Mössbauer emission spectroscopy at 73As(73Ge) was used to show that the charge state of the 73Ge antisite defect formed in the anion sub-lattice after the radioactive transformation of 73As was independent of the position of the Fermi level. In contrast, the 73Ge center in the cation sub-lattice of PbSe was an electrically active substitutional impurity. For the n-type samples, the spectrum corresponds to the neutral state of the donor center (73Ge2+), and for the p-type samples, the spectrum corresponds to the doubly ionised state (73Ge4+) of this center.

Mössbauer Study of the Ge Two-Electron Donor Centers in PbSe. E.I.Terukov, E.S.Khuzhakulov: Semiconductors, 2005, 39[12], 1369-70