Study On The Photoluminescence And Modulation Of Excitons In Two-dimensional Transition Metal Dichalcogenides

Two-dimensional transition metal dichalcogenides(TMDs)have rich physical properties,including spin-valley coupling,quantum Hall effect,and good stability.When it is thinned from a bulk to a monolayer,it interacts strongly with light,and the generated excitons can exist stably at room temperature and re-emit after recombination.This photoluminescence(PL)phenomenon is widely used in the field of optoelectronics.It exhibits unique potential,and the ultrafast interconversion of excitons and light is expected to realize applications in optical communication,optoelectronic storage and other fields at room temperature.A variety of methods have been proposed for the regulation of excitons,including strong acid treatment,electrical doping,laser writing gate voltage,plasma doping,etc.This paper systematically studies the preparation of single-layer material devices,exciton fluorescence detection and regulation.The power and time of laser irradiation,combined with the electrical gate voltage,can realize the regulation of single-layer WSe₂ excitons,which provides a new idea for the regulation of excitons.The specific research contents and main conclusions are as follows:(1)Based on the existing platform in the laboratory,the preparation and optimization of the heterojunction were systematically explored,including the effect of dry transfer and annealing on the interfacial contact of the heterojunction based on PDMS,PC,etc.In order to characterize the contact difference of the prepared heterojunctions,a room temperature fluorescent light path was built to systematically study the fluorescence properties of the monolayer WSe₂/MoS₂ heterojunction.An interlayer exciton emission peak was formed in the region,and the peak was at 1.60 e V.The photoluminescence imaging of the heterojunction revealed the transport phenomenon of interlayer excitons.The transport distance is?5?m and the PL intensity decays exponentially with the excitation point distance.(2)Single-layer MoS₂ and WSe₂ optoelectronic devices were prepared and their electrical properties were characterized.The changes of the PL spectra of excitons in the layers with the back gate voltage and excitation light intensity were explored,and the changes of excitons and charged excitons and the PL spectra were discussed.By applying gate voltage,the concentration of excitons and charged excitons in the material can be changed to control the PL intensity,and the control range is?300%.At the same time,we prepared an hBN-wrapped WSe₂ structure,used 405 nm laser illumination to excite defect carriers in hBN,and explored the change of intralayer exciton fluorescence emission caused by the diffusion of defect carriers into the monolayer material.Laser irradiation increased the PL intensity by up to?600%.(3)The regulation of the write gate voltage on the PL spectrum of the WSe₂/hBN heterojunction was systematically studied,and the regulation of the exciton PL spectrum by different write gate voltage,write power and read power was studied.After writing,it can be stored in a dark environment for at least 300 s,and the one-way control range can reach one order of magnitude.Spectral storage.By changing the write gate voltage and read power to achieve different reading of the same signal,the different reading curves are clearly separable and can maintain a good linear relationship.P-N junctions can be formed in the irradiated and unirradiated regions by using the localized write gate voltage,and the PL intensity ratio of the junction region is?400%.