He plasma treatment of transparent conductive ZnO thin films

The electrical resistivity, structure, and composition and work function of ZnO thin films deposited by sputtering and post-treated with He plasma were studied. First, the treating effects of ZnO films by He, Ar and H2 plasmas were compared. The electrical resistivity depended on the treated type of plasmas, the treated powers and times, and the thickness of film. The Ar plasma has the highest ion moment energy to disrupt the Zn-O bonding during treatment. The injection of H in ZnO can also act as the shallow donors to decrease the resistivity besides by desorption of weakly bonded oxygen species. The H2 and He plasmas have the etching effects on the surface of ZnO films at higher power and time. For the ZnO films before and after optimized He plasma treating, the electrical resistivity decreased from 104 to 7.0 × 10−3 Ω cm, the carrier concentration increased from 7.0 × 1015 to 1.8 × 102° cm−3, and the interstitial Zn and O vacancy deficiencies increased from 29.1 to 58.7% and 52.1 to 71.4%, and the work functions reduced from 8.5 to 7.6 eV, but with no significant change of crystal structure.