SixGe1-x alloy as efficient phonon barrier in Ge/Si superlattices for thermoelectric applications

By means of atomistic simulations we study how thermal transport is affected by several chemical and morphological parameters in Ge/Si superlattices. We predict thermal conductivity as a function of the alloy barrier stoichiometry and period ratio. Our final target is to provide some technologically useful guidelines for thermoelectric design. In particular, we estimate the optimal Si concentration in the alloy barrier providing a significant thermal conductivity reduction as needed to maximize the thermoelectric figure of merit. We find that thermal conductivity is strongly affected by the barrier stoichiometry x and we suggest 10% ≤ x ≤ 20% as the optimal quantity. Moreover, we observe a thermal conductivity non-monotonic dependence on the period ratio having a minimum for a 2:1 value.