To apply Si-based photodetectors in the near-infrared band and improve their responsivity. A regular and orderly microstructure array was formed on the surface of silicon-based photodetectors by plasma lithography. Besides, an film was grown on the microstructure surface by atomic layer deposition (ALD) to study its anti-reflection and passivation effects. The surface reflectivity and characteristic curves of the device were compared and the light responsivity of the device under 808 near-infrared light was calculated. It is found that the responsivity of the device is increased from 0.063 to 0.83.