On the corrosion of a promising photoelectrochemical material: The anodic dissolution of p-Si in fluoride electrolytes

A study of cyclic voltammetry of p-Si as a function of pH, fluoride ion concentration and electrode rotation rate was carried out. The i/V characteristics exhibit similar general tendencies: a very rapid current increase (porous silicon generation), followed by a first sharp peak, a narrow polishing plateau, another broad maximum and finally a second plateau covering several volts. Using the rotating disc electrode, the kinetic and diffusional current contributions in the anodic dissolution of p-Si in fluoride electrolytes are separated. The diffusion limitation seems to be due to the same species over the entire potential range studied. Impedance measurements at low frequencies confirm an inductive behaviour in the region of porous Si generation. In this regime, the series resistance R _sis 1-2 orders of magnitude higher than in other regimes. The presence of an interfacial silicon oxide layer in the region just beyond the first peak was evidenced through admittance results. The cyclic voltammograms show the appearance of current oscillations for voltages higher than ≅2·5 V. These oscillations are the finger-print of a characteristic resonance frequency of the interface, f ₀. In the same potential region, admittance measurements exhibit a resonance at the same characteristic frequency. Secondary resonances at f ₀ overtones were evidenced suggesting the existence of microscopic spontaneous oscillations of the oxide thickness.