Room temperature growth of wafer-scale silicon nanowire arrays and their Raman characteristics

We report a simple, inexpensive, and rapid process for large area growth of vertically aligned crystalline silicon nanowires (SiNWs) of diameter 40-200 nm and variable length directly on p-type (100) silicon substrate. The process is based on Ag-induced selective etching of silicon wafers wherein the growth of SiNWs was carried out using the aqueous HF solution containing Ag+ ions at room temperature in a Teflon vessel. Effect of etching time has been investigated to understand the evolution of SiNW arrays. It has been found that the length of SiNWs has a linear dependence on the etching time for small to moderate periods (0-2 h). However, etching rate decreases slowly for long etching times (> 2 h). Scanning electron microscopy was used to study the morphology of the SiNW arrays. Structural and compositional analysis was carried out using Raman spectroscopy and high-resolution transmission electron microscopy equipped with energy dispersive X-ray spectroscopy. Orders of magnitude intensity enhancement along with a small downshift and broadening in the first-order Raman peak of SiNW arrays was observed in comparison to the bulk crystalline silicon.