The Preparation And Characterization Of Bi₂Se₃ Topological Insulator Film And The Measurement Of Its Electrical Transport Properties

As a new type of quantum functional materials, topological insulator (TI) has insulating states in bulk and metallic states in surface. The spins of electrons in these surface states are tightly locked to their momentums due to the strong spin-orbit, and thus backscattering in the Dirac fermions by nonmagnetic impurities is prohibited due to the protection by time-reversal symmetry. TI thin films, a new group of two-dimensional (2D) crystals, can be employed to study some unique phenomenon, such as vicinity interactions in surfaces or interfaces and have potential applications in nano electronics, spintronics, and photoelectronics.Due to having layered structures bonded together by Van Der Waals interactions and relatively large bulk band gap, the TI Bi2Se3 thin films have attracted more attentions in physics, materials sciences, and nano electronics. In this work, Bi2Se3 thin films, Mn-doped Bi2Se3 thin films, and their heterostructure thin films have been grown on sapphire substrates by molecular beam epitaxy (MBE) method, and the investigations on these thin films have been carried out as followings:Firstly, the appropriate substrate temperatures and flux ratios are crucial to prepare high-quality thin films, which are important for all studies. In this work, the Bi2Se3 thin films are prepared by changing the substrate temperatures and the flux ratios, respectively. The optimized growth conditions of substrate temperatures of 390 ℃ and flux ratio of 10:1 between Se and Bi have been obtained by analyzing the RHEED, XRD, AFM, and EDS. Secondly, the electrical qualities of Bi2Se3 and Mn-doped Bi2Se3 thin films have comparatively been investigated.In this section, the Bi2Se3 and Mn-doped Bi2Se3 thin films have been grown at the substrate temperatures of 390℃ and at the flux ratio of 10:1 between Se and Bi sources. The influences of Mn doping on crystal parameters, magnetic resistances, and Hall resistances have been investigated. The results indicate that Bi2Se3 samples are n-type TI thin films.Lastly, the heterostructures of Bi2Se3 and Mn-doped Bi2Se3 thin films have been prepared and the the substrate effects on the electronic structures and electrical qualities have been studied.