SiGe/Si superlattice power generators

SiGe is one of the best thermoelectric materials for high temperature applications. Superlattice structures can further enhance the thermoelectric properties by reducing the thermal conductivity and by increasing the Seebeck coefficient via selective emission of hot electrons through thermionic emission. SiGe/Si superlattice structures were grown on a silicon wafer using molecular beam epitaxy. A single element SiGe/Si superlattice thermoelectric power generator was fabricated and characterized. The device element, a 3 μm thick SiGe/Si superlattice on a 3.95 μm SiGe buffer layer, was grown on 5 inch diameter 650 microns thick silicon substrate. Output power of 0.1 W/cm with a resistive load was measured with a temperature drop of 220°C across the generator element. There was a significant parasitic lead resistance. Simulations show that if the temperature drop is increased to 300°C, a power density of 1 W/cm can be achieved when working in impedance matching condition.