Many-Body GW Calculation of the Oxygen Vacancy in Zn0

Density-functional theory (DFT) calculations of defect levels in semiconductors based on approximate functionals are subject to considerable uncertainties, in particular due to inaccurate band-gap energies. Testing previous correction methods by many-body GW calculations for the O vacancy in ZnO, we find that: (i) The GW quasiparticle shifts of the V_o defect states increase the spitting between occupied and unoccupied states due to self-interaction correction, and do not reflect the conduction- versus valence-band character. (ii) The GW quasiparticle energies of charged defect states require important corrections for supercell finite-size effects. (iii) The GW results are robust with respect to the choice of the underlying DFT or hybrid-DFT functional, and the (2+/0) donor transition lies below midgap, close to our previous prediction employing rigid band-edge shifts.