Point Defect Changes in CuGaSe₂ Induced by Gas Annealing

Epitaxial CuGaSe₂ films were grown on GaAs substrates under Cu-excess conditions to obtain stoichiometric compositions. The films were annealed in Ar, Se_x or O₂ ambients with or without a Cu or Cu-Se cap layer with the intention of changing the intrinsic defect concentrations. Samples were evaluated using low-temperature photoluminescence (PL) measurements. Annealing of the samples dramatically changed the PL spectra indicating that not only interdiffusion had occurred, but defect species and populations were changed. Comprehensive consideration of the changes led to the conclusion that the emissions at 1.62 eV, 1.66 eV and in the range from 1.2 to 1.4 eV are related to specific defects of Se vacancies, Cu vacancy-Se vacancy complexes and interstitial Cu, respectively.