Fermi-level tuning of the Dirac surface state in (Bi 1-x Sb x ) 2 Se 3 thin films

We report on the electronic states and the transport properties of three-dimensional topological insulator (Bi Sb ) Se ternary alloy thin films grown on an isostructural Bi Se 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 Sb ) Se 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 Sb ) Se -based heterostructures provide a platform for extracting exotic topological phenomena.