MoS2 two-dimensional quantum dots with weak lateral quantum confinement: Intense exciton and trion photoluminescence

MoS2 two-dimensional quantum dots (2D-QDs) are one of the novel 2D materials. In this work, MoS2 2D-QDs were grown on SiO2/Si by chemical vapor deposition and their exciton and trion photoluminescence were studied in comparison to MoS2 flakes. The 2D-QDs have a round-like shape with the average lateral size of 40 nm and tri-layer structure. Both the structures show two photoluminescence bands associated to A and B excitons, but the reduction of lateral dimension in 2D-QDs causes a recognized emission blueshift attributed to the quantum confinement. At the same time, the A exciton band of 2D-QDs is asymmetric, being overlapped with the trion band. We supposed that nano-dimensioned lateral sizes create quantum confinement conditions when all the excited electrons are also weakly localized in the plane of 2D-QD and much more effectively bind with holes as an additional electron of trion. It should be emphasized that 2D-QD has emission efficiency 6 times higher compared to that from the flake, that also can be explained by the charge carrier localization. These new findings offer potential applications of 2D-QDs in nano-devices operating at room temperatures involving multicolor engineering and efficient modulation of optical properties by controlling the QD lateral sizes and thickness.