Phys. Status Solidi B 2000021 (2020)
The observation of helical surface states in Bi‐based 3D topological insulators (TIs) has been a challenge since their theoretical prediction. The main issue arises when the Fermi level shifts deep into the bulk conduction band due to unintentional doping. This results in the metallic conduction of the bulk which dominates the transport measurements and hinders the probing of the surface states in these experiments. Here, various strategies are investigated to reduce the residual doping in Bi‐based TIs. Flakes of Bi₂Se₃ and Bi_1.5Sb_0.5Te_1.7Se_1.3 are grown by physical vapor deposition and their structural and electronic properties are compared with mechanically exfoliated flakes. Using Raman spectroscopy, the role of the substrate in this process is explored, and the optimal conditions for the fabrication of high‐quality crystals are presented. Despite this improvement, it is shown that the vapor phase‐deposited flakes still suffer from structural disorder which leads to the residual n‐type doping of the bulk. Using magneto‐transport measurements, we find that exfoliated flakes show better electrical properties and are thus more promising for the probing of surface states.