Sintering Temperature-Dependent Chemical Defects and the Effect on the Electrical Resistivity of Thermoelectric ZnO

Thermoelectric properties of zinc oxide (ZnO) are largely influenced by its electrical property. In this paper, we investigated the correlation between the electrical resistivity and synthesis temperature for aluminum (Al)-modified ZnO. At constant Al doping, the electrical resistivity of ZnO exhibited sharp decrease with increase in sintering temperature due to the increased carrier density resulting from Al3+ substitution on Zn2+ sites. Photoluminescence analysis showed that segregation of Al in secondary phase, ZnAl2O4, promotes Zn2+ vacancy formation and consequently compensates the free electrons that dominate the electrical behavior at relatively low sintering temperature. The mechanism controlling the large change in electrical resistivity of dense ZnO, ranging from insulator (~107 ω cm) to semiconducting regime (~ 0.1 ω cm) has been discussed.