Quasiparticle Excitations and Charge Transition Levels of Oxygen Vacancies in Hafnia

TL;DR

This paper uses first-principles GW calculations to analyze the charge transition levels of oxygen vacancies in monoclinic hafnia, revealing their positive U nature and emphasizing the importance of electrostatic corrections.

Contribution

It introduces a reliable GW-based method for calculating defect levels and demonstrates the positive U character of oxygen vacancies in hafnia, contrasting previous reports.

Findings

Oxygen vacancies are positive U centers in hafnia.

Electrostatic corrections are crucial for accurate defect level calculations.

The transition levels can be reliably evaluated via two physical paths.

Abstract

We calculate the quasiparticle defect states and charge transition levels of oxygen vacancies in monoclinic hafnia. The charge transition levels, although they are thermodynamic quantities, can be critically dependent on the band gap owing to localized defect states. These quasiparticle defect level effects are treated using the first principle GW approximation to the self energy. We show that the quality and reliability of the results may be evaluated by calculating the same transition level via two physical paths and that it is important to include the necessary electrostatic corrections in a supercell calculation. Contrary to many previous reports, the oxygen vacancies in monoclinic hafnia are found to be a positive U center, where U is the defect electron addition energy. We identify a physical partitioning of U in terms of an electronic and structural relaxation part.