Light at the End of the Tunnel

In recent years, tunnel junctions have reemerged as promising candidates for the transduction of electrical to optical signals at the nanoscale. The process of interest is known as inelastic electron tunneling (IET), where a tunneling electron excites an optical mode while traversing the tunnel barrier. The main appeal of tunnel junctions lies in their size and bandwidth, both of which are unmatched by other electronic devices. However, their main disadvantage so far has been the overall low transduction efficiency. Recently, the realization of photon(1) and surface plasmon polariton (SPP)(2) sources based on IET, with efficiencies exceeding 1%, were reported. In this perspective, we critically analyze the factors that limit efficiencies and extract guidelines for the development of efficient photon and SPP sources.