Thallium dopant in lead chalcogenides: investigation methods and peculiarities

The body of experimental and theoretical data on transport phenomena, optical absorption, low-temperature heat capacity, tunnelling spectroscopy, magnetic susceptibility, superconductivity, and self-compensation are summarized for thallium-doped lead chalcogenides PbM (M = Te, Se, S) and PbM-based solid solutions. The physical properties of the semiconducting compounds are explained in a unified manner using the concept of resonance Tl states located in the valence band of the compound. The basic parameters of resonance impurity states are estimated and their dependences on temperature, pressure, and material composition are determined.