Enhanced ferroelectric properties of BiFeO₃ thin films utilizing four buffer layers: Nd₂O₃, Eu₂O₃, Ho₂O₃, and Er₂O₃

This paper investigates the ferroelectric and structural properties of BiFeO₃ thin films with four different RE₂O₃ (Nd₂O₃, Eu₂O₃, Ho₂O₃, and Er₂O₃) buffer layers fabricated on a SrRuO₃/n⁺-Si substrate through spin-coating. To analyze the BiFeO₃ films with RE₂O₃ buffer layers, various techniques, such as X-ray diffraction, secondary ion mass spectrometry, atomic force microscope, and X-ray photoelectron spectroscopy were employed to investigate the crystalline structures, depth profiles, surface topographies, and chemical compositions. It was found that the BiFeO₃ film with RE₂O₃ buffer layers exhibited improved electrical properties such as leakage current, remnant polarization, and coercive field compared to the control BiFeO₃ film without a buffer layer. Moreover, the Eu₂O₃ buffer layer exhibited the lowest leakage current of 2.05 × 10^–6 A/cm², the highest remnant polarization of 43.76 μC/cm², and the smallest coercive field of 188 kV/cm among all the RE₂O₃ buffer layers. The outcome is likely to have been caused by the introduction of Eu³⁺ ion to the BiFeO₃ film, which resulted in a reduction in surface roughness, a significant preferred orientation of (110), and an increased concentration of Fe³⁺ ion. Consequently, this inhibited the fluctuation of Fe³⁺ to Fe²⁺ ions and reduced the occurrence of oxygen vacancies.