Calculated electron paramagnetic resonance $g$-tensor and hyperfine parameters for zinc vacancy and N related defects in ZnO

Abstract

Various defects in ZnO, focused on substitutional N${}_O$ and N${}_2$ in various sites, O-site, interstitial and Zn-site are studied using first-principles calculations with the goal of understanding the electron paramagnetic resonance (EPR) center reported for N${}_2$ in ZnO and substitutional N on the O-site. The $g$ tensors are calculated using the gauge including projector augmented wave (GIPAW) method and compared with experiments. The $g$-tensor of the free N${}_2^{+}$ and N${}_2^{-}$ radicals and their various contributions within the GIPAW theory are analyzed first to provide a baseline reference for the accuracy of the method and for understanding the N${}_2$ behavior in ZnO. Previous controversies on the site location of N${}_2$ in ZnO for this EPR center and on the shallow or deep nature and donor or acceptor nature of this center are resolved. We find that the N${}_2$ on the Zn site is mostly zinc-vacancy like in its spin density and $g$-tensor, while for the O-site, a model with the N${}_2$ axis lying in-the basal plane and the singly occupied ${\pi }_g$-orbital along the {\bf c} axis provides good agreement with experiment. For the interstitial location, if the N${}_2$ is not strongly interacting with the surroundings, no levels in the gap are found and hence also no possible EPR center. The calculated $g$-tensors for N${}_O$ and $V_{Z}n$ are also found to be in good agreement with experiment. The effects of different functionals affecting the localization of the spin density are shown to affect the $g$-tensor values.

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