Chalcogenide Perovskites on the Verge of Ferroelectricity and Semiconductivity

Chalcogenide perovskites have emerged as promising semiconductors having a large optical absorbance, strong electronic polarizability, and high stability. BaZrS₃ is a paradigmatic example within this family of semiconductors. It has a band gap of 1.8 eV, which makes it promising for solar energy harvesting. However, experimentally, it is found to have a large electronic resistivity due to low mobility. It is unclear whether the low mobility in experimental samples arises due to the sample quality and defects or if it is intrinsic in nature. Here, using first-principles methods, we calculate the electron-phonon interactions and dominant scattering mechanisms. We find that the low mobility in BaZrS₃ arises from strong optical phonon scattering and hence is intrinsic in nature. We also find that the electron-phonon interaction, quantified using the Fröhlich coupling constant, in BaZrS₃ is intermediate between conventional semiconductors and ferroelectrics. We show that the Fröhlich coupling constant can be modified by controlling the strain and dimensionality. We show that the layered Ruddlesden-Popper phase, Ba₃Zr₂S₇, has mobility that is 1.6 times as the mobility in BaZrS₃ and can serve as a good semiconductor. We also show that under an epitaxial tensile strain, the Fröhlich coupling constant can be increased to reach a ferroelectric phase. Our results show that BaZrS₃, and related chalcogenide perovskites, can be tuned to show either semiconducting behavior or ferroelectricity.