Epitaxial SrTiO₃ films with electron mobilities exceeding 30,000 cm² V^-1s^-1

The study of quantum phenomena in semiconductors requires epitaxial structures with exceptionally high charge-carrier mobilities. Furthermore, low-temperature mobilities are highly sensitive probes of the quality of epitaxial layers, because they are limited by impurity and defect scattering. Unlike many other complex oxides, electron-doped SrTiO₃ single crystals show high (ĝ̂1/410 4 cm² V^-1s ^-1) electron mobilities at low temperatures. High-mobility, epitaxial heterostructures with SrTiO₃ have recently attracted attention for thermoelectric applications, field-induced superconductivity and two-dimensional (2D) interface conductivity. Epitaxial SrTiO₃ thin films are often deposited by energetic techniques, such as pulsed laser deposition. Electron mobilities in such films are lower than those of single crystals. In semiconductor physics, molecular beam epitaxy (MBE) is widely established as the deposition method that produces the highest mobility structures. It is a low-energetic, high-purity technique that allows for low defect densities and precise control over doping concentrations and location. Here, we demonstrate controlled doping of epitaxial SrTiO₃ layers grown by MBE. Electron mobilities in these films exceed those of single crystals. At low temperatures, the films show Shubnikov-de Haas oscillations. These high-mobility SrTiO ₃ films allow for the study of the intrinsic physics of SrTiO ₃ and can serve as building blocks for high-mobility oxide heterostructures.