Thermoelectricity of Al-doped ZnO at different carrier concentrations

Optimization of the carrier concentration is a key to improve the power factor of thermoelectricity. The carrier concentration of sintered zinc oxides was primarily controlled by impurity doping of aluminum and secondarily adjusted by defect concentration by varying the oxygen partial pressure in the range of 10¹ to 10⁴ Pa. The resultant carrier concentration measured at room temperature ranged from 1 to 1.8 × 10²⁰ cm⁻³, which drastically modified the thermoelectricity. The Jonker plot of the measured Seebeck coefficient and conductivity revealed deviation of the slope from k/e (where k is the Boltzmann constant and e is the elemental electric charge), which was attributed to a mobility variation with respect to the carrier concentration. The approach to estimating the optimum conductivity taking into account mobility variation is discussed. Finally, the optimum conductivity is estimated to be 1800 to 2000 S/cm for high-temperature operation (500 to 800 °C).