Silicon Mie Resonators for Highly Directional Light Emission from monolayer MoS2

📝 Abstract

Controlling light emission from quantum emitters has important applications ranging from solid-state lighting and displays to nanoscale single-photon sources. Optical antennas have emerged as promising tools to achieve such control right at the location of the emitter, without the need for bulky, external optics. Semiconductor nanoantennas are particularly practical for this purpose because simple geometries, such as wires and spheres, support multiple, degenerate optical resonances. Here, we start by modifying Mie scattering theory developed for plane wave illumination to describe scattering of dipole emission. We then use this theory and experiments to demonstrate several pathways to achieve control over the directionality, polarization state, and spectral emission that rely on a coherent coupling of an emitting dipole to optical resonances of a Si nanowire. A forward-to-backward ratio of 20 was demonstrated for the electric dipole emission at 680 nm from a monolayer MoS2 by optically coupling it to a Si nanowire.

💡 Analysis

Controlling light emission from quantum emitters has important applications ranging from solid-state lighting and displays to nanoscale single-photon sources. Optical antennas have emerged as promising tools to achieve such control right at the location of the emitter, without the need for bulky, external optics. Semiconductor nanoantennas are particularly practical for this purpose because simple geometries, such as wires and spheres, support multiple, degenerate optical resonances. Here, we start by modifying Mie scattering theory developed for plane wave illumination to describe scattering of dipole emission. We then use this theory and experiments to demonstrate several pathways to achieve control over the directionality, polarization state, and spectral emission that rely on a coherent coupling of an emitting dipole to optical resonances of a Si nanowire. A forward-to-backward ratio of 20 was demonstrated for the electric dipole emission at 680 nm from a monolayer MoS2 by optically coupling it to a Si nanowire.

📄 Content

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Silicon Mie Resonators for Highly Directional Light Emission from monolayer MoS2 Ahmet Fatih Cihan1, Alberto G. Curto1,2, Søren Raza1, Pieter G. Kik1,3
and Mark L. Brongersma1

1. Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, United States
2. Dep. Applied Physics and Institute for Photonic Integration, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands
3. CREOL, The College of Optics and Photonics, University of Central Florida, Florida 32816, United States

Abstract: Controlling light emission from quantum emitters has important applications ranging from solid-state lighting and displays to nanoscale single-photon sources. Optical antennas have emerged as promising tools to achieve such control right at the location of the emitter, without the need for bulky, external optics. Semiconductor nanoantennas are particularly practical for this purpose because simple geometries, such as wires and spheres, support multiple, degenerate optical resonances. Here, we start by modifying Mie scattering theory developed for plane wave illumination to describe scattering of dipole emission. We then use this theory and experiments to demonstrate several pathways to achieve control over the directionality, polarization state, and spectral emission that rely on a coherent coupling of an emitting dipole to optical resonances of a Si nanowire. A forward-to-backward ratio of 20 was demonstrated for the electric dipole emission at 680 nm from a monolayer MoS2 by optically coupling it to a Si nanowire.

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Main text: Achieving control over the radiation properties of quantum emitters is key to improving efficiency and realizing new functionality in optoelectronic systems. Bulky optical components have been developed for many years and are extremely effective in controlling the angular, polarization, and spectral properties of light emission. Recent advances in the fields of metallic and dielectric optical metamaterials and nanoantennas have now also enabled effective integration of solid-state emitters and control elements into inexpensive platforms.1–3 Such structures can manipulate light emission in the near-field of an emitter and thus hold a real promise to achieve even greater control over the emission process. For example, we will show how the undesired losses due to radiation of quantum emitters into a high-index substrate can be reduced by redirecting the emission upward with an antenna.
Whereas structures based on noble metals are currently most advanced in manipulating light-matter interaction at the nanoscale, they typically are complex in shape, display undesired optical losses, and are not compatible with most semiconductor device processing technologies. High-index semiconductor antennas can circumvent these issues while providing complex electrical and optical functions.2,4–14 Based on the mature fabrication infrastructure, silicon nanostructures appear particularly promising for optoelectronic applications.4,9–12,15–17 Semiconductor nanoparticles of simple geometric shapes have displayed directional scattering of plane waves when the renowned Kerker conditions are satisfied.12,16,18 When these conditions are met, directionality is naturally achieved through the coherent excitation of electric and magnetic dipole resonances in the particle and tuning the interference of the associated scattered fields.12,19,20 Thanks to their high refractive indices, semiconductor nanoparticles can satisfy the Kerker conditions in the visible spectral range.16,18,21 Given the ever-increasing importance of solid state light emitters and quantum nanophotonics, it is of great interest to 3

explore whether analogous conditions can be identified that will facilitate directional emission from quantum emitters and we answer this is important question positively in this work. As such, it nicely complements other low-loss approaches involving advanced semiconductor photonic crystals and leaky wave antenna structures to control spectral and angular emission properties.22–27 Directional emission with the help of nanometallic antennas has been analyzed theoretically in great detail and was demonstrated experimentally at optical frequencies.28–33 For semiconductor antennas, however, directional emission exploiting Mie resonances has been limited to theoretical proposals16,34–46 or experiments in the microwave regime.47 By modifying the conventional Mie theory to describe light scattering by a nanowire (NW) from a dipolar source as opposed to the standard plane-wave source, we reveal that directional emission with a silicon NW can be realized through a variety of mechanisms. Each of these directionality mechanisms involves optical interference effects that come about when the light emitted from a quantum emitter can follow different pathways to the far-field. For example, highly-directional emissi

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