On the tin impurity in the thermoelectric compound ZnSb: Charge-carrier generation and compensation

The technique for measuring the Hall coefficient and electrical conductivity in the thermal cycling mode is used to study the effect of the Sn impurity on the microstructure and properties of pressed ZnSb samples. Tin was introduced as an excess component (0.1 and 0.2 at%) and as a substitutional impurity for Zn and Sb atoms in a concentration of (2–2.5) at% The temperature dependences of the parameters of lightly doped samples are fundamentally like similar curves for ZnSb with 0.1 at% of Cu. The highest Hall concentration, 1.4 $\times$ 10$^{19}$ cm$^{-3}$ at 300 K, is obtained upon the introduction of 0.1 at% of Sn; the dimensionless thermoelectric figure of merit attains its maximum value of 0.85 at 660 K. The experimental data are discussed under the assumption of two doping mechanisms, which are effective in different temperature ranges, with zinc vacancies playing the decisive role of acceptor centers. In two ZnSb samples with SnSb and ZnSn additives, the charge-carrier compensation effect is observed; this effect depends on temperature and markedly changes with doping type. As in $p$-type AIV–BVI materials with a low Sn content, hole compensation can be attributed to atomic recharging Sn$^{2+}$ $\to$ Sn$^{4+}$. Types of compensating complexes are considered.