Density-functional studies of the electron states in the dilute magnetic semiconductor GaN:Mn revealed major differences for the case of the Mn impurity at the substitutional site (MnGa) versus the interstitial site (Mni). The splitting of the twofold and the threefold degenerate Mn(d) states in the gap were reversed between the two cases, which was explained in terms of the symmetry-controlled hybridization with the neighboring atoms. In contrast to MnGa, which acts as a deep acceptor, Mni acts as a donor, suggesting the formation of Coulomb-stabilized complexes such as MnGaMniMnGa, where the acceptor level of MnGa was passivated by the Mni donor. Formation of such passivated clusters might be the reason for the observed low carrier-doping efficiency of Mn in GaN. Even though the Mn states were located well inside the gap, the wave functions were spread far away from the impurity center. This was caused by the hybridization with the N atoms, which acquire small magnetic moments aligned with the Mn moment.

Electronic Structure of Substitutional versus Interstitial Manganese in GaN. Z.S.Popovic, S.Satpathy, W.C.Mitchel: Physical Review B, 2004, 70[16], 161308 (4pp)