Excellent antireflection properties of vertical silicon nanowire arrays

We report a simple approach to prepare cost effective antireflective surface directly on silicon wafers, which consists of arrays of vertically aligned silicon nanowires (VA-SiNWA). Large area VA-SiNWA were realized by silver induced wet chemical etching of p-silicon (1 0 0) substrates in aqueous HF and AgNO3 solution at room temperature. Length of Si wires (diameter in 50–300 nm range) was found to increase linearly with etching time (0–120 min). A remarkable reduction in reflectivity (Rλ) for surfaces with Si wires was observed. The value of Rλ less than 2% was realized in the 300–600 nm wavelength range in the case of ∼12 μm long Si wires, a value better than the best Rλ reported in anisotropically textured surface or single layer antireflection coatings. The VA-SiNWA behaves as a subwavelength structured surface that could suppress the reflectivity to a great extent. Such surfaces may have potential applications as antireflection surface for silicon solar cells.