ELECTRICAL AND OPTICAL PROPERTIES OF THALLIUM-DOPED PbTe.

The carrier-density and temperature dependences of the thermoelectric power alpha , electrical conductivity sigma , Hall coefficient R//H, and optical absorption coefficient of thallium-doped PbTe have been investigated in the temperature range 77 - 900 degree K. The action of thallium as a dopant was similar to the effect of sodium: an increase in Tl to 1 at. % caused the hole density to rise to (5 - 6) multiplied by 10**1**9 cm** minus **3. Introduction of Tl reduced strongly R//H sigma , particularly at low temperatures, produced a kink in the carrier-density dependence of alpha earlier than in the case of Na-doped PbTe, and shifted the maximum of R//H toward lower temperatures on increase in the Tl content. The experimental results are explained using a model of two valence bands and assuming additional scattering of carriers by the Tl ions.