Electron spectrum and scattering of charge carriers in PbTe:(Na + Te)

Within the framework of the two-band model with the interband scattering taken into account, the concentration dependences of kinetic coefficients in PbTe:(Na + Te) were calculated in the range of 100-300 K. The results of the comparison between calculated and experimental data for temperatures of ∼100 K have a contradictory character. The assumption about the existence of quasi-local states related to the introduction of Na + Te in the hole's energy spectrum makes it possible to overcome these difficulties. The resonance scattering of charge carriers in these states introduces both quantitative (electric conductivity) and qualitative (thermopower, Lorentz number) modifications in the temperature and concentration behavior of transport properties. On the basis of the analysis of results, the conclusion is made that the role of the resonance scattering is basic at low temperatures. The mechanism of formation of quasi-local states in the valence band of materials of this group is proposed.