The Effects of Defects and Acoustic Impedance Mismatch on Heat Conduction in SiGe Based Superlattices

The cross-plane thermal conductivity of four Si/Ge, Si/Si_0.4Ge_0.6, and Si_0.9Ge_0.1/Si_0.1Ge_0.9 superlattices was measured using the 3ω technique. All four superlattices were found to have thermal conductivity values between 1.8 and 3.5 W/m-K, which are below the values of typical Si_xGe_1−x alloys. The growth quality of these superlattices was evaluated qualitatively through the use of x-ray diffraction and transmission electron microscopy. These studies indicated that the superlattices contained a relatively high density of dislocations. The low thermal conductivity values are presumed to be due in large part to these dislocations.