Efficient Surface Plasmon Polariton Excitation and Control over Outcoupling Mechanisms in Metal–Insulator–Metal Tunneling Junctions

Surface plasmon polaritons (SPPs) are viable candidates for integration into on‐chip nano‐circuitry that allow access to high data bandwidths and low energy consumption. Metal–insulator–metal tunneling junctions (MIM‐TJs) have recently been shown to excite and detect SPPs electrically; however, experimentally measured efficiencies and outcoupling mechanisms are not fully understood. It is shown that the MIM‐TJ cavity SPP mode (MIM‐SPP) can outcouple via three pathways to i) photons via scattering of MIM‐SPP at the MIM–TJ interfaces, ii) SPPs at the metal–dielectric interfaces (bound‐SPPs) by mode coupling through the electrodes, and iii) photons and bound‐SPP modes by mode coupling at the MIM‐TJ edges. It is also shown that, for Al‐AlO(x)‐Cr‐Au MIM‐TJs on glass, the MIM‐SPP mode outcouples efficiently to bound‐SPPs through either electrode (pathway 2); this outcoupling pathway can be selectively turned on and off by changing the respective electrode thickness. Outcoupling at the MIM‐TJ edges (pathway 3) is efficient and sensitive to the edge topography, whereas most light emission originates from roughness‐induced scattering of the MIM‐SPP mode (pathway 1). Using an arbitrary roughness profile, it is demonstrated that various roughness facets can raise MIM‐SPP outcoupling efficiencies to 0.62%. These results pave the way for understanding the topographical parameters needed to develop CMOS‐compatible plasmonic circuitry elements.