Solar-blind ultraviolet photodetectors (SBPDs) exhibit significant potential for many fields, including military, civil, and medical sectors. In this paper, Si-doped Ga₂O₃ thin films were prepared by radio frequency magnetron sputtering. The effect of the argon-oxygen flow ratio on the physical properties of the films was studied. The analysis results of crystal structure, optical properties, and surface morphology indicate that the crystalline quality of the film is best when the argon-oxygen flow ratio is 30∶20. The Ga₂O₃∶Si thin film exhibits preferential growth along the $（\bar{4}02）$ crystal plane, with a smooth and flat surface without micro-holes, and an average transmittance of 90% in the range of 400 nm to 800 nm. We fabricated p-GaN/n-Ga₂O₃∶Si self-powered SBPDs using optimized preparation parameters. Under 254 nm illumination at 0 V, the device shows rise time and decay time of 0.450 and 0.509 s, respectively. The light-dark current ratio (PDCR), responsivity (R), and specific detectivity (D^*) are 23, 0.24 mA/W, and 1.67×10⁸ Jones, respectively. The time-response characteristics of the device under 0~-6 V bias were studied. Under 0 V, the device has a spike in response at the 254 nm irradiation. When a reverse bias is applied, the spike disappear. Finally, the energy band diagrams of the p-GaN/Ga₂O₃∶Si heterojunction before contact, after contact, and under reverse bias are analyzed.