Enhanced Power Factor and Increased Conductivity of Aluminum Doped Zinc Oxide Thin Films for Thermoelectric Applications

We report the structural, electrical and thermopower properties of un-doped and Al doped zinc oxide (ZnO) thin films. Al doping was carried out using 25 keV Al+ implantation with 0.1, 1 and 2% Al into ZnO. X-ray diffraction measurements showed that the lattice parameters were larger than the bulk values, which is consistent with the incorporation of Al atoms at interstitials. Al doping increased the electrical conductivity from 100 (Omega cm)(-1) in the un-doped ZnO film to 598 (Omega cm)(-1) in the 2% Al doped ZnO film. Electron doping by Al resulted in an increase in the carrier concentration and it had an advantageous effect on the mobility where it was highest for 2% doping. The absolute value of the Seebeck coefficient systematically increased for un-doped, 1% and 2% Al doped ZnO films where the room temperature values were -50.8, -60.9 and -66.3 mu V/K, respectively. The power factor increased significantly from 2.58 x 10(-5) W/mK(2) in un-doped ZnO film to 2.63x10(-4) W/mK(2) in 2% Al doped ZnO film. Our results suggest that the ion beam method is a suitable technique to enhance the thermoelectric properties of ZnO.