GGA + U study of native point defects in ZnRh2O4

Abstract

ZnRh2O4 spinel is the one of the most promising transparent conducting oxides for applications in optoelectronic technology. Energy levels and formation energies of native point defects, i.e. vacancies (V), interstitials (I), and cation antisites in ZnRh2O4 were analysed. Generalized gradient approximation (GGA) was supplemented by the +U on-site corrections imposed on d(Rh) and p(O) states. The inclusion of the pronounced distortions of the anion sublattice was necessary to obtain the correct band gap. U was treated as a free parameter, which allowed for the systematic study of the U-induced changes of the defect states. A diagram of the thermodynamic phase stability of ZnRh2O4 was obtained. ZnRh is the dominant acceptor that can be responsible for the observed p-type conductivity in ZnRh2O4. The low formation energy of ZnRh can make the intentional n-doping difficult. In the O-rich conditions the second important acceptor is VZn. The two dominant donors that can compensate ZnRh in Zn-rich and O-rich conditions are VO and RhZn, respectively. Growth conditions leading to the lowest concentrations of native defects were identified. Due to the pronounced occupancy dependence of the +U term, VO and RhZn are ‘negative-Ueff’ centres.