Origin of then-type andp-type conductivity of MoS2monolayers on a SiO2substrate

Ab initio density functional theory calculations are performed to study the electronic properties of a MoS${}_{2}$ monolayer deposited over a SiO${}_{2}$ substrate in the presence of interface impurities and defects. When MoS${}_{2}$ is placed on a defect-free substrate, the oxide plays an insignificant role since the conduction band top and the valence band minimum of MoS${}_{2}$ are located approximately in the middle of the SiO${}_{2}$ band gap. However, if Na impurities and O dangling bonds are introduced at the SiO${}_{2}$ surface, these lead to localized states, which modulate the conductivity of the MoS${}_{2}$ monolayer from $n$- to $p$-type. Our results show that the conductive properties of MoS${}_{2}$ deposited on SiO${}_{2}$ are mainly determined by the detailed structure of the MoS${}_{2}$/SiO${}_{2}$ interface, and suggest that doping the substrate can represent a viable strategy for engineering MoS${}_{2}$-based devices.