Optical Switching of Robust Ferroelectric Polarization on Epitaxial Hf_0.5Zr_0.5O₂ Integrated with BaTiO₃

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 HfO₂. However, HfO₂ has a very wide bandgap, limiting light absorption. So far, the proposed strategies to enhance light absorption in HfO₂-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 10⁸ cycles) and fast switching (< 50 ns), can be achieved in epitaxial Hf_0.5Zr_0.5O₂ films through an alternative strategy, BaTiO₃ capping. While ferroelectric properties are remarkable, we demonstrate that the presence of BaTiO₃ allows light absorption and the concomitant electric field generation, as supported by density functional theory calculations, which enables optical switching of polarization in Hf_0.5Zr_0.5O₂ under 405 nm illumination. It is observed that optical switching is more efficient in films with thicker BaTiO₃ capping layer. The high polarizability of BaTiO₃ 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 HfO₂ while preserving main functional properties.