First-principle Study On Regulation Of Surface And Interface Energy Band Of Topological Insulator Bi₂Te₃

Due to its peculiar surface and state spintronics properties,topological insulator has attracted great interest from researchers in related fields.The bulk of this kind of materials have the property of insulator,but its surface is metallic,and its topological surface state is not easy to be destroyed because it is protected by time inversion.Because of its special topological properties,topological insulator is of great research value in theoretical research and practical applications.For many years,researchers have devoted themselves to the research of finding materials with topological properties,preparation methods of such mateials and the control of electronic properties of such materials.Bi₂Te₃ is one of the most popular topological insulator materials,and the bulk of the material has a bandgap width which is much larger than that of room temperature,so Bi₂Te₃ can plays an important role in the application of quantum devices in the future.In the actual production and preparation process,intrisic defects in samples is inevitable.The intrinsic defects can be used as conducting carriers,and these defective carriers may obscure the transport properties of the surface states of the sample materials,resulting that the transport properties of the metallic surface of the material cannot be well utilized.In a large number of past studies,researchers have mostly focused on the influence of doping,applied electric field,magnetic field and stress field on the electronic properties of topological insulator Bi₂Te₃.In recent years,tuning of energy band of Bi₂Te₃ by surface state and interface has attracted much attention.The first principle calculations are used to study the regulation of surface state band structure of Bi₂Te₃,which can provide a theoretical basis for designing the spintronic properties of nano-scale topological insulator materials.In this paper,the first-principles method based on density functional theory is adopted to theoretically explore the related properties of topological insulators and their band tuning,and the following main research results are obtained:1.Energy band structure,density of state of Bi₂Te₃ bulk,s orbital and p orbital of Bi atom and Te atom are calculated respectively with and without SOC effect by first principle method.The results show that when SOC effect is not taken into account,the calculated electronic properties of Bi₂Te₃ bulk are quite different from the experimental results.The electronic properties of Bi₂Te₃ calculated with SOC are in good agreement with the experimental values.Therefore,SOC effect is taken into account in the subsequent calculation of surface states of Bi₂Te₃.We calculate the electronic properties of Bi₂Te₃ film surface eigenstates of 1QL-6QL respectively,and the results are in good agreement with the experimental results and relevant theoretical calculations.2.Bi₂Te₃ thin film of topological insulator grown on GaAs substrate is calculated by first principles method and SOC effect is considered.The results show that the coupling state between interface state and surface state can be obtained.Regulating the film thickness parameters of growing Bi₂Te₃,The results show that when the thickness of Bi₂Te₃ film is less than 3QL,the Fermi energy level of the intrinsic surface of Bi₂Te₃ thin film is below Dirac point,which is p-type.When the thickness of Bi₂Te₃ thin film is greater than or equal to 3QL,the Fermi level of the intrinsic surface state of Bi₂Te₃ thin film can be regulated to Dirac point.3.The spintronics properties of Bi₂Te₃ and MoS₂ two-dimensional laminated structures are studied by first principles method,and SOC effect is also considered.At the same time,the thickness parameter of Bi₂Te₃ is changed to regulate the electronic properties of the structutes.The results show that when the thickness of Bi₂Te₃ thin film is just 3QL,the Fenni level of the intrinsic surface state of Bi₂Te₃ thin film can be adjusted to Dirac point.When the thickness of Bi₂Te₃ film is less than 3QL（when it is 2QL）,the intrinsic surface state of Bi₂Te₃ film is n-type.When the thickness of Bi₂Te₃ film is greater than 3QL（4QL）,the intrinsic surface state of Bi₂Te₃ film is p-type.