Hexagonal-GaN heteroepitaxy layers have been grown on Si（111）substrate by MOCVD.The structure

morphology and optical properties of GaN epilayer is analyzed and characterized by various analysis method such as optical microscope

AFM

SEM

X-ray diffraction（XRD）

and Raman spectra

etc.Test results show that the crystal reveals the wurtzite structure with the（0002）crystal orientation and the heteroepitaxial growth of GaN has good single crystal quality

good directing property

smooth surface without crack.The Raman peaks of E2（high）and A1（LO）phonon mode have red shift according to relaxed GaN

which might be related to the tensile stress in GaN layer.But the AO phonon mode of Si have blue shift as its eigen frequency which shows the Si substrate suffered compressive stress.