Hot-carrier induced above-threshold light emission in plasmonic tunnel junctions

Light emission from electrically driven tunnel junctions, mediated by localized surface plasmons, have attracted much recent interests, showing that the emitted photon energies are limited by the applied voltage bias. Recent works have reported the above-threshold light emission in which the emitted photons have energies significantly above the applied voltage. However, the physical mechanism underlying this phenomenon, is elusive. Here we report systematic measurements of light emission from tunneling junctions made of different plasmonic materials and proposed a hot-carrier induced light emission mechanism. The characteristics and dynamics of the hot carriers is found to be set by the non-radiative plasmonic process. The reported light emission and electrically driven hot carrier generation opens new possibility in plasmonic chemistry and optoelectronic energy conversion applications.