Stoichiometric control and optical properties of BaTiO₃ thin films grown by hybrid MBE

BaTiO₃ is an appealing class of ferroelectric perovskite materials that has room-temperature ferroelectricity with a Curie temperature, Tc, of ∼120 °C. It has been extensively studied due to its superior dielectric, ferroelectric, piezoelectric, pyroelectric, and electro-optical properties. It has emerged as an excellent candidate for applications such as ferroelectric random-access memory, lead-free capacitors, photonic devices, ferroelectric energy conversion, and electro-optical devices.[1] Furthermore, strained BaTiO₃ exhibits both enhanced Tc and increased remanent polarization when compared to bulk BaTiO₃. However, while strain engineering through heteroepitaxial growth has proven to be a powerful strategy for obtaining new functionalities in complex oxides, achieving controlled and uniform stoichiometry in thin films is equally important, as defects can destroy ferroelectric behavior in materials.[2] Although conventional ultrahigh vacuum thin film growth techniques such as pulsed laser deposition and molecular beam epitaxy (MBE) are capable of producing high-quality oxide films, precise control over stoichiometry still remains challenging. Therefore, hMBE which has been demonstrated to provide superior control over cation stoichiometry was used in this study to grow BaTiO₃ thin films.

hMBE growth of BaTiO₃ thin films was performed using a solid elemental Ba source and a metal-organic precursor (Titanium(IV) isopropoxide) that was supplied via a gas inlet system. A series of thin films were grown on LSAT, GdScO₃ (110), and SrNbO₃ which was sputtered on GdScO₃ (110) as a transparent bottom electrode. In this talk, we will discuss the samples grown within the hMBE growth window which yielded films with constant out-of-plane lattice parameters and atomically smooth surface morphologies by XRD, RHEED, and AFM; as well as bulk-like optical constants (n, k) and coefficients by ellipsometry and SHG. This work demonstrates a large avenue to a lead-free ferroelectric for nonvolatile memories and electro-optic devices.



[1] K. J. Choi et al., Science (80-. )., vol. 306, no. 5698, pp. 1005–1009, 2004.

[2] R. C. Haislmaier et al., Adv. Funct. Mater., vol. 26, no. 40, pp. 7271–7279, 2016.