Zn vacancy-donor impurity complexes in ZnO

TL;DR

This study uses hybrid density functional theory to explore how zinc vacancies in ZnO interact with donor impurities, affecting their stability, charge states, and optical emissions, revealing potential for tunable luminescent properties.

Contribution

It provides new insights into the electronic and optical behavior of Zn vacancy-donor complexes in ZnO, highlighting how complexing alters charge states and luminescence.

Findings

Complexing Zn vacancies with donors removes charge-state transition levels.

Donor presence causes modest shifts in transition levels, explained by polaron energetics.

Complexed vacancies shift from non-radiative infrared to radiative visible emissions.

Abstract

Results from hybrid density functional theory calculations on the thermodynamic stability and optical properties of the Zn vacancy ($V_{\text{Zn}}$) complexed with common donor impurities in ZnO are reported. Complexing $V_{\text{Zn}}$ with donors successively removes its charge-state transition levels in the band gap, starting from the most negative one. Interestingly, the presence of a donor leads only to modest shifts in the positions of the $V_{\text{Zn}}$ charge-state transition levels, the sign and magnitude of which can be interpreted from a polaron energetics model by taking hole-donor repulsion into account. By employing a one-dimensional configuration coordinate model, luminescence lineshapes and positions were calculated. Due to the aforementioned effects, the isolated $V_{\text{Zn}}$ gradually changes from a mainly non-radiative defect with transitions in the infrared region in \textit{n}-type material, to a radiative one with broad emission in the visible range when complexed with shallow donors.