Photoexcitations and optical response of carrier-doped monolayer transition metal dichalcogenides and heterostructures from first principles

The optoelectronic properties of 2D semiconductors are highly sensitive to the surrounding dielectric environment, a direct result of intrinsic weak and highly non-local dielectric screening. Less studied is the role of free carrier density on those properties. While the ab initio GW plus BSE approach is the state-of-the-art method for the accurate prediction of one and two particle excitations, respectively, the BSE is typically solved in the static limit, acceptable if the exciton binding energy is much smaller than the plasma frequency, but inadequate for systems with finite carrier density displaying acoustic carrier plasmon energies below or nearly resonant with the exciton binding energy. We develop a plasmon-pole model that captures dynamical screening associated with free carriers and local-field effects. We apply this approach to study the doping-dependence of the QP and optical properties of a monolayer MoTe₂ and of organic-TMD bilayer interfaces. For the former, we predict a QP band gap renormalization of several hundreds meV, and a similar decrease in the exciton binding energy. For the interface, we predict a transition from type-I to type-II interface and the emergence of new interlayer excitons, resulting from an interplay between charge carrier screening and substrate screening.