Controlled synthesis of In-doped ZnO: the effect of indium doping concentration

Abstract

Three dimensional (3D) indium doped zinc oxide (In:ZnO) nanostructures are produced with the simple and reliable refluxed sol–gel technique. The influence of indium (In) doping concentration was studied by varying the quantity of In-dopant during synthesis. The morphologies of the produced samples observed using FE-SEM and TEM are nanoplates, flower and prism like. The hierarchical nanoprisms are aggregated for the evolution of nanoflower like structure with increased length and the width size of the prism. The produced In:ZnO is hexagonal wurtzite in structure with increased crystallite size from 21.7 to 32.3 ± 0.01 nm as In-doping level increased from 0 to 6.5 at.%. An improved crystal quality was revealed with decreased line broadening of the X-ray diffraction (XRD) measurements. The lattice parameters obtained from XRD measurements are observed to increase due to the incorporation of larger In³⁺ ionic radius at the Zn²⁺ ion lattices. The expansion of the lattice due to tensile strain caused the XRD diffraction peaks to shift towards the smaller angle. The bond length and dislocation density variations are in agreement with the variations of crystallite size and lattice parameters. The absorption band edge acquired using the UV–Vis diffuse reflectance measurements were observed to have red shifted due to the increased crystallite size with the increase in In-doping. The optical energy band gap decreased uniformly from 3.27 to 3.21 ± 0.01 eV as the amount of In-doping increased; which is in the range for optoelectronics device applications. Photoluminescence measurements depict both the near band gap emission at around 283 nm and deep level emission at about 618 nm. Both the emission bands were red shifted due to the incorporation of larger In³⁺ ion. An appropriate doping of group III In atom using the controlled refluxed sol–gel synthesis method helps to modify the material properties of ZnO for possible nano and microscale optoelectronics applications.