This paper presents an analysis of the characteristics of two gallium nitride (GaN) films grown on (0001) plane sapphire substrates by low-pressure metalorganic chemical vapor deposition (MOCVD) is presented. The GaN films were characterized by a variety of methods, including scanning electron microscopy (SEM), x-ray diffraction (XRD), photoluminescence (PL), and Raman scattering. SEM micrographs revealed that different growth conditions will lead to different surface morphology of the films. XRD measurements indicated that both films were highly oriented and mono crystalline. PL spectra for both samples exhibited an intense and sharp band edge peak at 3.42 eV with full width at half maximum (FWHM) of 15 and 35 meV respectively. Raman scattering showed that the peaks of E2(high) phonon mode were observed at 568.1 and 570.1 cm-1 respectively. The different growth mode of these films were linked to the growth conditions, in which the growth mechanism could be correlated with the shift of E2(high) phonon mode in Raman scattering.