Effects of Intrinsic Defects and Substrate Transfer Doping on the Electronic Structure of Sb_2Te_3 Thin Films on Graphene

摘要

We study how the electronic structure of the Sb_2Te_3 thin films on graphene changes with intrinsic defects and substrate transfer doping using first-principles calculations. We find that for freestanding Sb_2Te_3 thin films without defects band gap decreases with increasing film thickness, and that the behavior of three-dimensional topological insulators does not appear up to seven quintuple layers. The orbital degeneracy is broken by defects and substrate transfer doping, leading to the Rashba effect and a reduced band gap. By decreasing the defect ratio of Sb vacancies (V_(Sb)) as the primary source of p-type conductivity and increasing that of Te-on-Sb antisites (Te_(Sb)) as the primary source of n-type conductivity, coupled with a transfer doping using a graphene substrate, the energy band of Sb_2Te_3 thin films can be tuned from the p-type to the n-type. Differences in the local defects of Sb_2Te_3 can result in variations in the work function and intrinsic defects have a stronger effect on the work function than the graphene substrate.