Ferroelectric ZrO₂ Monolayers as Buffer Layers between SrTiO₃ and Si

Abstract

A monolayer of ZrO2 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) [1]). In our previous computational study, we reported on the multiple (meta)stable configurations of ZrO2 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) [2]). 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. SrTiO3. 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) SrTiO3/ZrO2/Si stacks exhibit multiple (meta)stable configurations and polarization profiles, i.e. zirconia monolayers can induce ferroelectricity in oxides such as SrTiO3 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. Low-energy ZrO x configurationsFigure 1: Low-energy relaxed configurations of monolayers with O:Zr = 1.0. Energies are per 2×1 in-plane cell.

First-Principles Investigation of Interfacial Reconstruction in Epitaxial SrTiO3/Si Photocathodes

“…An appropriate buffer layer is therefore necessary to prevent Si from being oxidized. Until now, numerous atomic structures have been proposed as buffer layers both theoretically − and experimentally. − Among them, as the first successful report for direct epitaxial growth of single-crystal STO on Si, elemental Sr for the preparation of the buffer layer is important and widely studied …”