Optical band gap of BiFeO{sub 3} grown by molecular-beam epitaxy

BiFeO{sub 3} thin films have been deposited on (001) SrTiO{sub 3} substrates by adsorption-controlled reactive molecular-beam epitaxy. For a given bismuth overpressure and oxygen activity, single-phase BiFeO{sub 3} films can be grown over a range of deposition temperatures in accordance with thermodynamic calculations. Four-circle x-ray diffraction reveals phase-pure, epitaxial films with {omega} rocking curve full width at half maximum values as narrow as 29 arc sec (0.008 deg.). Multiple-angle spectroscopic ellipsometry reveals a direct optical band gap at 2.74 eV for stoichiometric as well as 5% bismuth-deficient single-phase BiFeO{sub 3} films.