Single crystals were irradiated to various thermal neutron doses. The defects which were introduced by such irradiation were found to be optically active; giving rise to absorption bands with energies that ranged from 1.2 to 3.2eV. Bands which lay in the band-gap had a Gaussian shape. Their energies and widths were independent of the irradiation dose, but their intensities were proportional to it. Thermal annealing occurred in 2 stages, ending at around 500 or 720K. The centers which were responsible for the absorption bands were suggested to be Ga-vacancy-Ga interstitial complexes, in which the distance between the vacancy (acceptor) and the interstitial (donor) determined the energy and intensity of the absorption band, as well as the annealing temperature.

F.J.Manjón, A.Segura, V.Muñoz: Journal of Applied Physics, 1997, 81[10], 6651-6