Fabry-Perot Cavity-Enhanced Optical Absorption in Ultrasensitive Tunable Photodiodes Based on Hybrid 2D Materials

Monolayer two-dimensional (2D) transition metal dichalcogenides (TMDs) show interesting optical and electrical properties because of their direct bandgap. However, the low absorption of atomically thin TMDs limits their applications. Here, we report enhanced absorption and optoelectronic properties of monolayer molybdenum disulfide (MoS₂) by using an asymmetric Fabry-Perot cavity. The cavity is based on a hybrid structure of MoS₂/ hexagonal boron nitride (BN)/Au/SiO₂ realized through layer-by-layer vertical stacking. Photoluminescence (PL) intensity of monolayer MoS₂ is enhanced over 2 orders of magnitude. Theoretical calculations show that the strong absorption of MoS₂ comes from photonic localization on the top of the microcavity at optimal BN spacer thickness. The n/n⁺ MoS₂ homojunction photodiode incorporating this asymmetric Fabry-Perot cavity exhibits excellent current rectifying behavior with an ideality factor of 1 and an ultrasensitive and gate-tunable external photo gain and specific detectivity. Our work offers an effective method to achieve uniform enhanced light absorption by monolayer TMDs, which has promising applications for highly sensitive optoelectronic devices.