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Impact of Vicinal Sapphire (0001) Substrates on the High-Quality AlN Films by Plasma-Assisted Molecular Beam Epitaxy

AlN films grown by plasma-assisted molecular beam epitaxy on vicinal sapphire (0001) substrates were investigated. High structural and optical qualities were confirmed by high-resolution X-ray diffraction and 77 K cathodoluminescence measurements. It was found that changing the vicinal angles of sapphire substrates can easily control the surface morphologies of AlN films. Spiral-growth features were greatly suppressed. Furthermore, well-ordered straight monatomic-layer steps and multi-atomic-layer macro-steps were clearly observed by atomic force microscopy. Surface diffusion and step incorporation kinetics during the growth are the key-factors in determining the surface morphologies.