Enhancement Of Stability And Regulation Of Photoelectric Properties On Two-dimensional Semiconductor Material InSe

The discovery of graphene has led to the upsurge of research on two-dimensional semiconductor materials in the past decade.InSe is a member of the two-dimensional material family and has excellent optical and electrical properties.Its high intrinsic mobility(10³ cm²V^-1s^-1 at room temperature)and variable energy bandgap with the number of layers（1.26 eV-2.11eV）make it possess a huge application potential in infrared detection and other fields.However,the intrinsic thin layer（especially monolayer）InSe has a very weak PL response and easily oxidizes with oxygen and water in the atmosphere,placing irreparable damage on the material and thus greatly limiting its application.Therefore,an effective method to regulate the PL response of indium selenide and enhance its stability is crucial.In addition,vertically stacked heterojunctions from a variety of two-dimensional materials can be easily achieved and take full advantage of the properties of each two-dimensional material.Therefore,the research on two-dimensional material heterojunctions is also the current focus.In this paper,the optical properties of InSe were regulated and the stability of InSe was enhanced via self-built soft plasma treatment.We also fabricated InSe/graphene heterojunctions subsequently and studied the characteristics of electron transfer based on such structures.The main research work and results of the thesis are summarized as follows:1.The preparation methods of two-dimensional semiconductor materials and their heterostructures are introduced.The preparation process of indium selenide thin layers by mechanical exfoliation is described in detail.The as-prepared samples have high quality and few defects.The relationship between optical properties and the number of layers is characterized by both Raman spectroscopy and PL spectroscopy.2.The InSe thin layers were treated by mild oxygen plasma.By optimizing the experimental conditions,it has been found that oxygen treatment can produce a dense oxide layer on the InSe surface via AFM,optical microscopy and XPS measurements.The oxide layer can protect InSe from the destruction by oxygen and moisture,and thus improve the stability of InSe.The treated InSe can be completely preserved in the atmosphere for more than three weeks without performance degradation.3.Both the XPS and PL spectroscopy reveal that the oxygen atoms can replace Se atoms in the surface layer of InSe and bond with In atom,forming a ternary compound InSe_1-xO_x during the plasma treatment.Such compound can make the PL response shift from near infrared（1.25 eV）to visible range（2.15 eV）.In particular,the PL peak intensity of the 4 nm InSe sample reach maximum as 13 times larger as the original intensity at 8 minutes'treatment.4.We successfully prepare vertically stacked InSe/graphene heterostructures using dry transfer method.The top-layer graphene provides physical protection for InSe and improves its stability.Meanwhile,both the quenching of the InSe PL response and the transfer characteristics of the corresponding field effect transistor demonstrate that the electrons in InSe were transferred to graphene and thus make the latter doped.High-vacuum and low-temperature annealing experiments confirmed that such post annealing may increase the inter-layer coupling of heterojunction and promote the transfer of electrons.Furthermore,the heterojunctions composed of thin layer InSe are more sensitive to annealing.In summary,we enhance the stability of thin layer InSe via oxygen plasma treatment.The treated samples can be placed in the atmosphere for more than three weeks.In addition,the oxygen plasma treatment enhances the PL response of InSe in the visible light range.Finally,by means of fabricating InSe/graphene heterojunctions,and studying the electron transfer effect on such structures,we successfully regulate the opto-electronic properties of InSe in many ways,thus providing a brand new idea for the application of this material.