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

摘要

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 0 wt.%, 2 wt.%, 5 wt.%, 7 wt.% and 10 wt.%. The test result shows that Ta element in the film is in the state of Ta~(5+). The ratio of O/Zn is 84.73% for ZnO:Ta film doped with 5 wt.% Ta_2O_5, 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 9.4-13.5 ran. AFM studies indicate the maximum average particle size 94.46 nm and the minimum surface roughness 4.480 nm can be obtained for the ZnO:Ta films with the Ta_2O_5 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 Ta_2O_5 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 Ta_2O_5 content. The ZnO:Ta films containing 5 wt.% Ta_2O_5 presents the maximum optical band gap 3.38 eV. These findings shows that the highest figure of merit obtained is 2.20 × 10~(-4)Ω~(-1) for the as-grown ZnO:Ta films doped with 5 wt.% Ta_2O_5.