Optical properties of high aspect ratio plasma etched silicon nanowires: fabrication-induced variability dramatically reduces reflectance

In this work we investigate both experimentally and theoretically the optical properties of aligned, perpendicular to the substrate, high aspect ratio (AR), plasma etched Si nanowires (SiNWs) with controlled variability. We focus on the role of imperfections in fabrication, which manifest themselves as dimensional variability of SiNW, lattice defects or positional randomization. SiNW arrays are fabricated by e-beam lithography (perfectly ordered array) or colloidal particle self-assembly (quasi-ordered array) followed by cryogenic Si plasma etching, which offers fast etch rate (up to 3 μ m min −1 ) combined with clean, smooth, and controllable sidewall profile, but induces some dimensional variability on the diameters of the SiNWs. Sub-200 nm diameter SiNWs having AR as high as 37:1 are demonstrated. The total reflectance of SiNWs is below 2% in a wide range of the optical spectrum. We experimentally demonstrate improved light absorption when moving from a perfectl...

A Smyrnakis, E Almpanis, V Constantoudis, N Papanikolaou and E Gogolides

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