Multi-scale micro-nano structures prepared by laser cleaning assisted laser ablation for broadband ultralow reflectivity silicon surfaces in ambient air

To meet the ultra-broadband perfect absorption of visible-infrared light on silicon surfaces, a green, efficient and economical method for fabricating multi-scale micro-nano composite structures in ambient air is proposed. We experimentally demonstrate laser cleaning assisted femtosecond laser ablation for fabricating anti-reflection structures. Laser cleaning technology not only effectively eliminates oxide deposition on the laser textured surfaces, but also manufactures the small scale fine-microstructures and nanostructures. A focused ellipse laser spot is innovatively applied to realize large area and energy decays continuously multiple laser cleaning of laser-treated surfaces, and solve the problem that new oxide deposition is generated in the cleaning process. The processing efficiency is also increased by 4.8 times. The average reflectance of 2.06% is reached from 300 to 2500 nm. Great enhancement of infrared light absorption of silicon from 2.5 to 16 μm is realized experimentally. The average reflectance is reduced to 4.98% with a broadband reflectance below 6.6%. Especially, a reflectance below 5.0% from 2.5 to 10 μm and an average reflectance of 4.3% is achieved, which is the least reported to date by laser processing techniques as far as we know. This strategy for anti-reflection structures is excellent candidate for future optoelectronic devices.