Strongly Enhanced Photoluminescence and Raman Signals of Monolayer 2D Materials via Substrate Induced Interference
Yen-Chun Chen1*, Han Yeh1, Wen-Hao Chang1
1Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
* presenting author:Yen-Chun Chen,
Two-dimensional (2D) monolayer transition metal dichalcogenides (TMDCs), such as WSe2 and MoS2, with direct bandgap, strong exciton binding energy and valley-contrast chiral optical selection rules, are promising for developing atomically-thin electronics and optoelectronics1. However, their low quantum efficiency in light emissions and the weak light absorptions considerably hinder the implementation of TMDCs for practical photonic devices. Enhancing light absorptions in and emissions from TMDCs is a concentrated issue. Here we demonstrated that the emissions and absorptions of monolayer WSe2 can be strongly enhanced by multiple reflections from a platform using distributed Bragg reflectors (DBRs). Comparing with WSe2 flakes on glass substrates, 25 and 34 times enhancements on photoluminescence (PL) and Raman intensities can be obtained for WSe2 flakes lying on DBRs with suitably designed center wavelengths. Numerical calculations considering both excitation and emission enhancements caused by the DBR induced interference fit the experimental data very well. The DBR platforms also strongly enhance the optical nonlinearity 2D materials, as evident from the highly enhanced second harmonic generations and two-photon PL from monolayer WSe2. The DBR substrates provide a broadband and large-area platform for enhancing light incoupling and outcoupling for 2D materials, which can be applied in practical 2D optoelectronic devices, such as light emitting diodes (LEDs) and solar cells.

Keywords: Transition metal dichalcogenides, Outcoupling efficiency, Distributed Bragg reflectors, Optical nonlinearity