H-stabilized shallow acceptors in N-doped ZnO

摘要

The origin of the p-type conductivity in N-doped ZnO has been a long standing puzzle for many years because isolated N_O is considered to be a deep acceptor. Recently, the p-type doping has been attributed to the shallow acceptor No - VZn complex that is supposedly being converted from a N_(Zn) - V_O complex at the Zn-terminated surface [L. Liu et al., Phys. Rev. Lett. 108, 215501 (2012)]. By performing first-principles calculations, we demonstrate that the p-type N_O - V_(Zn) pair is easy to form in bulk N-doped ZnO through the charge transfer and acceptor-acceptor level repulsion without the need of the special growth surface. More importantly, the N_O - V_(Zn) pair can be further stabilized through hydrogenation, forming the more stable shallow acceptor complexes (N_O - nH) - V_(Zn) (n = 1-2) with an ionization energy of less than 162 meV, in good agreement with the experiment. These new shallow acceptor complexes are proposed to be responsible for the p-type conductivity of the N-doped ZnO.