Morphological and optical characterizations of different ZnO nanostructures grown by mist-CVD

Abstract

In this study, the effects of growth temperatures, post-growth treatment, and substrate cleaning recipes on structural, morphological, luminescence, and growth kinetics of ZnO nanostructures grown by mist Chemical Vapor Deposition method (mist-CVD) on SiO2/Si substrates are investigated. The grown ZnO nanostructures have polycrystalline wurtzite (wz) hexagonal crystal structure according to X-ray Diffraction (XRD) measurements. However, the lower growth temperature is found to lead to the formation of ZnO nanostructures oriented in the [0002] direction. From Atomic Force Microscope (AFM) measurements, it is seen that the Root Mean Square (RMS) values decrease with decreasing growth temperature. In addition, it is shown that the surface covering is tightly dependent on decreasing growth temperature of the ZnO nanostructures. The hexagonal and triangular pyramid-like ZnO nanostructures are grown on the surface according to the Scanning Electron Microscope (SEM) measurements. The wurtzite type of crystallization is also demonstrated by confocal Raman measurements. The characteristic vibration modes related to Zn and O motion in the lattice are found to be ~435 cm− 1 and ~100 cm− 1 , respectively. The luminescence properties are studied by low-temperature (10 K) Photoluminescence (PL) measurements. The spectra are dominated by the transition related to the donor-bound exciton (DBE) with a peak position typically observed at ~369 nm (3.362 eV) in hexagonal ZnO structures. Defect-related transitions are observed to be strongly correlated with growth temperature and post-growth treatment.