Study On Heterojunction Photodetectors Based On Two-dimensional MoS₂ And WS₂ Films

High-performance broadband photodetectors have extremely important application value in military and civilian fields such as remote infrared light detection,night vision,remote sensing,optical communication,security inspection,etc.,therefore photodetectors are widely studied.So far,high-performance infrared photodetection with different device structures based on silicon?Si?,gallium arsenide?GaAs?,indium gallium arsenide?In GaAs?,and mercury cadmium telluride?Hg Cd Te?has been developed.However,these photodetectors currently have obvious shortcomings,such as toxicity of heavy metals,complex and expensive manufacturing processes,low-temperature working conditions,high energy consumption,etc.,which seriously hinder their further widespread application.With the increasing demand for high-performance infrared photodetectors in various fields,there is an urgent need to suppress the dark current of the photodetector,improve the photoresponse,and greatly reduce the size,weight,and power consumption of the infrared detector and price to improve device performance from the perspective of materials and device structures about photodetectors.To meet the above requirements,we must look for new infrared detection materials or new device structures.Recently,two-dimensional nanomaterials with unique optical and electrical characteristics provide a new platform for the development of advanced optoelectronic devices.Among them,two-dimensional transition metal chalcogenides?TMDs?have a wide adjustable band gap,high carrier mobility and excellent chemical stability,and are ideal materials for constructing photodetectors.At the same time,the weaker light absorption characteristics of ultra-thin two-dimensional materials lead to poorer detection performance.Constructing a 2D/3D mixed dimension van der Waals heterojunction device is one of the strategies to effectively improve the device performance.Due to two-dimensional layered materials does not rely on the characteristics of lattice matching,we can build van der Waals heterostructures with other materials.Combined with the advantages of two-dimensional layered materials and other materials,this heterojunction can improve the absorption efficiency of incident light.At same time,the built-in electric field in the heterojunction can accelerate the separation of photogenerated electron-hole pairs.These heterojunction are used to manufacture new high-performance photodetectors.In order to achieve high-performance infrared detection,in this study,we selected two-dimensional MoS₂ and WS₂ thin films and three-dimensional GaAs semiconductor to construct a 2D/3D mixed-dimensional vd W heterojunction infrared photodetector.The main research results are as follows:First of all,we successfully synthesized large-area two-dimensional MoS₂ and WS₂thin films in a tube furnace by thermal decomposition,and characterized these two 2D materials by X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,atomic force microscopy?AFM?,Raman spectroscopy,scanning electron microscopy?SEM?,for the crystal structure and composition,morphology,thickness,etc.The results show that we successfully prepared high-quality two-dimensional MoS₂ and WS₂ thin films.Secondly,a self-driven infrared photodetector of MoS₂/GaAs 2D/3D mixed dimension van der Waals heterojunction was prepared.The prepared MoS₂/GaAs heterojunction photodetector exhibits a wide spectral response from deep ultraviolet?DUV?to near infrared?NIR?,with a responsivity of 35.2 m A/W and a specific detectivity of up to 1.96×10¹³ Jones,and the response speed of 3.4/15.6?s.Thirdly,we successfully prepared WS₂/GaAs type-II van der Waals heterojunction self-driven broadband photodetector.The photodetector has a significant photoresponse in a wide band spectrum from 200 nm to 1550 nm.At zero bias,the device has a dark current as low as 59.7 p A.Under the illumination of the 808 nm near-infrared light,the device exhibits responsivity of up to 527 m A/W,an ultra-high minimum detection light intensity of 17 n W/cm² and the external quantum efficiency up to 80%.While the device has a cut-off frequency of 3 d B up to 10 k Hz and a response speed of 21.8/49.6?s.The device also exhibits excellent near-infrared imaging capabilities.It can be used as an infrared image sensor with excellent imaging capabilities.