The Ca dopant site was investigated by means of ion channelling. Metal-organic chemical vapor deposited nitride on c-plane sapphire substrates was implanted with 40Ca to a dose .of 1015/cm2. The results indicated that more than 80% of the Ca atoms were near to Ga sites, even in as-implanted samples. However, they were displaced by about 0.02nm from the Ga sites. The Ca atoms moved to the exact Ga sites during annealing at 1100C, but the annealing did not change the apparent fraction of substitutional Ca. It was suggested that the displaced Ca atoms in as-implanted samples were electrically compensated due to the formation of complex defects with donor-like point defects, and that the CaGa became electrically active when these complex defects were broken up and the point defects diffused away during annealing at 1100C.

Lattice Location of Ca in GaN using Ion Channelling. H.Kobayashi, W.M.Gibson: Applied Physics Letters, 1999, 74[16], 2355-7