Fermi-level tuning of epitaxial Sb ₂Te ₃ thin films on graphene by regulating intrinsic defects and substrate transfer doping

High-quality Sb ₂Te ₃ films are obtained by molecular beam epitaxy on a graphene substrate and investigated by in situ scanning tunneling microscopy and spectroscopy. Intrinsic defects responsible for the natural p-type conductivity of Sb ₂Te ₃ are identified to be the Sb vacancies and Sb _Te antisites in agreement with first-principles calculations. By minimizing defect densities, coupled with a transfer doping by the graphene substrate, the Fermi level of Sb ₂Te ₃ thin films can be tuned over the entire range of the bulk band gap. This establishes the necessary condition to explore topological insulator behaviors near the Dirac point.