Defects in CuGaSe2 thin films grown by MOCVD

Optical and electrical properties of CuCaSe2/GaAs(001) heteroepitaxial layers as a function of chemical composition are presented. The photoluminescence (PL) spectra observed for Cu-rich epitaxial layers are interpreted in a model consisting of one donor and two acceptor levels with ionization energies of 80, 50 and 10 meV, respectively. The radiative recombination of Ga-rich samples is dominated by broad donor-acceptor-pair bands that shift to lower energies with decreasing Cu/Ga-ratio. The peak energies of these broad emissions are strongly excitation power-dependent showing a blueshift of up to 17 meV per decade. The observed PL properties of Gn-lich samples are discussed in terms of strong compensation as supported by Hall measurements, Hall mobilities of above 250 cm(2)/V s have been found for near stoichiometric, slightly Ga-rich epitaxial layers. The electrical properties of CuGaSe2/GaAs(001) grown under Cu-rich conditions are found to be influenced by a Cu,Se secondary phase as expected from the Cu-Ga-Se phase diagram. (C) 2000 Elsevier Science S.A. All rights reserved.