Observations of two-dimensional quantum oscillations and ambipolar   transport in the topological insulator Bi2Se3 achieved by Cd doping
  We present a defect-engineering strategy to optimize the transport properties of the topological insulator Bi2Se3 to show a high bulk resistivity and clear quantum oscillations. Starting with a p-type Bi2Se3 obtained by combining Cd doping and a Se-rich crystal-growth condition, we were able to observe a p-to-n-type conversion upon gradually increasing the Se vacancies by post annealing. With the optimal annealing condition where a high level of compensation is achieved, the resistivity exceeds 0.5 Ohmcm at 1.8 K and we observed two-dimensional Shubnikov-de Haas oscillations composed of multiple frequencies in magnetic fields below 14 T. 
Zhi Ren, A. A. Taskin, Satoshi Sasaki, Kouji Segawa, Yoichi Ando
cond-mat.mtrl-sci