Surface, bulk, and interface electronic states of epitaxial $BiFeO3$ films

The authors report on the depth-resolved cathodoluminescence spectroscopy studies of the surface, bulk, and interface-localized electronic states in the band gap of epitaxial $BiFeO3$ thin films. The $BiFeO3$ films show a near band edge emission at 2.7 eV and defect emissions at energies varying from 2.0 to 2.5 eV. The overall results clearly suggest that the electronic structure, especially the defect states and their spatial distributions, of $BiFeO3$ films are strongly dependent on the growth conditions and method, stoichiometry, and strain, so that understanding and controlling them are crucial to optimize $BiFeO3$ film properties.