High-mobility La-doped BaSnO3 thin films with sheet carrier concentrations relevant to transistors

With demonstrated room-temperature mobilities in single crystals and thin films exceeding 300 cm2 V−1 s−1 and 180 cm2 V−1 s−1, respectively, the transparent conducting oxide La-doped BaSnO3 is of great interest for electronics. Unfortunately, the sheet carrier concentration of the films in which such high mobilities are achieved exceeds 6 × 1013 cm−2, which is too high to be pinched off in most transistor structures. Here, we investigate more than 200 La-doped BaSnO3 films grown on (100) MgO with lower sheet carrier concentrations—in the (1–6) × 1013 cm−2 range—to elucidate the mobilities that can be achieved in the channel layers of transistors that have a chance of being pinched off. Our study provides information on how the mobility trades off with film thickness and doping within this device-relevant design space. The La-doped BaSnO3 films were grown by suboxide molecular-beam epitaxy in an adsorption-controlled regime, with excess SnO provided during growth and exhibit carrier concentrations on the order of 1 × 1019 cm−3, thicknesses ranging from 5 to 38 nm, surfaces with rms roughness <1 nm, and mobilities as high as 106 cm2 V−1 s−1 at room temperature. The fraction of lanthanum dopants that are electrically active ranges from 40% to 68%; this fraction increases with increasing SnO excess (the SnO:Ba flux ratio) during growth.