Silicon Mie Resonators for Highly Directional Light Emission from monolayer MoS2 (1709.04999v1)

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 of Silicon Mie Resonators for Directional Light Emission from Monolayer MoS₂

This paper investigates the directional light emission from monolayer MoS₂ by employing silicon (Si) nanowire (NW) resonators based on Mie theory. It extends the conventional Mie scattering theory developed for plane waves to address the scattering of dipole emissions, providing both theoretical and experimental insights into how Si NWs can control light directionality, polarization, and spectral characteristics.

Core Concepts and Methodologies

The paper explores the coherent coupling between quantum emitters like MoS₂ and Si NWs to manipulate the emission properties. Such manipulation is fundamental to enhancing the efficiency and functionality of optoelectronic systems, typically achieved with bulky optical components. Si-based antennas offer a compatible platform for advanced semiconductor device processing technologies, which poses an advantage over noble metal-based antennas known for their complexity and higher optical losses.

The authors modify Mie theory to explore light scattering by NWs from dipolar sources rather than plane waves. This modification allows the identification of directionality mechanisms involving optical interference effects, showcasing instances where emitted light can travel different paths to the far field. Two key mechanisms are highlighted: the dominance of an electric dipole resonance in NWs, and Kerker scattering involving electric and magnetic dipole excitations.

Experimental Findings and Theory

The experimental results demonstrate a forward-to-backward emission ratio of 20 for MoS₂ emitters coupled with Si NWs at visible wavelengths. The ability to achieve such enhanced directionality is attributed to controlling the NW-emitter distance, which influences the excitation efficiencies of various multipoles. This is pivotal in refocusing light emission upward, thus reducing radiation losses into substrates.

Directional emission is supported by confocal optical microscopy and verified through techniques like mild Ar plasma etching, which optimizes emission collection by removing non-directionally emitting regions. Further, the paper identifies spectral shifts in emission wavelengths achieved through variations in NW size, a consideration stemming from resonance changes with NW dimensions.

The paper's analytical approach describes scattering efficiency in terms of both radial distance and dipole-to-NW distance and demonstrates spectral and NW size dependencies of the top-to-bottom (T/B) emission ratio using simulations consistent with experimental outcomes.

Implications and Future Directions

The implications for quantum emitters and solid-state photonic systems are significant. This research provides insights into manipulating emission processes at the source level, leveraging dielectric antennas to achieve control over directionality and spectral characteristics. It opens pathways for developing high-performance single-photon sources or metasurfaces with dense arrays of semiconductor nanostructures for enhanced light extraction efficacy.

Further exploration could focus on optimizing NW geometries and configurations to refine control over emission properties in diverse photonic applications while addressing broader challenges in quantum nanophotonics and solid-state lighting.

In summary, the modification of Mie theory along with the practical demonstration of Si polymorphic resonators marks a sophisticated step towards efficient and directional light emission designs. The paper demonstrates both theoretical prowess and applied viability, promising consequential advancements in the integration of photonic structures into versatile optoelectronic systems.