Sub-Band-Gap Photoresponse Caused by Hot Electron Injections in Au Nanorod Decorated van der Waals Semiconductor Monolayers

Hot electrons in metal nanostructures can be exploited in a wide range of optical functions, including photocatalysis, surface-enhanced Raman scattering, photodetectors and photovoltaics. Here, we report the sub-band-gap ( E g ) photoresponse in Au-nanorod decorated van der Waals ( vdW ) semiconductor, MoS 2 and WSe 2 , monolayers (MLs). We found that hot electrons, optically excited in Au nanorod (NR) arrays at sub- E g radiations, can be injected into vdW ML semiconductors over Schottky barriers, producing substantial photocurrents in n -type MoS 2 and p -type WSe 2 ML photodetectors, as well as photovoltages in n -MoS 2 / p -WSe 2 ML stack junctions. Moreover, by using spectrally and light-polarization resolved measurements, we showed that these sub- E g excitations of hot electrons can be modulated by tuning the plasmon resonance to the shape-controlled AuNRs.