Material characterizations of Al:ZnO thin films grown by aerosol assisted chemical vapour deposition.

In the present work, optical, electrical, structural and morphological characterization of polycrystalline thin films of ZnO and Al:ZnO have been reported. Aerosol assisted chemical vapour deposition technique has been adopted for the growth of the films on the glass substrate at 480 °C. Al-fraction in Al:ZnO thin films was determined by using energy dispersive x-ray analysis. In the visible to near-infrared regions, all the films were found to exhibit high average transmittance ≥80%. Blue shift of energy bandgap, from 3.20 to 3.50 eV, has been observed with increasing Al-fraction in the Al:ZnO thin films. For highly doped Al:ZnO thin films, both theoretical and experimentally measured values of carrier concentration (≈ 10 20 cm −3 ) were greater than Mott's critical value (≈ 10 19 cm −3 ) and supports the blue shift of the bandgap. The figures of merit of the films are found to be around 10 −2 Ω −1 suggesting the applicability of Al:ZnO thin films as a transparent electrode. The observed variation of carrier effective mass with increasing Al-doping agrees quantitatively well with the theoretical calculations. At high Al-fraction (≥ 12 at .%), the compressive strain generated in ZnO lattice is due to the presence of amorphous Al 2 O 3 or AlO x at the grain boundaries. X-ray diffraction suggests that the films were single phase and polycrystalline in nature. Atomic force microscopy of Al:ZnO films reveals a systematic change in surface morphology with increasing Al-fraction in the films. The results demonstrate the potentiality of producing thin films of transparent conducting oxides with good electrical, optical, structural and morphological properties via a low-cost deposition technique. [ABSTRACT FROM AUTHOR]