Two-dimensional electron gas in the KNbO₃:Y ultrathin film

First-principles calculations are used to study KNbO₃:Y ultrathin film. The conducting two-dimensional electron gas (2DEG) is found in KNbO₃:Y film, whereas SrTiO₃:Y superlattice is insulating [Science 331, 886 (2011)]. The carrier density of 2DEG of KNbO₃:Y film is twice that of LaTiO₃/SrTiO₃ superlattice, which is in agreement with the theoretical results of KNbO₃:La superlattice. It is found that the charge densities of different monolayers are modulated by the polarization effect of KNbO₃. We predict that 2DEG may be in other rare-earth atoms-doped KNbO₃ film.