Radiative recombination via intrinsic defects in CuxGaySe2

A detailed analysis of the radiative recombination processes in CuxGaySe2 epitaxial layers is presented aiming at an investigation of the intrinsic defect levels as a function of chemical composition. CuxGaySe2 is grown by metalorganic vapor phase epitaxy to allow a precise control of composition. Temperature and excitation intensity dependent photoluminescence is used to identify different recombination mechanisms and to determine the ionization energies of the defect levels involved. Defect-correlated optical transitions in Cu-rich epilayers are described in a recombination model consisting of two acceptor and one donor levels showing ionization energies of (60 +/- 10) meV, (100 +/- 10) meV, and (12 +/-5) meV, respectively. The identification of a shallow compensating donor in CuxGaySe2 and the assignment of the 100 meV state to an acceptor are the most important new aspects in this model. Photoluminescence properties of layers showing Ga-rich compositions are discussed in a model of highly doped and highly compensated semiconductors-the model of fluctuating potentials. (C) 2001 American Institute of Physics.