XPS and AES studies on iron-oxide-coated Si photoanodes with a negative flatband potential

We report the first efficient photoanode with a negative flatband potential, consisting of n-Fe2O3 and n-Si. An anodic current of ∼0.8 mA/cm2 was observed at 0 V SCE in 0.1 M KOH solution under an illumination of ∼60 mW/cm2. A photocurrent rose at ∼−0.3 V SCE under the same condition. An electronbeam evaporation of Fe, followed by its oxidation at 700 °C under 5×10−2 Torr was successful in obtaining an efficient photoanode. The surface structure was analyzed using x-ray photoemission spectroscopy (XPS) and Auger-electron spectroscopy (AES) techniques and capacitance-voltage measurements. XPS spectra revealed that the surface structure was composed of Fe2O3-Fe3O4-Si. XPS signals showed that the SiO2 phase also coexisted at the top surface probably due to interdiffusion of Si. Depth profiles were obtained by the AES technique.