Ferroelectric Properties of MBE Grown BTO/STO:Nb Layer.

Barium titanate (BaTiO3, BTO) is an archetypal ferroelectric of broad technological relevance. Molecular beam epitaxy (MBE) offers compelling advantages for BTO thin film growth, such as superior crystalline quality and epitaxial integration with semiconductor substrates. However, the low oxygen partial pressures inherent to MBE environments, together with the challenges associated with precise stoichiometry control when using elemental sources, promote composition imbalances and oxygen vacancy formation and make MBE-grown BTO films significantly less documented than their pulsed laser deposition (PLD) or sputtered counterparts. Here, we present a detailed study of the ferroelectric response of an epitaxial MBE-grown BTO thin film, combining synchrotron-based X-ray diffraction with temperature- and frequency-dependent electrical characterizations, including the first Rayleigh analysis reported for an MBE-grown BTO layer and only the third direct demonstration of ferroelectricity in such films based on macroscopic P(E) and ε(E) loops. The film exhibits a soft ferroelectric response-low coercive field (12 kV/cm), high tunability (≃65%), and a large Rayleigh coefficient reflecting significant irreversible domain wall motion. We show that this response is governed by a landscape of weak oxygen vacancy pinning centers, whose effect is amplified by the high structural quality, full plastic relaxation, and pure c-oriented single-domain state of the film. These results provide a physically grounded picture of the ferroelectric response of MBE-grown BTO thin films, offering a solid basis for device optimization.