Ab initio study of p-type origin of SnSe and the alloying behavior of SnSe_1-xS_x

Recently, SnSe single crystal has been found to exhibit excellent thermoelectric performance with an extremely high ZTvalue of 2.6. Although this high ZT value has attracted considerable attention, the microscopic origin of p-type character of SnSe has yet to be clearly understood. Here, by combining scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we find that the most dominant Sn vacancies [1] move the Fermi energy inside the dispersive valence band and produce extra holes throughout the system. On the other hand, other intrinsic vacancies create a nondispersive donor level and generate immobile electrons localized near the vacancy site. In addition, we first directly probed the microscopic structures of SnSe_1-xS_x alloys and their structural evolution at the atomic level by combining STM experiments with DFT calculations [2]. [1] Appl. Phys. Lett., 110, 262106 (2017). [2] Phys. Chem. Chem. Phys., 19, 21648 (2017).