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.