Investigation of Bi2Te3 doping with elements from VIII B column of Periodic Table

Abstract

Previous studies have demonstrated that the fabricated topological insulators (TIs) are always heavily doped by intrinsic defects, vacancies and antisites. These defects pin the Fermi level to the bulk band edges and make it difficult to characterize the transport properties of topological states. Bi2Te3 behaves as an n-type semiconductor due to these defects and the Dirac point is buried deep below the EF. Thus, Fermi level tuning has become a technologically important issue in TI research. Single crystal samples with the nominal composition Bi2-xMxTe3 (M = Fe, Ru, Os, x = 0, 0.02, 0.04, 0.06) were grown by heating stoichiometric mixtures of elements followed by cooling in a horizontal furnace from 1073 K to 823 K at a rate of 6 K per hour. The crystal was subsequently annealed at 823 K for 350 h and quenched in air. Samples were examined with X-ray Diffraction and Electron Spectroscopy for Chemical Analysis. Electronic structure of samples was measured with k-space microscope via equienergetic cuts through the first Brillouin zone (BZ). The images were taken in the binding energy interval (+1, -2) eV. Electronic states in the vicinity of gap with an aspect of the Fermi edge location in the bulk were theoretically mapped using ab initio VASP code. The calculations were done by including relaxation, spin-orbit interaction and with the doped atoms in the substitutional (Bi) or interstitial positions.