Sub Band-Gap Photoresponse 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 (Eg) photoresponse in Au-nanorod decorated van der Waals (vdW) semiconductor, MoS2 and WSe2, monolayers (MLs). It was found that hot electrons, optically excited in Au nanorod (NR) arrays at the sub band-gap (Eg) radiations, can be injected to vdW ML semiconductors over Schottky barriers, producing substantial photocurrents in n-type MoS2 and p-type WSe2 ML photodetectors, as well as photovoltages in n-MoS2/p-WSe2 ML stack junctions. Moreover, by spectrally and light-polarization resolved measurements, we showed that these sub band-gap (Eg) excitations of hot electrons can be modulated by tuning the plasmon resonance at the shape controlled Au NRs.1