Molecular beam epitaxy growth of BaTiO3 thin films and crucial impact of oxygen content conditions on the electrical characteristics

In this study, high quality crystalline BaTiO3 films were fabricated in different oxygen content conditions on Nb-doped SrTiO3 (001) substrates by molecular beam epitaxy (MBE). BaTiO3 epitaxial film presents a critical thickness of 6.4 nm and is almost entirely relaxed on SrTiO3 with a thickness of ~ 50 nm. The electrical properties of 50 nm strain-free BaTiO3 films were investigated by both macro- and microscopic measurements. Their electrical characteristics were found to be strongly influenced by different oxygen content conditions used during the preparation or annealing of the samples. Limited molecular oxygen partial pressure in a MBE chamber probably leads to a great amount of oxygen vacancies in the oxide film and results in rectification behavior of the oxygen-deficient BaTiO3-x/SrTiO3:Nb interface. Several approaches such as using atomic oxygen ambiance during the growth, annealing under elevated oxygen pressure were employed in order to decrease the oxygen vacancy density and these approaches eventually permit obtaining BaTiO3 films with good ferroelectric characteristics.