High-quality Sb2Te3 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 Sb2Te3 are identified to be the Sb vacancies and SbTe antisites in
agreement with first-principles calculations. By minimizing defect densities, coupled with a transfer
doping by the graphene substrate, the Fermi level of Sb2Te3 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.