Migration of Zn Vacancy and Acceptor Clustering in ZnO:N under Strain: DFT and Optical Studies

The current study was inspired by the observation of separated regions grouping donors and acceptors in ZnO:N, which was reported using photoemission spectroscopy, surface photovoltage, and cathodoluminescence imaging [Phys. Rev. Appl. 2022, 18, 044021; Phys. Status Solidi A 2023, 220, 2200466]. The correspondence of these regions with individual crystallites suggests that strain may have a significant influence on the formation of shallow acceptor levels in ZnO. In the present paper, using density functional theory, we investigate the electronic and diffusion properties of Zn vacancy in the presence of the NOH2 group in ZnO:N from the point of view of the efficient formation of VZnNOHx acceptor complexes. We show that strain noticeably affects the migration properties of zinc vacancy. In particular, compressive strain facilitates the migration of Zn vacancy, and if it is high enough, the migration barrier drops to zero. It is also shown that the VZnNOHx complexes are easily formed in the presence of CiH2 groups. Photoluminescence spectra measured for ZnO:N films showing different strain conditions and cathodoluminescence images support the above conclusions.