Electron-phonon processes in semiconductors at low temperatures

The thermal conductivity and thermopower are simultaneously studied in the semiconductors HgSe, HgTe, InP, GaAs, Cd$_x$H$_{1-x}$Te, and Ag$_2$S in which the effect of electron drag by phonons was detected at low temperatures $T$. It is found that $x$ = 1–3 in the dependences $K_{\mathrm{ph}}\propto T^{-x}$. It is shown that the underestimated values of $x$ are caused by phonon scattering at certain defects. It is also found that the maxima of $K_{\mathrm{ph}}(T)$ and $\alpha_{\mathrm{ph}}(T)$ coincide in all studied crystals, except for Ag$_2$S. For the first time, it is found that the strong effect $\alpha_{\mathrm{ph}}\propto T^{-3}$ is observed in Ag$_2$S, the $\alpha_{\mathrm{ph}}$ maximum is at $T$ = 16 K, and the $K_{\mathrm{ph}}$ maximum is at 27 K. The results obtained are in agreement with Callaway and Herring theory. The effect of magnetic field on the drag thermopower $\alpha_{\mathrm{ph}}(T)$ in $n$-Cd$_x$Hg$_{1-x}$Te (in which the strong dependence $\alpha_{\mathrm{ph}}\propto T^{-3}$ and the strong effect of the magnetic field on it are detected) is considered for the first time. The results are compared with the Askerov theory. The force parameter $A_{\mathrm{ph}}(\varepsilon)$ of the drag effect and its dependence on magnetic field are determined.