The behavior of rare earth dopants in GaN was investigated by means of theoretical techniques. The density functional based tight-binding method was extended to include orbital dependent potentials (LDA+U and SIC-like) in attempt to model the 4f states of lanthanide impurities within a realistic crystal model. Results were presented of an investigation into the structural and energetic properties of rare earth (Eu, Er and Tm) point defects in GaN. Lanthanide ions (either isolated or complexed with GaN native defects) prefer the Ga-site. Among the investigated defects the REGaVN pairs were the most promising candidates as luminescent centers, while interstitial lanthanides were found not to be compatible with the observed luminescence. Differences in the behavior of the single lanthanide ions were explained in terms of different 4f -shell occupation and ion size.

Theoretical Study of Rare Earth Point Defects in GaN. S.Sanna, B.Hourahine, T.Frauenheim, U.Gerstmann: Physica Status Solidi C, 2008, 5[6], 2358-60