The impact of native defects and hydrogen on the electronic and optical properties of BiFeO₃

There is great interest in materials that exhibit simultaneous ferroeletric and magnetic properties, so called multiferroics, for applications in spintronics and memory devices that can be addressed both magnetically and electrically. BiFeO₃ (BFO) is an important example of this class of materials, despite displaying an antiferromagnetic ground state. Recent experiments indicate that BFO is also a promising material for solar cells that explores a ferroelectric photovoltaic (FPV) effect, as an alternative to conventional photovoltaic devices. A large photocurrent effect and above bandgap voltage has been observed in BFO under illumination. For these applications, the behavior of point defects and excess charge can play a major role in the materials performance. Understanding the behavior of excess electrons and holes introduced by native defects or impurities in BFO is therefore of fundamental importance to the development of these new devices. We use density functional calculations with a hybrid functional to study the impact of electrons in the conduction band or holes in the valence band on the magnetization and ferroelectric ordering, paying special attention to carrier localization. We also study the behavior of hydrogen impurities and their interaction with native defects.