Liquid junctions for characterization of electronic materials. I. The potential distribution at the Si/methanol interface

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Abstract
Photoelectrochemical cells consisting of n-type 〈100〉-Si wafers in methanolic solutions of ferrocene derivatives with LiClO4 as the supporting electrolyte have been analyzed using a complementary set of impedance spectroscopy, electroreflectance, and current-voltage measurements. The results were interpreted in terms of charge accumulation modes correlated with junction parameters such as space-charge layer, surface states, Fermi-level pinning, and the possible presence of an insulating layer at the interface. The impedance of these junctions is interpreted in terms of an equivalent circuit. The Fermi level is partially pinned at a potential about 0.2 eV below the conduction band and is completely pinned at potentials positive to midgap. The electroreflectance results agree well with the impedance. The effect of an HF etching on the properties of the cells will be discussed. We have also compared the results in the methanolic solution with an aqueous electrolyte. The potential distribution obtained in this case is very similar to the ferrocene solution.