Effects of implantation with 150 keV protons and 350 keV deuterium ions on deep levels spectra and electrical and recombination properties of n-GaN samples were studied for fluences between 8 x 10(13) and 5 x 10(15) cm(-2). Implantation led to substantial decrease of the electron concentration so that after the highest dose used, the samples became highly resistive with the Fermi level pinned near 0.3-0.4 eV from the conduction band edge. We also observed a strong degradation of the minority carriers diffusion length and a very strong decrease of the band edge luminescence intensity in the heavily implanted samples. Deep levels spectra measurements showed that proton implantation led to introduction of deep electron traps with activation energies near 0.2, 0.3, 0.45, 0.75 and 0.95 eV and of deep hole traps with activation energies of 0.25, 0.6 and 0.9 eV. The results strongly indicate that among these traps, the 0.75 eV electron traps and/or the 0.6 eV hole traps are most likely responsible for the lifetime degradation. Strong recovery of the electric conductivity of the implanted samples was observed starting with annealing temperatures near 250 degreesC, whereas no recovery of the luminescent characteristics could be observed for annealing temperatures as high as 700 degreesC. We compare the results with previously published data on proton and He implantation of GaN and discuss possible implications of our findings for practical use in GaN devices isolation.