Optical properties of quasi-tetragonal BiFeO_3 thin films

摘要

Optical transmission spectroscopy and spectroscopic ellipsometry were used to extract the optical properties of an epitaxially grown quasi-tetragonal BiFeO_3 thin film in the near infrared to near ultraviolet range. The absorption spectrum is overall blue shifted compared with that of rhombohedral BiFeO_3, with an absorption onset near 2.25 eV, a direct 3.1 eV band gap, and charge transfer excitations that are ～0.4 eV higher than those of the rhombohedral counterpart. We interpret these results in terms of structural strain and local symmetry breaking.