Facile fabrication of periodic arrays of vertical Si nanoholes on (001)Si substrate with broadband light absorption properties

This study presents a facile and straightforward approach to fabricating periodic arrays of Au nanodisks and vertically aligned, depth- and morphology-controllable Si nanoholes on (001)Si substrates by combining self-assembled nanosphere lithography, selective Au wet etching, and Au nanodisk-catalyzed Si etching processes. All of the etching experiments were carried out in aqueous solutions at room temperature without using complex photolithography and hard-mask patterning processes. The shape, diameter, and spacing of the produced vertical Si nanoholes corresponded well to those of the catalytic Au nanodisks used, and the nanohole depth could be readily tuned from sub-micrometer to several micrometers by adjusting the Au nanodisk-catalyzed Si etching time. The Si substrates with nanohole-textured surfaces exhibited depth-dependent hydrophobic behaviors and broadband (400–1650 nm) light absorption properties. The measured integrated absorptance was found to increase with increasing the depth of Au nanodisk-embedded Si nanoholes and can reach up to 95% in the visible light region and 60% in the near-IR region. The resulting broadband absorption enhancement can be attributed to the combined effects of multiple scattering of light and localized surface plasmon resonance. The obtained results present the exciting prospects that the new combined approach proposed here would offer potential applications in constructing various high-efficiency nanohole array-based optoelectronic and photovoltaic devices.