Structural analysis of iron oxide coated n-silicon heterojunction photoanodes

The iron oxide/n-Si heterojunction electrode was investigated as a possible efficient photoanode with the iron oxide prepared under various conditions. The oxide structure was studied by RBS (Rutherford backscattering spectrometry) and XPS (X-ray photoelectron spectroscopy) techniques and the correlation between photocharacteristics and its oxide structure was discussed. The iron oxide prepared by thermal oxidation and reactive-evaporation methods. The photocurrent in a 0.2 mol dm^-3 KOH solution was found to strongly depend on the preparation of the iron oxide. The reactive-evaporated Fe₂O₃/n-Si electrode showed the most effective characteristics of photoresponse and the 60 min thermally oxidized Fe₂O₃/n-Si electrode gave the best results in the thermally oxidized oxide system. The compositional analysis by RBS indicated that the oxide is formed stoichiometrically as Fe₂O₃ and that small amounts of a heavy-mass and a tungsten impurity are present in the thermally oxidized and the reactive-evaporated oxides, respectively. The XPS analysis of the chemical state of the iron in the oxide showed that the chemical state of the iron oxide formed by thermal oxidation varies as a function of depth and that the iron oxide formed by reactive- evaporation is in a almost constant chemical state throughout the film.