NONSTOICHIOMETRY OF THE CRYSTAL-LATTICE OF ANTIMONY TELLURIDE

A single crystal of antimony telluride, grown from elements of semiconductor purity by means of the Bridgman method, is characterised by the departure from stoichiometry as determined from energy dispersive X-ray spectroscopy, by the concentration of free charge carriers p as obtained from the interpretation of the reflectivity spectra in the plasma resonance frequency range, by its density d, and by lattice parameters a and c. The investigated crystal of stoichiometry Sb2Te2.948 has the following values: p = 6.714 x 10(19) cm(-3), d = (6.50 +/- 0.01) g cm(-3), a = 0.42643(5) nm, c = 3.0427(4) nm. The departure from stoichiometry is explained using a model taking into account the existence of antisite Sb'(TE) defects as well as tellurium and antimony vacancies in the crystal lattice: this model in connection with the experimental data allows us to calculate the concentration of Sb'(Te), defects and to determine their formation energy E(AS) = (0.32 +/- 0.01) eV.