High-mobility electron gas in Sr2TiO4/SrTiO3 heterostructure engineered by vertical Ruddlesden–Popper faults

High-mobility electron gases in SrTiO3-based heterostructures have been mainly synthesized on single TiO2 terminated SrTiO3 substrates. Here, we show a high-mobility electron gas observed in a Sr2TiO4/SrTiO3 heterostructure based on an untreated SrTiO3 substrate with mixed termination, showing the mobility value up to 28 000 cm2 V−1 s−1 at 2 K. SrO–SrO vertical Ruddlesden–Popper faults in the Sr2TiO4 film provide escape channels for oxygen atoms under high temperatures, enabling the as-grown tuning of oxygen vacancies in the SrTiO3 layer during film deposition and reversible after-growth modulation in a thermal annealing process.