GaN have sphalerite structure (Cubic-GaN) and wurtzite structure (hexagonal GaN). We report the HGaN epilayer with a LT-AlN buffer layer has been grown on Si(1 1 1) substrate by metal-organic chemical vapor deposition (MOCVD). According to the FWHM values of 0.166 degrees and 14.01cm(-1) of HDXRD curve and E-2 (high) phonon of Raman spectrum respectively, we found that the crystal quality is perfect. And based on the XRD spectrum, the crystal lattice constants of Si (a = 5.3354 angstrom) and H-GaN (a(epi) = 3.214 angstrom c(epi) = 5.119 angstrom) have been calculated for researching the tetragonal distortion of the sample. These results indicate that the GaN epilayer is in tensile strain and Si substrate is in compressive strain which were good agreement with the analysis of Raman peaks shift. Comparing with typical values of screw-type (D-screw = 7 x 10(8) cm(-2)) and edge-type (D-edge = 2.9 x 10(9) cm(-2)) dislocation density, which is larger than that in GaN epilayers growth on SiC or sapphire substrates. But our finding is important for the understanding and application of nitride semiconductors. (C) 2010 Published by Elsevier B. V.