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Silicon‐based photodetectors show attractive prospects due to their convenient preparation, high detectivity, and complementary metal–oxide–semiconductor compatibility. However, they are currently limited by low responsivity and sharp decay at sub‐bandgap wavelength. Although the aforementioned limitation can be partly solved by femtosecond laser processing, the surface defects and carrier activation rates result in a large dark current and narrow spectral response, which are unsatisfactory. Herein, rapid thermal annealing and hydrogenated surface passivation are introduced to elevate the broad‐bandgap responsivity and signal to noise ratio and to suppress the dark current. At optimal conditions, a sub‐bandgap responsivity of 0.80 A W−1 for 1550 nm at 20 V at room temperature is obtained, comparable with commercial germanium photodiodes and much higher than previously reported silicon photodiodes. Moreover, the prepared photodetector responded to spectral range from 400 to 1600 nm, with responsivity reaching 1097.60 A W−1 for 1080 nm at 20 V, which is the highest in reported silicon photodetectors. Simultaneously, the device shows competitive detectivity (1.22 × 1014 Jones at −5 V) due to the post‐processing procedures and suppressed dark current (7.8 μA at −5 V). The results show great prospects for black silicon in infrared light detection, night vision imaging, and fiber‐optic communication. [ABSTRACT FROM AUTHOR]