Properties of light-emitting porous silicon photoetched in aqueous HF∕FeCl3 solution

The formation of yellow-light-emitting porous silicon (PSi) layers in a HF solution with adding an oxidizing agent FeCl3 is presented. The PSi layers are formed by photoetching under Xe lamp illumination. The photoluminescence (PL) intensity is strongly dependent on the FeCl3 concentration and shows a maximum at x∼25 wt % [50 wt % HF:(x wt % FeCl3 in H2O)=1:1]. The surface topography as characterized by atomic force microscopy reveals features on the order of 20−100 nm with a root-mean-squares roughness of ≤2 nm. The Fourier-transform infrared spectroscopy shows a new absorption peak at ∼1100 cm−1, which is assigned to the surface oxide stretching mode and grows larger with increasing etching time. The stain etched samples also show PL emission, but they are synthesized only at higher x concentrations (≥20 wt %). The PSi formation mechanism can be explained with the aid of a surface energy-band diagram of n-type silicon in the HF∕FeCl3 electrolyte.