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

Abstract 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.