Hybrid functional calculations for native defects and dangling bonds in $\alpha$-Al$_2$O$_3$

Al$_2$O$_3$ is a promising material for use as a gate dielectric in III-V-based MOS devices, including in GaN-based transistors. Recent developments indicate that despite the relatively high structural quality, the presence of charge traps and fixed-charge centers near the interface between the oxide and nitride still poses serious problems for device performance. Native defects and dangling bonds in the Al$_2$O$_3$ dielectric or in the vicinity of the interface are the most likely causes. To aid in the identification of these centers, we perform density functional calculations with a hybrid functional for point defects and dangling bonds in $\alpha$-Al$_2$O$_3$. We determine the position of the defect transition levels in the gap of the oxide, and analyze the level positions with respect to the nitride band edges. Our results show that O vacancies and Al dangling-bonds can produce charge traps and Al interstitials act as fixed charges in GaN-based $n$-MOSFETs.