Fermi level tuning and a large activation gap achieved in the   topological insulator Bi_{2}Te_{2}Se by Sn doping
  We report the effect of Sn doping on the transport properties of the topological insulator Bi_{2}Te_{2}Se studied in a series of Bi_{2-x}Sn_{x}Te_{2}Se crystals with 0 \leq x \leq 0.02. The undoped stoichiometric compound (x = 0) shows an n-type metallic behavior with its Fermi level pinned to the conduction band. In the doped compound, it is found that Sn acts as an acceptor and leads to a downshift of the Fermi level. For x \geq 0.004, the Fermi level is lowered into the bulk forbidden gap and the crystals present a resistivity considerably larger than 1 Ohmcm at low temperatures. In those crystals, the high-temperature transport properties are essentially governed by thermally-activated carriers whose activation energy is 95-125 meV, which probably signifies the formation of a Sn-related impurity band. In addition, the surface conductance directly obtained from the Shubnikov-de Haas oscillations indicates that a surface-dominated transport can be achieved in samples with several um thickness. 
Zhi Ren, A. A. Taskin, Satoshi Sasaki, Kouji Segawa, and Yoichi Ando
cond-mat.mtrl-sci