Tuning the Fermi level in Bi2Se3 bulk materials and transport devices

Bi2Se3 has been predicted to be a three-dimensional (3D) topological insulator (TI) with Dirac fermions residing on the two-dimensional (2D) surface. Unique transport properties such as high carrier mobility due to the suppressed backscattering are expected for the Dirac fermions. In order to eliminate the contribution of the bulk carriers, therefore, to place the Fermi level in the band gap of Bi2Se3, we first introduce various amounts of Ca dopants into the crystal to realize the bulk insulating state. Then by avoiding uncontrolled heating and electron beam irradiation in the nanofabrication process, we maintain the insulating state in thin devices. By sweeping the gate voltage, we have observed a conductivity minimum that is expected for the Dirac fermions in the band gap of 3D TIs.