Field-induced water electrolysis switches an oxide semiconductor from an insulator to a metal

Water is composed of two strong electrochemically active agents, H ⁺ and OH^- ions, but has not been used as an active electronic material in oxide semiconductors. In this study, we demonstrate that water-infiltrated nanoporous glass electrically switches an oxide semiconductor from insulator to metal. We fabricated a field-effect transistor structure on an oxide semiconductor, SrTiO₃, using water-infiltrated nanoporous glass-amorphous 12CaO·7Al₂O₃ -as the gate insulator. Positive gate voltage, electron accumulation, water electrolysis and electrochemical reduction occur successively on the SrTiO₃ surface at room temperature. This leads to the formation of a thin (∼3 nm) metal layer with an extremely high electron concentration (10₁₅-10 ₁₆cm^-2), which exhibits exotic thermoelectric behaviour. The electron activity of water as it infiltrates nanoporous glass may find many useful applications in electronics or in energy storage.