Doping of spray-pyrolyzed ZnO thin films through direct diffusion of indium: Structural optical and electrical studies

Effect of thermal diffusion of indium in ZnO thin films, prepared using spray pyrolysis technique, is discussed. ZnO:In films were characterized using different techniques such as x-ray diffraction (XRD), photoluminescence, electrical resistivity measurements, and optical absorption and transmission. The XRD analysis showed that all the films had a preferred (002) orientation. There was no considerable change in peak height or full width at half maximum, due to the variation in doping percentage. Peak positions corresponding to (002) and (101) planes were slightly shifted to lower 2θ values. Optical band gap also decreased slightly with indium concentration, and for higher indium concentration percentage of transmission reduced very much. Drastic decrease in resistivity was observed and two activation energies (30 and 15 meV) were obtained for the doped samples. These levels were identified as due to zinc interstitials and/or due to indium at zinc lattice and impurity related defect levels. Photoluminescence measurements gave two emissions. In this, one was the near band-edge (NBE) emission and the other was the blue-green emission. As doping concentration increased, the NBE emission shifted to higher wavelength while the blue-green emission was shifted to lower wavelength (blueshift).