Metal-assisted chemical etching in $HF/H2O2$ produces porous silicon

A simple and effective method is presented for producing light-emitting porous silicon (PSi). A thin $(d$<10 nm) layer of Au, Pt, or Au/Pd is deposited on the (100) Si surface prior to immersion in a solution of HF and $H2O2.$ Depending on the type of metal deposited and Si doping type and doping level, PSi with different morphologies and light-emitting properties is produced. PSi production occurs on the time scale of seconds, without electrical current, in the dark, on both $p$- and $n$-type Si. Thin metal coatings facilitate the etching in HF and $H2O2,$ and of the metals investigated, Pt yields the fastest etch rates and produces PSi with the most intense luminescence. A reaction scheme involving local coupling of redox reactions with the metal is proposed to explain the metal-assisted etching process. The observation that some metal remains on the PSi surface after etching raises the possibility of fabricating in situ PSi contacts.