We have employed synchrotron-based core level photoemission measurements and near-edge x-ray absorption fine structure spectroscopy to identify and characterize nitrogen interstitials in p-type GaN, created by nitrogen bombardment. From absorption measurements around the nitrogen K edge we have identified nitrogen interstitial levels within the band gap, in good agreement with theoretical predictions. The reduction in band bending determined from photoemission measurements was explained by the acceptor-like character of these defects. Argon bombardment produces nitrogen vacancies and the metallic Ga phase at the surface, which will produce the increased band bending and pinning of the surface Fermi level closer to the conduction band minimum. (c) 2005 American Vacuum Society.