The Thermoelectric Properties of Ge/SiGe based superlattices: from materials to Energy Harvesting Modules

We report recent progresses in the characterization of the vertical electrical and thermal properties of multilayered silicon germanium (SiGe) materials for thermoelectric coolers and generators. Superlattice structures p- and n-type doped with different barriers and quantum well thicknesses were grown by Low Energy Plasma Enhanced Chemical Vapor Deposition. The electrical and thermal characterizations were performed using fully integrated metrology structures, microfabricated on the surface of the sample. Heaters, thermometers and electrical contacts were integrated onto the device to allow a simultaneous measurement of the electrical, thermal and Seebeck coefficient for the extraction of the figure of merit ZT. Enhancements in the Seebeck coefficient up to 450 mu V/K and the reduction of the thermal conductivity down to 2.2 W/mK are mainly attributed to the low dimensionality of the system. Preliminary tests on microfabricated modules are performed on a non-optimized material and device dimensions as proof of concept for next generation devices.