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Interplay between O defects and SiC stacking at the SiC/SiO$_2$ interface

We investigate the effect of SiC stacking on the 4H-SiC/SiO$_2$ interface, both in the presence and absence of O defects, which appear during thermal oxidation, via first principles calculations. It is known that 4H-SiC(0001) has two different surface types, depending on which of the two lattice sites, $h$ or $k$, is at the surface [K. Arima \textit{et al}., Appl. Phys. Lett. \textbf{90}, 202106 (2007)]. We find interlayer states along the conduction band edge of SiC, whose location changes depending on the interface type, and thus too the effect of defects. When $h$ sites are directly at the interface, O defects remove interfacial conduction band edge states. On the other hand, when $k$ sites are at the interface, the conduction band edge is insensitive to the presence of O defects. These differences will impact on the operation of SiC devices because the most commonly used SiC based metal-oxide-semiconductor field-effect transistors rely on the electronic structure of the conduction band.