Measurements of the band alignment at coherent α-Ga2O3/Al2O3 heterojunctions

The band alignment at a coherent α-Ga2O3/Al2O3 heterointerface was evaluated by analyzing X-ray photoemission spectra for an α-Al2O3 film and an α-Ga2O3/Al2O3 multi-quantum wells grown coherently on sapphire substrates. The measured bandgaps of α-Ga2O3 and α-Al2O3 were 5.7 and 8.7 eV, and the conduction- and valence-band offsets were 2.7 and 0.3 eV, respectively. The smaller valence-band offset is attributed the large contribution of localized O 2p orbitals at the top of the valance band in the oxides. These results complete our understanding of the band alignment of the α-(Al x Ga1− x )2O3 system in conjunction with the previously reported band offsets at α-Ga2O3/(Al x Ga1− x )2O3 heterojunctions (0.1 ≤ x ≤ 0.8).