Energy formation of antisite defects in doped Sb2Te3 and Bi2Te3 crystals

The free carrier concentration of the Sb2−xInxTe3, Bi2−xInxTe3 and Bi2Te3−xSx crystals has been determined from the values of the Hall constants and the free carrier concentration of the Sb2−xTlxTe3 has been calculated from the plasma resonance frequency; with increasing value of x, the hole concentration decreases. As the incorporation of the elements In, Tl and S into the lattice Sb2Te3 or Bi2Te3, respectively, gives rise to the uncharged defects InxSb, TlxSb, InxBi and SxTe, the x causes the decrease of the antisite defects concentration. The proven effect is explained in the following way: the antisite defects can be created only in crystals whose atoms are bound by weakly polarized bonds. The incorporation of In, Tl and S atoms into the crystal lattice of Sb2Te3 or Bi2Te3 increases the bond polarity, the ionicity of ternary crystals increases. This unfavorably affects the increase of antisite defects whose concentration decreases. The change of the bond polarity is considered from the changes discovered in the formation energy of antisite defects of the above mentioned ternary crystals.