High-pressure thermoelectric characteristics of Bi$_2$Te$_3$ semiconductor with different charge carrier densities

The measurements of the absolute values of the thermopower and of the relative electrical resistance have been performed for $n$ type Bi$_2$Te$_3$ under hydrostatic pressure up to $9$ GPa at room temperature. Under pressures exceeding $5$ GPa and up to the phase transition (at $7$ GPa), the samples with the charge carrier density below $10^{19}\,$cm$^{-3}$ exhibit an anomalous growth of the thermopower. For the purest sample ($n=10^{18}\,$cm$^{-3}$), the thermopower is as high as $+150\,\mu$V/K. The pressure dependence of the electrical resistance for $n$-Bi$_2$Te$_3$ does not exhibit any anomalies up to the pressure corresponding to the phase transition ($7$ GPa). Thus, the state with the giant thermoelectric efficiency is found in Bi$_2$Te$_3$ under pressure before the phase transition.