| Summary: | The high breakdown electric field, n-type doping capability, availability of high-quality substrates, and high Baliga’s figure of merit of Ga<sub>2</sub>O<sub>3</sub> demonstrate its potential as a next-generation power semiconductor material. However, the thermal conductivity of Ga<sub>2</sub>O<sub>3</sub> is lower than that of other wide-bandgap materials, resulting in the degradation of the electrical performance and reduced reliability of devices. The heterostructure formation on substrates with high thermal conductivity has been noted to facilitate heat dissipation in devices. In this work, Ga<sub>2</sub>O<sub>3</sub> thin films with an Al<sub>2</sub>O<sub>3</sub> interlayer were deposited on SiC substrates by radio frequency sputtering. Post-deposition annealing was performed at 900 °C for 1 h to crystallize the Ga<sub>2</sub>O<sub>3</sub> thin films. The Auger electron spectroscopy depth profiles revealed the interdiffusion of the Ga and Al atoms at the Ga<sub>2</sub>O<sub>3</sub>/Al<sub>2</sub>O<sub>3</sub> interface after annealing. The X-ray diffraction (XRD) results displayed improved crystallinity after annealing and adding the Al<sub>2</sub>O<sub>3</sub> interlayer. The crystallite size increased from 5.72 to 8.09 nm as calculated by the Scherrer equation using the full width at half maximum (FWHM). The carrier mobility was enhanced from 5.31 to 28.39 cm<sup>2</sup> V<sup>−1</sup> s<sup>−1</sup> in the annealed Ga<sub>2</sub>O<sub>3</sub> thin films on Al<sub>2</sub>O<sub>3</sub>/SiC. The transfer and output characteristics of the Ga<sub>2</sub>O<sub>3</sub>/SiC and Ga<sub>2</sub>O<sub>3</sub>/Al<sub>2</sub>O<sub>3</sub>/SiC back-gate transistors reflect the trend of the XRD and Hall measurement results. Therefore, this work demonstrated that the physical and electrical properties of the Ga<sub>2</sub>O<sub>3</sub>/SiC back-gate transistors can be improved by post-deposition annealing and the introduction of an Al<sub>2</sub>O<sub>3</sub> interlayer.
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