Research On Performance Control Of Photodetectors Based On Two-Dimensional Transition Metal Chalcogenide

Two-dimensional transition metal chalcogenides（TMDs）have moderate bandgap,high carrier mobility,and strong light-matter interactions,and photodetectors based on them have shown great application potential.Although a large number of high-performance photodetectors based on TMDs have been studied and reported,they still face several problems,such as low light absorption and carrier separation efficiency,mutual constraints among response speed,responsivity,and response wavelength.etc.,which greatly hinders their application.To solve the above problems,this paper performs a series of investigations on improving the performance of TMDs-based photoconductive and heterojunction optoelectronic devices.The main research contents and conclusions are as follows:1.The comprehensive performance of surface charge transfer-doped Re S₂photodetectors was improved by controlling the number of layers.F₄-TCNQ molecules are used to do p-type doping on the Re S₂ photodetectors with different layers.The relationship between the number of layers,doping effect and optoelectronic performance is revealed.According to this relationship,4 layers of Re S₂ are selected for doping,which can not only reduce the density of deep traps,but also form a vertical p-n junction.Thus,the response time and responsivity can be improved at the same time,the response time is 5s,and the responsivity is 5 A/W.2.A unilateral-depleted Mo S₂/WSe₂ heterojunction decorated with Pb S quantum dots was designed and fabricated.The n-type multilayer WSe₂ and Mo S₂ are used to construct a wide unilateral-depleted heterojunction to enhance the separation efficiency of carriers.Then,a photosensitive Pb S QDs layer was decorated the Mo S₂/WSe₂heterojunction to improve the light absorption efficiency of the device.Electrical measures confirmed the formation of a unilaterally depletion region,while spectroscopic and optoelectronic measures demonstrated that the photogenerated electrons transferred from Pb S QDs to the heterojunction contribute to the photocurrent.The device exhibits a broadband photovoltaic response from 405 to 1064 nm,with a maximum responsivity of 0.76 A/W,a specific detectivity of 5.15×10¹¹ Jones,and a-3d B cutoff frequency of over 10 k Hz.3.A photodetector with gain were fabricated by coupling Mo S₂/WSe₂heterojunction with graphene field-effect transistors（GFETs）.Mo S₂ was used as the gating layer of GFET.The photogenerated holes on Mo S₂ diffuse laterally under the excitation of light,and the holes diffuse to the bottom of the graphene,which induced the gating effect and thus photoresponse in GFET.Due to the ultrahigh mobility of graphene,the device got a high gain.Compared with the pristine Mo S₂/WSe₂heterojunction,the responsivity of the coupled device is improved by 2 to 3 orders of magnitude,and the highest value reaches 50 A/W.