Investigation On The Fabrication And Photoelectric Properties Of Two-Dimensional Materials/Semimetal Nanoparticles Composite Structures

Two-dimensional materials have been favored by researchers in recent years due to their excellent optoelectronic properties.Photodetectors are an important application of two-dimensional materials in the direction of optoelectronic devices,and are widely used in the fields of remote sensing,thermal imaging,and guidance.The development of fast and highly sensitive photodetectors with broadband response is of great scientific significance and application value.Due to the inherent performance defects of 2D materials,photodetectors based on a single 2D material have encountered difficulties in achieving highly sensitive detection or fast response.In order to address the above problems and develop novel photodetectors,the construction of semi-metallic nanoparticles/two-dimensional material composite structures has become a feasible solution.The plasmon effect brought by the introduction of semi-metallic nanoparticles can enhance the interaction between matter and light,and thus improve the light absorption capacity of the device.Hot electrons generated in plasmonic nanostructures can avoid processes such as defect state confinement in the photoelectric conversion process,and are expected to speed up photoelectric conversion.In addition,the resonance absorption may break the limitation of the traditional semiconductor band gap on photodetection to broaden the working band.In view of this,based on the research experience of the research group in plasma,a H₂plasma-assisted fabrication process was developed to prepare semi-metallic nanoparticles/two-dimensional material composite photodetectors.First,WO_x（x<3）plasmonic nanostructures with obvious light absorption effect were fabricated by mask deposition and subsequent H₂plasma treatment.In addition,four kinds of WO_x/2D material composite photodetectors were constructed,and their properties were studied and analyzed.Finally,the top Mo S₂ layer was doped by NH₃ plasma to further enhance the performance of the WO_x/Mo S₂ photodetector.The main research contents of the thesis are as follows:1.A H₂ plasma-assisted technology that can produce WO_x semi-metallic nanoparticles was developed to achieve controllable preparation of plasmonic nanostructures with strong light absorption.The particle morphology and composition variation during the plasma treatment were systematically studied.The reaction equation as well as the morphology and composition variation models of the WO₃ nanoparticles treated by H₂ plasma were proposed.The theoretical analysis results and the actual measured light absorption can be mutually verified.2.Two kinds of WO_x/2D material composite structures were proposed,and two kinds of WO_2.4/graphene photodetectors were constructed by adjusting the fabrication process.Both detectors show excellent light detection capabilities in the following aspects:the responsivity in the visible light region is 770 times more than that of pure graphene;both have the detection capability for low-power lasers,and the minimum response power reaches 141 n W;both can work under the near-infrared laser of 940 nm that graphene cannot detect;the response speed of both reaches 20 ms.3.The composite structure was successfully applied to Mo S₂,and two kinds of WO_2.4/Mo S₂ photodetectors were fabricated.The devices have higher responsivity and detectivity than the WO_2.4/graphene photodetectors.The highest responsivity reaches 1612 A/W.It also has the ability to detect n W-level weak light and near-infrared detection.In addition,the response time of the devices is only 1/4 of that of the pristine Mo S₂ one.Experiments on graphene and Mo S₂ show that the composite structure has the potential to achieve high sensitivity and fast broad-spectrum detection,and has the universality of being applied to a variety of materials.4.The composite structure device was modified by NH₃ plasma.As a result,the free electron concentration in Mo S₂ was increased by n-type doping induced by such NH₃ plasma treatment.This further improved the detection performance of the devices.The optimization of the photodetector performance relies on three aspects:research on plasmonic structure,surface modification of two-dimensional materials,and design of composite structures.This work may provide a new method for the development of novel and high-performance photodetectors.