We investigate a valleytronic method to enhance net phonon absorption by electrons (phonon valleytronics), enabling improved in situ thermoelectric cooling in heterostructured semiconductor devices. We show that electron energy filtering at a heterojunction barrier, combined with tailored valley offsets, generates a nonequilibrium carrier distribution that favors certain intervalley phonon absorption transitions. Using an analytic model and ensemble Monte Carlo simulations for thin ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ barriers, we demonstrate that this effect leads to a thermionic current sustained by phonon absorption-mediated $\mathrm{\Gamma }\to \mathrm{L}/\mathrm{X}$ transitions. With intervalley phonon harvesting, the phonon-electron conversion efficiency (coefficient of performance) increases by a factor of more than two compared with conventional solid-state thermionic energy filtering, under moderate bias at 300 K.

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• Electron-phonon coupling
• Thermionic emission
• Thermoelectric cooling
• Thermoelectric effects
• Valley degrees of freedom