Investigation of the GaN/Al₂O₃ Interface by First Principles Calculations

Abstract

Metal–oxide–semiconductor field effect transistors (MOSFETs) based on GaN have been studied for high‐power performance because of the wide bandgap of GaN. Although Al2O3 is a promising dielectric film for GaN power devices, the interface structure of GaN/Al2O3 has not been revealed microscopically. We prepared two interface models with Ga–O bonds and Ga–Al bonds at the interface. Because the Ga–O bond is stronger than the Ga–Al bond, the Ga–O bonds are preferentially formed at the interface. When the Ga–Al bonds appear at the interface, they introduce defect levels in the bandgap of GaN. On the other hand, when the interface consists of Ga–O bonds, some defect structures can appear depending on the oxygen density. In oxygen‐rich conditions, dangling bonds appear at the N atoms and their states appear around the valence band maximum.

Accurate Band Offset Prediction of Sc2O3/GaN and θ-Al2O3/GaN Heterojunctions Using a Dielectric-Dependent Hybrid Functional

“…First-principles calculations were performed using the Vienna ab initio simulation package (VASP) with the projector augmented wave (PAW) pseudopotentials. , The lattice constants were optimized using the Perdew-Burke-Ernzerhof (PBE) functional with the van der Waals correction of density functional theory PBE-D3­(BJ). The predicted lattice constants are in great agreement with the experimental values , compared to other theoretical works. − The structural relaxations are based on a k -grid density of about 0.2 Å –1 . The band gaps of GaN, Sc 2 O 3 , and θ-Al 2 O 3 have been predicted by various functionals, including local-density approximation (LDA), generalized gradient approximation (GGA), − meta-GGA, , and dielectric-dependent hybrid (DDH) functionals .…”

“…33 Previous studies selected this α-Al 2 O 3 to form a heterojunction with GaN because of the relatively suitable lattice between α-Al 2 O 3 and GaN. 34,25 However, the big bandgap (∼8.8 eV) and larger mass density of α-Al 2 O 3 are very different from the ALD-prepared amorphous structure. θ-Al 2 O 3 (space group C2/m) with a mass density of around 3.5 g/cm 3 and a band gap of around 6.6 eV is much closer to these amorphous structures.…”

“…Chokawa et al reported that the Ga−O interface has fewer defect states than other interfaces. 25 Ga dangling bonds can be completely saturated with interfacial oxygen atoms.…”

“…The hexagonal α phase is the experimentally stable form of Al 2 O 3 , well-known as corundum, found in nature . Previous studies selected this α-Al 2 O 3 to form a heterojunction with GaN because of the relatively suitable lattice between α-Al 2 O 3 and GaN. , However, the big bandgap (∼8.8 eV) and larger mass density of α-Al 2 O 3 are very different from the ALD-prepared amorphous structure. θ-Al 2 O 3 (space group C 2/ m ) with a mass density of around 3.5 g/cm 3 and a band gap of around 6.6 eV is much closer to these amorphous structures. , Here, we have chosen θ-Al 2 O 3 , which is stretched to an orthogonal structure to match the GaN (0001) surface.…”

“…For Al 2 O 3 , the Ga–O bonding interface is the most stable compared to other bonding interfaces because both Ga and Al are trivalent and the bonding properties of atoms at the interface are similar to their bulk crystals. Chokawa et al reported that the Ga–O interface has fewer defect states than other interfaces . Ga dangling bonds can be completely saturated with interfacial oxygen atoms.…”