Al_χGa_<1-χ>N (0≦χ≦0.4) layers with thin AlN buffer layers are grown on sapphire (0001) substrates at a temperature of about 1000℃ by MOVPE. By the double crystal X-ray diffratometry the Al_χGa_<1-χ>N layers are found to composed of many mosaic crystallites with vauious orientations. The variation in the crystallite orientation can be much reduced and the surface morphorogy (smoothness and uniformity) of Al_χGa_<1-χ>N is far improved by using the AlN buffer layer. The reason for such an effect of the AlN buffer layer is discussed in detail by the growth mechanism based on the phenomenological model.
