Heterostructure integrated thermionic refrigeration

Thermionic emission in heterostructures is investigated for integrated cooling of high power electronic and optoelectronic devices. This evaporative cooling is achieved by selective emission of hot electrons over a barrier layer from the cathode to the anode. As the energy distribution of emitted electrons is almost exclusively on one side of Fermi energy, upon the current flow, strong carrier-carrier and carrier-lattice scatterings tend to restore the quasi equilibrium Fermi distribution in the cathode by absorbing energy from the lattice, and thus cooling the emitter junction. An analytic expression for the optimum barrier thickness is derived. It describes the interplay between Joule heating in the barrier and heat conduction from the hot to the cold junction. It is shown that by choosing a barrier material with high electron mobility and low thermal conductivity it is possible to cool electronic devices by 5 to 40 degrees in a wide range of temperatures.