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Supersaturated S-doped black silicon (Si) samples are produced by femtosecond laser fabrication in mixed atmosphere of sulfur hexafluoride and oxygen (SF6/O2). The surface morphology with cone-microstructures has been observed in black Si samples fabricated in mixed atmosphere. After thermal annealing, the absorption below bandgap of black Si is obviously reduced. Moreover, the contents of sulfur in black Si samples obtained in mixture are also decreased by the lead in of oxygen. In contrast, an obvious increase of valent state ratio of Si4+ (SiO2) to Si0 (Si) is observed after the implantation of oxygen due to the formation of SiO2 in S-doped Si. Based on the passivation effect of SiO2, we have produced near-infrared black Si photodiode devices and showed photo-response properties of the devices. A notable photo-response of 11 mA/W at −3 V (26.6 mA/W at −5 V) for near-infrared 1.31- \mu \textm detection light is obtained for the photodiode fabricated in mixture, which outweigh the performance of photodiode fabricated in pure SF6 atmosphere. [ABSTRACT FROM PUBLISHER]