Resistivity Reduction of Nanostructured Undoped Zinc Oxide thin Films for Ag/ZnO Bilayers Using APCVD and Sputtering Techniques

Nanostructured undoped zinc oxide (ZnO) thin films were deposited using atmospheric pressure chemical vapor deposition (APCVD) on glass substrates using zinc acetate dehydrate [C4H6O4Zn center dot 2H(2)O, ZnAc] in less than 2 minutes for each sample. In order to reduce the resistivity of ZnO films, a very thin layer of Ag was deposited on top of the films via the sputtering method to reduce resistivity from 2.89 to 0.31 Omega.cm, using only a 30 angstrom silver coating. Structural, electrical and optical properties of the resulting bilayers were also investigated. The results show a polycrystalline structure in higher temperatures compared to rather amorphous ones in lower temperatures such as 325 degrees C. The XRD patterns of the optimum polycrystalline films were identified as a hexagonal wurtzite structure of ZnO with the (002) preferred orientation. Also, sheet resistance decreased from 17.8 MO/square to 28.9 KO/square for the temperatures of 325 degrees C to 450 degrees C ,respectively. Based on the physical properties of undoped ZnO, substrate temperature is an important factor which affects the crystallite size and modifies electrical parameters. UV-vis measurements revealed a reduction in the transparency of the layers with increasing substrate temperature. A sharp cut-off was observed in ultraviolet regions at around 380 nm.