Photoelectronic Performance Of Two-dimensional WS₂/MoS₂ Vertical Heterostructures

The two-dimensional?2D?atomically thin-layered semiconductor material has a unique electronic structure and quantum confinement effect,and the weak van der Waals?vdW?interaction between the layers makes it possible not only to be directly exfoliated,but also to be reassembled arbitrarily according to our needs without considering the constraints of lattice matching.2D vdW heterostructures constructed by integrating two or more 2D materials together can create extra functions compared with one-component materials,meantime;render us a high freedom degree in structural design due to the plenty of species.Particularly,the large family of 2D TMDs with rich bandgap provides a broad platform for the development of new material properties and the multifunctional integration of micro-nano electronic devices.Many novel physical properties or phenomena caused by interlayer coupling of 2D vdW heterostructures,especially for the discovery of some universal rules,have become the focus of research.On the basis of previous literature research,this thesis takes the most common WS₂/MoS₂ heterostructures as the research object,and studies some new properties or new applications in the optical or optoelectronic field caused by the interlayer coupling of the heterojunction.The main research contents are as follows:Based on the few layers WS₂/MoS₂ heterostructures prepared by mechanical exfoliation and target-transfer techniques,we studied,for the first time,the infrared detection performance of this system.Due to the limitation of the intrinsic band gap,the single WS₂ and MoS₂ do not have the infrared?1030 nm?response.However,after forming the heterostructure,strong interlayer of the Type II heterojunction coupling shrinks the energy interval in the heterojunction area,rendering heterostructures longer wavelength detection ability compared to individual components.In addition,to improve the weak light absorption of indirect band gap materials in heterojunctions,Au NPs pattern,prepared by anodic aluminum oxide?AAO?template evaporation method,were transferred onto the device surface.With the surface plasmon resonance?SPR?effect,infrared?1030 nm?responsibility of heterostructures is enhanced by 25 times,while maintaining a high response speed.This interlayer coupling induced infrared light detection and SPR enhancement strategy provides a new design idea for the research of high performance infrared light detectors.Secondly,we fabricated WS₂/MoS₂ bilayer heterostructures by mechanical transfer based on CVD-grown monolayer MoS₂ and WS₂,and then using second harmonic generation?SHG?as probe,studied gate voltage induced changes of interlayer stacking mode,as well as electronic structure and even phase.The structure is closely related to the properties,and the stacking mode plays an important role in the interlayer coupling strength of the heterojunction.Especially for the mechanical transfer heterostructures,the stacking order is usually deviated from the ideal state,existing interlayer twisting,translation,or spacing,which would significantly influence interlayer coupling strength and physical properties of heterojunction.The SHG signal can sensitively reflect the symmetry,orientation of the crystal and stacking order of the heterojunction.Therefore,we are going to detect the stacking order by using SHG as a probe,and tune gate voltage to modulate the stacking order,electronic structure and coupling strength of the heterojunction,which will be of great significance to the future study of heterojunction.