Fermi-level tuning of the Dirac surface state in (Bi_1−xSb_x)₂Se₃ thin films

We report on the electronic states and the transport properties of three-dimensional topological insulator (Bi_1−xSb_x)₂Se₃ ternary alloy thin films grown on an isostructural Bi₂Se₃ buffer layer on InP substrates. By angle-resolved photoemission spectroscopy, we clearly detected Dirac surface states with a large bulk band gap of 0.2–0.3 eV in the (Bi_1−xSb_x)₂Se₃ film with x  =  0.70. In addition, we observed by Hall effect measurements that the dominant charge carrier converts from electron (n-type) to hole (p-type) at around x  =  0.7, indicating that the Fermi level can be controlled across the Dirac point. Indeed, the carrier transport was shown to be governed by Dirac surface state in 0.63  ⩽  x  ⩽  0.75. These features suggest that Fermi-level tunable (Bi_1−xSb_x)₂Se₃-based heterostructures provide a platform for extracting exotic topological phenomena. (paper)