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

A simple and effective method is presented for producing light-emitting por ous silicon (PSi). A thin (d < 10 nm) layer of Au, Pt, or Au/Pd is deposite d 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 leve l, PSi with different morphologies and light-emitting properties is produce d. PSi production occurs on the time scale of seconds, without electrical c urrent, in the dark, on both p- and n-type Si. Thin metal coatings facilita te the etching in HF and H2O2, and of the metals investigated, Pt yields th e 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 possib ility of fabricating in situ PSi contacts. (C) 2000 American Institute of P hysics. [S0003-6951(00)05542-X].