  CuGaS2 films grown by physical vapour deposition have been studied by
photoluminescence (PL) spectroscopy, using excitation intensity and temperature
dependent analyses. We observe free and bound exciton recombinations, three
donor-to-acceptor (DA) transitions, and deep-level transitions. The DA
transitions at ~ 2.41 eV, 2.398 eV and ~ 2.29 eV are attributed to a common
donor level ~ 38+-5 meV and three shallow acceptors at ~ 76 meV, ~ 90 meV and
210 meV above the valence band. This electronic structure is very similar to
other chalcopyrite materials. The donor-acceptor transitions are accompanied by
phonon replicas. Cu-rich and near-stoichiometric material is dominated by the
transitions due to the acceptor at 210 meV. All films show deep-level
transitions at ~ 2.15 eV and 1.85 eV due to broad deep defect bands. Slightly
Cu-deficient films are dominated by intense transitions at ~ 2.45 eV,
attributed to excitonic transitions and the broad defect transition at 2.15 eV.
