Fast and broadband MoS2 photodetectors by coupling WO3–x semi-metal nanoparticles underneath

Coupling two-dimensional (2D) materials with plasmonic nanoparticles (NPs) holds great potential for enhancing the photodetection performance in 2D photodetectors. However, there are limitations in the detection spectral range and response speed of plasmonic 2D photodetectors based on transition metal dichalcogenides (TMDs) like MoS2. We have developed a fast and broadband MoS2 photodetector (denoted as MoS2/WO3–x) by coupling semi-metal sub-stoichiometric WO3–x NPs beneath, in contrast to traditional WO3–x/MoS2 photodetectors with the opposite positions of MoS2 and WO3–x NPs. The photodetection performance is 10 times higher than the WO3–x/MoS2 structure, and 100 times higher than the pristine MoS2 device, broadening the spectrum to near-infrared (NIR), achieving a maximum responsivity and detectivity that can reach 1.8 × 104 A W–1, 4.62 × 1013 Jones, respectively, under 940 nm illumination. The response speed exceeds the state-of-the-art MoS2 photodetectors based on composite structures, unprecedentedly reaching the order of tens of microseconds. Theoretical understanding of WO3–x NPs as well as light interaction with the MoS2 layer reveal that the exceptional photoelectric performance can be attributed to the synergistic effect of both the semimetal nature of the underneath WO3–x NPs and the intact nature of the top MoS2 layer. The mechanism enhances optical absorption, expands the spectral range, and simultaneously speeds up optoelectronic effects.