On momentum conservation and thermionic emission cooling

TL;DR

This paper investigates whether relaxing momentum conservation can enhance thermionic cooling performance, finding that such relaxation offers limited benefits except in specific heterojunction cases, and highlighting the importance of conduction channels.

Contribution

It provides a detailed analysis of momentum conservation effects in thermionic devices, clarifying when non-conservation can or cannot improve current and cooling performance.

Findings

Non-conservation overestimates current in many cases

In heterojunctions with heavy barrier mass and low barrier height, non-conservation can increase current

Thermionic cooling benefits from relaxing momentum conservation are generally limited

Abstract

The question of whether relaxing momentum conservation can increase the performance of thermionic cooling device is examined. Both homojunctions and heterojunctions are considered. It is shown that for many cases, a non-conserved lateral momentum model overestimates the current. For the case of heterojunctions with a much heavier effective mass in the barrier and with a low barrier height, however, non-conservation of lateral momentum may increase the current. These results may be simply understood from the general principle that the current is limited by the location, well or barrier, with the smallest number of conducting channels. These results also show that within thermionic emission framework, the possibilities of increasing thermionic cooling by relaxing momentum conservation are limited. More generally, however, when the connection to the source is weak or in the presence of scattering, the situation may be different. Issues that deserve further study are identified.