Ultra low lattice thermal conductivity and high carrier mobility of monolayer SnS and SnSe: a first principles study.

Using density functional theory, we systematically investigate the lattice thermal conductivity and carrier mobility of monolayer SnX (X = S, Se). The room-temperature ultra low lattice thermal conductivities found in monolayer SnS (6.41 W m K) and SnSe (3.82 W m K) are attributed to the low phonon velocity, low Debye temperature, weak bonding interactions, and strong anharmonicity in monolayer SnX. The predicted values of lattice thermal conductivity are lower than those of other two-dimensional materials such as stanene, phosphorene, monolayer MoS, and bulk SnX. High phonon-limited carrier mobilities are obtained for the monolayer SnX. For example, the electron mobility of monolayer SnS is 756.60 cm V s and the hole mobility is 187.44 cm V s. The electron mobility of these monolayers is higher than their hole mobility due to the low effective mass of electrons and low deformation constants, which makes them n-type materials. Due to their ultra low lattice thermal conductivities coupled with high carrier mobilities, monolayer SnX materials may be promising materials for thermoelectric applications.