Quantum-Confined Stark Effect in a MoS₂ Monolayer van der Waals Heterostructure

The optics of dangling-bond-free van der Waals heterostructures containing transition metal dichalcogenides are dominated by excitons. A crucial property of a confined exciton is the quantum confined Stark effect (QCSE). Here, such a heterostructure is used to probe the QCSE by applying a uniform vertical electric field across a molybdenum disulfide (MoS₂) monolayer. The photoluminescence emission energies of the neutral and charged excitons shift quadratically with the applied electric field, provided that the electron density remains constant, demonstrating that the exciton can be polarized. Stark shifts corresponding to about half the homogeneous linewidth were achieved. Neutral and charged exciton polarizabilities of (7.8 ± 1.0) × 10^-10 and (6.4 ± 0.9) × 10^-10 D m V^-1 at relatively low electron density (∼10¹² cm^-2) have been extracted, respectively. These values are one order of magnitude lower than the previously reported values but in line with theoretical calculations. The methodology presented here is versatile and can be applied to other semiconducting layered materials.