Control of Two-Dimensional Excitonic Light Emission via Photonic Crystal
This paper explores the manipulation of excitonic light emission from monolayer tungsten diselenide (WSe₂) through the integration with a photonic crystal (PhC) with cavities. Monolayers of transition metal dichalcogenides (TMDCs) like WSe₂ have gained recognition as promising optoelectronic materials due to their exceptional semiconducting properties at the two-dimensional limit and their strong light-matter interactions. However, effective control over their light emission remains underdeveloped. This paper provides a significant advance in this direction by demonstrating enhanced photoluminescence and directional emission from WSe₂ when paired with a PhC.
The authors employed a configuration in which a monolayer TMDC is transferred onto a photonic crystal structure. This architecture overcame several challenges inherent in previous designs, such as fabrication difficulties and inefficient light extraction due to optical restrictions at the air-semiconductor interface. Specifically, the paper details an enhancement in photoluminescence of up to 60 times compared to non-photonic crystal substrates and demonstrates effective coupling to cavity modes, with measurable peak emissions polarized and controlled through PhC structure design.
The integration of TMDCs with PhCs as seen in this work presents advantages such as enabling the whole monolayer surface for electronic device fabrication, avoiding the discomfort of total internal reflection loss channels, and achieving strong interaction with guiding modes due to the ultra-thin nature of the TMDC layer. Moreover, it maintains the integrity of the light-emitting monolayer by the after-PhC fabrication transfer approach, circumventing fabrication-induced degradation issues faced by other embedded designs.
Photonic crystals and their cavities provide an efficient platform for manipulating light emissions by utilizing the photonic band-gap effect, which inhibits spontaneous emission and redistributes light emission vertically, acting akin to a 2D optical antenna. This work capitalized on such phenomena, evidencing control over both the polar and azimuthal emission angles by tweaking the lattice parameters.
The theoretical underpinnings involving the Purcell effect were carefully investigated, emphasizing the spontaneous emission rate's enhancement achieved by coupling the monolayer's excitonic emission with the PhC cavity modes. This strategic resonant enhancement through cavity coupling and the observed diffraction grating effect promise potential applications in energy-efficient photon sources and the development of 2D nano-lasers.
Future implications of this research could lead to the creation of atomically thin LEDs integrated with photonic crystal cavities, providing possibilities in single-mode emissions, applications in optoelectronic communications, sensing, and efficient optical computing. Moreover, the directional light emission observed might leverage highly efficient and controlled photon sources, adding value to hybrid 2D materials in cutting-edge optoelectronic device engineering. In conclusion, this paper showcases a pioneering approach to controlling 2D excitonic light emission, unlocking new capabilities for TMDCs integrated with photonic structures.