Effect of anodization current density on pore geometry in macroporous silicon

Macroporous silicon films were fabricated by electrochemical etching of p?-type silicon with a resistivity range of 9.0?13.0 ? cm for 10?min in an electrolyte containing hydrofluoric acid, water, and acetonitrile. Samples were studied using scanning electron microscopy. The onset of macropore formation was observed to occur at a current density of ?3.6 mA?cm?2. At larger current densities, cross-sectional micrographs revealed macropores of approximately columnar shape. Average pore diameter was estimated from plan view micrographs using an image processing algorithm and found to be consistent with a square root dependence on the etching current density in the range investigated.