Doping of IV-VI semiconductors and the energy spectrum of holes with resonance states taken into account

Kinetic phenomena in the Pb0.5Sn0.5Te solid solution have been studied in wide ranges of concentrations and temperatures in the case of two types of acceptor doping: with overstoichiometric tellurium and with a combination of equal amounts of Na and Te atoms; in the latter case, two additives amounting to 1.0 and 1.5 at % of each element have been used. Hole densities attained in this case significantly exceeded the largest values corresponding to the Pb0.5Sn0.5 Te:Te samples. For both types of acceptors, the hole concentration in the solid solution is found to be a factor of 2 higher than in PbTe with the same level of doping. The specific features of behavior of the Hall coefficient, thermopower, and electrical conductivity are interpreted in the context of a model of a single-valence-band spe ctrum with a wide band of resonant levels. The mechanism of formation of resonant levels in PbTe and Pb0.5Sn0.5 Te solid solutions is discussed.