Orientation-dependent band offsets between (Al_xGa_1-x)₂O₃and Ga₂O₃

Band alignments between Al2O3 and Ga2O3 are investigated for four different orientations [(100), (010), (001), and (2 ¯01)] using density functional theory with a hybrid functional. By comparing with explicit interface calculations, we confirm that alignments can be reliably extracted from slab calculations that take atomic relaxation and strain into account. The presence of pseudomorphic strain shifts the average electrostatic potential as well as the band edges. Tensile strain in Al2O3 is found to lower the conduction band; the absolute deformation potential is calculated to be -9.5 eV for Al2O3 and -9.1 eV for Ga2O3. Our results show that the largest conduction-band offset will occur at a pseudomorphic (AlxGa1-x)2O3/Ga2O3 interface with the (100) orientation, allowing us to estimate the density of the two-dimensional electron gas in a modulation-doped field-effect transistor.