Defect-mediated transport and electronic irradiation effect in individual domains of CVD-grown monolayer MoS₂

The authors study the electrical transport properties of atomically thin individual crystalline grains of MoS₂ with four-probe scanning tunneling microscopy. The monolayer MoS₂ domains are synthesized by chemical vapor deposition on SiO₂/Si substrate. Temperature dependent measurements on conductance and mobility show that transport is dominated by an electron charge trapping and thermal release process with very low carrier density and mobility. The effects of electronic irradiation are examined by exposing the film to electron beam in the scanning electron microscope in an ultrahigh vacuum environment. The irradiation process is found to significantly affect the mobility and the carrier density of the material, with the conductance showing a peculiar time-dependent relaxation behavior. It is suggested that the presence of defects in active MoS₂ layer and dielectric layer create charge trapping sites, and a multiple trapping and thermal release process dictates the transport and mobility characteristics. The electron beam irradiation promotes the formation of defects and impact the electrical properties of MoS₂. Our study reveals the important roles of defects and the electron beam irradiation effects in the electronic properties of atomic layers of MoS₂.