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 BiFeO(3) thin films grown on SrTiO(3)(001) substrates by ultrahigh vacuum sputtering reveal a bandgap of 2.69-2.73 eV for highly strained similar to 70 nm thick BiFeO(3) films. This bandgap value agrees with theoretical calculations and recent experimental results of epitaxial BiFeO(3) films, demonstrating only minimal bandgap change with lattice distortion. Both absorption and cathodoluminescence spectra show defect transitions at 2.20 and 2.45 eV, of which the latter can be attributed to defect states due to oxygen vacancies. (c) 2008 American Institute of Physics.