We analysed the effect of 70 keV nitrogen ion implantation in n-GaN to 1014-1016 cm-2 dose by optical absorption, Raman spectroscopy and photoluminescence. Optical absorption spectra of unimplanted samples gave a band gap of 3.4 eV. On implantation with N +, the optical absorption was noticeable at energy below the band gap, also presumably, arising out of defects and disorder produced by ion implantation. E2 (high) and A1 (LO) Raman modes of GaN layer have been observed and analysed. The behavior of Raman shift and FWHM of GaN modes with N+ dose are explained on the basis of implantation-induced lattice damage. The PL spectra of unimplanted samples showed a peak at 3.4 eV corresponding to the band gap of GaN and an emission at 2.3 eV which is normally attributed to NGa antisite defects. On irradiation with N+ ion there was a drastic increase in the intensity of emission at 2.3 eV. This suggests that the defect responsible for the emission of 2.3 eV increases on N+ implantation. At higher doses, additional emission bands at 2.2 and 2.45 eV were observed in the PL spectra, which might be due to the defect complexes. © 2003 Elsevier B.V. All rights reserved.