The electronic structures of β-phase (AlxGa1-x)2O3 studied by DFT calculations

Abstract

Band gap engineering by alloying Ga2O3 with Al2O3 can expand the accessible bandgap for power electronics and high electron mobility transistor. For such applications, it is important to known the evolution of the electronic structure with composition and the respective band offsets between β-(AlxGa1-x)2O3 and Ga2O3. In this work, we use first-principles calculations to investigate the crystal structure, band gap and electronic structure of β-(AlxGa1-x)2O3 alloys for various Al compositions. We found that the increase of the band gap of β-(AlxGa1-x)2O3 alloys from 4.86 eV (x = 0) to 5.80 eV (x = 0.5). In β-(AlxGa1-x)2O3 alloys, the conduction band minimum (CBM) shifts upward with increasing Al content, due to the contribution of Al 3s states replacing Ga 4s states at the conduction band edge. In contrast, the valence band maximum (VBM) exhibits a relatively small downward shift. This is primarily attributed to the weakened Ga 3d–O 2p interaction at the VBM, where the p–d repulsion typically acts to push the VBM upward. We observe that β-(AlxGa1-x)2O3 alloys show type I (straddling) band alignment with β-Ga2O3. The effective mass of β-(AlxGa1-x)2O3 alloys increases with higher aluminum content, which can be explained by the less delocalized Al 3s orbitals in place of the more delocalized Ga 4s orbitals at the conduction band minimum.