Bioinspired Si subwavelength gratings by closely-packed silica nanospheres as etch masks for efficient antireflective surface

We experimentally investigate the antireflective properties of various silicon (Si) subwavelength grating (SWG) structures using closely-packed silica nanospheres monolayers with different sizes as etch masks and a subsequent inductively coupled plasma (ICP) etching, together with theoretical calculations based on a rigorous coupled wave analysis method. The geometric structure of Si SWGs is optimized by changing the size of nanospheres and ICP etching parameters. The antireflective properties depend strongly on the period, height, and shape of the hexagonally ordered SWG structures, especially correlated with ICP etching parameters. For an optimized Si SWG structure with a rounded cone shape, the reflectance is significantly reduced, indicating a low reflectance of <4.4% over a wide wavelength region of 300–1100 nm. From theoretical analysis, the reflectance of rounded cone-shaped Si SWG structures is minimized with a period of ∼300–350 nm and heights of >750 nm, which is reasonably consistent with the experimental results. The angle-dependent antireflection characteristics are also discussed.