Energy formation of antisite defects in doped Sb 2Te 3 and Bi 2Te 3 crystals

Abstract

The free carrier concentration of the Sb 2−xIn xTe 3, Bi 2−xIn xTe 3 and Bi 2Te 3−xS x crystals has been determined from the values of the Hall constants and the free carrier concentration of the Sb 2−xTl xTe 3 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 Sb 2Te 3 or Bi 2Te 3, respectively, gives rise to the uncharged defects In x Sb, Tl x Sb, In x Bi and S x Te, 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 Sb 2Te 3 or Bi 2Te 3 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.