Fabry-Perot cavity enhanced light-matter interactions in two-dimensional van der Waals heterostructure

Despite monolayer transition metal dichalcogenide (TMD) shows a direct band gap property, its atomic thickness causes poor light absorption that severely limits its practical applications. For improving the optical gain of TMD, however, many approaches were proposed such as complicated fabrication process that compromises the stability and reliability of two-dimensional (2D) materials, which further limits the device scalability. In this work, a simple method is reported to engineer the light-matter interactions in few-layer molybdenum disulfide (MoS2) and tungsten diselenide (WSe2) via an asymmetric Fabry-Perot cavity (FPc). The cavity is based on the hybrid integration of TMD/hexagonal boron nitride (h-BN)/Au/SiO2 heterostructure realized through layer-by-layer stacking. By modulating the underlying h-BN thickness, constructive resonant absorption can be achieved by multiple internal reflections, which significantly increases the Raman and optical absorption of MoS2 and WSe2. Leveraging on the enhanced light-matter interactions, we further integrate this asymmetric Fabry−Perot cavity into WSe2/MoS2 van der Waals heterostructure (vdWH) to realize high performance photodiode and photovoltaic devices, leading to a ~5 folds increase in photodiode responsivity and a peak external quantum efficiency (EQE) of 7.5%. This work demonstrates an effective way towards hybrid integration of Fabry-Perot cavity with 2D materials, which could offer a potential pathway for enabling novel optoelectronic devices, such as 2D light-emitting diodes (LEDs) and solar cells.