Doping content dependencies on the structure modification and bandgap broadening of Al induced sol-gel derived ZnO nanostructures

This paper reports the Al doping content dependence on structure modification and band gap widening of sol-gel synthesised Al-doped ZnO thin films. The precursor, solvent and stabiliser used to prepare ZnO solution were Zinc Acetate Dihydrate, 2-propanol and ethanolamine, respectively. Molarity fractions of 0, 4, 6 and 8% of Al (NO3)(2) as dopant source was incorporated into ZnO host system and prepared by individual buffer solutions. The prepared sols were subsequently deposited onto ITO glass substrates, and the resultant thin films were characterised. XRD patterns exhibit the polycrystalline nature of pure and doped ZnO films, with preferred orientations correspond to (1 0 0), (0 0 2) and (1 0 1) planes. Lattice shrinking is indicated by the decrease lattice constant c due to axial compression. Peaks shifting towards higher angle are observed implying a structural modification over doped thin films that affects the optical properties, which agrees with the lattice shrinking. The absorption edge has an obvious blueshift to the shorter wavelength with increased do pant content. The thin films' energy bands were procured by Tauc's linear extrapolation and was found to be broadening from 3.32 eV to 3.34 eV in 6% Al-doped ZnO. There exists a significant correlation between the applied doping level and the extend of variation of structural properties and ultimately, lattice imperfection. Doping of smaller-atom-sized Al into ZnO concedes with the Burstein-Moss principles. 6% Al doping imposes the highest peak shift and ultimately has the highest impact on lattice parameter and energy band.