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

Abstract

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–AlOX–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 AlOX 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.

Light-Emitting Electrochemical Cells Based on Nanogap Electrodes

“…The observed temperature dependence excludes indirect light emission mechanisms such as energy transfer via inelastic electron tunneling to the (localized) surface plasmon resonance of the electrodes or photoactive molecules in the junctions. In addition, light emissions due to above mechanisms would be accompanied by a variety of wavelengths depending on the characteristics of the nanogap electrode. − We recently reported on nanoscale vacuum discharge with metal plasma as another mechanism for the electrically induced light emission from nanogap electrodes . Although the light emission due to this mechanism is also suppressed at low temperatures, the response time of the current to the applied bias was much faster than that observed in this study (Figures , S2, and S4).…”

“…Although single molecules are considered ideal optical nanomaterials, realizing a molecular-scale current-induced light source for molecular-scale research and applications in quantum technology has been a challenge . Research is actively ongoing on single-molecule electroluminescence (EL) for scanning probe microscopy systems − and fixed nanogap electrode systems, − for which several types of light-emitting processes have been reported such as a direct process based on exciton formation due to bipolar charge injection into a single molecule or nanomaterial from an electrode − , and indirect processes via inelastic electron tunneling and localized surface plasmons. − …”

“…On the other hand, light emission via indirect processes in the fixed nanogap electrodes has been frequently reported. − Particularly, such nanogap systems are promising for applications in nanoscale optical antennas. − However, the properties of light emission via the indirect process are highly dependent on various conditions, such as the electrode material, geometry, applied voltage, and temperature. Therefore, careful device design and control are necessary.…”

Light-Emitting Plasmonic Tunneling Junctions: Current Status and Perspectives

“…Also, more stable light emission was demonstrated using an AC voltage instead of a DC voltage to drive the tunneling junction. 96 It is worth mentioning that the self-oxide layer on the silicon surface is also an excellent insulating layer. The MIS tunneling junction can also excite the hybrid plasmonic modes among the silicon and gold electrodes, 97 and it may be a potential solution for large-scale light-emitting tunneling junctions.…”

“…Thus, at an early age, the experiments were usually carried out under vacuum and low-temperature conditions to isolate the influences of air and heat. Also, more stable light emission was demonstrated using an AC voltage instead of a DC voltage to drive the tunneling junction . It is worth mentioning that the self-oxide layer on the silicon surface is also an excellent insulating layer.…”