Abstract
The epitaxial Bi2Te3 topological insulator (TI) thin films grown on sapphire (0001) by molecular beam epitaxy (MBE) were studied by using X-ray photoemission spectroscopy (XPS) and synchrotron radiation angle-resolved photoemission spectroscopy (ARPES). The Bi2Te3 films, grown at fixed substrate temperature with the different Te/Bi flux ratio for each samples, and used the XPS to calculate the chemical composition ratio. And sharp metallic states and Dirac cone were also observed by ARPES. Interestingly, we also observed that the doping level in Bi2Te3 films can be fine turned by varying the Te : Bi composition ratio systematically to form either p- or n-type films. The electronic properties of bulk Bi2Te3 crystals are usually dominated by electron donors, resulting in n-type conductivity. When the donors dominate, the Dirac point is buried deep below the Fermi level, which makes it difficult to characterize the topological transport properties and to develop topological devices that rely on the behavior of surface Dirac fermions. To compensate for the unintentional donors, a high-concentration of extrinsic dopants, for example, more than 0.67% Sn [13] or 1% Cd, [14] has been introduced into Bi2Te3. And the intrinsic doping is the other way, in principle, we can tuning the density of the anti-site defect by controlling the growth condition. The anti-site defect controlled by tuning the substrate temperature had been successfully demonstrated. In this work we tried another way to generate the anti-site defect, the variation of growth flux ratio(Te/Bi ratio) was tried to generate the atomic anti-site defect, and got the amount control.