The solubility limits of Ga and N in ZnO were evaluated via secondary ion mass spectrometry (SIMS). ZnO single crystals were implanted with Ga+ and/or N+ ions at room temperature. The implanted samples were subsequently annealed at a temperature of 850 degreesC in O-2 atmosphere. The values of solubility limit for Ga and N were evaluated from the plateau in the depth profile of the concentrations. We found that the N solubility limit increases by a factor of 400-0.16 atom% in the co-implanted ZnO compared with that in N-implanted sample without Ga. The formation of ZnGa2O4 and the swelling of N-2 were also observed in the cross sectional TEM images after annealing. (C) 2002 Elsevier Science B.V. All rights reserved.