Investigation of indium insertion effects on morphological, optical, electrical impedance and modulus properties of ZnO thin films

In:ZnO thin films with different indium concentrations (0% In, 1% In, 3% In, 5% In, and 7% In) were synthesized using successive ionic layer adsorption and reaction method. X-ray diffraction (XRD) analysis revealed that all synthesized thin films are well crystallized in the wurtzite phase with the crystallites preferentially oriented toward (002) direction, and demonstarted that crystallite size decreases with In insertion. The energy dispersive X-ray analysis analysis (EDX) confirmed In concentration and the stoichiometric increase in In/ZnO ratio of the synthesized ZnO thin films. The surfaces of all synthesized thin films were analyzed by atomic force microscopy (AFM) in order to understand the effect of indium insertion on the surface morphology. The surface roughness of the films decreased with the increase in In content, likely as a result of the formation of smaller grain size calculated by XRD which was clearly displayed by AFM images. The optical properties of the synthesized thin films were investigated by the absorption coefficient variation. The measured energy bandgap values increased with In insertion and were in a range close to the bandgap of intrinsic ZnO semiconductor. Electrical characterization was achieved using two-contact structure method by DC and AC analyses. The DC study revealed that the measured electrical resistance decreases from 7.25 x 10(9) Omega to 1.05 x 10(9) Omega with increasing In concentration from 0% to 7%. The same behavior was also demonstarted using complex AC impedance and modulus analyses of the thin films. Such analyses also revealed that upon indium insertion, the influence of grain boundaries significantly predominates and has a non-Debye type of relaxation. In addition, activation energies were estimated from the impedance and modulus spectra and their values were approximately the same.