On the Shape of the Close-to-Band-Edge Photoluminescent Emission Spectrum in Compensated CuGaSe2

Abstract

Photoluminescence (PL) properties of compensated as-grown and air-annealed CuGaSe2 single crystals, grown by the vertical Bridgman technique, in the edge emission spectral region were studied. The intensity maximum of the broad asymmetrical PL band at T = 8 K was found to be at hνmax = 1.586 eV. After air annealing at 673 K for 15 min the PL band shifts towards higher energies, and its intensity slightly decreases but the shape remains the same. It is shown that this typical asymmetric PL 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 defects. The average depth of these fluctuations is determined by the Debye-Hïckel correlation in the distribution of donors and acceptors. The low-temperature air-annealing reduces the concentration of charged defects, but the sample remains highly compensated.