Hyperbolic Phonon Polariton Electroluminescence as an Electronic Cooling Pathway

Engineering of the cooling mechanism is of primary importance for the development of nanoelectronics. While radiation cooling is rather inefficient in current electronic devices, the strong anisotropy of 2D materials allows for enhanced efficiency because their hyperbolic electromagnetic dispersion near phonon resonances allows them to sustain much larger (approximate to 10(5)) number of radiating channels. In this review, radiation cooling in 2D materials is addressed. The hyperbolic dispersion of electromagnetic waves is presented, and how the spontaneous fluctuations in current in a 2D electronic channel can radiate thermal energy in its hyperbolic surrounding medium is described. Both the regime of thermal current fluctuations and out-of-equilibrium current fluctuations can be described within the same framework leading to superPlanckian thermal emission and electroluminescent cooling. A recent experimental investigation on graphene-on-hBN transistors using electronic noise thermometry is discussed. In high mobility semimetal-like graphene at large bias, a steady-state out-of-equilibrium situation is caused by Zener tunneling of electrons, opening a route for electroluminescence of hyperbolic electromagnetic modes. Electroluminescent cooling is particularly prominent once the Zener tunneling regime is reached: observed cooling powers are nine orders of magnitude larger than in conventional LEDs.