Doping and defect formation in thermoelectric ZnSb doped with copper

The Hall and thermoelectric coefficients, and also the electrical conductivity in ZnSb:Cu and ZnSb:CuSb samples with a copper content as high as 0.6 at% are measured under thermocycling conditions 300–720–300 K. It is shown that the behavior of properties is determined by the existence of two temperature regions with different types of variation in the Hall concentration and the mechanism of charge-carrier scattering. The behavior becomes markedly more complex in the case where temperature hysteresis appears as a result of cooling; this hysteresis brings about additional features in the variation in properties. The two mentioned doping regions (in the range of 300–500 K with the maximum hole concentration 2.5 $\times$ 10$^{19}$ cm$^{-3}$ and at temperatures higher than 500 K with the maximum hole concentration 7.2 $\cdot$ 10$^{19}$ cm$^{-3}$) are characterized by carrier scattering with the involvement of both acoustic phonons and charged impurities; in this case, the relative contribution of the latter depends significantly on the composition of the dopant, temperature and the way of its variation. Cooling the samples to 77 K brings about a large decrease in the Hall mobility; this effect disappears only at $\sim$650 K. The interrelated processes of doping and of the formation (with subsequent transformation) of defects, which occupy neutral sites in the lattice, are related to variations in the sample microstructure.