Characterization of electronic structure and defect states of thin epitaxial BiFeO3 films by UV-visible absorption and cathodoluminescence spectroscopies

UV-visible absorption and cathodoluminescence spectra of phase-pure epitaxial BiFeO3 thin films grown on SrTiO3(001) substrates by ultrahigh vacuum sputtering reveal a bandgap of 2.69–2.73eV for highly strained ∼70nm thick BiFeO3 films. This bandgap value agrees with theoretical calculations and recent experimental results of epitaxial BiFeO3 films, demonstrating only minimal bandgap change with lattice distortion. Both absorption and cathodoluminescence spectra show defect transitions at 2.20 and 2.45eV, of which the latter can be attributed to defect states due to oxygen vacancies.