First-principles study of As interstitials in GaAs: Convergence, relaxation, and formation energy

TL;DR

This study uses first-principles calculations to analyze arsenic interstitials in GaAs, focusing on convergence, defect properties, and formation energies, revealing that large supercells are necessary for accurate defect state descriptions.

Contribution

It demonstrates the importance of large supercells for accurate defect state and transition level calculations in GaAs, providing detailed formation energies for various defects.

Findings

217-atom supercells needed for defect state convergence

As interstitials have lower equilibrium concentrations than As antisites in certain conditions

Formation energies depend on chemical potential and Fermi level

Abstract

Convergence of density-functional supercell calculations for defect formation energies, charge transition levels, localized defect state properties, and defect atomic structure and relaxation is investigated using the arsenic split interstitial in GaAs as an example. Supercells containing up to 217 atoms and a variety of {\bf k}-space sampling schemes are considered. It is shown that a good description of the localized defect state dispersion and charge state transition levels requires at least a 217-atom supercell, although the defect structure and atomic relaxations can be well converged in a 65-atom cell. Formation energies are calculated for the As split interstitial, Ga vacancy, and As antisite defects in GaAs, taking into account the dependence upon chemical potential and Fermi energy. It is found that equilibrium concentrations of As interstitials will be much lower than equilibrium concentrations of As antisites in As-rich, $n$-type or semi-insulating GaAs.