1 Department of Physics and Astronomy, Science and Technology, Aarhus University2 Department of Chemistry, Science and Technology, Aarhus University3 iNano-School, Science and Technology, Aarhus University4 Department of Physics and Astronomy, Faculty of Science, Aarhus University, Aarhus University5 unknown6 Department of Physics and Astronomy, Science and Technology, Aarhus University7 Department of Chemistry, Science and Technology, Aarhus University
Angle-resolved photoelectron spectroscopy is used for a detailed study of the electronic structure of the topological insulator Bi2Se3. Nominally stoichiometric and calcium-doped samples were investigated. The pristine surface shows the topological surface state in the bulk band gap. As time passes, the Dirac point moves to higher binding energies, indicating an increasingly strong downward bending of the bands near the surface. This time-dependent band bending is related to a contamination of the surface and can be accelerated by intentionally exposing the surface to carbon monoxide and other species. For a sufficiently strong band bending, additional states appear at the Fermi level. These are interpreted as quantized conduction band states. For large band bendings, these states are found to undergo a strong Rashba splitting. The formation of quantum well states is also observed for the valence band states. Different interpretations of similar data are also discussed.
Semiconductor Science and Technology, 2012, Vol 27