Study On The Spectrocopic And Optoelectronic Properties Of Two-Dimensional Transition Metal Dichalcogenide And Their Heterostructures

As emerging two-dimensional layered semiconductor materials,transition metal chalcogenide compounds（abbreviated as TMDs）have high carrier mobility and adjustable bandgap,which show important application prospects in optoelectronic devices.With the continuous development of science and technology,people have higher requirements for the performance of photodetectors.A single TMDs material cannot meet the requirements of fast response and high sensitivity in optoelectronic devices at the same time.This requires us to constantly innovate and propose novel structures and concepts to solve the difficulties and challenges encountered in the application of TMDs in optoelectronic devices.TMDs heterojunction refers to two or more layers of man-made materials maintained by van der Waals forces that are formed by stacking different TMDs.These two-dimensional heterostrutures have show novel and interesting physical properties.At the same time,the van der Waals heterojunction based on two-dimensional materials has a sharply defined interface,which opens up a new way of regulating the electronic and optical properties of materials at the atomic level.It also enables the develepment of a series of ultra-thin,high-performance,flexible electronic and optoelectronic devices,including field effect transistors,wearable electronics,photodetectors,solar cells,and light emitting diodes（LEDs）.The purpose of this thesis is to study the Raman,photoluminescence（PL）spectroscopy of TMDs and their heterostructures,and photodetectors based on heterostructures.It is also shown that the coupling interactions of heterostructures can be enhanced by means of laser irradiation to achieve devices with improved performance.Following are the main achievements:1.One to four layers of TMDs were prepared by mechanical exfoliation.The number of layers of TMDs was determined by means of optical contrast and Raman spectroscopy.The change of Raman and PL spectra with the number of layers was analyzed,which provides useful information for the selection of appropriate TMDs materials fpr the preparation of heterojunctions.2.A vertical heterojunction based on stacking of WS₂,WSe₂,MoS₂,and MoTe₂ materials was designed and prepared.The difference in the Raman and PL spectra of the junction regions and non-junction regions is analyzed and the mechanisms are discussed.3.The effects of laser irradiation on the optical and electrical properties of WS₂/MoTe₂ heterojunction were studied.It was found that the laser irradiation can enhance the interaction and charge transfer between the two materials and lead to a significant increase in the photo detection performance of heterojunction.