Origin of the n-type and p-type conductivity of MoS2 monolayers on a SiO2 substrate

Ab initio density functional theory calculations are performed to study the electronic properties of a MoS2 monolayer deposited over a SiO2 substrate in the presence of interface impurities and defects. When MoS2 is placed on a defect-free substrate, the oxide plays an insignificant role since the conduction band top and the valence band minimum of MoS2 are located approximately in the middle of the SiO2 band gap. However, if Na impurities and O dangling bonds are introduced at the SiO2 surface, these lead to localized states, which modulate the conductivity of the MoS2 monolayer from nto p-type. Our results show that the conductive properties of MoS2 deposited on SiO2 are mainly determined by the detailed structure of the MoS2/SiO2 interface, and suggest that doping the substrate can represent a viable strategy for engineering MoS2-based devices.