Synthesis and characterization of photoferroic BiCoO₃

Photoferroics have received increased interest of late, with recent power efficiencies reaching over 8%. However, band gaps of 3 eV or greater in the most common polar materials leaves the room for growth as solar absorbers limited. This has led to further work in the modeling and development of new polar materials, with a focus in band gap tuning. In line with the well-studied BiFeO₃, electronic structure calculations were performed on BiMO₃ perovskite structures to determine band gaps, dielectric functions, and piezoelectric tensors of the corresponding material. Of those explored, BiCoO₃ showed promise as a low band gap semiconductor with a predicted gap of 2.08 eV, a polar P4mm structure, and a predicted relative permittivity of 44.6. To follow up on these predictions, BiCoO₃ films were grown via combinatorial pulsed laser deposition, with a multi-target system of Bi₂O₃ and CoO. The substrate, temperature, chemistry and partial pressure of oxygen were varied to determine the best conditions for achieving a P4mm structure. Epitaxial strain was used to create high quality films with an aligned internal polarization, from which photoferroic testing was performed after completing a metal-semiconductor-metal structure.