We have carried out a systematic Raman study on Si-, C-, Mg-and Be-implanted GaN layers. In the as-implanted GaN layers, new Raman bands around 293-300, 360 and 666-671 cm −1 have appeared. From the phonon-dispersion curves for hexagonal GaN, the 293-300 cm −1 and 666-671 cm −1 bands are assigned to the highest acoustic-phonon branch and the optical-phonon branch at the Brillouin zone boundaries, respectively. Several new modes at 168, 199, 320 and 346 cm −1 are also observed in the Raman spectra of Be-implanted GaN after post-implantation annealing and could be associated with Be-related local vibrational modes in GaN. In the Si-implanted GaN, we have also observed a new local vibrational mode at 612 cm −1 after thermal annealing.