Optical properties of silicon nanowires obtained by metal-assisted chemical etching using gold nanoparticles

Owing to their unique structural and physical properties, silicon nanowires are a promising material for electronics, photovoltaics, photonics, sensors, and biomedicine. Despite the many methods available for the synthesis of silicon nanowires, metal-assisted chemical etching is currently one of the most promising for their cost-effective production. In most works, silver nanoparticles are used as a catalyst for the chemical reaction of crystalline silicon etching. However, the use of gold nanoparticles in metal-assisted chemical etching can significantly affect the morphology and optical characteristics of the prepared samples. In this work, silicon nanowires are synthesized by metal-assisted chemical etching of crystalline silicon using gold nanoparticles. According to high-resolution scanning and transmission electron microscopy, the resulting nanowires have a diameter of about 100 nm and consist of a crystalline core about 50 nm in diameter coated with a SiO$_2$ shell about 25 nm thick with silicon nanocrystals at the interface. The porosity of the silicon nanowire arrays, which has been estimated from their specular reflection spectra and has been calculated using the Bruggeman effective medium model, is 70%. At the same time, the samples exhibit an extremely low (3–7%) total reflection in the spectral region of 250–1000 nm and an increase in the intensities of interband photoluminescence and Raman scattering compared to the initial crystalline silicon substrate, caused by the light localization effect. In addition, the photoluminescence of nanowires has been detected in the range of 500–1000 nm with a maximum at 700 nm, which is explained by the radiative recombination of excitons in silicon nanocrystals with a size of 3–5 nm.