Tuning Interfacial Excitonic Binding in Twisted Two-Dimensional MoS2 Bilayers

Two-dimensional (2D) layered molybdenum disulfide (MoS2) has attracted much attention due to its outstanding intrinsic properties and diverse applications. Defects and heterostructures usually play an important role in tailoring the various properties of MoS2 based 2D materials. And strong excitonic effect due to the quantum confinement in 2D MoS2 may be responsible for large variation of electric and optical properties. Here, we propose to study the excitonic effect in 2D MoS2 monolayer, bilayer and various MoS2/2D heterostructures including possible defect species using first-principles calculations. The defect energy level, fundamental band gap, optical gap, exciton binding energy and exciton charge density will be determined to investigate how the electronic structure and optical response correlate with the atomic structure disorder including defects and stacking orders in MoS2 layers and MoS2/2D heterostructures. We will employ a first-principles method for large scale calculations of electronic excitations in solids based on density functional theory with optimally tuned and range-separated hybrid functional, which has been proven to successfully reproduce one-particle energy levels and two-particle excitations from the state-of-the-art GW plus Bethe-Salpeter equation calculations in many solids. Our systematic investigation of the excitonic defect in MoS2 will further deepen our understanding of this novel 2D atomically thin semiconductor and pave the way for manipulating the electronic and optical properties of 2D MoS2 based materials through defect and heterstructure engineering to further improve and extend their applications in catalysis, electronics and optoelectronics.