Anodization studies on low-doped n-type silicon in aqueous electrolytes have systematically shown the formation of macropores. In this paper, we show the possibility to produce microporous silicon in low-doped n-type substrates. We use the temperature gradient zone melting doping technique to realize a deep back side p-n junction as a hole provider to obtain microporous silicon layers. It is believed that the transition from macroporous to microporous formation is linked to hole injection to the anodic HF vertical bar Si interface. To corroborate this hypothesis, we have investigated the back side p-n junction injection efficiency by Synopsis Sentaurus simulations. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3507411] All rights reserved.