Pyroelectric properties of the wide-gap semiconductor CdS in the low-temperature region

Spontaneous polarization, thermally stimulated conductivity and depolarization are comprehensively studied in the range from 4.2 to 300 K on nonstoichiometric $n$-type CdS crystals grown from the gas phase in an argon atmosphere at $T$ = 1450 K. The objects of study are initial samples and samples polarized by a weak electric field at $T$ = 4.2 K. Sample polarization results in a decrease in the conductivity $\sigma_{33}$ due to restructurization of the entire energy level spectrum associated with the formation of donor-acceptor pairs. The latter processes also contribute to the temperature dependences of the spontaneous polarization and the pyroelectric effect, characterized by the formation of anomalies below 15 K and the formation of thermoelectret. The role of an uncontrollable oxygen impurity in the formation of CdS cationic conductivity above 270 K, associated with the decay of a fraction of donor-acceptor pairs, is discussed. In the temperature range from 20 to 250 K, the pyroelectric coefficient and spontaneous polarization are independent of external influences within experimental error; at $T$ = 200 K, they are $\Delta P_s$ = -(6.1 $\pm$ 0.2) $\times$ 10$^{-4}$ C/m$^2$ and $\gamma_s$ = -(4.1 $\pm$ 0.3) $\times$ 10$^{-5}$ C/m$^2$ K.