Ultra low lattice thermal conductivity and high carrier mobility of monolayer SnS2 and SnSe2: a first principles study

Abstract

Using density functional theory, we systematically investigate the lattice thermal conductivity and carrier mobility of monolayer SnX₂ (X = S, Se). The room-temperature ultra low lattice thermal conductivities found in monolayer SnS₂ (6.41 W m⁻¹ K⁻¹) and SnSe₂ (3.82 W m⁻¹ K⁻¹) are attributed to the low phonon velocity, low Debye temperature, weak bonding interactions, and strong anharmonicity in monolayer SnX₂. The predicted values of lattice thermal conductivity are lower than those of other two-dimensional materials such as stanene, phosphorene, monolayer MoS₂, and bulk SnX₂. High phonon-limited carrier mobilities are obtained for the monolayer SnX₂. For example, the electron mobility of monolayer SnS₂ is 756.60 cm² V⁻¹ s⁻¹ and the hole mobility is 187.44 cm² V⁻¹ s⁻¹. 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 SnX₂ materials may be promising materials for thermoelectric applications.