β-Ga ₂O ₃-based deep-ultraviolet photodetector (PD) has versatile civil and military applications especially due to its inherent solar-blindness. In this work, pristine and N-doped β-Ga ₂O ₃thin films are prepared on c-plane sapphire substrates by radio frequency magnetron sputtering. The influences of N impurity on the micromorphology, structural and optical properties of β-Ga ₂O ₃film are investigated in detail by scanning electron microscopy, X-ray diffraction, and Raman spectra. The introduction of N impurities not only degrades the crystal quality of β-Ga ₂O ₃films, but also affects the surface roughness. The β-Ga ₂O ₃films doped with N undergoes a transition from a direct optical band gap to an indirect optical band gap. Then, the resulting metal-semiconductor-metal (MSM) PD is constructed. Comparing with the pure β-Ga ₂O ₃-based photodetector, the introduction of N impurities can effectively depress dark current and improve response speed of the β-Ga ₂O ₃device. The N-doped β-Ga ₂O ₃-based photodetector achieves a dark current of 1.08 × 10 ^–11A and a fast response speed (rise time of 40 ms and decay time of 8 ms), which can be attributed to the decrease of oxygen vacancy related defects. This study demonstrates that the acceptor doping provides a new opportunity for producing ultraviolet photodetectors with fast response for further practical applications.