Characteristics of ZnO thin films doped by various elements

We have investigated the effects of Al, K and Co dopant elements on the properties of ZnO thin films deposited by CBD method on glass substrates. Changing in morphology, structural parameters, ionization energies of impurity levels, absorption behavior and optical band gap values were investigated through scanning electron microscopy (SEM), X-Ray diffraction (XRD), resistance–temperature measurement (R–T) and ultraviolet–visible spectroscopy (UV–vis) techniques. From the SEM observations, various morphologies (rod-like, flower-like and rice-like) were observed. Those morphological variations were attributed to the change in stable growth mechanism of intrinsic ZnO, induced by different atomic radius and different electronegativity of dopants. XRD results indicated that all orientations are well indexed to hexagonal phase crystalline ZnO. The impurity level ionization energy values (ΔE) were estimated as 0.32/0.13/0.07 eV; 0.34/0.15 eV; 0.40/0.13 eV and 0.48/0.22 eV for the Al, K, Co doped samples and i-ZnO, respectively. Optical band gap values were found that the doped samples' were higher than the intrinsic one's. This increasing (blue shift) was attributed to a deterioration which occurred in the lattice of the structures after doping. This effect was also supported by the structural results.

► Various morphologies (rod-like, flower-like and rice-like) were observed.
► Variations were attributed to the change in stable growth mechanism of i-ZnO.
► Wurtzite structured ZnO nanorods with preferred orientation were obtained.
► The impurity level ionization energies were estimated through R–T curves.
► Band gap of the samples were found in between 3.18–3.25 eV.