LOW-TEMPERATURE PHOTOLUMINESCENCE SPECTRA OF LAYERED SEMICONDUCTOR TLGAS2

Photoluminescence (PL) spectra of TIGaS2 layered single crystals were studied in the wavelength region 500-860 nm and in the temperature ran ge 9.5-293 K. We observed a total of three PL bands centered at 568 nm (2.183 eV, A-band), 718 nm (1.727 eV, B-band) and 780 nm (1.590 eV, C -band) at various temperatures. We have also studied the variations of the A-and B-band intensities vs excitation laser density in the range from 7 x 10(-2) to 9 W cm(-2). The A- and B-bands were found to be du e to radiative transitions from the deep donor levels located at 0.362 and 0.738 eV below the bottom of the conduction band to the shallow a cceptor levels at 0.005 and 0.085 eV located above the top of the vale nce band, respectively. The proposed energy-level diagram permits us t o interpret the recombination processes in TlGaS2 layered single cryst als. (C) 1997 Elsevier Science Ltd.