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Published online by Cambridge University Press: 10 February 2011
We have investigated the Ca dopant site within the GaN lattice using ion channeling in combination with Rutherford backscattering spectrometry (RBS), particle induced x ray emission (PIXE) and nuclear reaction analysis (NRA). Metalorganic chemical vapor deposition (MOCVD) grown GaN on c-plane sapphire substrates implanted with 40Ca at a dose of 1×1015 cm−2 with post-implant annealing were investigated. The channeling results indicate that more than 80% of Ca are near Ga sites even in as-implanted samples, however, they are displaced by ∼ 0.2 Å from the Ga sites and that the Ca goes to the exact Ga sites after annealing at 1100°C. We think that the displaced Ca in the as-implanted samples are electrically compensated due to formation of complex defects with donor like point defects, such as CaGa-VN and/or CaGa-GaN, and that CaGa becomes electrically active when these complex defects are broken and the point defects diffuse away with annealing at 1100°C.