Thermal Conductivity of Si/SiGe Superlattice Film

It has been proposed that the use of superlattice structure is effective for reduction of lattice thermal conductivity in the direction perpendicular to superlattice interfaces which can lead to improvement of figure of merit. In this work, we have evaluated the thermal conductivity of Si/SiGe superlattice structure films by theoretical analysis and experimental studies. In experiments, the ultra-high vacuum chemical vapor deposition (UHVCVD) has been employed to formation the Si/Si_0.71Ge_0.29 superlattice film. The cross-plane thermal conductivity of a Si/Si_0.71Ge_0.29 superlattice is measured based on the 3 ω method. In theoretical analysis, we use the Boltzmann transport equation to analyze the phenon transport in superlattice film. We compared the thermal conductivities of several Si/Si_0.71Ge_0.29 superlattice structure films by changing the thickness of Si and Si_0.71Ge_0.29. The results indicate that increasing the period (one layer Si and one layer Si_0.71Ge_0.29) length will lead to increase acoustic mismatch between the adjacent layers, and hence increased interfacial thermal resistance. However, if the total thickness of the superlattice film is fixed, reducing the period length will lead to decreased effective thermal conductivity due to the increased number of interfaces.