Twist angle dependent high degree of anisotropic emission and phonon scattering in WS2/NbOCl2 heterostructures

Abstract

van der Waals (vdWs) heterostructures provide a superior platform to combine different low-dimensional materials together to tune their physical properties for different types of applications. Specifically, anisotropic heterostructures possess polarization-sensitive optical and electronic properties, which are highly needed in novel optoelectronic devices. However, the achieved degree of polarization (DOP) for the previously investigated heterostructure is relatively low and the induced polarization mechanism and key factors determining the DOP are still unclear. Here, we successfully fabricated an anisotropic TMDC/NbOCl₂ heterostructure to break the rotation symmetry of WS₂. Taking advantage of the strong anisotropy in NbOCl₂, we achieved a high DOP of Raman scattering (0.813) and photoluminescence emission (0.801). Furthermore, we demonstrated that this anisotropy is also valid for bilayer WS₂ with indirect exciton emissions. Twist angle is demonstrated to be an effective approach for further tuning the DOP. Density functional theory calculations reveal that increasing the coupling is twist angle dependent, leading to a twist angle-dependent DOP in the NbOCl₂/TMDC heterostructure. Moreover, heterostructure formation also reduces intervalley scattering, leading to the observed valley polarization of WS₂ at room temperature. Based on these findings, we proposed a conceptual framework to search for vdWs heterostructures with a high DOP. These findings are of critical importance in designing highly efficient anisotropic quantum emitters and optoelectronic devices using vdWs heterostructures.