Electrically motivated atomic migration and defect formation in Bi0.5Sb1.5Te3 compounds

Current-induced Ag migration behavior and defect formation mechanism in p-type Bi0.5Sb1.5Te3 (BST) compounds are investigated. By applying an electric current of 170 A/cm2 through a hot-pressed BST at 150 °C with one side attached to a thin Ag foil, Ag2Te secondary phases precipitate first in the BST and decompose subsequently after extended current stressing time. Ag elements migrate in BST toward the cathode side with a D⋅Z* product of 8 × 10−7 cm2/s, where D and Z* are diffusivity and electromigration effective charge number of Ag in BST, respectively. The van der Waals gap between two neighboring Te layers is identified to be the major path for Ag electromigration. Electrically motivated Ag atoms take Sb lattice sites eventually by forming AgSb acceptor defects in BST. The electrical resistivity of current-stressed BST was lowered by one order of magnitude as a result of greatly increased carrier concentration. The study demonstrates a route of adjusting electrical properties of BST compounds through the current-induced doping process.