Architectures And Characterization Of Topological Insulator Sb₂Te₃ And Semiconductor Heterostructure

Topological insulator is a kind of special material which is insulator but has the metal conductive surface state.And the surface state originates from its own internal strong spin-orbit coupling,which is composed of electrons that have spin polarization of massless Dirac type.That's why the topological insulator has the novel topological quantum property of time reversal symmetry protection.At present,in the topological insulator and semiconductor heterostructure,it has been proved that by using its topological property the non-trivial edge channel on the heterointerface can be created.And combining the semiconductor technology and the excellent layered performance of topological insulator,the properties of traditional semiconductor materials will be obviously improved and the surface state of topological insulator will be maintained.Then the new type spin or optoelectronic devices will be constructed and provide new platform for the continued innovation and prosperity of traditional semiconductors.However,the current research on the architecture of the heterogeneous topological insulator is more concentrated in the superconductor and ferromagnet,and the research of semiconductor heterostructures just starts,only with a few systems grown and developed.What's more,in the structure which has been constructed,its chemical characteristics and physical mechanism has not been thoroughly studied,so there is still a long way to practical application.Therefore,this work still needs further investment and exploration,so as to exert its great potential.The preparation technology of topological insulator and semiconductor heterojunction can make use of molecular beam epitaxy,which can precisely control the thin film growth,and then the exploration and research of heterojunction interface properties can be realized.In the face of the current situation of topological insulator and semiconductor heterostructure,this paper constructed Sb₂Te₃/Ge,Sb₂Te₃/Si and Sb₂Te₃/ZnTe heterojunction,which provide important help for the realization of topological insulator heterojunction applications in spin and optoelectronic devices,the main results are as follows:?1?Sb₂Te₃/Ge heterojunction are successfully grown on the GaAs?001?substrate by molecular beam epitaxy method.Compared with the samples that obtained under different conditions,the growth condition was optimized.The morphology of the sample is very uniform and the crystalline is high because of the layered characteristics of topological insulator.The cross-section HR-TEM shows the crystal symmetry and the sharp interface of the two materials.The Raman reflection confirms that the thin film has a strong characteristic peak consistent with the bulk material.The XPS test shows that Sb₂Te₃ has no chemical shift on the heterogeneous surface,which indicates that the metal surface of Sb₂Te₃ is retained.What's more,the results of Ge band bending also reflect that the Fermi level pinning effect can not be occured by inserting the topological insulator between Ge and ferromagnetic metal.The valence band and conduction band offset at the Sb₂Te₃/Ge heterojunction interface are 0.25 0.1 eV and 0.07 0.11 eV.The arrangement of the energy level is different from that of the common gate dielectric layer and the junction formed by Ge,which can support the further study of the transmission characteristics.Because topological insulator has a similar crystal structure and van der Waals layered characteristics to Sb₂Te₃,the results presented in this chapter can provide a reference for other topological insulator integrated with Ge spin application.?2?We have used van der Waals epitaxial growth of Sb₂Te₃ on the Si substrate.The surface reconstruction of Si is a method to solve the problem of mismatch between two dimensional materials and three-dimensional substrates.The characterization of epitaxial Sb₂Te₃ thin films shows that they have good quality.Through XPS and UPS characterization we can find that the topological surface of Sb₂Te₃ thin film isn't destroyed because of the existence of a large number of dangling bonds on the surface of the Si.However,the energy level distribution on the Sb₂Te₃/Si heterojunction interface shows that the heterojunction is a Type-II type heterostructure,which can provide additional carrier transport freedom,and can be used to design optical and electrical devices.Because of the strong built-in electric field at the interface of Sb₂Te₃/Si,the formation mechanism of the photocurrent is changed.In the experiment,it is confirmed that there is a significant light response under illumination.This structure is based on the Si-basis semiconductor,which greatly increases the possibility of the application of this type of high-performance optoelectronic devices.?3?Combined with the second chapter,in order to solve the problem of too large dark current in Sb₂Te₃/Si heterojunction,we introduce the ZnTe barrier layer in the Sb₂Te₃/Si heterojunction.According to the growth characteristics of ZnTe,the ZnTe epitaxial layer with Zn and Te terminated surface was obtained by changing the growth temperature on the surface of Si substrate.The epitaxial growth of Sb₂Te₃ on different termination surfaces of ZnTe shows that the ZnTe epitaxial layer plays an important role in inhibiting the effect of the Si dangling bonds.And the Sb₂Te₃ films show better morphology and crystallinity.By comparing the optical and electrical properties of Sb₂Te₃ heterostructures on different termination surfaces,it is found that the interfacial properties of Sb₂Te₃ and ZnTe dominate the performance.High temperature growth of Te?2 x 1?surface of the ZnTe epitaxial layer can effectively improve the dark carrier transport constraints,so as to effectively enhance the photoelectric properties of the heterostructure.This chapter grew the topological insulator Sb₂Te₃ and semiconductor ZnTe interface implements 2D single carrier transmission channel,the special properties will provide new ideas for the realization of topological insulator based optoelectronic devices with high performance.