Enhanced ferroelectricity and band gap engineering of (1-x)BiFeO₃-xSrTiO₃ thin films

The (1-x)BiFeO₃-xSrTiO₃ (BFO-xSTO, x = 0, 0.05, 0.10, 0.20, 0.30) solid solution thin films were fabricated by a sol–gel method. The X-ray diffraction patterns showed that a phase transition appeared as the SrTiO₃ modified BiFeO₃. The structural properties of all the samples were analyzed by Raman spectroscopy. Scanning electron microscope images showed that all thin films have dense and uniform surface morphology. Compared with that of BiFeO₃ thin film, BFO-xSTO enhanced its ferroeletric properties significantly. BFO-0.20STO thin film possessed the lowest leakage current and larger polarization with well-defined ferroelectric hysteresis loop. In order to investigate the optical properties, ellipsometric spectra of BFO-xSTO thin films on Si substrates were measured and the experimental data were fitted by using a model consisting of air/roughness/BFO-xSTO/Si(100). The optical constants and the band gaps of BFO-xSTO thin films were obtained. The optical band gaps linear increase with the increasing of SrTiO₃ content. The results indicate a promising ability for improving the BiFeO₃ ferroelectricity by introducing SrTiO₃ to enable functionality as multiferroic informational storage devices while tuning the BiFeO₃ band gap as a wide band gap photovoltaic material.