Effect of alkali-metal and some quaternary-ammonium cations on the anodic dissolution of p-Si in fluoride media

A systematic study of the anodic dissolution rate upon changing the cations of the supporting electrolyte has been performed for a wide range of electrolyte compositions. The usable range of fluoride concentrations is limited by the solubility of the fluoride salt in the case of Li⁺, and by the solubility of the hexafluorosilicate salt in the case of K⁺, Rb⁺ and Cs⁺. When limitations due to solubility are avoided, the anodic dissolution rate has been found to depend markedly upon the concentration of the supporting electrolyte and the nature of its cation (alkali-metal or quaternary-ammonium). Changing the cation may result in variations in anodic currents of more than one order of magnitude. This variation appears entirely due to a variation of the kinetic contribution to the anodic current, and is associated with a catalytic effect in the dissolution rate of the interfacial oxide by the fluoride species.