Morphological and Electrical Features of Porous Silicon Prepared by Metal-Induced Chemical Etching

Porous silicon (PS) was produced by the metal-induced chemical etching of p-type Si wafers. Patterned platinum dots (~ 300 μm) were deposited on a Si wafer by DC magnetron sputtering for 15 s. When the H₂O₂ fraction in the etchants consisting of HF and H₂O₂ was increased from 0.3 to 24%, the etching behavior changed from “pore formation” to “electropolishing.” The etching reaction activation energy also changed from 0.20 to 0.36 eV in the ln J–K(current–etchant temperature) relationships. The etched morphologies exhibited different structures, such as nano-scaled sponge-like and 3D micro-scaled pore structures, according to the H₂O₂ ratio. The etched layers contained a Si quantum structure, amorphous Si phase, and SiO_x. These phase ratios changed according to the etching behavior. The Si nanocrystallite size changed from ~ 3.0 to 4.6 nm, emitting optical features in the band gap range of 1.73 to 1.88 eV. The fluorescence region varied according to the H₂O₂ contents. The fluorescence preferentially occurred at the interface between the metal circle and Si wafer in the case of etched PS by an etchant containing a lower hydrogen peroxide ratio. In contrast, the fluorescence increased in the non-coated region from 19.5 to 24.0%.