Extended X-ray absorption fine structure studies of GaN epilayers doped with Er

The structural properties of Er doped GaN epilayers were studied by means of extended X-ray absorption fine structure (EXAFS) measured at the Er LIII and Ga K-edges. The samples were doped with Er in-situ during growth by molecular beam epitaxy (MBE). The Ga local structure was found to be the same in all samples studied. Er LIII-edge EXAFS showed that when growth conditions were gradually changed from Ga-rich to Ga-poor, an increase in Er concentration from 0.15 at.% to 0.64 at.% is accompanied by the sequential formation of ErGaN, ErGaN clusters with locally high Er content and finally a pure ErN component. This study indicates that Er incorporation into GaN is enhanced under Ga-poor conditions, at the expense of the formation of Er-rich clusters and ErN precipitates.