Nonequilibrium electrical generation of surface phonon polaritons

Notwithstanding its relevance to many applications in sensing, security, and communications, electrical generation of narrow-band midinfrared light remains highly challenging. Unlike in the ultraviolet or visible spectral regions, few materials possess direct electronic transitions in the midinfrared and most that do are created through complex band-engineering schemes. An alternative mechanism, independent of dipole-active material transitions, relies instead on energy lost to the polar lattice through the Coulomb interaction. Longitudinal phonons radiated in this way can be spectrally tuned through the engineering of polar nanostructures and coupled to localized optical modes in the material, allowing them to radiate midinfrared photons into the far field. A recent theoretical work has explored this process, providing for the first time an indication of its technological relevance when compared to standard thermal emitters. In order to do so, it has nevertheless used an equilibrium model of the electron gas, making the use of this model difficult to inform the design of an optimal device to experimentally observe the effect. The present paper removes this limitation, describing the electron gas using a rigorous self-consistent nonequilibrium Green's function model, accounting for variations in material properties across the device and electron-electron interactions. Although the instability of the Schr"odinger-Poisson iteration limits our studies to the low-bias regime, our results demonstrate emission rates comparable to that of room-temperature thermal emission despite such low biases. These results provide a pathway to the design of a confirmatory experiment of this new emission channel, which could power a new generation of midinfrared optoelectronic devices.