Molecular dynamics study on the contribution of anisotropic phonon transmission to thermal conductivity of silicon

The analysis of the contribution of anisotropic phonon transmission to thermal conductivity is helpful to focus on high-energy phonons in heat transport. We calculated a series of anharmonic phonon properties and heat transport properties of Si by Fourier projection method from atomic trajectories. Under this theoretical scheme, we have obtained very consistent results with the experimental data through very low computational cost, especially the anharmonic phonon properties at high temperature. We carefully analyze the contribution of different phonons to thermal conductivity and the anisotropic feature of phonon. It is found that the longitudinal acoustic (LA) phonons have the special thermal broadening near the point L at the boundary of the Brillouin zone. The optical phonons cannot be safely ignored in the study of heat transport, especially the longitudinal optical phonon that shows a large contribution to thermal conductivity at room temperature. The thermal conductivity contribution of different phonons varies with temperature. The anisotropic features of the contribution of different phonons to thermal conductivity are mainly reflected in the short-wavelength phonons. Our work explains the reason why other research works have different opinions on whether LA phonon is the main contributor of thermal conductivity. These investigations also provide insights for further understanding phonon heat transport and distribution of high-energy phonons.