Performance Limits of Graphene Hot Electron Emission Photoemitters

Hot electron emission from waveguide-integrated graphene has been recently shown to occur at optical power densities multiple orders of magnitude lower than that of metal tips excited by sub-work-function photons. However, the experimentally observed electron emission currents are small, which limits the practical uses of such a mechanism. Here, we explore the performance limits of hot electron emission in graphene through experimentally calibrated simulations. Two regimes of nonequilibrium emission in graphene are identified, (i) single particle hot electron emission, where an electron is excited by a photon and emitted before losing significant energy through scattering; and (ii) ensemble hot electron emission, where the photon source causes nonequilibrium heating of the electron population beyond the electron lattice temperature. It is shown that, through appropriate selection of photon energy, optical power density, and applied electric field, hot electron emission can be used to create ultrahigh current electron emitters with ultrafast temporal responses in both the single particle and ensemble heating regimes. These results suggest that, through appropriate design, hot electron emitters may overcome the limitations of thermionic and field emitters.