Silicon quantum dot/black silicon hybrid nanostructure for broadband reflection reduction

Abstract

The incorporation of silicon quantum dots (Si QDs) onto black silicon (b-Si) as a hybrid nanostructure has resulted in reflectance reduction over a wide spectral range (300–1000 nm). Si QDs were derived from porous Si (P–Si) by anodic electrochemical etching and ultrasonication whereas b-Si was fabricated by the two-step metal assisted chemical etching (MACE) technique. Si QDs with average diameter of 1.8 ± 1.1 nm are suitable for photon down-conversion of UV light (365 nm) into the visible (665 and 740 nm). As a hybrid nanostructure, smaller sized Si QDs exhibited better surface coverage on the b-Si nanopillar sidewalls resulting in enhanced broadband reflection reduction, particularly at 600 nm and beyond. At wavelength of 600 nm, the Si QD/b-Si nanostructure exhibited a reflectance reduction from 9.9% to 6.5% with a more pronounced reduction towards the longer wavelengths, attributed to refractive index matching and optical confinement within the Si nanostructure. Photocurrent enhancement in the UV-blue excitation region is attributed to photon down-conversion (UV to visible) by Si QDs to the underlying b-Si.