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 Moessbauer 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 Moessbauer 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