First-principles analysis of phonon thermal transport properties of two-dimensional WS_2/WSe_2 heterostructures

The van der Waals(vd W) heterostructures of bilayer transition metal dichalcogenide obtained by vertically stacking have drawn increasing attention for their enormous potential applications in semiconductors and insulators. Here,by using the first-principles calculations and the phonon Boltzmann transport equation(BTE), we studied the phonon transport properties of WS_2/WSe_2 bilayer heterostructures(WS_2/WSe_2-BHs). The lattice thermal conductivity of the ideal WS_2/WSe_2-BHs crystals at room temperature(RT) was 62.98 W/m K, which was clearly lower than the average lattice thermal conductivity of WS_2 and WSe_2 single layers. Another interesting finding is that the optical branches below 4.73 THz and acoustic branches have powerful coupling, mainly dominating the lattice thermal conductivity. Further, we also noticed that the phonon mean free path(MFP) of the WS_2/WSe_2-BHs(233 nm) was remarkably attenuated by the free-standing monolayer WS_2(526 nm) and WSe_2(1720 nm), leading to a small significant size effect of the WS_2/WSe_2-BHs. Our results systematically demonstrate the low optical and acoustic phonon modes-dominated phonon thermal transport in heterostructures and give a few important guidelines for the synthesis of van der Waals heterostructures with excellent phonon transport properties.