Self-interaction effects in (Ga,Mn)As and (Ga,Mn)N

The electronic structures of Mn-doped zincblende GaAs and wurtzite GaN are calculated using both standard local-spin density functional theory (LSDA), and a novel pseudopotential self-interaction-corrected approach (pseudo-SIC), able to account for the effects of strong correlation. We find that, as expected, the self-interaction is not strong in (Ga,Mn)As, because the Fermi energy is crossed by weakly correlated As p-Mn d hybridized bands and the Mn 3d character is distributed through the whole valence band manifold. This result validates the extensive literature of LSDA studies on (Ga,Mn)As, including the conclusion that the ferromagnetism is hole-mediated. In contrast, the LSDA gives a qualitatively incorrect band structure for (Ga,Mn)N, which is characterized by localized Mn 3d bands with very strong self-interaction. Our pseudo-SIC calculations show a highly confined hole just above the Fermi energy in the majority band manifold. Such a band arrangement is consistent with (although by no means conclusive evidence for) a recent suggestion [Phys. Rev. B 033203 (2002)] that formation of Zhang-Rice magnetic polarons is responsible for hole-mediated ferromagnetism in (Ga,Mn)N.