A as-based etching method for the fabrication of porous silicon was developed. It consists of exposing silicon samples to a mixture of oxygen (0(2)) and nitrogen dioxide (NO2) gases, and hydrogen fluoride (HF) and water vapors. The morphology, structure, porosity, photo luminescence properties, refractive index, and extinction coefficient of the porous layers, for various O-2 : NO2 flow rate ratios were investigated. The porous layers were characterized by island-like structures, attributed to the condensation of etchant-laden drops. Sections of porous silicon, with an average porosity and thickness of 88% and 1230 nm, respectively, were dispersed within a porous silicon inatrix characterized by an average porosity and thickness of 79% and 301 min, respectively. In addition to the striking difference in thickness between the islands and matrix, the morphology of the porous layer surface was different between the two areas. The size and density of the islands were found to strongly depend on the 0,: NO, flow rate ratio. Furthermore, the porous layers demonstrated a strong photo luminescence emission at an average peak wavelength of 658 nm. (c) 2005 Elsevier B.V. All rights reserved.