Unraveling Structural and Optical Properties of Two-Dimensional MoxW1–xS2 Alloys

Abstract

Ordered defects in two-dimensional (2D) transition-metal dichalcogenides (TMDs) could function as single-photon emitters and quantum-dot qubits in quantum information technologies. Alloying is a commonly used method to introduce such ordered defects in TMDs. However, the structural, vibrational, optical, and excitonic properties of the ordered defects in TMDs remain poorly understood. In this work, we provide a comprehensive study of 2D MoxW1–xS2 alloys from first principles. We found that defect stripes can be formed in MoxW1–xS2 alloys with the lowest energy configuration at x ∼ 0.5. We identify a unique Raman fingerprint for the striped defect configurations. Both defect quantum dots and striped defects in MoxW1–xS2 are shown to trap excitons. The optical gap of the MoxW1–xS2 alloys redshifts as the Mo content increases, but the excitons remain strongly bound. We predict that excitons at the lateral heterostructure of WS2 and MoS2 are delocalized with a strong charge-transfer character.