Functional perovskite oxides may enable entirely new electronic device concepts, ranging from negative capacitance to charge amplification in phase change devices. A major challenge is the intrinsically poor charge carrier mobility of most perovskite oxides, typically no better than 1 ‑ 10 cm²V^-1s^-1 at room temperature. Recent reports of room temperature mobilities of ~300 cm² V^‑1s^‑1 in single crystals of La-doped BaSnO₃ have therefore generated significant excitement. In addition, BaSnO₃has a wide band gap (~ 3 eV), which makes it of interest as a new transparent conducting oxide and as a wide band gap semiconductor for power electronics. Furthermore, it would allow for integration of functional perovskite oxides on a lattice- and symmetry-matched, high-mobility, semiconducting channel.

Electronic devices require the growth of high-quality films with low defect densities. High-mobility BaSnO₃ thin films have been challenging to grow. Molecular beam epitaxy (MBE) is a low energetic deposition technique and routinely produces the highest mobility semiconductor and functional oxide films. However, stoichiometry control in MBE of perovskite oxides can be challenging. We show that in the MBE of perovskite stannates using a Sn metal source, volatile SnO consumes all active oxygen in the growth environment, leaving behind only Sn droplets at low growth temperatures. No film growth occurs at high temperatures. We discuss a modified MBE approach, which supplies pre-oxidized SnO_x. This technique addresses issues in the stoichiometry controls in MBE of ternary stannates related to volatile SnO formation and enables growth of epitaxial, stoichiometric BaSnO₃. A second challenge is the lack of lattice-matched substrates. We discuss the effect of lattice mismatch on the growth and transport properties of BaSnO₃ by comparing the properties of films grown on SrTiO₃ and PrScO₃ substrates. We show that the carrier mobility doubles as the lattice mismatch is reduced by a factor of two, indicating that high misfit dislocation densities are the main limiting factor in further improving carrier mobilities. We demonstrate room temperature electron mobilities of 150 cm² V^-1s^-1 at carrier densities of 7×10¹⁹ cm^-3 in BaSnO₃ films grown on PrScO₃ using the modified MBE technique. We will discuss the prospects for further improving the carrier mobilities and reducing the carrier densities.