Thickness-dependent excitonic properties of WSe2/FePS3 van der Waals heterostructures

Abstract

van der Waals heterostructures (vdWHs), with their flexible combination of various two-dimensional (2D) materials, are continuously revealing new physics and functionalities. 2D magnetic materials have recently become a focus due to their fascinating electronic and spintronic properties. However, there has rarely been any investigation of the optical properties of 2D magnetic materials-based heterostructures. Herein, we construct a new WSe₂/FePS₃ heterostructure, in which WSe₂ works as a “sensor” to visualize the thickness-dependent properties of FePS₃. As characterized by photoluminescence (PL) spectra, whether under or on top of the FePS₃, the PL intensity of the monolayer WSe₂ is strongly quenched. The quenching effect becomes more obvious as the FePS₃ thickness increases. This is because of the efficient charge transfer process occurring at the WSe₂/FePS₃ interface with type II band alignment, which is faster for thicker FePS₃, as is evident from transient absorption measurements. The thickness-dependent charge transfer process and corresponding excitonic properties are further revealed in low-temperature photoluminescence spectra of WSe₂/FePS₃ heterostructures. Our results show that the thickness of 2D magnetic materials can work as an experimental tuning knob to manipulate the optical performance of conventional 2D semiconductors, endowing van der Waals heterostructures with more unexpected properties and functionalities.