Effect of cation concentration and annealing temperature on structural, morphological, optical, and electrical properties of spin coated zinc-tin-oxide thin films

The current report focuses on the properties of Zinc–Tin-Oxide (ZTO) thin films coated on quartz substrates via spin coating technique. The two parameters considered during the thin film preparation and post deposition treatment include the cation concentration (Zn and Sn) in the precursor solutions and air annealing temperatures. Films were grown by using precursor solutions with different concentrations in the range 0.2–0.6 M and annealed at various temperatures between 600 and 900 °C. The X-ray diffraction studies revealed that the films annealed at 700 °C exhibit high crystallinity with a mixed phase of Zn₂SnO₄ and SnO₂ for all the cation concentrations. FESEM images infer the growth of these films with closely packed porous structure uniformly covering the substrate. Raman spectra revealed the presence of characteristic vibrational modes of Zn₂SnO₄ at 378 and 669 cm⁻¹ for higher cation concentration samples annealed at 700 °C. The optical studies revealed that the films exhibited high transmittance and the bandgap estimated was found in the range of 3.6–3.9 eV for all films. The visible light emissions due to defect centres located within the forbidden gap in ZTO films was evident through the photoluminescence studies. The electrical measurements of the annealed samples for different cationic concentrations yielded resistivity values in the range of 10³ to 10² Ω-cm.