A first-principles study of phonon transport properties of monolayer MoSe2

MoSe2 as one of the promising two-dimensional transition metal dichalcogenides (TMDCs) recently emerged as promising alternative of graphene for nano-electronic and opto-electronic devices. However, the heat removal is a critical issue for devices using two-dimensional (2D) materials, and low thermal conductivity of monolayer MoSe2 can significantly affect the performance and reliability of electronic devices. In this study, we use the density functional theory (DFT) and the phonon Boltzmann transport equation (BTE) to study the phonon transport properties of monolayer MoSe2 and compared the results with MoS2. The iterative solution of the BTE is used to predict the thermal conductivity of MoSe2, which is compared with the relaxation time approximation. Model for considering effect of sample size and defects are developed for monolayer MoSe2. Our results show the impact of sample size, Se vacancies, boundary and anharmonic phonon scattering on the thermal conductivity of MoSe2. Defect model is built based on the phonon scattering caused by the missing atom mass and the change of force constants between the under-coordinated atoms near the vacancies. Results indicate that the presence of 1%, 2% and 4% Se vacancies decrease the thermal conductivity of monolayer MoSe2 by 11.2%, 23.4% and 46.2% at room temperature. The results from this work will help in understanding the mechanism of phonon transport in 2D materials and provide insights for the future design of MoSe2-based electronics.