Temperature Dependence of Electrical Properties of ZnO Nanorods Array

Abstract

Zinc oxide nanostructures (nanotubes, nanorods, nanowhiskers, etc.) are a promising material for various electronics devices for power system and green energy such as piezoelectric energy harvesters and solar cells. Electrical properties of ZnO nanorods grown on a glass substrate by the hydrothermal method in an aqueous solution of zinc nitrate were investigated in this work. The SEM micrograph shows that the grown nanorods are vertically oriented and the XRD pattern confirms its crystallinity with (002) preferred orientation. The temperature dependent resistivity of ZnO nanorods array measured from 300 to 523 K shows variation in resistance from 5·109 Ω to 3·106 W and temperature hysteresis and region with positive temperature coefficient of resistance at the heating that was not observed at cooling. The origin of this behavior is explained with the two competing processes - thermal generation of electrons and oxygen species adsorption on the ZnO surface. Oxygen adsorption leads to decrease in the number of oxygen vacancies that are electron donors, and consequently to a decrease in conductivity of ZnO nanorods. The values of activation energy of conductivity were calculated from the slope of linear regions on the Arrhenius plot which are 0.246, 1.466 and 0.248 eV for the heating curve and 0.650 and 0.315 eV for the cooling curve.