The effect of thermotunneling on the thermoelectric figure of merit

Thermotunneling terms the thermoelectric effect in narrow tunnel junctions associated with a temperature gradient across the tunnel junction as the driving force for electron transport. The thermoelectric figure of merit characterizes the suitability of a material in applications for thermoelectric energy conversion. An advantage of thermotunneling in vacuum tunnel junctions is the complete blocking of heat transfer by phonons raising hope for improved thermoelectric conversion efficiency of future thermotunneling devices. However, thermotunneling is generally accompanied by radiative heat transfer enhanced by photon tunneling. Using analytical modeling the paper studies the combined influence of both electronic and radiative heat transfer on the thermoelectric figure of merit of a thermotunneling junction to assess the potential of thermotunneling devices for improvements in conversion efficiency. Based on a free electron model applied to highly reflective low resistivity metals as material of the junction electrodes it is found that the thermotunneling figure of merit is significantly less than the dimensionless thermoelectric figure of merit around 1 of the best thermoelectric materials known.