Effect of annealing temperature on the structural, optical, and photodetection properties of chemically synthesized Ag/CuO/ITO thin films
摘要
This study investigates the effect of annealing temperature from the as-deposited state to 450 °C on the structural, optical, and electrical properties of copper oxide thin films prepared by a simple chemical method. Film thickness varied between 870 and 710 nm, while X-ray diffraction confirmed a monoclinic structure with crystallite sizes in the range of 24–42 nm. The optical band gap decreased from 1.79 eV to 1.29 eV with annealing, accompanied by changes in optical constants such as a refractive index of 2.81 and an absorption index of 1.04 for the film annealed at 350 °C. SEM images showed a clear morphological evolution, with agglomerated clusters at low temperatures gradually transforming into well-defined grains at higher annealing temperatures. XPS confirmed the oxidation state progression from mixed Cu+/Cu2+ in the as-deposited and 150 °C films to complete Cu2+ stabilization above 250 °C, along with reduced surface hydroxyl species at higher annealing. Hall effect measurements showed that the film annealed at 350 °C exhibited the best transport properties, with a minimum resistivity of 2.54 × 102 Ω·cm, maximum conductivity of 3.94 × 10–3 S·cm−1, hole concentration of 2.39 × 1018 cm−3, Hall coefficient of 2.61 cm3·C−1, and mobility of 1.03 × 10–2 cm2·V−1·s−1. The electrical and optical improvements at this temperature are ascribed to enhanced crystallinity, oxygen stoichiometry, and film adhesion. In addition, I–V measurements of Ag/CuO/ITO films annealed at 350 °C yielded an ideality factor of 2.39, barrier height of 0.74 eV, photosensitivity of 676.55%, quantum efficiency of 14.24%, responsivity of 11.89 mA/W, and detectivity of 7.52 × 1010 Jones. These results suggest that 350 °C is the optimal annealing temperature for achieving high-quality CuO thin films suitable for photodetector and solar cell applications.