Effect of period length distribution on the thermal conductivity of Si/Ge superlattice

Si/Ge superlattices (SLs) have shown tremendous promise as effective thermoelectric materials due to their remarkable thermal insulating performance over bulk counterparts. In the present study, the thermal conductivity of Si/Ge SLs with different period length distributions (gradient and random) was investigated using non-equilibrium molecular dynamics simulation (NEMD). The simulation results revealed that (i) The thermal conductivities of SLs with gradient and random period significantly decrease at relatively low temperature and they weakly depends on the sample total length compared to that of the uniform period SLs, which is induced by the destroying of coherent phonons; (ii) The thermal conductivity is not sensitive to temperature, which is mainly induced by the competition of phonons localization weakness and phonon-phonon scattering enhancement as the temperature increases; (iii) The thermal conductivities of the gradient and random SLs demonstrate the same dependence on period length, sample total length and temperature. It indicates that the variation of period length distribution has little effect on the phonons transport mechanisms in the aperiodic SLs. •The thermal conductivities of superlattices with different geometric structures under different temperatures were studied.•The gradient and random period lengths have strong destructive effects on phonons coherent transport of in superlattices.•The competition of phonons localization and scattering contributes to weak temperature sensitivity of thermal conductivity.