The mechanism of valence-state formation in the IV-VI alloys doped with rare-earth impurities is analyzed with respect to certain properties of narrow-gap semiconductors. The mean-field approximation in the slave-boson representation is used to account for the strong electron correlation at the impurity. The energy, width, and filling factor of the impurity level are calculated as a function of both the band gap and position of the chemical potential. We also calculate the temperature dependence of the magnetic susceptibility of an impurity. It is shown that mixing to coupled conduction- and valence-band states makes the properties of rare-earth dopants sensitive to the band gap and Fermi level in the narrow-gap semiconductor host.

• Received 10 August 1998

DOI:https://doi.org/10.1103/PhysRevB.59.15190