Conventional and total momentum filtered thermionic devices

Conventional solid-state and vacuum thermionic devices restrict the flow of electrons between the hot and cold reservoirs according to the magnitude of their momentum in the direction of transport only. Recently it has been suggested that devices may be developed where the filtering of transmitted electrons occurs according to their total momentum. We compare the performance of these two different methods of electron momentum filtering in single barrier and resonant tunneling thermionic refrigeration devices. It is shown that total momentum filtered single barrier refrigerators always outperform conventional single barrier refrigerators due to their larger heat current which is particularly important when the thermal conductivity of the system is significant. We show that whilst conventionally filtered resonant tunneling thermionic refrigerators are outperformed by total momentum resonant tunneling thermionic refrigerators in many conditions, their performance is superior at (1) high temperatures or (2) when the transmission energy is very close to the Fermi energy.