Enhancement in green luminescence of ZnO nanorods grown by dc-unbalanced magnetron sputtering at room temperature

Abstract ZnO nanorods are one of the most studied materials for optoelectronics applications, thanks to their superior properties, such as high-surface-to-volume ratio, unique chemical, and physical properties. Sputtering method is believed as a promising technique to fabricate ZnO nanorods in a large-scale area. However, this method requires high substrate temperature which may provoke intermixing of samples at the interface. In the present study, the optical properties of ZnO nanorods grown by room-temperature DC-unbalanced magnetron sputtering at room temperature are studied. ZnO thin film is also deposited as a reference. By selected sputtering parameters, SEM images show that the nanorods are grown mainly horizontal on the silicon substrate with a diameter of ~90 nm. Spectroscopic ellipsometry is used as the main optical characterization in the present study. The excitonic states of ZnO nanorods are suppressed compared to the thin film due to the high concentration of oxygen vacancies (VO) leading to excitonic screening effects. This result is also supported by UV–Visible spectra, which shows a high optical transition of ZnO nanorods in the visible region. Photoluminescence spectra confirm that the ZnO nanorods have a high density of VO defects as indicated by a dominant green emission located at 2.42 eV. The value of IGreen/IUV in ZnO nanorods is 12.019 which is much higher than the thin film with a value of 0.158. Our results suggest that nanorods structure improved green emission in ZnO materials and can be applied as a light-emitting device.