Abstract
The structural and electronic properties of rare-earth (RE) (Eu, Er, and Tm) related defect pairs in GaN have been investigated theoretically. Based on total-energy calculations, their possible role in the luminescence process is discussed. In all charge states, the lanthanides show a strong preference for the Ga-lattice site, either as isolated substitutional or complexed with intrinsic defects. With respect to the electronic valence, a proper description of correlation effects of the strongly localized electrons is shown to be crucial, especially if the is paired with donors like the Ga interstitial or the N vacancy. The pairs formed by substitutionals and vacancies or interstitials lower the symmetry and are found to locally distort the environment. By this, they are quite effective in relaxing the selection rules for the luminescent intra--shell transitions. While for -type GaN, the next-nearest-neighbor pair pair is energetically favored, for -type GaN, the pair provides the most stable configuration and introduces shallow levels close to the conduction band, which can act as assistant levels in the luminescence process.
1 More- Received 19 June 2009
DOI:https://doi.org/10.1103/PhysRevB.80.104120
©2009 American Physical Society