Inverted pyramid structure on monocrystalline silicon processed by wet etching after femtosecond laser machining in air and deionized water

The micro-structured silicon has been preliminarily applied to improve the surface and optical properties of micro-solar cells, micro-optical systems, and aerospace engineering. However, the morphological changes and optical properties of monocrystalline silicon during femtosecond laser machining assisted with chemical etching are not clear, especially in a liquid environment. In this paper, monocrystalline silicon was ablated by femtosecond laser in air and deionized water respectively and then etched by alkaline potassium hydroxide (KOH). The reflectivity, absorptivity, and transmissivity of monocrystalline silicon were tested. Experimental results showed that inverted pyramid (IP) structure could be processed on a monocrystalline silicon wafer by ablating the surface with a high-power laser under the air environment and a low-power laser under the deionized water environment, followed by KOH etching. Meanwhile, the optical properties of the monocrystalline silicon with IP structure were effectively improved.