Electrical properties of aluminum-doped zinc oxide (AZO) nanoparticles synthesized by chemical vapor synthesis

摘要

Aluminum-doped zinc oxide nanoparticles have been prepared by chemical vapor synthesis,which facilitates the incorporation of a higher percentage of dopant atoms, far above thethermodynamic solubility limit of aluminum. The electrical properties of aluminum-doped andundoped zinc oxide nanoparticles were investigated by impedance spectroscopy. Theimpedance is measured under hydrogen and synthetic air between 323 and 673 K. Themeasurements under hydrogen as well as under synthetic air show transport propertiesdepending on temperature and doping level. Under hydrogen atmosphere, a decreasingconductivity with increasing dopant content is observed, which can be explained by enhancedscattering processes due to an increasing disorder in the nanocrystalline material. Thetemperature coefficient for the doped samples switches from positive temperature coefficientbehavior to negative temperature coefficient behavior with increasing dopant concentration. Inthe presence of synthetic air, the conductivity firstly increases with increasing dopant content bysix orders of magnitude. The origin of the increasing conductivity is the generation of freecharge carriers upon dopant incorporation. It reaches its maximum at a concentration of 7.7%of aluminum, and drops for higher doping levels. In all cases, the conductivity under hydrogenis higher than under synthetic air and can be changed reversibly by changing the atmosphere.