Strain tuning of ferroelectric and optical properties of rhombohedral-like BiFeO₃ thin films on SrRuO₃-buffered substrates

Rhombohedral-like (R-like) BiFeO₃ (BFO) thin films with a SrRuO₃ (SRO) buffer layer have been deposited on a range of lattice mismatched substrates, including single crystalline (001)-oriented LaAlO₃ (LAO), SrTiO₃ (STO), MgO and TiN-buffered Si substrates. A wide range of strain states in BFO films have been achieved on these substrates. Ferroelectric measurements indicate that the film strain state affects the polarization of the BFO films. The bandgap of R-like BFO films follows the trend that highly compressive strain in BFO thin films leads to a larger bandgap. This study indicates that the physical properties including bandgap and ferroelectricity of BFO films, can be effectively tuned on large lattice mismatch substrates even with partial strain relaxation. Furthermore, the integration of ferroelectric BFO on SRO-buffered Si substrates suggests the possible application of strained BFO in Si-based electronic and optical devices.