Density functional theory calculations for investigation of atomic structures of 4H-SiC/SiO$_2$ interface after NO annealing

TL;DR

This study uses density functional theory to model the atomic structures of the 4H-SiC/SiO₂ interface after NO annealing, showing how nitrogen incorporation reduces interface defect states and aligns with experimental observations.

Contribution

The paper presents novel atomic models of the 4H-SiC/SiO₂ interface post-NO annealing, highlighting the formation of a nitride layer that reduces defect states.

Findings

Nitrogen atoms preferentially accumulate at the interface.

NO annealing removes CO bonds, eliminating gap states.

The proposed structures match experimental nitrogen density measurements.

Abstract

We propose the atomic structures of the 4H-SiC/SiO$_2$ interface for the $a$, $m$, C, and Si faces after NO annealing. Our proposed structures preferentially form at the topmost layers of the SiC side of the interface, which agrees with the experimental finding of secondary-ion mass spectrometry, that is, the N atoms accumulate at the interface. In addition, the areal N-atom density is on the order of 10$^{14}$ atom/cm$^2$ for each plane, which is also consistent with the experimental result. Moreover, the electronic structure of the interface after NO annealing, in which the CO bonds are removed and the nitride layer only at the interface is inserted, is free from gap states, although some interface models before NO annealing include the gap states arising from the CO bonds near the valence band edge of the bandgap. Our results imply that NO annealing can contribute to the reduction in the density of interface defects by forming the nitride layer.