Electronic structure of transition-metal impurities in p-type ZnO

The self-interaction-corrected local spin-density approximation is used to investigate the ground-state valency configuration of transition metal (TM=Mn, Co) impurities in p-type ZnO. Based on total energy considerations, we find a stable localized TM2+ configuration for a TM impurity in ZnO if no additional hole donors are present. Our calculations indicate that the (+/0) donor level is situated in the band gap, as a consequence of which the TM3+ becomes more favorable in p-type ZnO, where the Fermi level is positioned near the top of the valence band. When codoping with N, it emerges that the conditions for the applicability of the Zener model as proposed by Dietl [Science 287, 1019 (2000)] are fulfilled only in the scenario where the N concentration exceeds the TM impurity concentration.