Compensation mechanism for N acceptors in ZnO

We present a mechanism for the compensation of N acceptors in ZnO through real-space multigrid electronic structure calculations within the local-density-functional approximation. We find that at low N doping levels using a normal ${\mathrm{N}}_2$ source, O vacancies are the main compensating donors for N acceptors, while N acceptors are compensated via the formation of defect complexes with Zn antisites at high doping levels. When an active plasma ${\mathrm{N}}_2$ gas is used to increase the N solubility, N acceptors are still greatly compensated by ${\mathrm{N}}_2$ molecules at oxygen sites and N-acceptor–${\mathrm{N}}_2$ complexes, explaining the difficulty in achieving low-resistivity p-type ZnO.