Carrier transport mechanisms in cathodically biased meso‐porous p⁺‐Si against solutions containing Fe²⁺ and Co²⁺ species

Abstract

This work reports on the use of the cyclic voltametry technique to study the electrochemical behavior of porous p+‐type silicon (PS) contacted by aqueous solutions containing Fe2+ and Co2+ electro‐actives species. Current‐potential (I‐V) measurements were performed on both flat and porous silicon substrates and different Fe2+ concentrations were considered. With flat Si, similar I‐V characteristic behaviors were obtained in 0.1 M Fe2+ and 0. 1 M Co2+ solutions, except that iron can be deposited from a potential more cathodic than cobalt. With porous Si, different I‐V characteristic behaviors were observed and a diffusion‐like current peak was detected in the presence of Fe2+ species. The observed current peak is located near the standard redox potential of iron. However, its intensity is lower than that of Fe2+ ions diffusion current peak and it does not increase as Fe2+ concentration increases. A three‐step carrier transport mechanism was proposed to show that the current peak could be attributed to iron nucleation on the pore walls via electroless deposition. Accordingly the difference observed in PS I‐V characteristics was attributed to the fact that electroless deposition on pore walls occurs at a potential for which the reduction of Co2+ ions is faster than that of Fe2+ ones and it can also occur at the pore bottom via electrodeposition. These results are used to explain the poor pore filling rate with iron, reported elsewhere. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)