Band Alignment in Polar Nitride Heterojunctions

Aluminum scandium nitride (AlScN) has shown promise for its high-K dielectric properties, enhanced piezoelectricity, enhanced electro-optic response, and ferroelectricity. For application in high electron mobility transistors (HEMTs), AlScN/GaN interfaces have been created with higher 2DEG densities than achievable in AlGaN/GaN interfaces. Understanding the band alignments at heterojunction interfaces is important for potential applications in HEMTs. Extracting these values from both first-principles calculations and experiments has proven difficult for the commonly used [0001] direction in wurtzite nitrides, due to the presence of spontaneous and piezoelectric polarization fields along that direction. While band alignments have been calculated for non-polar directions, it is not clear how much the orientation affects the results. In this work, we use density functional theory calculations along with a recently developed methodology to control polarization fields in slab calculations [1] to obtain band offsets in the [0001] direction. The method accounts for the piezoelectric and spontaneous polarization effect by passivating slabs with modified pseudo-hydrogen atoms. We apply the approach to calculate the band alignment of an AlN/GaN interface and then to AlGaN and AlScN alloy interfaces on GaN.

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