DOE OSTI2019
The wide gap perovskite semiconductor BaSnO 3 has attracted much interest since the discovery of room temperature electron mobility up to 320 cm 2 V -1 s -1 in bulk crystals. Motivated by applications in oxide heterostructures, rapid progress has been made with BaSnO 3 films, although questions remain regarding transport mechanisms and mobility optimization. Here we report on a detailed study of epitaxial BaSnO 3 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 (similar to 10 19 to 10 20 cm -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 BaSnO 3 is found to be essentially reversible over an exceptional gate voltage window (approaching +/- 4 V), 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 Schrodinger-Poisson and Thomas-Fermi modeling to extract accumulation layer electron densities and mobilities. Electrostatic electron densities approaching 10 14 cm -2 are shown to increase room temperature mobility by up to a factor of similar to 24. These results lay the groundwork for future studies of electron-density-dependent phenomena in high mobility BaSnO 3 , and significantly elucidate oxide electrolyte gating mechanisms.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗