Research Of Van Der Waals Heterostructure Photodetectors Based On Two-dimensional WSe₂

As an important part of sensors,photodetectors play a crucial role in military and defense,aerospace,image sensing,and optical communication.Two-dimensional transition metal dichalcogenides are a class of two-dimensional materials with semiconducting properties,whose band gaps can be changed with their decreasing layers.And the light-matter interaction gets stronger when their thickness is getting smaller.Tungsten diselenide(WSe₂)is a member of transition metal dichalcogenides.It is a good way to integrate WSe₂ and MoS₂ to fabricate the van der Waals(vd Ws)heterostructure due to the dangling bond-free surface and the weak vd Ws interaction.This work focuses on the high Schottky barrier in the electrode contact interfaces which impairs the photodetection ability of WSe₂/MoS₂ heterostructure and the weak light absorption of two-dimensional materials.The WSe₂ and MoS₂ flakes were exfoliated to construct vd Ws heterostructure.Several characterization methods were employed to explore the impact of the electrode contact interfaces and the surface plasmon resonance effect on the structure of the device and optoelectronic properties of the WSe₂/MoS₂ heterostructure.First,for the high Schottky barriers in the electrode contact interfaces,the vd Ws electrodes were employed to eliminate the pinning effect and reduce the Schottky barriers.In this work,the effect of different electrodes on the photoresponse of WSe₂/MoS₂heterostructure was investigated and the method of optimizing the optoelectronic properties of WSe₂/MoS₂ heterostructure by employing the graphene/ITO hybrid electrodes was proposed.The results showed that the WSe₂/MoS₂ heterostructure with hybrid electrodes had the high responsivity of 1236.5 A W^-1,detectivity of 1.23×10¹³Jones,the fast photoresponse of 270/130?s,and a wide detection range from 405 nm to980 nm.Compared to those heterostructures with sputtered electrodes,the WSe₂/MoS₂heterostructure with hybrid electrodes had the vd Ws contact feature,the graphene layer with high carrier mobility and the ITO layer which had a low work function difference to graphene.Therefore,the damage to the surface of heterostructure during the sputtering process was avoided and hence the transportation of photogenerated carriers in the heterostructure/electrode interface was optimized.Next,in order to improve the absorption of TMDs based heterostructure,the localized surface plasmon resonance(LSPR)was introduced to the surface of the WSe₂/MoS₂ heterostructure.The simulation result based on the finite-element method showed that the localized surface plasmon resonance was induced in Au nanoparticles under the incident light,which enhanced the electric field at the interface between the Au nanoparticles and the heterostructure thus improving the light absorption capacity of the heterostructure.Consequently,the microstructure of Au nanoparticles(Au NPs)was fabricated on the surface of WSe₂/MoS₂heterostructure via the dropping and annealing process,which improves the light absorption of heterostructure as the excited LSPR effect in the Au NPs under the illumination.The results show that the responsivity of WSe₂/MoS₂ heterostructure with200 nm Au NPs increased from 0.08 A W^-1 to 1.8 A W^-1.The heterostructure achieved enhanced photoresponse.Therefore,the vd Ws heterostructure based on tungsten diselenides via local modification is potential for high-performance photodetectors and has great prospects for next-generation electrical and optoelectrical devices.