Ferroelectric ZrO₂ monolayers as buffer layers between SrTiO₃ and Si

A monolayer of ZrO$_{2}$ has recently been grown on the Si(001) surface and shown to have ferroelectric properties, which signifies the realization of the lowest possible thickness in ferroelectric oxides [M. Dogan et al., Nano Lett., 18 (1) (2018)]. In our previous computational study, we reported on the multiple (meta)stable configurations of ZrO$_{2}$ monolayers on Si, and how switching between a pair of differently polarized configurations may explain the observed ferroelectric behavior of these films [M. Dogan and S. Ismail-Beigi, arXiv:1902.01022 (2019)]. In the current study, we conduct a DFT-based investigation of (i) the effect of oxygen content on the ionic polarization of the oxide, and (ii) the role of zirconia monolayers as buffer layers between silicon and a thicker oxide film that is normally paraelectric on silicon, e.g. SrTiO$_{3}$. We find that (i) total energy-vs-polarization behavior of the monolayers, as well as interface chemistry, is highly dependent on the oxygen content; and (ii) SrTiO$_{3}$/ZrO$_{2}$/Si stacks exhibit multiple (meta)stable configurations and polarization profiles, i.e. zirconia monolayers can induce ferroelectricity in oxides such as SrTiO$_{3}$ when used as a buffer layer. This may enable a robust non-volatile device architecture where the thickness of the gate oxide (here strontium titanate) can be chosen according to the desired properties.