Low-temperature synthesis of BaTiO₃ thin film by molecular beam epitaxy

The oxide perovskite BaTiO₃ is a prototypical displacive ferroelectric material with high-performance ferroelectric/piezoelectric properties. The structural simplicity of BaTiO₃ makes it possible to integrate it with other functional materials in a single crystalline form, such as with superconducting cuprates and semiconducting Si, MgO, and Ge, providing an opportunity to electrically control functional properties of adjacent layers. The synthesis of high-quality BaTiO₃ as thin films at low temperatures may allow the integration of ferroelectrics with other materials and devices that require a reduced thermal budget. We describe our synthesis of BaTiO₃ thin films by molecular beam epitaxy at various temperatures and find that ferroelectric epitaxial BaTiO₃ can be grown at temperatures as low as ~310 °C. Using reflection high energy diffraction, we demonstrate surface mobility of BaO and TiO₂ adatoms that are high enough to promote ferroelectric crystal growth at low temperatures.