Binding energy of the hybrid exciton in heterostructures of colloidal CdSe-ZnS quantum dots and two-dimensional transition metal dichalcogenides

Using continuum model calculations within the framework of the $\mathbit{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbit{p}$ approach and effective mass approximation, we theoretically study the physical properties of the hybrid exciton state in type-II heterostructures composed of two-dimensional monolayer transition metal dichalcogenides (2D TMDs) and zero-dimensional (0D) CdSe-ZnS core-shell quantum dots (QDs). Interactions between an electron located in the lowest unoccupied molecule orbital (LUMO) state of the QD and a hole in the valence band of the 2D TMD along with their effects on charge distribution and exciton binding energy are self-consistently calculated via solving the Schr\"odinger and Poisson equations. We show that (i) the hole wave function of the 2D TMD is tightly bounded within several unit cells by an electron located in the LUMO state of the QD while the distribution of the electron wave function is marginally changed by the Coulomb attraction from the hole in the 2D TMD; (ii) the binding energies of the hybrid exciton decrease from 110 to 25 meV with the radius of the CdSe core increasing from 2 to 8 nm, which is several times lower than that of the exciton of 2D TMDs; and (iii) the exciton binding energies of heterostructures composed by different 2D TMD materials are similar. We explain the size dependence of exciton binding energy as the result of the delocalization of the electron wave function with QD size and attribute the similar binding energy obtained in different 2D/0D heterostructures to the weak dielectric screening effect of different 2D TMDs on electron-hole interaction. These results indicate that the physical properties of a hybrid exciton in 2D/0D heterostructures is dominated by the properties of the QD instead of the 2D TMDs. We further compare our calculated exciton binding energy with the corresponding experimental result; good agreement between experiment and theory provides evidence for the validity of our theoretical approach.