Band alignment at epitaxial BaSnO₃/SrTiO₃(001) and BaSnO₃/LaAlO₃(001) heterojunctions

We have spectroscopically determined the optical bandgaps and band offsets at epitaxial interfaces of BaSnO₃ with SrTiO₃(001) and LaAlO₃(001). 28 u.c. BaSnO₃ epitaxial films exhibit direct and indirect bandgaps of 3.56 ± 0.05 eV and 2.93 ± 0.05 eV, respectively. The lack of a significant Burstein-Moss shift corroborates the highly insulating, defect-free nature of the BaSnO₃ films. The conduction band minimum is lower in electron energy in 5 u.c. films of BaSnO₃ than in SrTiO₃ and LaAlO₃ by 0.4 ± 0.2 eV and 3.7 ± 0.2 eV, respectively. This result bodes well for the realization of oxide-based, high-mobility, two-dimensional electron systems that can operate at ambient temperature, since electrons generated in the SrTiO₃ by modulation doping, or at the BaSnO₃/LaAlO₃ interface by polarization doping, can be transferred to and at least partially confined in the BaSnO₃ film.