Thermoelectric figure of merit and quantum mobility of holes in single crystals of antimony telluride doped with copper

The thermoelectric properties of Sb$_{2-x}$Cu$_{x}$Te$_{3}$ single crystals (0 $\le x\le$ 0.10) synthesized by the Bridgman method are studied in the temperature range of 77 K $<T<$ 350 K. It turns out that the hole concentration and electrical conductivity strongly increase, while the Seebeck coefficient slightly decreases when Sb$_2$Te$_3$ crystals are doped with copper. The thermal conductivity of crystals doped with copper is somewhat higher than that of the initial Sb$_2$Te$_3$ crystals. As a result, the thermoelectric figure of merit $ZT$ increases with increasing copper content at $T>$ 300 K. In addition, the quantum mobility of holes $\mu_q$ in Sb$_{2-x}$Cu$_{x}$Te$_{3}$ (0 $\le x\le$ 0.10), Sb$_{2-x}$Sn$_{x}$Te$_{3}$ (0 $\le x\le$ 0.01), and Sb$_{2-x}$Tl$_{x}$Te$_{3}$ (0 $\le x\le$ 0.05), single crystals is measured using data on the Shubnikov–de Haas (SdH) effect. Electron paramagnetic resonance (EPR) measurements show that copper ions in the studied samples are most likely in the spinless Cu$^{+1}$ state.