Enhanced light emission from gap plasmons in nano-strip MIM tunnel junctions

Abstract

Electrical excitation of light using inelastic electron tunneling is a promising approach for the realization of ultra-compact on-chip optical sources with high modulation bandwidth. However, the practical implementation of these nanoscale light sources presents a challenge due to the low electron-to-photon transduction efficiencies. Here, we investigate designs for the enhancement of light generation and out-coupling in a periodic Ag-SiO2-Ag tunnel junction due to inelastic electron tunneling. The structure presents a unique advantage of a simple fabrication procedure as compared to the other reported structures. By efficiently coupling the gap plasmon mode and the lattice resonance, we achieve a resonant enhancement in the local density of optical states up to three orders of magnitude and enhanced radiative efficiency of ~0.53, 30% higher as compared to the uncoupled structure.

Tunable directional emission from electrically driven nano-strip metal–insulator–metal tunnel junctions

“…The width of the source (S) as well as the directors ( D ) is taken as 35 nm, with the central element acting as the source, and is resonant at a wavelength of λ ∼ 695 nm. 19 The different emission channels when the central nano-strip is excited are also depicted, with θ g being the outcoupling angle of the scattered SPs. The far-field radiation pattern for the grating is shown in Fig.…”

“…To mimic the current flow within the device, a dipole is placed at different positions within the gap of the source element ( S R / S L ) with dipole moment along the direction of flow of current ( y -axis). 19 The emitted intensity is collected and incoherently added (and averaged) at five different locations within the gap. Since the excitation source is a point dipole, a finite domain size of 35 μm truncated by PML (perfectly matched layer) boundary conditions is used to collect maximum emission from the simulated structure.…”

“…Following its initial demonstration in 1976, 16 MIM tunnel junctions have been extensively used to electrically excite surface plasmons (SPs) and photons via inelastic electron tunneling (IET) under an applied bias. [17][18][19][20][21] The electrons tunnel inelastically through the dielectric tunneling barrier between two electrodes and lose a part of their energy to various available modes, both bound and radiative, as dened by the local density of optical states (LDOS). The tunneling current predominantly excites the gap plasmon mode within the barrier, which then outcouples to propagating SPs and freespace photons.…”