Effect of AlN Buffer Layer on AlGaN/α-Al2O3Heteroepitaxial Growth by Metalorganic Vapor Phase Epitaxy

AlxGa1-xN(0≦x≦0.4) films grown on sapphires are found to be composed of many mosaic crystallites with various orientations by means of double-crystal X-ray diffractometry. This fluctuation of orientation can be considerably reduced and the surface morphology (smoothness and uniformity) of the film can be remarkably improved by the preceding deposition of the AlN buffer layers. A phenomenological model, which can explain the effect of the AlN buffer layer on the surface morphology and the crystalline quality of AlGaN films, is proposed.