Morphological, structural and optical properties of silver treated zinc oxide thin film

Abstract

Zinc oxide (ZnO) thin film with an ultrathin layer of silver (Ag) atop was fabricated on glass substrate and a simple post-deposition annealing was carried out. A systematic observation was conducted to monitor morphological, structural and optical properties. The detailed morphological analysis by scanning electron microscope revealed that ZnO film surface became irregular with small pores dispersed all over the surface after the treatment, whereas the surface became smother with an ultrathin layer of Ag atop. Nucleation of Ag nanoparticles was observed initiated at the beginning of treatment. Preferential film orientation along c-axis with wurtzite hexagonal structure and a peak shift to red after treatment was confirmed by X-ray diffraction. Further investigation revealed that a stress relaxation from −0.51 GPa (compressive stress) to 0.58 GPa (tensile stress), grain growth from 13 to 31 nm and recrystallization with decreasing lattice constant (c) from 5.2655 to 5.1395 A occurred after treatment. A reduction in optical band gap from 3.31 to 3.25 ± 0.01 eV was observed after the treatment with a slight increase in transmittance. At higher annealing temperatures, the weak photoluminescence emission did show blue shift from 367 to 364 nm and 362 nm. Elemental and compositional analysis was carried out by X-ray photoelectron spectroscopy. Such characteristics shift in structural and optical properties, in fact, plays a crucial role in determining device performances and overall efficiency.