Effects of confinement and environment on the electronic structure and exciton binding energy of MoS2 from first principles

Using GW first-principles calculations for few-layer and bulk MoS2, we study the effects of quantum confinement on the electronic structure of this layered material. By solving the Bethe-Salpeter equation, we also evaluate the exciton energy in these systems. Our results are in excellent agreement with the available experimental data. Exciton binding energy is found to dramatically increase from 0.1 eV in the bulk to 1.1 eV in the monolayer. The fundamental band gap increases as well, so that the optical transition energies remain nearly constant. We also demonstrate that environments with different dielectric constants have a profound effect on the electronic structure of the monolayer. Our results can be used for engineering the electronic properties of MoS2 and other transition-metal dichalcogenides and may explain the experimentally observed variations in the mobility of monolayer MoS2.