Electrochemical impedance spectroscopy of 6H-SiC in aqueous hydrofluoric acid

Polarization and electrochemical impedance spectroscopy of p-type 6H-SiC el ectrodes in an aqueous hydrofluoric acid solution is performed during the f ormation of porous SiC. The polarization of p-type SiC permits the identifi cation of the flatband voltage, a Tafel-like region, and a limiting current which is attributed to the onset of the electropolishing regime. For some of the potential range studied over which porous layers form, the impedance data are characterized by a single high-frequency semicircle and there is a second low-frequency semicircle at intermediate potentials. The dependenc e of the fitted capacitance and resistance on the applied voltage suggests that the SiC-electrolyte interface is controlled under different regimes of potential by the space-charge layer, the interaction with surface states, and the formation of a passivating film. (C) 2001 The Electrochemical Socie ty.