Waveguide-Integrated Light-Emitting Metal–Insulator–Graphene Tunnel Junctions

Abstract

Ultrafast interfacing of electrical and optical signals at the nanoscale is highly desired for on-chip applications including optical interconnects and data processing devices. Here, we report electrically driven nanoscale optical sources based on metal− insulator−graphene tunnel junctions (MIG-TJs), featuring waveguided output with broadband spectral characteristics. Electrically driven inelastic tunneling in a MIG-TJ, realized by integrating a silver nanowire with graphene, provides broadband excitation of plasmonic modes in the junction with propagation lengths of several micrometers (∼10 times larger than that for metal− insulator−metal junctions), which therefore propagate toward the junction edge with low loss and couple to the nanowire waveguide with an efficiency of ∼70% (∼1000 times higher than that for metal−insulator−metal junctions). Alternatively, lateral coupling of the MIG-TJ to a semiconductor nanowire provides a platform for efficient outcoupling of electrically driven plasmonic signals to low-loss photonic waveguides, showing potential for applications at various integration levels.

Light-Emitting Plasmonic Tunneling Junctions: Current Status and Perspectives

“…The h-BN should be transferred to the device area, but the yield of tunneling junctions is badly affected by the transfer method, for example, the bumbles formed in the transfer process. In addition to the insulator layer, 2D materials can also be used as transparent electrodes, such as graphene. ,− Also, the Femi level can be easily tuned with electric gating, which means the emission intensity can be adjusted actively and used for developing high-efficiency tunneling plasmonic devices. , …”

“…(c) Direct excitation of SPPs in a single silver nanowire with a graphene electrode. Reproduced from ref . CC BY 4.0.…”

“…Due to the large damping and mismatch between the highly confined gap modes and the propagating modes, the excitation of SPPs via the IET process is limited by a low coupling efficiency. Thus, transparent graphene was used as the electrode to excite the SPPs directly instead of the Au electrode (Figure c) . What is more, structure design is required to improve the coupling efficiency.…”

Tuning Overbias Plasmon Energy and Intensity in Molecular Plasmonic Tunneling Junctions by Atomic Polarizability

“…Plasmonics has a wide range of applications in catalysis, sensing, subwavelength imaging, plasmon enhanced spectroscopy and lasing. − Plasmons at interfaces can be excited not only by photons but also by high energy electrons in transmission electron microscopy (TEM) − or low energy tunneling electrons in scanning tunneling microscopy − and metal–insulator–metal (MIM) tunnel junctions − via inelastic tunneling (IET) which may find applications as nanoscale light sources, data processing devices, or integrated optical circuits. Plasmonic molecular junctions are interesting for in operando single-molecule Raman spectroscopy, , controlled plasmonic grafting of molecular junctions, and hot carrier generation. − We have shown that the generated plasmons can be controlled at the molecular level, where orientation of the molecules modulates polarization, and the structure of the molecules determines intensity and the dynamics of the light emission.…”

Broadband Tunable Infrared Light Emission from Metal-Oxide-Semiconductor Tunnel Junctions in Silicon Photonics

“…Since the first demonstration in 1976 of such inelastic tunneling light emission in MIM tunnel junctions, research has spread out to studies in scanning tunneling microscopes − (STM), metallic nanophotonic geometries, − as well as metal oxide semiconductor (MOS) tunnel junctions. − Internal quantum efficiencies (emitted inelastic vs total tunneling rate) of ∼32% have been achieved by utilizing the large local optical density of states (LDOS) inherent to highly confined gap plasmons and an inelastic transition-tailored multiquantum-well structure . In other work, the significance of conserving the tunneling electrons’ momentum has been nicely demonstrated with graphene electrodes. , And since tunnel junctions generate many hot electrons, discussions about all the possible plasmon emission mechanisms are still ongoing. , …”