Electrical and optical properties of aluminum-doped zinc oxide sputtered from an aerogel nanopowder target
ZnO:Al thin films doped with different aluminum concentrations were deposited onto glass substrates by rf-magnetron sputtering at ambient temperature using, for the first time, nanocrystalline powder synthesized by the sol-gel method. The aluminum doping concentration was varied from 2.0 to 4.5 at.%. All the films exhibited an intensive (002) XRD peak, indicating that they have c-axis-preferred orientation. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to study the morphology of the films. They have a typical columnar structure and a very smooth surface. The optical transmittance spectra showed a good transmittance higher than 90% within the visible region. The best conductors, with an optical band gap of 3.46 eV and a minimum resistivity of 5.4 × 10-4 Ω cm, were obtained for ZnO:Al films containing 3.0 at.% of aluminum. Due to their good optical and electrical properties, ZnO:Al films are promising candidates for use as transparent electrodes in solar cells.