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The wide gap perovskite semiconductor BaSnO3 has attracted much interest since the discovery of room temperature electron mobility up to 320cm2V-1s-1 in bulk crystals. Motivated by applications in oxide heterostructures, rapid progress has been made with BaSnO3 films, although questions remain regarding transport mechanisms and mobility optimization. Here we report on a detailed study of epitaxial BaSnO3 electric double layer transistors based on ion gel electrolytes, enabling wide-doping-range studies of transport in single films. The work spans an order of magnitude in initial n doping (∼1019 to 1020cm-3, with both oxygen vacancies and La), film thicknesses from 10-50 nm, and measurements of resistance, Hall effect, mobility, and magnetoresistance. In contrast with many oxides, electrolyte gating of BaSnO3 is found to be essentially reversible over an exceptional gate voltage window (approaching ±4V), even at 300 K, supported by negligible structural modification in operando synchrotron x-ray diffraction. We propose that this occurs due to a special situation in BaSnO3, where electrochemical gating via oxygen vacancies is severely limited by their low diffusivity. Wide-range reversible modulation of transport is thus achieved (in both electron accumulation and depletion modes), spanning strongly localized, weakly localized, and metallic regimes. Two-channel conduction analysis is then combined with self-consistent Schrödinger-Poisson and Thomas-Fermi modeling to extract accumulation layer electron densities and mobilities. Electrostatic electron densities approaching 1014cm-2 are shown to increase room temperature mobility by up to a factor of ∼24. These results lay the groundwork for future studies of electron-density-dependent phenomena in high mobility BaSnO3, and significantly elucidate oxide electrolyte gating mechanisms.
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