Hybrid functional calculations ofDXcenters in AlN and GaN

Abstract

Using hybrid functional calculations, we investigate the formation of $DX$ centers in GaN and AlN. We find that O, Si, and Ge are shallow donors in GaN, but form stable $DX$ centers in AlN for Fermi-level positions near the conduction band. Using a linear interpolation, we estimate the composition at which the onset of $DX$ behavior will occur in AlGaN alloys. Based on these predictions, we identify Si as the most effective donor for high Al-content AlGaN, and explain a number of seemingly conflicting experimental results for Si-doped AlGaN. Although based on size matching Ge was expected to be superior to Si as a shallow donor, it actually turns out to be more prone to $DX$-center formation.