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

## TL;DR

This paper studies how buffer layers affect the formation and chemistry of BiFeO3 films on silicon, aiming to improve their integration for electronic applications.

## Contribution

The study introduces a method using Ti and TiO2 buffer layers to control the surface chemistry and phase stability of BiFeO3 films on silicon.

## Key findings

- Ti-buffered films show more consistent Bi/Fe surface ratios compared to TiO2-buffered films.
- Oxygen chemistry is the most sensitive indicator of near-surface disorder in BiFeO3 films.
- Intermediate-to-high substrate temperatures with moderate-to-low oxygen pressures favor near-stoichiometric BiFeO3 formation.

## Abstract

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.