Liquid-encapsulated Czochralski (LEC) grown undoped semi-insulating (SI) gallium arsenide (GaAs) single crystals have been implanted with 120 keV nitrogen ion (N+) of fluences 1 × 1014, 1 × 1015 and 1 × 1016 cm-2. Raman scattering studies of the as-grown and implanted samples have been carried out at room temperature and analyzed. It is observed that the A1(LO) phonon mode frequency decreases with increase of fluence, whereas the full width at half maximum (FWHM) increases and the area under the peak decreases. All these effects are due to the lattice disorder induced by the implantation. The implanted samples have been annealed at 673 K. They show a partial recovery of the A1(LO) phonon mode frequency and the FWHM which tend towards the unimplanted values due to partial annealing of the implantation-induced lattice damage. The post-implantation annealed samples show an increase of the area under the peak due to the enhanced Raman scattering caused by the surface roughness which was caused by the implantation. This increase in area was less at high fluences because of the residual lattice damage induced by the implantation, which caused the decrease of the area. © 2001 Elsevier Science B.V.