Plasmon enhanced light emission in molybdenum disulfide

Hot-electron (HE) transfer process in hybrid metal nanoparticle capped layered two-dimensional dichalcogenides (TMDs) can result in the modification of dielectric constant as well as doping of the semiconductor. Hot-carrier transfer process due to optical excitation is an attractive mechanism for enhancing the efficiency of photodetectors or photovoltaic devices. However, HE driven processes are usually non-radiative in nature and are not usually utilized in light emitting system. In this work, it has been demonstrated that by using the optical excitation resonant to plasmons in the hybrid structure, hot electrons are transferred from metal to semiconductor that causes the formation hybridized exciton-plasmon state that eventually gives rise to the enhanced photoluminescence (PL) emission. The localized surface plasmon (LSP) induced off-resonant to the emitted photons has also been utilized to enhance the PL emission. TMDs such as single monolayer Molybdenum Disulfide (MoS 2 ) material has high exciton binding energy, which can facilitate strong exciton-plasmon interaction. The light emitted from MoS 2 structure is weak due to intervalley scattering in indirect-gap multilayer structures or due to relatively low absorption of direct-bandgap monolayer structure. Hybrid Ag-MoS 2 plasmonic structures were realized by nucleating silver film of optimum thickness into islands by nucleation on chemical vapor deposition (CVD) grown monoloyer MoS2 structure. The LSP energy of the system is centered at 2.33 eV, with the two exciton absorption peaks at 1.85 and 2.0 eV. The carrier dynamics studied by ultrafast time-resolved spectroscopy reveals HE mediated hybridization of exciton within 700 fs. The emisson energy at 1.83 eV can be tuned by the input power due to HE transfer from Ag to MoS 2 . A three-fold enhancement in the PL intensity has also been observed.