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Epitaxial growth and electrical properties of g-Al2O3 films on b-Ga2O3(010) substrates were investigated regarding the prospect of a gate oxide in a b-Ga2O3-based MOSFET. The g-Al2O3 films grew along the [110] direction and inherited the oxygen sublattice from b-Ga2O3 resulting in the unique in-plane epitaxial relationship of g-Al2O3 $[\bar{1}10]$ [?] b-Ga2O3[001]. We found that the g-Al2O3 layer had a band gap of 7.0 eV and a type-I band alignment with b-Ga2O3 with conduction- and valence-band offsets of 1.9 and 0.5 eV, respectively. A relatively high trap density ([?] 2 x 1012 cm[?]2 eV[?]1) was found from the voltage shift of photoassisted capacitance-voltage curves measured for a Au/g-Al2O3/b-Ga2O3 MOS capacitor. These results indicate good structural and electric properties and some limitations hindering the better understanding of the role of the gate dielectrics (a g-Al2O3 interface layer naturally crystallized from amorphous Al2O3) in the b-Ga2O3 MOSFET.

Sputter-deposited indium-tin oxide (ITO) electrodes became ohmic contacts for unintentionally doped b-Ga2O3(010) substrates with a carrier concentration of 2 x 1017 cm[?]3 after rapid thermal annealing in a wide range of annealing temperatures of 900-1150 degC. The formation of an ohmic contact is attributed to interdiffusion between ITO and b-Ga2O3, as evidenced by the results of transmission electron microscopy and energy-dispersive X-ray spectroscopy. The interdiffusion decreases the band gap and increases the donor concentration of b-Ga2O3 at the interface, and forms an intermediate semiconductor layer desirable for carrier transport. The ITO ohmic contact is particularly useful for future b-Ga2O3 devices operated at high temperatures.