Epitaxial tilting of GaN grown on vicinal surfaces of sapphire

The epitaxial tilting effect of GaN films grown on vicinal (0001) surfaces of sapphire and its relationship with the offcut angles and the substrate surface steps have been revealed using synchrotron Laue method and high-resolution x-ray diffraction. This effect is a general consequence of the large out-of-plane lattice mismatch between GaN and sapphire and can be explained by the extended Nagai theory based on the step configurations. The large lattice tilts and their formation mechanism indicate that the substrate surface morphology may be a very important factor that influences the epitaxy process and the crystalline quality of GaN films in vicinal surface epitaxy.