Facile Two-Step van der Waals Epitaxial Growth of Bi2S3/ReS2 Heterostructure with Improved Saturable Absorption

2D van der Waals (vdW) heterostructure provides a novel platform to modulate linear and nonlinear optical (NLO) properties for optical devices by interface engineering. However, NLO properties and mechanisms based on vdW heterostructures are far from complete understanding. Herein, two-step vdW vapor epitaxial growth by either physical or chemical vapor deposition methods is successfully demonstrated to synthesize uniform Bi2S3/ReS2 vdW heterostructures in large area. Type-II band-alignment of these heterostructures is confirmed by X-ray photoelectron spectroscopy combined with the UV-Vis spectra. The enhanced NLO response of Bi2S3/ReS2 films is observed with high saturable absorption coefficient (approximate to-445 cm GW(-1)), large modulation depth (approximate to 10.5%), and low saturation intensity (approximate to 105 GW cm(-2)). Energy level model based on type-II charge transfer process is used successfully to understand the optical physics process at the interface of the vdW heterostructures. Constructing heterostructures with two-step vdW vapor epitaxial growth provides a new method to design high-performance nonlinear photonic devices with 2D materials.