Two-dimensional Heterostructure Based Photodetectors

Graphene has been demonstrated to be an appealing alternative to traditional semiconductors because of its excellent optoelectrical properties and successful applications in diverse fields,especially in photodetection.Graphene photodetectors can convert a broad spectrum of light?ultraviolet[UV]to terahertz[THz]?into electrical signals,and this range is unmatched by any photodetector based on traditional semiconductors.However,the low responsivity intrinsic to graphene photodetectors is a potential drawback,because graphene lacks a bandgap and has a low optical absorption??2.3%?.This paper is mainly about the graphene-black phosphorus heterojunction,molybdenum disulfide-tungsten disulfide heterojunction and graphene-molybdenum carbide heterojunction photodetector.By using the heterostructure devices,we can realize the broadband detection,high responsivity and so on.Broadband graphene-black phosphorus heterostructure photodetector with high responsivitywe demonstrate a graphene-BP heterostructure photodetector with ultrahigh responsivity and long-term stability at telecom wavelengths.In our device architecture,a top layer of graphene functions not only as an encapsulation layer but also as a highly efficient transport layer.Under illumination,photoexcited electron-hole pairs generated in BP are separated and injected into graphene,significantly reducing the Schottky barrier between BP and the metal electrodes and leading to efficient photocurrent extraction.The graphene-BP heterostructure phototransistor exhibits a long-term photoresponse at a telecommunications wavelength?1550 nm?with an ultrahigh photoresponsivity(up to 3.3×10^-3 AW^-1),photoconductive gain?up to 1.13×109?and a rise time of about 4 ms.Considering the thickness-dependent bandgap in BP,this material represents a powerful photodetection platform able to sustain high performance in the infrared?IR?wavelength regime with potential applications in optical communication.WS₂-MoS₂ vertical heterostructure photodetector based on CVD methodWe demonstrate scalable production of periodic patterns of few-layer WS₂,MoS₂ and their vertical heterojunction arrays by thermal reduction sulfurization process.In this method,a two-step chemical vapor deposition approach was developed to effectively prevent the phase mixing of TMDs in unpredicted manner,thus affording a well-defined interface between WS₂ and MoS₂ in vertical dimension.As a result,large scale,periodic arrays of few-layer WS₂,MoS₂ and their vertical heterojunctions can be produced with desired size and density.Photodetectors based on the as-produced MoS₂/WS₂ vertical heterojunction arrays were fabricated and a high photoresponsivity of 2.3 AW^-1,at excitation wavelength of 450 nm was demonstrated.Flexible photodetector devices using MoS₂/WS₂ heterojunction arrays were also demonstrated with reasonable signal/noise ratio.Graphene-Mo2C heterostructure photodetectorTransition metal carbides is a family that combining the properties of metal and ceramic materials,which has a superior performance and application.High quality transition metal carbides is indispensable for two-dimension photodetector.In order to solve the problem of low responsivity of pure graphene device,we built a heterostructure by using graphene and molybdenum carbide.Molybdenum carbide has superconducting properties,thus the graphene-Mo2C photodetector can have a high responsivity,and also can realized from visible to near infrared detection.