Electronic structure and optical responses of nanocrystalline BiGaO ₃ films: A combination study of experiment and theory

High-quality nanocrystalline BiGaO₃ (BGO) films have been prepared by a modified sol-gel method. X-ray diffraction analysis shows that the films are polycrystalline and exhibit an orthorhombic structure. The dispersion functions near infrared-ultraviolet region were extracted by fitting spectroscopic ellipsometry with the Tauc-Lorentz model. Moreover, first-principle calculations on dielectric functions and band gap were carried out, which are in good agreement with the experimental results. It was found that BGO belongs to an indirect band gap oxide with the fundamental gap of about 2.17 eV, which is suitable for ferroelectric based photovoltaic devices.