Influence of femtosecond laser pulse energy on the surface reflection of black silicon in alkaline solution

A highly efficient approach for reducing the reflection of the black silicon surface is demonstrated, in which the black silicon is fabricated in alkaline solution via a femtosecond laser irradiation. The junglelike microstructures are formed on the surface of the black silicon. Compared to the polished silicon, the black silicon can significantly suppress the surface reflection. Throughout the region of visible light, the average minimum reflectance of the blackened surface is about 5.6%. Meanwhile, in order to get an optimal laser energy, we investigated the evolution on silicon surface as a function of incident pulse energy. Taking into account the height of junglelike microstructures and the reflectance of black silicon samples, the optimal laser energy is 1400 μJ. By choosing the right laser energy, it is possible to fabricate the highly absorptive black silicon. These results are of extreme importance in the control of surface morphology and the modification of material surface.