Isotope and strain effects on thermal conductivity of silicon thin film

In this paper, non-equilibrium molecular dynamics simulations (NEMD) are employed to study the effects of isotope and in-plane strain on the thermal conductivity of silicon thin film. The results show that the thermal conductivity of silicon thin film decreases with the isotope concentration at the lower concentration and increases with the isotope concentration at the higher concentration, respectively. In addition, simulations on the strained film indicate that the thermal conductivity decreases monotonously with the applied strain. To achieve a fundamental understanding of the physical mechanisms, phonon density of states (DOS) and phonon dispersion are analyzed in details. High frequency phonons are found to be sensitive to the impurity, which leads to the reduction of phonon group velocity. For the strained thin film, high frequency phonons, especially of transverse optical (TO) phonon branch, play an important role in the change of thermal conductivity. Our findings suggest the great potential of tailoring the thermal properties by isotope and mechanical strain.