Band Alignments and Polarization Effects in III-V Nitride Heterojunctions

Aluminum Scandium Nitride (AlScN) has shown promise for its high-K dielectric properties, enhanced piezoelectricity, enhanced electro-optic response, and ferroelectricity. Devices taking advantage of these properties are built on heterojunction interfaces. Knowing the band alignment at these interfaces is vital to understand device performance and operation. Extracting these values from first-principles calculations and experiments has proven difficult for the commonly used [0001] growth direction, due to the presence of spontaneous and piezoelectric polarization fields. While band alignments have been calculated for non-polar directions, the extent to which the orientation affects the results is unclear. In this work, we perform density functional theory calculations, with a methodology to control polarization fields in slab calculations [1], to obtain band offsets in the [0001] direction. The methodology accounts for the polarization effects by passivating slabs with modified valence pseudo-hydrogen atoms. We also investigate the impact of the built-in fields on atomic structure and find that the change in structure can be attributed to the inverse piezoelectric effect. We apply this approach to calculate the band alignment of a GaN/AlN interface and extend the approach to find the alignments of GaN/AlGaN and GaN/AlScN interfaces.

[1] S.-H. Yoo, M. Todorova, J. Neugebauer, and C. G. Van de Walle, Phys. Rev. Appl. 19, 064037 (2023).