Donorlike behavior of rare-earth impurities in PbTe

The Hall coefficient, thermoelectric power, and electrical conductivity in PbTe doped with La, Pr, Sm, and Gd are investigated in the temperature range (77-700) K. The impurity atoms act as donors with an electrical activity that increases with temperature until the fraction of electrically active lanthanide atoms (Ln) reaches values close to or slightly more than half of their total number. A decrease in the electron mobility and a change in the thermoelectric power relative to their values in PbTe[I] are also noted. At low temperatures, the Seebeck coefficient in PbTe[Ln] is found to be higher than in PbTe[I], while at high temperatures it is lower. The data are interpreted by invoking a band of impurity resonant states, whose energetic position and number are functions of composition and temperature. The experimental data imply that when La and Pr dope PbTe, the electrical activity of the compound is dominated by intrinsic donorlike defects that form when Ln is incorporated in the ratio LnTe. (C) 1998 American Institute of Physics.