Two-electron germanium centers with a negative correlation energy in lead chalcogenides

It is shown that the charge state of the ⁷³Ge antisite defect that arises in anionic sublattices of PbS, PbSe, and PbTe after radioactive transformation of ⁷³As does not depend on the position of the Fermi level, whereas the ⁷³Ge center in cationic sublattices of PbS and PbSe represents a two-electron donor with the negative correlation energy: the Mössbauer spectrum for the n-type samples corresponds to the neutral state of the donor center (Ge²⁺), while this spectrum corresponds to the doubly ionized state (Ge⁴⁺) of the center in the p-type samples. In partially compensated PbSe samples, a fast electron exchange between the neutral and ionized donor centers is realized. It is shown by the method of Mössbauer spectroscopy for the ¹¹⁹Sn isotope that the germanium-related energy levels are located higher than the levels formed in the band gap of these semiconductors by the impurity tin atoms.