Si/Ge Superlattice Structures for Thermoelectric Power Generation

Research conducted at RTI into the use of thin films, in particular superlattice materials, for thermoelectric power generation has focused on three materials families: Bi$_{2}$Te$_{3}$, PbTe, and Si/Ge. The Bi$_{2}$Te$_{3}$-based superlattice materials have already produced record ZT (thermoelectric figure-of-merit) and devices using these low temperature materials ($\sim $200\r{ }C) have surpassed bulk performance during power generation. RTI has also developed the growth of Si/Ge superlattice films as well as their fabrication into power generation devices applications at higher temperatures ($\sim $500\r{ }C). Results presented will include confirmation of superlattice structure via X-ray diffraction, showing well formed satellite peaks indicative of a high-quality superlattice. In addition, data will be presented that shows the lowering of thermal conductivity by the superlattice structure with nearly a 5x reduction in lattice thermal conductivity compared to the alloy film. Initial thin-film power device results showing $>$2{\%} efficiency and 2x improvement of ZT over SiGe alloys, at $\Delta $T of 378K and T$_{mean}$ of 484K, will be presented.