Rare earth doped III-nitrides for optoelectronics

Rare-earth (RE) doped III-nitrides, prepared by in-situ doping during growth or by ion implantation and annealing, are promising materials for visible light emitting displays. In addition, they are extremely challenging theoretically, on account of the complexity of the sharp inter-4f optical transitions, which are allowed only through the mixing by non-centrosymmetric crystal fields of the inner 4f orbitals with higher-lying states of opposite parity. We review recent experimental and theoretical work on Er-, Eu- and Tm-doped III-nitride compounds and alloys which has been carried out with a view to establishing the lattice location of RE in these materials and the probable nanostructure of the centres which are responsible for their luminescence. The isolated site REIII is found to be both optically and electrically inactive, but in association with neighbouring intrinsic defects (most probably nitrogen vacancies) REIII can generate a small family of similar optically active sites. Such a family is held to be responsible for the site multiplicity that is a common feature of the spectroscopy of RE-doped III-nitrides.