Band alignments of β-Ga2O3 with MgO, Al2O3 and MgAl2O4 measured by x-ray photoelectron spectroscopy

High-k and wide bandgap materials arc necessary to work as gate dielectrics and surface passivation layers in beta-phase gallium oxide (beta-Ga2O3) based metal-oxide-semiconductor (MOS) devices. The band offsets between these materials and beta-Ga2O3 play an important role in the properties of the devices. In this work, we grew beta-Ga2O3 thin films on MgO, sapphire and MgAl2O4 single crystal substrates by the radio-frequency magnetron sputtering method, and used x-ray photoelectron spectroscopy to measure the beta-Ga2O3/MgO, beta-Ga2O3/Al2O3, and beta-Ga2O3/MgAl2O4 heterointerfaces. The valence band offsets were determined to be -0.65(+/- 0.17) eV (staggered gap, type II alignment), 0.57(+/- 0.07) eV (straddling gap, type I alignment), and 0.64(+/- 0.23) eV (straddling gap, type I alignment) for beta-Ga2O3 on sapphire (0001), MgO (100), and MgAl2O4 (100) substrates, leading to the large conduction band offsets of over 2 eV accordingly. The results suggested that these materials can be used to construct heterojunctions with beta-Ga2O3 in MOS devices for their excellent electron confinement properties.