Annealing-induced modifications in Al doped ZnO thin films: Correlating temperature with structural and photoelectrical properties

This research investigates the influence of annealing temperature on the structural, morphological, optical, and electrical properties of Al doped ZnO thin films synthesized using a cost-effective sol–gel spin coating technique. The films were annealed at temperatures ranging from 100°C to 500°C to evaluate temperature-dependent modifications in material behavior and performance. X-ray diffraction (XRD) analysis confirmed the hexagonal wurtzite crystal structure of ZnO, with a notable enhancement in crystallinity and grain orientation at elevated annealing temperatures. Field emission scanning electron microscopy (FESEM) revealed distinct morphological transitions from loosely aggregated nanoparticles to well-defined crystalline grains as the annealing temperature increased. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) further validated the successful incorporation of Al into the ZnO lattice and the preservation of the ZnO structure. Optical absorption measurements exhibited a red shift in the absorption edge with rising temperature, resulting in a reduction of the optical band gap from 3.16 eV to 2.96 eV. Photocurrent analysis demonstrated a significant improvement in photoresponse for highly annealed samples, attributed to enhanced crystallinity and optimized surface morphology. Additionally, a consistent decrease in electrical resistivity with increasing annealing temperature indicates improved carrier transport. Overall, the study highlights the critical role of annealing temperature in tailoring the functional properties of Al-doped ZnO thin films for advanced optoelectronic applications.