Thermoelectric properties of ZnO doped with the group 13 elements

Investigation on thermoelectric properties of ZnO doped with the group 13 elements revealed that addition of M₂O₃ (M = Al, Ga, In) to ZnO all increased the electrical conductivity significantly, whereas the absolute values of the Seebeck coefficient moderately decreased. The increase in the electrical conductivity was smaller for the dopant with the heavier element, being in good agreement with a decrease in the carrier mobility. However, the thermal conductivity was also suppressed by Ga and In doping, particularly at the lower temperature region. Even with the smaller power factor values, the figure of merit of (Zn_0.98M_0.02)O (M = Ga or In) was equal to that of the Al-doped one up to ca. 600 °C, owing to the suppression of the thermal conductivity.