Al@Al₂O₃ core-shell plasmonic design for the dilemma between high responsivity and low dark current of MoS₂ photodetector

The localized surface plasmon resonance (LSPR) effect induced by metal nanoparticles (NPs) can solve the problem of low light absorption in two-dimensional (2D) materials limited by atomic scale. However, the accompanying problem is the rise in dark current due to plenty of electrons from metal NPs injecting into the 2D materials, which decreases the performance of plasmonic photodetectors. Here, we designed the structure of Al NPs coated with Al₂O₃ by low temperature oxidation treatment method to balance the dilemma between high photoresponse and low dark current. Raman spectrum and finite-difference time-domain simulations were used to verify that Al₂O₃ does not affect the LSPR effect of Al NPs. Compared to that of the pristine MoS₂/Al photodetector, the MoS₂/Al@Al₂O₃ plasmonic photodetector achieved a fourfold decrease in dark current, threefold increase in detectivity, and 1.5-fold increase in responsivity. As a result, the optimized plasmonic device achieves a high responsivity of ∼1719 A/W, an excellent detectivity of ∼6.0 × 10¹¹ Jones, and an ultra-fast response speed of ∼15 ns. Our work reveals that constructing metal NPs covered by ultra-thin oxide layer is a feasible strategy for plasmonic photodetectors to decrease dark current and achieve high performance index.