Hopping conduction via strongly localized impurity states of indium in PbTe and its solid solutions

Abstract

Experimental investigations of the transport phenomena (electric conduction; Seebeck, Hall, and Nernst-Ettingshausen effects) in PbTe and Pb1−xSnxTe solid solutions with high content of In impurity (up to 20 at. %) at temperatures of up to 400 K are reviewed. Many properties of these substances are similar to those of noncrystalline materials. The experimental data are analyzed in terms of hopping conduction via strongly localized impurity states related to In atoms. Temperature dependences of transport coefficients, which are uncommon to IV–VI compounds; inversion of thermoelectric power with negative Hall coefficient; and a positive Nernst-Ettingshausen coefficient are accounted for. The activation energy of hopping conduction, which characterizes the effective energy spread of impurity levels; the effective radius of the wave function; and the energy dependence of the density of localized states are found from experimental data. The discussion of the experimental data on hopping conduction is preceded by a brief description of resonance and deep localized electron states related to indium impurities in IV–VI compounds. Particular attention is given to the specific features of impurity states in samples with high In content, in which the hopping conduction is observed.