Ultrafast laser-induced black silicon, from micro-nanostructuring, infrared absorption mechanism, to high performance detecting devices

As the foremost semiconductor, silicon (Si) is the ‘lifeblood’ of the modern microelectronics and optoelectronics industries. The development of Si infrared (IR) photodetectors is of great significance for Si-based optoelectronic integration and communication. The use of black Si, which can extend the absorption edge of the Si bandgap to IR wavelengths below the bandgap, is a promising strategy to make IR detectors directly integrated on Si wafers for optical communication and detection. To produce black Si, ultrafast laser pulses in an ambient atmosphere or an atmosphere including precursors are used to fabricate periodically arranged micro-nanostructures and induce various defects on Si surfaces. This phenomenon leads to a ‘black’ color because of a strong absorption from visible light to IR light. In this review, the surface morphology, crystalline structures, hyperdoping, IR absorption properties, and optoelectronic devices of black Si fabricated by ultrafast lasers over the past 20 years are systematically summarized, focusing especially on its most important application for IR photodetectors. Finally, future prospects and strategies for improvement are suggested. It is expected that black Si can be a competitive candidate for IR optoelectronics in the future if thermostable IR absorption, a low concentration of free carriers, and a high photoelectric conversion efficiency of black Si can be achieved.