Synthesis Of Wafer-Scale Two-Dimensional WTe₂ Thin Films And Investigation Of Their Infrared Photodetector Propertiess

In recent years,two-dimensional materials have made major breakthroughs in material types,synthesis methods and practical applications.Among them,two-dimensional transition metal dichalcogenides（TMDs）,as an important part of two-dimensional materials,have more unique advantages while inheriting many advantages of two-dimensional materials,and are suitable for building high-performance photodetectors.Among the numerous two-dimensional TMDs,the emerging layered two-dimensional semimetal TMDs not only have the advantages of wide band and ultrafast response speed brought by no bandgap and extraordinary optoelectronic properties,but also have linear electronic dispersion and ultrathin layered structure,which can enhance the generation of photo-generated carriers and improve the quantum efficiency and responsivity of photodetection.Therefore,two-dimensional layered semimetal TMDs are ideal materials for constructing high-performance fast-response broadband infrared photodetectors.Although two-dimensional semimetallic TMDs hold great promise in infrared photodetectors,photodetectors based on them are still limited by several factors.First,the difficulty of large-area fabrication of the material greatly affects its application in integrated photodetection;second,the ultra-thin nature leads to its weak light absorption;third,an unbiased operating mode is required to reduce the dark current;fourth,the transient lifetime of excitons in semimetallic materials is very short,which exacerbates the problem of carrier separation.In response to the above problems,we have studied infrared photodetectors in terms of material preparation and device construction.In terms of materials,we investigate the infrared-sensitive semi-metal tungsten ditelluride（WTe₂）in two-dimensional TMDs and design a reproducible synthesis process for wafer-scale WTe₂ thin films.In terms of devices,a two-dimensional/three-dimensional（2D/3D）mixed-dimensional van der Waals heterojunction was constructed to realize high-performance broadband infrared photodetection at room temperature.The main research contents and results of this paper are as follows:（1）Wafer-scale high-quality two-dimensional WTe₂ films were synthesized by van der Waals growth method.The synthesized films were characterized and analyzed by high-resolution transmission electron microscopy（HR-TEM）,X-ray diffractometer（XRD）,Raman spectroscopy（Raman）and other characterization methods.（2）A graphene（Gr）/WTe₂/Si 2D/3D mixed-dimensional van der Waals heterojunction infrared photodetector was constructed.Under 0 V bias and 980 nm illumination,the device exhibits a current switching ratio of up to 10⁶,responsivity of497.2 m A/W,external quantum efficiency of 62.9%,and specific detectivity of3.1×10¹² Jones.It has microsecond-level response speed,nanosecond-level tracking capability for short-pulse optical signals,and ultra-broadband detection capability from 265 nm to 10.6μm.In addition,it has a room-temperature specific detectivity of over 10⁸ Jones in the mid-and long-wave infrared region.Meanwhile,it has a good single-pixel room temperature 10.6μm infrared imaging capability.On this basis,a WTe₂/Si 8×8 array device was constructed,which shows good device performance uniformity and excellent room temperature mid-and long-wave infrared imaging capabilities.（3）A WTe₂/Ge 2D/3D mixed-dimensional van der Waals heterojunction infrared photodetector was constructed.Under 0 V bias,the detector has a current on-off ratio greater than 10⁴ at 1550 nm,a responsivity of 1.06 A/W,and an external quantum efficiency of 84.5%.And it has the detection ability of ultra-broadband,and can detect optical signals rapidly and stably in the 3.0μm,4.6μm,and 10.6μm wavebands.