Self-assembled Horseshoe Type Shape Transitions in Morphology of Cu Substituted ZnO.

Cu doped ZnO thin films are prepared by the Spray Pyrolysis Technique (SPT) on glass substrate. XRD analysis shows that the films are polycrystalline with hexagonal structure. Intensity of (002) peak is highest indicating a c-axis oriented grains in pure ZnO film. The crystallite size reduces and strain increases with Cu incorporation in the direction of c-axis. AFM images indicate that the grains are self-assembled in the horseshoe type ring shape. At higher doping these rings are totally converted into small grains. Optical band gap decreases from 3.28 eV (pure ZnO film) to 3.25 eV (3% Cu doped ZnO film) and increases further with Cu incorporation. This may be attributed to the presence of excitons in the system. [ABSTRACT FROM AUTHOR]