It was observed that He+ bombardment increased the relative intensity of the so-called blue emission and resistivity of film samples, and decreased the intensity of the near-bandedge photoluminescence. Because the intensity of the main peak was sharply decreased, the fine structure of the near-bandedge photoluminescence after He+ bombardment was observed. Upon comparing the observed sharp lines with the photoluminescence peaks of O-doped material, it was concluded that O could produce a complex which was characterized by a marked localization of free carriers and a large lattice distortion. The zero-phonon line of this defect had an energy which was close to the band-gap energy of GaN.

V.A.Joshkin, C.A.Parker, S.M.Bedair, L.Y.Krasnobaev, J.J.Cuomo, R.F.Davis, A.Suvkhanov: Applied Physics Letters, 1998, 72[22], 2838-40