First-principles study for orientation dependence of band alignments at the 4H-SiC/SiO₂ interface

The orientation dependence of band alignments and the formation of dipoles at the 4H-SiC/SiO2 interface are theoretically investigated on the basis of first-principles calculations. The calculations demonstrate that the offsets of valence and conduction bands depend on the surface orientation and chemical bonds at the 4H-SiC/SiO2 interface. When we exclude the interfaces with C-O bonds which result in CO desorption, the calculated conduction band offset (CBO) on the Si-face with Si-O bonds is larger than those on the C-face with C-Si bonds and m-face with both Si-O and C-Si bonds. Furthermore, it is found the atomic configurations at the 4H-SiC/SiO2 interface result in the formation of dipoles, whose magnitude is large for Si-O and C-O bonds. The formation of large dipoles significantly changes the band structure of 4H-SiC, resulting in large conduction bands offset. Therefore, the formation of a Si-O bond with large dipoles at the interface is of importance in order to obtain a large CBO. The calculated results give insights into improving the reliability of SiC MOSFETs.