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

Electrically driven nanoantennas for on-chip generation and manipulation of light have attracted significant attention in recent times. Metal-insulator-metal (MIM) tunnel junctions have been extensively used to electrically excite surface plasmons and photons via inelastic electron tunneling. However, the dynamic switching of light from MIM junctions into spatially separate channels has not been shown. Here, we numerically demonstrate switchable, highly directional light emission from electrically driven nano-strip Ag-SiO₂-Ag tunnel junctions. The top electrode of our Ag-SiO₂-Ag stack is divided into 16 nano-strips, with two of the tunnel junctions at the centre (S _L and S _R) acting as sources. Using full-wave electromagnetic simulations, we show that when S _L is excited, the emission is highly directional with an angle of emission of -30° and an angular spread of ∼11°. When the excitation is switched to S _R, the emission is redirected to an angle of 30° with an identical angular spread. A directivity of 29.4 is achieved in the forward direction, with a forward-to-backward ratio of 12. We also demonstrate wavelength-selective directional switching by changing the width, and thereby the resonance wavelength, of the sources. The emission can be tuned by varying the periodicity of the structure, paving the way for electrically driven, reconfigurable light sources.