Optical Switching of Robust Ferroelectric Polarization on Epitaxial Hf0.5Zr0.5O2 Integrated with BaTiO3

Abstract Optical switching of ferroelectric polarization is of interest for wireless and energy-efficient control of logic states. So far, this phenomenon has been widely demonstrated only in ferroelectric perovskites, while studies on other emerging ferroelectrics remain limited. In this regard, the paradigmatic example of a technologically relevant ferroelectric material is HfO 2 . However, HfO 2 has a very wide bandgap, limiting light absorption. So far, the proposed strategies to enhance light absorption in HfO 2 -based systems are detrimental to ferroelectric properties, i.e., bandgap lowering or on-purpose defect introduction, which reduce switchable polarization and increase the presence of leakage currents. Here, we show that good ferroelectric properties, i.e., sizeable polarization (up to 15 μC cm −2 ), low leakage current (under 10 –6 A cm −2 ), high endurance (up to 10 8 cycles) and fast switching (< 50 ns), can be achieved in epitaxial Hf 0.5 Zr 0.5 O 2 films through an alternative strategy, BaTiO 3 capping. While ferroelectric properties are remarkable, we demonstrate that the presence of BaTiO 3 allows light absorption and the concomitant electric field generation, as supported by density functional theory calculations, which enables optical switching of polarization in Hf 0.5 Zr 0.5 O 2 under 405 nm illumination. It is observed that optical switching is more efficient in films with thicker BaTiO 3 capping layer. The high polarizability of BaTiO 3 contributes to minimizing degradation in the ferroelectric response of the system. The results presented here indicate that appropriate designs can be followed to obtain optical switching of polarization in ferroelectric HfO 2 while preserving main functional properties.