ИСТИНА

Silicon nanowires (SiNWs), manufactured using weakly toxic chemistry, have great potential for applications in the field of photovoltaics, photonics and sensorics. Here SiNWs were prepared by the metal assisted chemical etching method, where the commonly used HF has been successfully replaced with NH4F. The mechanism of the etching process and the effect of the pH values of H2O2:NH4F solutions on the structural and optical properties of SiNWs were studied in detail. It is shown that as the pH of H2O2:NH4F decrease, the shape of the SiNWs changes from pyramidal to vertical. By impedance and Mott-Schottky measurements it was shown that the SiOx layer thickness and electrolyte potential are strongly affected by pH. With increasing pH of electrolyte OCP of the cell decreases reducing silicon oxidation rate. Silver assisted chemical etching of silicon can be ascribed to facilitated transport through Si/SiOx/Ag interface. All samples exhibit a strong decrease of the total reflectance to 5-10% at the wavelength less than 800 nm in comparison to c-Si. Also the intensities of interband photoluminescence and Raman scattering for SiNWs increase strongly as opposed to corresponding value fоr c-Si, but depends both from the length and the shape of SiNWs: they were larger for long pyramidal nanowires. This effect can be explained by the light localization in such inhomogeneous optical medium as SiNW layers. This work was supported by the Russian Science Foundation (Grant № 17-12-01386).