First-principles LDA+U calculations of the Co-doped ZnO magnetic semiconductor

Electronic structure of CoxZn1-xO magnetic semiconductor was investigated by means of density functional calculations using local density approximation (LDA) and LDA+U schemes. The Hubbard U-Co implemented in the calculation was determined by means of constrained-density-functional calculations in contrast with the early investigating methods which treated the U as an adjustive parameter. The antiferromagnetic order between nearest-neighbor magnetic ions via the middle O ion was predicted when the intrinsic defects such as O vacancies and Zn interstitials were not taken into account. In sharp contrast with the half-metallic characteristic predicted by most previous theoretical calculations, the CoxZn1-xO system has semiconductor band structures, which is in good agreement with the results of photoemission spectroscopy. The absence of state near the Fermi level revealed in this paper also accords with the poor conductivity of the on-site samples observed experimentally.