Study On Gold Nanoparticle Enhanced Performance Of Two-dimensional WS₂ Photodetector

The discovery of graphene has aroused researchers'interest in van der Waals layered materials.,Semiconductor transition metal chalcogenides(TMDC)belong to van der Waals layered material.Because of its excellent electrical and optical properties,such as high carrier mobility,suitable band gap,strong light material interaction,large absorption coefficient and large exciton interaction,etc.These characteristics make it possible to fabricate high performance optoelectronic devices.As one of the most promising optoelectronic devices,photodetectors are widely used in optical imaging,communication,biomedicine and other fields.The layered tungsten disulfide with atomic thickness has good flexibility and transparency,which makes it possible to prepare flexible photodetectors.in this paper,tungsten disulfide film is used as the core material,and the interface modification of gold nanoparticles is used to improve the performance of photoconductive detector.Here I will introduce my paper's main contents.(1)exploring The best growth window of tungsten disulfide film,including the effects of temperature,flow rate,the distance from substrate to tungsten trioxide source and time point of heating sulfur powder,through controlling variable method to study the growth quality of tungsten disulfide film.The experimental result shows that the best window for the growth of tungsten disulfide thin films in the tube furnace with single temperature zone is that,Heating temperature of sulfur powder is 170?,Heating temperature of tungsten trioxide source is 950?,Distance between substrate and tungsten trioxide source is 16.5cm,When the temperature of WO3 reaches 700?,the sulfur powder is heated,The flow rate of argon is 40sccm and that of hydrogen is 4sccm.(2)Fabrication of single-layer tungsten disulfide/gold nanoparticles composite photodetector.based on wet transfer method transfers Large area Au particles to WS₂ film with lossless.witch can support to make single-layer tungsten disulfide/gold nanoparticles composite photodetector.The test result shows that Au nanoparticles can reduce the dark state current of single-layer WS₂detector,increase the switching ratio and normalized detection rate,but the photocurrent decreases in a certain extent.The main reason is that the work function of WS₂ is smaller than that of Au,and Schottky barrier is formed at the contact between WS₂ and Au.Au nanoparticles are randomly distributed on the single WS₂ film,which is equivalent to the existence of a randomly distributed potential barrier on the single WS₂ film.The electron motion on the WS₂film is scattered by the randomly distributed potential barrier,which leads to the decrease of the effective mobility and the dark state current.Under illumination,due to the existence of Au nanoparticles,the local surface plasmon effect is produced,the optical absorption near Au nanoparticles is enhanced,and the photogenerated electron density is greatly enhanced.The photocurrent is proportional to the carrier concentration and mobility.The increase of electron density can't fully compensate the decrease of carrier mobility,so the photocurrent decreases to a certain extent(3)Fabrication of multilayer tungsten disulfide/gold nanoparticles composite photodetectors.The results show that the gold nanoparticles can reduce the dark current of the multilayer tungsten disulfide detector,At the same time,the responsivity,switching ratio and normalized detective of the device can be increased.The reason for the performance improvement is that the Schottky barrier formed by Au nanoparticles and multilayer WS₂ has a strong influence on the WS₂ layer near the Au particles,but it weakens away from the Au particles,so the electron mobility decreases little.At the same time,the light absorption of multilayer WS₂ becomes more and more,which can absorb more light and produce more photo generated carriers under the local field enhancement effect of plasmon.Therefore,compared with multilayer WS₂ without Au,the performance of multilayer WS₂ with Au nanoparticles is improved.(4)Finite difference time domain(FDTD)was used to simulate Au nanoparticles and WS₂ film.The simulation results show that the introduction of Au nanoparticles can form plasmons,,witch can enhance local electric field,and then the absorption of WS2 to light is increased...