Preparation, microstructure and photoelectrical properties of Tantalum-doped zinc oxide transparent conducting films

Abstract

Transparent and conducting Tantalum-doped zinc oxides thin films have been prepared for the first time by RF magnetron sputtering method on glass and silicon substrates at room temperature. The doped contents are 0wt.%, 2wt.%, 5wt.%, 7wt.% and 10wt.%. The test result shows that Ta element in the film is in the state of Ta5+. The ratio of O/Zn is 84.73% for ZnO:Ta film doped with 5wt.% Ta2O5, which indicates the films is in a state of oxygen deficiency. As the content of Ta increases, the crystallite size has been estimated to be in the range of 9.4–13.5nm. AFM studies indicate the maximum average particle size 94.46nm and the minimum surface roughness 4.480nm can be obtained for the ZnO:Ta films with the Ta2O5 content of 5 wt.%. These structural changes are accompanied by significant variations of electrical property and optical property. The resistivity of this film first decreases and then increases with the increase of the Ta2O5 content. The optical property analysis shows that the average transmittance in the visible range is above 85% for all the films. The optical band gap value of the film initially increases and then shows a decrease with the increase of the Ta2O5 content. The ZnO:Ta films containing 5 wt.% Ta2O5 presents the maximum optical band gap 3.38eV. These findings shows that the highest figure of merit obtained is 2.20×10−4Ω−1 for the as-grown ZnO:Ta films doped with 5wt.% Ta2O5.