Cation effects on the anodic dissolution of n-Si in fluoride electrolytes

Under strong illumination and in the anodic range, current-potential characteristics of n-Si | fluoride-electrolyte interfaces exhibit the same shape as those of p-Si. The increase of the photocurrent observed in the presence of alkali-metal cations of increasing size is interpreted as for p-Si: in the electropolishing regime, cations act as catalysts for the dissolution of the silicon-oxide layer covering the electrode. In the dark, a negative flatband-potential shift and a decrease in the anodic current are observed in the presence of alkali-metal cations of increasing size. This behaviour, which takes place on hydrogenated surfaces, is accounted for in a kinetic model in which electrochemical transfer takes place through negatively-charged surface states. Cation adsorption favours the presence of a negative charge at the surface, hence the negative charge is increased, thereby decreasing the flatband potential and the charge-transfer rate.