Doping properties of Pb and Ge in Bi2Te2 and Sb2Te3

The electrical conductivity ó and the Seebeck coefficient S of p-Bi2 Te2 and Sb2 Te3 are measured vertically to the trigonal c-axis in dependence on the Pb or Ge contents determined by spectro-graphic analysis. The solubility limit is determined to 0.3 atyo Pb in Bi2 Te2 and to 1 at% Pb or Ge in Sb2 Te3. The doping properties of Pb and Ge in Sb2 Te3 can be described also quantitatively by incorporation into the Sb lattice sites. Contrary to Sb2 Te3 in Bi2 Te2 Pb is electrically inactive incorporated within a concentration interval of 0.04 to 0.24 atyo. Taking into consideration the production of acceptors in the electrically active concentration range the doping behaviour of Pb in Bi2 Te2 can be interpreted as incorporation of Pb into three energetically different lattice sites corresponding to their chemical bonds. These results corroborate a description of S and ó in terms of a single valence band model and particularly for p-Bi2 Te3 interms of a parabolic band model and predominant acoustical lattice scattering.