Doping and Defect Structure of Tetradymite-Type Crystals

Nonstoichiometry of tetradymite-type crystals A (2) (V) B (3) (VI) that are grown from stoichiometric melts leads to the formation of native defects in the crystal lattice (predominantly antisite defects, A (B) (-1) and vacancies V (B) (+2) in the anion sublattice). This paper summarizes the basic ideas concerning a point defect model in A (2) (V) B (3) (VI) crystals. It turns out that a variety of doping elements interact with the native defects. Such interactions alter the concentration of free charge carriers, affect the doping efficiency, and modify the transport properties. Detailed understanding of the defect structure in tetradymite-type crystals is very important as it impacts on the efficiency of these materials when used as active elements in thermoelectric coolers.