Spatial Control over Stable Light-Emission from AC-Driven CMOS-Compatible Quantum Mechanical Tunnel Junctions

The potential application of quantum mechanical tunnel junctions as subdiffraction light or surface plasmon sources has been explored for decades, but it has been challenging to create devices with subwavelength spatial control over the light or plasmon excitation. This paper describes spatial control over the electrical excitation of surface-plasmon polaritons (SPPs) and photons in large-area junctions of the form of Al–AlO_X–Cu complementary metal-oxide-semiconductor (CMOS)-compatible tunnel junctions. Nanoscale spatial control (smallest feature sizes of 150 nm) is achieved by locally fine-tuning the thickness of the AlO_X tunneling barrier resulting in large local tunneling currents and associated SPP excitation rates. Mostly, plasmonic tunnel junctions are studied under DC operation with a relatively large bias (and associated currents) to observe light emission at optical frequencies. Large voltages risk device failure and reduce device lifetimes. Here it is demonstrated that the operational lifetime of AC-driven plasmonic tunnel junctions is improved by a factor of three. Under DC conditions, slow processes that lead to device failure (e.g., undesirable electromigration leading to shorts) readily occur, thus limiting the device decay time to 9.2 h; but under AC operation, such processes are slow with respect to the voltage changes prolonging the decay time beyond 18.0 h.