Thermal conductivity reduction mechanisms in superlattices and their implications for nanostructured thermoelectric materials

G. Chen, B. Yang, D. Borca-Tasciuc, R.G. Yang, T. Harris, C. Dames, M. Takashiri

Mechanical Engineering Department, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

The large thermal conductivity reduction observed in superlattices has led to the reports of significantly increased thermoelectric figure-of-merit by several groups. The potential mechanisms of thermal conductivity reduction in superlattices were scrutinized from different angles over the last few years. In this paper, we will review the current status on the understanding of the heat conduction mechanisms in superlattices. Among several potential mechanisms such as the density of state change, the group velocity reduction, and the interface scattering, we show, by comparing model results with experimental data, that the interface scattering, particularly diffuse interface scattering, plays the most important role leading to the experimentally observed thermal conductivity reduction of superlattices. This understanding points to some new strategies for engineering nanostructured thermoelectric materials that will be discussed in the paper.