Electron paramagnetic resonance measurements of Er-doped 6H–SiC and wurtzite GaN samples were compared to total energy calculations based upon density functional theory in order to investigate the well-known luminescence of the intra 4f-shell transition at 1540nm, useful in light-emitting diodes or lasers. The highly correlated f-electrons of Er were treated within an LDA+U approach. It was considered how pairs of an Er-ion with intrinsic defects could be responsible in GaN and SiC for relaxing the selection rules for intra 4f-shell transitions. In the case of GaN, the electron paramagnetic resonance investigation indicated the presence of a nitrogen vacancy next to the Er-ion. Through controlled generation of intrinsic defects in 6H–SiC single crystals and electron paramagnetic resonance measurements, support was found for the corresponding model in SiC: predicting defect pairs consisting of an Er ion and a neighbouring carbon vacancy. It was concluded that low-energy irradiation was a promising means for enhancing Er-luminescence.

Microscopic Structure and Energy Transfer of Vacancy-Related Defect Pairs with Erbium in Wide-Gap Semiconductors. A.Konopka, S.Greulich-Weber, V.Dierolf, H.X.Jiang, U.Gerstmann, E.Rauls, S.Sanna, W.G.Schmidt: Optical Materials, 2011, 33[7], 1041-4