As the concentration of intrinsic defects becomes sufficiently high in O-deficient ZnO, interactions between defects led to a significant reduction in their formation energies. It was shown that the formation of both O vacancies and Zn interstitials became significantly enhanced by a strong attractive interaction between them, making these defects an important source of n-type conductivity in ZnO.

Rich Variety of Defects in ZnO Via an Attractive Interaction Between O Vacancies and Zn Interstitials: Origin of n-Type Doping. Kim, Y.S., Park, C.H.: Physical Review Letters, 2009, 102[8], 086403