Linking structure and surface morphology with optical properties of trivalent metals doped ZnO thin films grown by spray pyrolysis

• Systematic comparison of Al, Cr, Fe, Sm and La doped ZnO films • Identical spray pyrolysis conditions enable direct dopant comparison • Dopants induce distinct structural and morphological evolution • Grain size variations correlate with optical band gap changes • Low-level doping tunes absorption edge and electronic structure ZnO thin films doped with trivalent elements have been widely investigated, yet comparative studies under identical processing conditions remain limited. In this work, a systematic analysis of ZnO thin films doped with Al³⁺, Cr³⁺, Fe³⁺, Sm³⁺, and La³⁺ is presented, with doping concentrations in the range of 0.1–1 at.% using spray pyrolysis under controlled and identical growth conditions. This approach enables direct evaluation of dopant-specific effects on structural, morphological, and optical properties. X-ray diffraction confirms the preservation of the wurtzite ZnO structure with dopant-dependent variations in crystallite size and lattice parameters. Surface analysis reveals distinct morphological evolution depending on dopant type, indicating differences in growth kinetics and defect formation. Optical measurements show systematic changes in absorption edge position and band gap energy, which correlate with grain size and dopant nature. The results demonstrate that low-level trivalent doping provides an effective route to tune ZnO thin film properties, highlighting the importance of controlled comparative studies for understanding dopant-driven material behavior.