Monocrystalline epitaxial GaN films were irradiated with fast (E >1MeV) or with fast or thermal neutrons. These conditions permitted the separation of the effect of transmutational doping with Ge due to nuclear reactions from that of thermal neutrons upon damage production. High-resolution X-ray diffraction revealed an expansion of the c-lattice parameter, after irradiation, which was reversed after annealing at 1000C. The effect of neutron irradiation upon the optical properties of GaN samples was investigated using photoluminescence and Raman spectroscopy. With above-bandgap excitation the spectra of the as-irradiated sample with fast and thermal neutrons was dominated by broad emission bands in the UV and yellow spectral range whereas no photoluminescence was observed for the fast neutron as-irradiated sample. Annealing the as-irradiated samples promoted damage recovery and changes were observed in the photoluminescence spectra. Raman scattering spectra indicated an increase in the intensity of the disorder activated phonons revealing greater lattice damage for irradiation with fast and thermal neutrons.

Defect Studies on Fast and Thermal Neutron Irradiated GaN. K.Lorenz, J.G.Marques, N.Franco, E.Alves, M.Peres, M.R.Correia, T.Monteiro: Nuclear Instruments and Methods in Physics Research B, 2008, 266[12-13], 2780-3