Defects and effects of high doping levels in CaSnO₃

Alkaline-earth stannates, e.g. CaSnO₃, SrSnO₃, BaSnO₃, are wide band gap semiconductors in the perovskite crystal structure, and are candidate materials for applications in high power elec- tronics and ultraviolet (UV) photodetectors. They are characterized by a dispersive conduction band derived from the Sn 4s orbitals and, therefore, are expected to display high electron mobility. They can be grown epitaxially on non-native substrates, and high densities of free electrons have been reported. Most defects discussed in the literature are oxygen vacancies, cationic antisites, and Schottky defects. Understanding their role in determining electronic conductivity and optical properties is essential for device development. Here, we use hybrid density functional calculations to investigate the impact of native defects and impurities on their electronic and optical properties, aiming to understand the sources of n-type conductivity, the effects of high doping levels on the structural parameters, and the more relevant compensation centers. The results are discussed in light of carrier transport, optical absorption, and soft/hard X-ray photoemission spectroscopy and serve as a basis for defect engineering.