||In this thesis, the growth of c-plane zinc oxide (ZnO) epitaxial films on nitridated c-LiGaO2 substrates by a homemade thermal chemical vapor deposition. Use Zinc Acetylacetonate was used as zinc precursor. High purity oxygen and nitrogen are used as reaction gas and carrier gas, respectively. We control the quality of films by optimizing the parameters of growth temperature, growth pressure and oxygen partial pressure. The properties of the ZnO films were investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), photoluminescence spectra (PL), Raman spectra (Raman) and transmission electron microscopy(TEM).|
The results show that the crystal quality and surface morphologyies of c-plane ZnO films are strongly related to the growth temperature, growth pressure and oxygen partial pressure. When growth temperature is 575℃, the ZnO XRD signal is the strongest and hexagonal shapes of the zinc oxide grains are obvious and with direction. The results of changing growth pressure showed that when the pressure is 300torr, the film is the smoothest. The XRD results show that the FWHM decreases with the growth pressure increase. This phenomenon caused improvement of crystal quality, and FWHM values reach a minimum at 0.13°, 300torr.
Finally, in a fixed total oxygen and nitrogen mixed gas flow rate (1000sccm), we changed the flow rate of oxygen reactive gas, The results showed that when the ratio of nitrogen and oxygen were changed from 1:3 to 3:1, the XRD signals are obvious strong and all of the FWHM are less than 0.2 °. The SEM images show flat with continuous film morphologies, while the partial pressure of oxygen are further increase or decrease, the XRD signals drop, and the FWHM values increase, the SEM images show distributed granular, with obvious grain boundary morphologies.
To further analysis of ZnO epitaxial films, the epitaxied orientation relationship was studied by TEM selected area electron diffraction analysis. The shift of XRD diffraction peaks and Raman spectra characteristic peak of E2 demonstrated the occurrence of interned stress during the epitaxial growt. Photoluminescence spectra results can infer the yellow-green emission was caused by defect, not by the cerium doped substrate.