Distributed Bragg Reflectors as Broadband and Large-Area Platforms for Light-Coupling Enhancement in 2D Transition-Metal Dichalcogenides.

Two-dimensional (2D) semiconductors, particularly the direct-gap monolayer transition metal dichalcogenides (TMDs), are currently being developed for various atomically thin optoelectronic devices. However, practical applications are hindered by their low quantum efficiencies in light emissions and absorptions. While photonic cavities and metallic plasmonic structures can significantly enhance the light-matter interactions in TMDs, the narrow spectral resonance and the local hot spots considerably limit the applications when broadband and large area are required. Here, we demonstrate that a properly designed distributed Bragg reflector (DBR) can be an ideal platform for light-coupling enhancement in 2D TMDs. The main idea is based on engineering the amplitude and phase of optical reflection from the DBR to produce optimal substrate-induced interference. We show that the photoluminescence, Raman, and second harmonic generation signals of monolayer WSe can be enhanced by a factor of 26, 34, and 58, respectively. The proposed DBR substrates pave the way for developing a range of 2D optoelectronic devices for broadband and large-area applications.