On the shape of the close-to-band-edge photoluminescent emission spectrum in compensated CuGaSe2

Photoluminescence (PL) properties of compensated as-grown and air-annealed CuGaSe2 single crystals, grown by the vertical Bridgman technique, in the e dge emission spectral region were studied. The intensity maximum of the bro ad asymmetrical FL. band at T = 8 K was found to be at hv(max) = 1.586 eV. After air annealing at 673 K for 15 min the PL band shifts towards higher e nergies, and its intensity slightly decreases but the shape remains the sam e. It is shown that this typical asymmetric pi, band is not associated with a certain acceptor level but originates from the band-tail recombination. The valence band tail is formed by the potential fluctuations of charged de fects. The average depth of these fluctuations is determined by the Debye-H uckel correlation in the distribution of donors and accepters. The low-temp erature air-annealing reduces the concentration of charged defects, but the sample remains highly compensated.