Structural, optical and electrical properties of transparent conductive ZnO:Ca films prepared by rf magnetron sputtering from aerogel nanopowders

In the present work, we have deposited calcium doped zinc oxide thin films by magnetron sputtering technique based nanocrystalline particles elaborated by sol-gel method. In the first step, the nanoparticles were synthesized by sol-gel method using supercritical drying in ethyl alcohol. The structural studied by X-ray diffractometry indicates that CZO has a polycrystalline hexagonal wurzite structure with a grain size of about 30 nm. Transmission electron microscopy (TEM) measurements have shown that very small particles of CZO are present in the aerogel powder. In the second step, calcium-doped zinc oxide (CZO) films were deposited onto glass substrates by rfmagnetron sputtering at ambient temperature using. The effects of calcium on structural, electrical, morphological and optical properties were investigated. It is found that all the thin films have a preferential c-axis orientation. With increase of Ca doping, the peak position of the (0 0 2) plane is shifted to the high 2θ values. A minimum resistivity of 5.10−3 Ω cm is obtained for the film doped with 3% Ca. The films are highly transparent in the visible wavelength region with a transmittance higher than 85% and optical band gap ranging from 3.30 to 3.42 eV.