Possible Origin of Ferromagnetism in an Undoped ZnO d0 Semiconductor

First-principles calculations were employed to investigate the effect of native defects and a hydrogen-related defect complex on ferromagnetism in an undoped ZnO semiconductor. The results show that the zinc vacancy (V-Zn) could lead to a moment of 1.73 mu B in the undoped ZnO supercell, while the oxygen vacancy could not, but the formation energy of the zinc vacancy is much higher than that of the oxygen vacancy. When the hydrogen atom is doped in imperfect ZnO, the formation energy of V-Zn+H-I sharply decreases, compared with that of V-Zn. Meanwhile, the V-Zn+H-I defect complex can induce a 0.99(0.65) mu B moment in the Zn15HIO16 supercell. Furthermore, the total energy of the ZnO supercell with two defect complexes for the ferromagnetic phase is lower than that for the antiferromagnetic phase, and the calculated results show that a strong magnetic coupling exists in the ferromagnetic phase. As an unintentionally doped element, H usually appears in ZnO prepared by many methods. So the ferromagnetism in the ZnO do semiconductor most probably arises from the defect complex of the zinc vacancy and H.