Enhanced Optical Absorption and Emission from Monolayer WS2 Integrated Onto a TiO2 Nanohole Array.

Monolayer transition metal dichalcogenides (TMDCs) have extensive applications in the field of optics and optoelectronics by virtue of their unique band structures and excitonic properties. Although possessing high absorption coefficient and emission efficiency, they suffer from low optical absorptance due to the atomic scale thickness, which limits their photoluminescence and optoelectronic performance. In spite of intense research efforts on absorption enhancement of monolayer TMDCs by optical cavities, such as plasmonic and all‐dielectric nanoresonators, there inevitably exists a competition of absorption between them because of the loss in cavities. Here, strong absorption enhancements of monolayer WS2 integrated onto a TiO2 nanohole array fabricated by colloidal lithography are reported. It achieves theoretically a tenfold and experimentally a sixfold enhancement of absorption within monolayer WS2 near the band edge when TE and TM modes of the TiO2 nanohole array spectrally overlap with the A exciton. This result can be attributed to the near perfect reflection and near field localization properties of the resonant modes in TiO2 nanohole arrays. Further, the photoluminescence of monolayer WS2 is also significantly improved owing to the increased absorption of WS2 as well as Purcell effect. Such heterostructure paves the way for designing high‐efficiency sources, photodetectors, and photovoltaic devices. [ABSTRACT FROM AUTHOR]