Topological Surface State Regulation and Photoelectric Properties of Topological Insulator Bi2Se3
Author:Li Ming Ze
Supervisor:zhang zhi dong wang zhen hua
As the size of transistor in an integrated circuit continues to decrease,it is close to the physical limit of the silicon production process,and the heating problem becomes more and more serious,leading that the energy consumption from heating is close to half of the total energy consumption in the integration circum.How to reduce the collision and dispersion of electrons in materials used in the integrated circuit,the orderly high-speed operation of electrons to reduce energy consumption is an urgent problem in the field of spintronics.The topological surface states in topological insulator containing a linear energy dispersion relationship due to the strong spin-orbit coupling,which makes the surface state electrons have a spin momentum locking effect,so that the electrons in different spin directions move toward the opposite reverse direction without back dispersion effect.Electrons can achieve high-speed,energy-free transport.The topological insulator Bi2Se3 has the largest energy gap,and the simplest surface energy band structure in the second type of three-dimensional topological insulator,but it is easy to form intrinsic defects(antisite defect Bise,Se vacancy Vse)during the preparation process,so the electrical and optical transport processes are dominated by body electrons,resulting in surface state electrical and optical properties are not good.How to suppress the contribution of the bulk state effect and enhance the transport property of surface state electrons is the key direction we need to study.Based on these considerations,the regulating functions of element doping effects and geometry on the electrical and optical properties of the topological insulator Bi2Se3 are investigated.(1)It is proposed to use non-magnetic element Cu and magnetic element Cr doping as an effective mean to control the topological insulator Bi2Se3 surface state.The non-magnetic element Cu doping causes the temperature-dependent linear magnetoresistance behavior from the enhanced surface state in Bi2Se3.The magnetic element Cr doping causes the linear dispersion relation of the surface state to be broken and the temperature-independent parabolic magnetoresistance appears in Bi2Se3.Therefore the non-magnetic element Cu doping is an effective way to enhance the topological surface state and magnetic element Cr doping can break the topological surface state.And the transition from linear magnetoresistance to parabolic magnetoresistance is an effective criterion for the transition from a topological nontrival state to a trival state.In the study of the electrical transport properties of Cu-doped Bi2Se3,novel charge delocalization and relaxation behavior were also found and the mechanism of interaction was explored.(2)A new continuous film of a direction-controllable vertical nanoplate is proposed to control the surface state of the topological insulator Bi2Se3.This type of regulation differs from the usual way in enhancing the surface state by suppressing its bulk carrier concentration and adjusting its chemical potential.This innovation of structural design can achieve a high specific surface area of the film,and increase the proportion of the surface state in the film,thereby achieving surface state enhancement.(3)It is proposed to optimize the photoelectric performance of the topological insulator Bi2Se3 through chemical potential and geometric structure.A film with a high specific surface area can be realized by a vertically grown nanoplate structure,thereby having a high effective light absorbing area.And further suppressing the bulk carrier concentration by Cu doping can enhance the transport property of surface state electrons greatly.Therefore the regulation of chemistry potential and geometry can improve the performance of the topological insulator Bi2Se3 thin film photodetector.