Interface properties of thermally oxidized n-GaN metal–oxide–semiconductor capacitors

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We report on the interface properties of thermally oxidized n-GaN metal–oxide–semiconductor capacitors fabricated on sapphire substrates. 100-nm-thick β-Ga2O3 was grown by dry oxidation at 880 °C for 5 h. From secondary ion mass spectrometry measurements, an intermediate Ga oxynitride layer with graded compositions is clearly observed at the β-Ga2O3/GaN interface. Capacitance–voltage measurements show a deep depletion feature and a low interface state density of ∼5.5×1010 eV−1 cm−2. Additionally, no discrete interface traps can be detected by deep-level transient spectroscopic measurements. These results indicate that the surface Fermi level is unpinned at the β-Ga2O3/GaN interface, which may be associated with the presence of the interfacial Ga oxynitride layer.