Temperature Dependent Thermal Conductivity of Symmetrically Strained Si/Ge Superlattices

Experimental evidence for a significant thermal conductivity reduction has been reported in recent years for GaAs/AlAs, Si/Ge, and Bi2Te3/Sb2Te3 superlattices. Previously reported experimental studies on Si/Ge superlattices are based on samples grown by metal oxide chemical vapor deposition (MOCVD) on GaAs substrates with Ge buffers. In this work, we present experimental results on the temperature dependent thermal conductivity of symmetrically strained Si/Ge superlattices grown by molecular beam epitaxy (MBE) as a function of the superlattice period and the growth temperature. Thermal conductivity measurements are performed using a differential 3ω method. In this technique, the temperature drop across the superlattice film is experimentally determined and used to estimate the thermal conductivity of the film. Transmission electron microscopy (TEM) is employed to study the quality of the superlattice and the influence of the growth temperature on the superlattice structure. For all the superlattices studied, the measured thermal conductivity values are lower than that of the Si0.5Ge0.5 alloy. Furthermore, the measured thermal conductivity of a 40Å period Si/Ge superlattice with high dislocation density is comparable to the calculated minimum thermal conductivity of the constituent bulk materials.