(Invited) Porous Structure Produced By Metal-Assisted Etching of Silicon

Metal-assisted etching of silicon can produce porous silicon and silicon nanowires by simply immersing metal-modified silicon in a hydrofluoric acid solution without electrical bias [1]. Such etching proceeds by a local galvanic cell mechanism consisting of local anodic dissolution of silicon and local cathodic reduction of an oxidizing agent, such as oxygen [2, 3] or hydrogen peroxide, on catalytic metal. The structure of porous silicon is widely controlled from nanometer to sub-millimeter scale in pore size and from straight to an ants’ nest like in pore morphology by changing etching conditions [1-3]. We fabricate various porous structures on silicon wafers, and apply them to antireflection of solar cells and autocatalytic electroless formation of metal-nanorods and metal films on silicon surfaces. The structure of porous silicon is easily controlled in the nanometer scale with changing etching conditions such as kind, size, and distribution of metal catalysts, kind and concentration of oxidizing agent, intensity of photoillumination, and etching time. Recently, we found that general corrosion occurred on the top surface of the silicon substrate around the metal particles even under the dark condition [4]. The general corrosion depended on the metal species and it was explained by the formation and dissolution of a mesoporous layer. [1] Z. Huang, N. Geyer, P. Werner, and U. Gösele, Adv. Mater., 23, 285 (2011). [2] S. Yae, Y. Kawamoto, H. Tanaka, N. Fukumuro, and H. Matsuda, Electrochem. Comm., 5, 632 (2003). [3] S. Yae, M. Tashiro, M. Abe, N. Fukumuro, H. Matsuda, J. Electrochem. Soc., 157, D90 (2010). [4] A. Matsumoto, H. Son, M. Eguchi, K. Iwamoto, Y. Shimada, K. Furukawa, and S. Yae, RSC Adv., 10, 253 (2020).