Electrochemical doping is recently recognized phenomenon wherein an oxygen redox couple in an adsorbed water film tends to pin the Fermi level in semiconductors at the electrochemical potential of the redox couple. This leads to reversible exchange of electrons between the semiconductor and ambient atmosphere that depends on the band line up of the semiconductor with respect to the ambient. This process gives rise to multitude of effects that affect both the electronic and optical properties of materials. For example, this process gives rise to p-type surface conductivity in undoped hydrogenated diamond1, 2, 3 , semiconducting single walled nanotubes and graphene.4 The p-type conductivity arises when the Fermi level of the semiconductor is higher than the redox potential of the electrochemical reaction. In case of GaN and ZnO, the electrochemical redox reactions affects both defect related and band edge luminescence. These observations are explained by electron transfer between the oxygen electrochemical redox couple and mid-gap states in the GaN and ZnO. The above effects are reversible and have been observed on single crystals, nanowires and polycrystalline samples.
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