a1 Department of Physics, Strathclyde University, Glasgow, G4 0NG, Scotland, U.K.
a2 CLRC Daresbury Laboratories, Warrington, WA 4AD, England, UK
a3 IKS, Katholieke Universiteit Leuven, 3001 Leuven, Belgium.
This presentation reviews recent lattice location studies of rare earth (RE) ions in GaN by electron emission channelling (EC) and X-ray absorption fine structure (XAFS) techniques. These studies agree that RE ions at low concentrations (whether they are incorporated during growth or introduced later by ion implantation) predominantly occupy Ga substitutional sites, as expected from considerations of charge equivalence. We combine this result with some examples of the well-documented richness of optical spectra of GaN:RE3+ to suggest that the luminescence of these materials may be ascribed to a family of rather similar sites, all of which feature the REGa defect.