be responsible for the obser ved A- and B-bands in the PL spectra, respectively. A simple energy level d iagram explaining the recombination process is proposed. (C) 2001 Elsevier Science Ltd. All rights reserved.