Silicon nanowires self-purification by metal-assisted chemical etching of metallurgical silicon

The purity of metallurgical-grade silicon can be increased to solar grade by metal-assisted chemical etching (MaCE). Metal impurities are removed during the formation of porous silicon nanowires (NW). We present a chemical etching model to explain the different levels of chemical reduction for various metals with pore growth during etching. Our study not only highlights the importance of controlling the metal ion concentration and selecting metal types for engineering porous features in NWs, but also explains the reason for the difficulty in removing noble metals such as Cu.