Rint 2000 pc

The Sn-doped single-crystal β-Ga 2 O 3 wafer (Novel Crystal Technology, Inc.) with an orientation of (-201) was cut to a size of 9.0 × 9.0 × 0.7 mm 3 . These Ga 2 O 3 substrates were successively rinsed with acetone and methanol in an ultrasonic bath for 5 min each. To fabricate Au-NPs on the surface of Ga 2 O 3 , a thin gold layer was deposited onto the substrates by electron-beam evaporation at room temperature. The deposition pressure was approximately 2.0 × 10 -6 Pa, and the evaporation rate was set to approximately 0.16 Å s -1 . Subsequently, the samples were annealed in air at 800 °C for 1 h. The fabrication processes are shown in Fig. S3 in the ESI. † The particle size of Au-NPs was controlled by changing the thickness of the Au film. The TiO 2 layer was deposited by a commercial hot-wall flow-type ALD reactor (SUNALETM R series, Picosun, Finland) at 300 °C with a deposition rate of 0.05 nm per cycle. TiCl 4 and deionized water vapor were used as the Ti and O sources, and N 2 was used as the carrier gas and purge gas. The pulse time and purge time were set as 0.1 and 4.0 s, respectively. X-Ray diffraction chart was applied to check the phase structure of Ga 2 O 3 by RIGAKU RINT-2000/PC using Cu Kα radiation. The valence of Ga, Ti and O was measured by an X-ray photoelectron spectrometer (XPS, JPS-9200, JEOL).