Topological insulator is a new kind of topological material. Its body state is an insulating state with band gap, while its surface state (or edge state) is a metal state without band gap and protected by topology.

Bi2Se3 is proposed to be a kind of three-dimensional topological insulator, and it is confirmed by angle resolved photoelectron spectroscopy that Bi2Se3 is a three-dimensional topological insulator with Dirac conical surface electronic structure. However, the chemical properties of this kind of materials are complex, and there are usually various crystal defects in the actual crystals, such as Se vacancy, Bi occupying se (or Te) to form anti-site defects, etc., which lead to the materials often show metal properties and seriously hinder the study of the surface states of topological insulators. Therefore, how to realize bulk insulating properties and detect surface state electrons has become an important research aspect of topological insulators. The research shows that the above phenomena can be avoided to a great extent by element substitution. At present, the bulk insulation topological insulator systems obtained by this method mainly include Bi2Te2Se, SnxBi1.1-xSb0.9Te2S, SnxBi1-xSbTeSe2 and TlxBi2Te3+y.