Research Of Fabrication And Properties Based On Graphene/TMDC Photoconductive Devices

Graphene has attracted much attention for its unique physical and chemical properties since its discovery.For example,high mobility,wide electromagnetic absorption spectrum,good conductivity and transparency,these excellent physical properties make graphene widely used in infrared photodetectors and high-frequency devices,and graphene can also be used in transparent conductive materials.However,the zero band gap structure and low light absorption?only 2.3%?make the graphene photodetector low responsivity.Another two-dimensional?2D?transition metal dichalcogenides?TMDC?,which is complementary to graphene,has an layer-dependent band-gap?1.06-2.88 eV?,strong light-matter interactions,and higher light absorption than graphene,and has become another research hotspot after graphene.TMDC has unique structure.There are no hanging bonds on the surface of the material,covalent bonds within the molecule and van der Waals force between layers.so the assembly of two-dimensional material heterostructures is of great significance for improving the performance of photodetectors.In this paper,the graphene and TMDC?MoS₂?WS₂?heterostructures photoconductive devices are mainly studied.The main contents of this paper are as follows:Firstly,the transfer technology of two-dimensional materials is studied.High-quality transfer is the key to fabricate two-dimensional material heterostructures and their applications in flexible devices.The transfer of graphene mainly uses PMMA wet transfer.Since the thin atomic layer and its strong flexibility of graphene,wrinkles and cracks are prone to occur during the transfer process.Therefore the hydrophilic treatment of target substrate,graphene back etching,etc.have been tried.By characterizing the surface of the transferred films,it is determined that the graphene prepared by us has a single layer structure,and the surface is relatively clean and could be transferred in a large area.At the same time,rosin transfer is attempted.After transfer,the surface impurities of graphene are less,but the transfer area is smaller.Similarly,we take the MoS₂ film as an example.The transfer of MoS₂ is slightly different from that of graphene.Polystyrene?PS?is mainly used as the support layer.The transfer process is similar to that of graphene.The characterization results show that the surface of MoS₂ is homogeneous and three-layer structure.Secondly,the electrical properties of graphene and MoS₂ after transfer are analyzed.Graphene and MoS₂ field effect transistors are constructed to study the electrical properties of the two materials.In the process of pattern array preparation,graphene pattern is mainly written by laser direct lithography,while MoS₂ pattern is mainly written by mask lithography.The advantage of laser direct writing lithography is that it can accurately fabricate specific electrodes shape in specific positions of two-dimensional materials,and the cost is low.Mask lithography is faster and simpler than laser direct writing,but the graphics are limited by mask graphics and the cost of production is high.Through the electrical analysis of the two materials,we obtain that the carrier mobility of monolayer graphene is 1765 cm²/?V·s?and that of three-layer MoS₂ is 5.2 cm²/?V·s?.I_on/I_off is 10³.Finally,metal/Graphene/MoS₂ heterostructures photoconductive detectors are fabricated by transfer process,and their photoelectric properties are tested.That graphene contacts with metal electrodes is typical Ohmic contact.The responsivity of devices under650 nm laser is 10.2 A/W,but the response time is slow,its rise time is about 60 s,the decay time is about 50 s..The device has obvious negative photoconductivity and its response mechanism is explained.At the same time,the system of spectral responsivity test has been improved.