Role of Buffer Layers in Defect Chemistry and Parasitic Phase Formation of BiFeO₃ Films on Silicon

Achieving the reliable integration of bismuth ferrite with silicon requires precise control over phase formation, cation stoichiometry, and near-surface oxygen chemistry. In this study, BiFeO₃ films were deposited by pulsed laser deposition onto Ti- and TiO₂-buffered Si substrates under varied oxygen partial pressures and substrate temperatures. Structural, morphological, and chemical evolutions were investigated using X-ray diffraction, scanning electron microscopy, and combined survey and high-resolution X-ray photoelectron spectroscopy. Both buffer types yield polycrystalline BiFeO₃ films; Ti-buffered samples exhibit lower variations in Bi/Fe surface ratios, whereas TiO₂buffered films show a reduced contribution from hydroxyl-related oxygen species at the surface. X-ray photoelectron spectroscopy confirms that Bi and Fe remain exclusively in the trivalent state under all growth conditions. High-resolution oxygen spectra demonstrate that oxygen chemistry is the most sensitive indicator of near-surface disorder, reflecting contributions from lattice oxygen and surface hydroxylation arising from ambient exposure. Minor Bi₂O₃ phases persist across the investigated deposition window; however, their evolution, together with surface oxygen trends, indicates that intermediate-to-high substrate temperatures combined with moderate-to-low oxygen pressures provide the most favorable conditions for stabilizing near-stoichiometric BiFeO₃. Overall, the results highlight oxide buffer layers as effective regulators of surface chemistry, enabling a scalable route for integrating BiFeO₃ films on silicon.