Simulation of the geometric and electronic structures and properties of extrinsic defects involving germanium in lead telluride

Cluster simulation of the bulk and surface of crystalline lead telluride has been performed in the framework of the hybrid density functional theory B3LYP method with the use of the LANL2 pseudopotential with the corresponding double-zeta basis set. Different variants of doping germanium atoms in a PbTe single crystal and at its surface have been examined. Clusters of different sizes have been considered. For the optimal cluster, containing 112 atoms, the state where a germanium atom occupies a cationic position is the most stable. Impurity atoms, as well as impurity atoms and vacancies, show a weak tendency for association. Formation of a singular surface is accompanied by differential relaxation. The charge state of germanium atoms in the bulk and at the surface is virtually the same and somewhat decreases upon association with vacancies.