Promoting the Performance of 2D Material Photodetectors by Dielectric Engineering.

Low light absorption and limited carrier lifetime are two limiting factors hampering the further breakthrough of the performance of 2D materials (2DMs)-based photodetectors. This study proposes an ingenious dielectric engineering strategy toward boosting the photosensitivity. Periodic dielectric structures (PDSs), including SiO 2 /h-BN, SiO 2 /Al 2 O 3 , and SiO 2 /SrTiO 3 (STO), are exploited to couple with 2D photosensitive channels (denoted as PDS-2DMs). The responsivity, external quantum efficiency, and detectivity of an optimized SiO 2 /STO (300 nm) -WSe 2 photodetector reach 89081 A W -1 , 2.7 × 10 7 %, and 1.8 × 10 13 Jones, respectively. These performance metrics are orders of magnitude higher than a pristine WSe 2 photodetector, enabling reliable sub-1 pW weak light detection. Based on systematic characterizations and first-principle calculations, such dramatic performance improvement is associated with the promoted direct bandgap transition, reduced exciton binding energy, and PDS-induced periodic intramolecular built-in electric field across the atomically thin channels, which efficiently separates the photoexcited electron-hole pairs. More inspiringly, this strategy is also successfully exploited to 2D WS 2 photodetectors, demonstrating broad applicability. As a whole, this work promises an exceptional avenue to ameliorate 2DM photodetectors and opens up a new horizon "dielectric optoelectronics," simultaneously highlighting the role of dielectric environment during analyzing the fundamentals of 2DM devices.