Band-Gap Tuning in Ferroelectric Bi2FeCrO6 Double Perovskite Thin Films

We report in this work on the variation of the optical band gap and structural properties of epitaxial Bi2FeCrO6 films grown by pulsed laser deposition on SrTiO3(001) substrates. It is shown that the band gap can be tuned by varying the laser repetition rate during deposition which has a strong impact on the Fe/Cr order inside the Bi2FeCrO6 double perovskite structure. Ab initio band structure calculations unambiguously show that the presence of antisite defects leads to an increase of the gap of about 0.25 eV with respect to the one calculated in the ideal structure. It is also shown that with increasing Fe/Cr disorder the saturation magnetization is strongly reduced along with the difference between the Fe and Cr valences. These results suggest that the band gap of Bi2FeCrO6 can effectively be engineered by modulating the deposition conditions, thus paving the way for applications such as photovoltaic conversion, memory writing, and direct CMOS integration.