Porous silicon nanowire arrays fabrication through one-step metal-assisted chemical etching

One-step metal-assisted chemical etching (MACE) was used to fabricate porous silicon nanowire arrays. Also, the effects of doping level, AgNO₃ concentration, and HF concentration on the morphology and structure of porous silicon nanowire were investigated. The results show that the higher doping level is beneficial for etching the silicon wafer and forming silicon nanowire arrays. This is because the higher doping level introduces more impurities and defects on the surface of the silicon wafer, and at the same time, the Schottky barrier between the silicon wafer with the higher doping level and the solution is lower. Thus, the silicon wafer is easier to oxidate to form nanowire arrays. The AgNO₃ concentration plays a critical role in the fabrication of the porous silicon nanowire arrays during the one-step MACE process. If AgNO₃ concentration is too low or too high, corrosion pits and collapsed clusters of nanowires could form on the surface of the silicon wafer. When AgNO₃ concentration was 0.02 mol·L^-1, silicon nanowires grew and became longer, eventually forming a porous array of silicon nanowire. In the meantime, as silicon nanowires grew, capillary stress between nanowires caused agglomeration at the top of some nanowires. Furthermore, when HF solution concentration exceeded 4.6 mol·L^-1, the length of silicon nanowire increased with increasing HF concentration. Furthermore, a porous structure was formed on top the silicon nanowire, and the porosity of the silicon nanowires increased with increasing HF concentration. This was due to a large number of Ag⁺ random nucleations at the top of the nanowires, and lateral etching of the silicon nanowires occurred. In the end, the formation process of the porous silicon nanowires is explained by a model based on the experimental phenomena. It is attributed to the deposition of silver ions and the oxidation of dissolved silicon substrates.