| Since the successful separation and characterization of graphene,material science has made significant breakthroughs in the field of two-dimensional layered materials research.This unique nanomaterial exhibits many unprecedented excellent properties,thus attracting widespread attention.Meanwhile,it has promoted the development of research on new two-dimensional layered materials,which have unique layered structures,outstanding optical,electrical,transmission characteristics,and significant stability,ensuring that they become potential candidates for high-performance electrons and photoelectrons.In addition to single-layer two-dimensional materials,the construction of two-dimensional van der Waals heterojunctions by integrating two or more two-dimensional materials together through different stacking methods has been studied theoretically and experimentally.The two-dimensional material heterojunction constructed in this way exhibits more novel physical and chemical properties compared to single-layer materials,such as high carrier mobility and perfect optical response.It can be widely used in the design of field-effect transistors,photodetectors,light-emitting diodes,and other optoelectronic devices.The band structure of the 2D materials plays a decisive role in its corresponding properties,such as photoelectric properties.Therefore,the main research content of this dissertation is to explore new 2D material heterojunction structures and their electronic properties,and combine different methods,such as strain engineering,to regulate the electronic properties of heterojunctions.Produce novel and interesting properties.Based on the density functional theory,we systematically studied the heterostructure of 2D materials under different conditions and its band structure evolution,optical properties,thermoelectric properties and interfacial charge transfer properties.The main research results obtained are as follows:1.The structure,electronic properties,and optical properties of MSe2/C3N（M=Mo and W）vd W heterostructures were studied.Research has shown that they are all indirect bandgap semiconductors with type II band alignment.Among them,the band gap of Mo Se2/C3N heterojunction is only 0.04 e V,while that of WSe2/C3N heterojunction is 0.26e V.A smaller bandgap means that electron transitions are easier.Through differential charge analysis,it is known that the flow direction of charges at the interface and the formation of a strong built-in electric field between the two heterojunctions can effectively prevent the recombination of charge carriers and prolong their lifespan.Use in-plane biaxial strain to tune band gaps and band edges.The results indicate that strain can significantly modulate the band structure and generate interesting electronic properties.By studying the optical properties of MSe2/C3N（M=Mo and W）vd W heterostructures,it was found that the optical properties of MSe2 and C3N monolayers and MSe2/C3N heterostructures exhibit anisotropy.The static dielectric constant of heterojunctions is often greater than that of isolated monolayers,indicating that the formation of heterojunctions helps to increase the static dielectric constant,thereby improving the polarization of the system.From the analysis of absorption spectra,heterojunctions have strong absorption of ultraviolet light in specific directions and energy ranges,and can be used to make optical storage devices,as well as ultraviolet light shielding or ultraviolet detector devices.2.We studied the structure,electronic properties,optical properties,and transport characteristics of Mo S2/Be2C heterojunction.And a detailed analysis was conducted on the changes in the density of states of the heterojunction structure and electronic properties under the application of in-plane biaxial strains and external electric fields,respectively.The research results indicate that the band alignment of the Mo S2/Be2C heterojunction is type II.The position of heterojunction CBM and VBM can be changed through strain engineering.For example,when the tensile strain increases to 4%,the band gap of the heterostructure decreases,and an indirect to direct band gap transition occurs.The compressive strain leads to a transition from type II to type III band alignment.When an external electric field is applied,the heterojunction can maintain type II band align-ment,but the band gap decreases and increases with the applied positive and negative electric fields.The results indicate that the electronic properties of the Mo S2/Be2C heterojunction can be regulated by biaxial strain and external electric field.The study of its optical properties also indicates that the heterojunction spectrum under consideration can be adjusted by applying tensile or compressive strain.The spectra obtained from the x-polarization direction represent the red and blue shifts of the spectra under strain and stress,respectively,while the reverse behavior of the spectra in the z-direction is similar to the results of existing Be2C monolayer studies.3.We studied the structure and electronic properties of Mo S2/Sc Cl3 heterojunction,as well as how its biaxial strain and external electric field affect the band gap,band align-ment,and optical properties of the heterojunction.Its structure shows an II type band alignment with an indirect bandgap of 1.55 e V.The electronic properties of hetero-structures can be effectively regulated through strains and external electric fields.As the compressive or tensile strain increases,the band gap decreases.A transition from type II band alignment to type I was observed during tensile strain.When a positive electric field is applied and the bandgap is maintained at about 1.55 e V,the type II heterostructure transitions to type I.But as the negative electric field increases and the bandgap decreases,the type II heterostructure can be retained.4.The dependence of interface properties on the number of layers in 1T’/2H Mo S2vd W heterojunctions was studied.The results indicate that 1T’-Mo S2 forms a p-type contact with 2H-Mo S2,while SBH is layer dependent.As the number of layers of 1T’-Mo S2 increases from 1L to 5L,SBH decreases from 30 me V to-75me V.This allows for adjusting SBH by selecting an appropriate number of layers.This work provides an important method for contact engineering and improves the performance of devices based on 2H-Mo S2. |
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