Structure dependent luminescence evolution of c-axis-oriented ZnO nanofilms embedded with silver nanoparticles and clusters prepared by sputtering

• c-Axis-oriented ZnO–Ag composite thin films were successfully prepared by sputtering.
• The surface grains of the ZnO–Ag thin films featured clusters that consisted of many ZnO crystallites and Ag particles.
• A decrease of oxygen-related point defects in ZnO thin films can be realized with proper Ag additions.

ZnO–Ag composite thin films with various degrees of Ag addition were grown on c-axis-oriented sapphire substrates by sputtering. By varying the Ag sputtering power level from 3 to 13 W, the effects of Ag addition in 80-nm-thick ZnO thin films could be determined. The X-ray diffraction patterns revealed that ZnO thin films prepared with and without Ag co-sputtering exhibited highly c-axis-oriented crystallographic features. Scanning electron microscopy and transmission electron microscopy images show that a high Ag content caused the ZnO crystallites and Ag nanoparticles (or Ag clusters) to group and form clusters of grains during thin-film growth. The X-ray photoelectron spectrometer measurements demonstrate a decrease of oxygen-related point defects in ZnO thin films with proper Ag additions. The blue emission band dominated the photoluminescence characteristics of pure ZnO and 3 W Ag co-sputtered ZnO thin films. The blue emission band was markedly quenched, and the UV emission band was significantly enhanced when the Ag-sputtering power level was raised to above 9 W. These are attributed to a reduction of zinc vacancies and an improvement of the exciton transition process by using proper Ag additions. The experimental results in this work show that the photoluminescence characteristics of ZnO thin films could be adjusted by varying the content of the Ag in ZnO thin films.