Heat Management

As an example, the latter topic of nano-coolers is based on the thermionic cooling concept proposed by Mahan in the 90’s [G. D. Mahan, J. Appl. Phys. 76, 4362-4366 (1994) https://doi.org/10.1063/1.357324].

In this regime, the absence of a local equilibrium leads to different temperatures between electrons and phonons, raising the opportunity to obtain higher cooling efficiency than in conventional thermoelectric devices.

As an example of thermionic cooling heterostructure, Figure 1-A) shows an asymmetric double-barrier GaAs-AlGaAs device [A. Yangui, M. Bescond, T. Yan, N. Nagai, and K. Hirakawa, Nature Commun. 10, 4504 (2019) https://doi.org/10.1038/s41467-019-12488-9].

In this structure, "cold" electrons are injected into the quantum well (QW) via a resonant tunneling effect through a thin potential barrier (referred as “emitter barrier”). "Hot" electrons are extracted from the QW through a thermionic process above the thick AlGaAs alloy (referred as “collector barrier”), extracting the activation energy W from the lattice via phonon absorption. As a result, the lattice of the QW cools and the one of the collector heats.

Figure 1-B) schematically illustrates how the nonequilibrium electron and lattice systems in the QW interact with each other. The electron system is cooled through “evaporation” over the collector barrier. The colder electron system in the QW is in close contact with the warmer lattice system via electron-phonon interaction. The electron system is then warmed up by the lattice system through phonon absorption, while the lattice system in the QW is cooled down by the electron one (by “thermionic cooling”).

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