Anodic etching characteristics of n-type silicon in aqueous hydrofluoric acid HF/C2H5OH/H2O/KIO3 (HF/KIO3) and HF/C2H5OH/H2O (HF) electrolytes are investigated using photoluminescence (PL), optical microscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The PL intensity at similar to 1.8-1.9 eV shows a maximum for the sample formed in the HF/KIO3 electrolyte at anodic current density of i(a)approximate to 15 mA/cm(2), while no strong PL emission is observed for samples formed in the HF electrolyte at lower i(a) values than similar to 100 mA/cm(2). Optical microscopy reveals macropores, a few micrometers or more in square length, on the HF/KIO3-formed surfaces. The SEM images also reveal micropores in size up to similar to 1 mu m. The densities of such macro- and micropores increase with increasing i(a). The HF electrolyte also produces macropores but for i(a) larger than 30 mA/cm(2) and micropores larger than 1 mA/cm(2). The AFM-revealed microporous sizes are on the order of 10-100 nm, which are much larger than the sizes required to induce quantum confinement effects. The anodic etching mechanism can be explained with the aid of a surface energy-band diagram of n-Si in the HF/KIO3 electrolyte. (c) 2007 The Electrochemical Society.