Thermoelectric property of different thickness ZnO films grown by gas discharge activated reaction evaporation

The ZnO films were deposited by gas discharge activated reaction evaporation (GDARE) on glass substrates. The impacts of the deposition conditions on its thermoelectric property were studied. The microstructures of the films were characterized with X-ray diffraction and atomic force microscopy. The results show that the film thickness strongly affects its microstructures and properties. For instance, as the thickness of the films increased, the nano-grains with size varying from 30~70 nm grew and exhibit a preferred growth orientation, along the c-axis normal to the surface. All the ZnO films have fairly high thermoelectric power; at 440 K, Seebeck coefficient, S, of a 200 nm thick ZnO films was found to be 600 μV/K. At a given temperature, its resistivity, ρ, and its Seebeck coefficient, S, decreased with an increase of the thickness. At 440 K, the 600 nm thick ZnO film possesses the best thermoelectric property. Possible mechanism was also discussed.