An ab initio investigation of Bi₂Se₃ topological insulator deposited on amorphous SiO₂

We use first-principles simulations to investigate the topological properties of Bi₂Se₃ thin films deposited on amorphous SiO₂, Bi₂Se₃/a-SiO₂, which is a promising substrate for topological insulator (TI) based device applications. The Bi₂Se₃ films are bonded to a-SiO₂ mediated by van der Waals interactions. Upon interaction with the substrate, the Bi₂Se₃ topological surface and interface states remain present, however the degeneracy between the Dirac-like cones is broken. The energy separation between the two Dirac-like cones increases with the number of Bi₂Se₃ quintuple layers (QLs) deposited on the substrate. Such a degeneracy breaking is caused by (i) charge transfer from the TI to the substrate and charge redistribution along the Bi₂Se₃ QLs, and (ii) by deformation of the QL in contact with the a-SiO₂ substrate. We also investigate the role played by oxygen vacancies (${\text{V}}_{\text{O}}$) on the a-SiO₂, which increases the energy splitting between the two Dirac-like cones. Finally, by mapping the electronic structure of Bi₂Se₃/a-SiO₂, we found that the a-SiO₂ surface states, even upon the presence of ${\text{V}}_{\text{O}}$, play a minor role on gating the electronic transport properties of Bi₂Se₃. (paper)