P-type SiGe/Si Superlattice Cooler

The fabrication and characterization of single element p-type SiGe/Si superlattice coolers are described. Superlattice structures were used to enhance the device performance by reducing the thermal conductivity between the hot and the cold junctions, and by providing selective emission of hot carriers through thermionic emission. The structure of the samples consisted of a 3 μm thick symmetrically strained Si0.7Ge0.3/Si superlattice grown on a buffer layer designed so that the in-plane lattice constant is approximately that of relaxed Si0.9Ge0.1. Cooling up to 2.7 K at 25 °C and 7.2 K at 150 °C were measured. These p-type coolers can be combined with n-type devices that were demonstrated in our previous work. This is similar to conventional multi element thermoelectric devices, and it will enable us to achieve large cooling capacities with relatively small currents.