Native Defects in ZnO Nanowires: Atomic Relaxations, Relative Stability, and Defect Healing with Organic Acids

The geometry and formation energies of intrinsic defects in ZnO nanowires have been investigated with the self-consistent-charge density functional tight-binding method (SCC-DFTB). We have calculated the atomic relaxations and formation energies for neutral and charged defects using an empirical potential alignment procedure. Oxygen vacancies and zinc interstitials have been found the lowest energy defects under Zn-rich conditions, with oxygen interstitials and zinc vacancies favored under O-rich conditions. Most defects have been found favorable on the surface of the wire; except to the charged oxygen interstitials, which prefer inner positions because of a better charge accommodation observed there. Besides, we have also investigated the interaction between oxygen vacancies and carboxylic acids, demonstrating that an oxidation-reduction reaction may explain the suppression of green luminescence bands experimentally observed for organic-coated ZnO nanowires.