# Zn vacancy as a polaronic hole trap in ZnO

## TL;DR

This study uses hybrid density functional theory to reveal that Zn vacancies in ZnO act as deep polaronic hole traps, influencing luminescence properties and requiring symmetry-breaking for accurate modeling.

## Contribution

It demonstrates the importance of initial symmetry-breaking in hybrid DFT calculations to accurately capture polaronic hole localization at Zn vacancies in ZnO.

## Key findings

- Zn vacancy is a deep polaronic acceptor trapping localized holes on O ions.
- Symmetry-breaking is essential to observe hole localization in calculations.
- Zn vacancy likely causes infrared, not visible, luminescence in n-type ZnO.

## Abstract

This work explores the Zn vacancy in ZnO using hybrid density functional theory calculations. The Zn vacancy is predicted to be an exceedingly deep polaronic acceptor that can bind a localized hole on each of the four nearest-neighbor O ions. The hole localization is accompanied by a distinct outward relaxation of the O ions, which leads to lower symmetry and reduced formation energy. Notably, we find that initial symmetry-breaking is required to capture this effect, which might explain the absence of polaronic hole localization in some previous hybrid density functional studies. We present a simple model to rationalize our findings with regard to the approximately equidistant thermodynamic charge-state transition levels. Furthermore, by employing a one-dimensional configuration coordinate model with parameters obtained from the hybrid density functional theory calculations, luminescence lineshapes were calculated. The results show that the isolated Zn vacancy is unlikely to be the origin of the commonly observed luminescence in the visible part of the emission spectrum from \textit{n}-type material, but rather the luminescence in the infrared region.