Abstract: Black silicon was prepared with polycrystalline silicon by plasma immersion ion implantation. The microstructure, optical absorbance and lifetime of minority carriers of the black silicon were characterized by scanning electron microscopy (SEM), UV-VIS-NIR spectrophotometer and microwave photoconductive decay (μ-PCD), respectively. The results show that the black silicon has a porous structure. The average absorbance of the black silicon is above 94% in the visible region. The average lifetime of minority carriers in the black silicon is 5.68 μs. The effect of immersion parameters on the black silicon was investigated. It is found that the gas flux ratio of SF₆ to O₂ plays an important role in the microstructure and properties, and its optimum value is 2.80.