Characterizations of GaN films and GaN/AlN super-lattice structures grown on vicinal sapphire (0Â 0Â 0Â 1) substrates by RF-MBE

GaN films and GaN/AlN super-lattice structures (SLs) grown by plasma-assisted molecular beam epitaxy (RF-MBE) on vicinal sapphire (0 0 0 1) substrates are characterized by various techniques. It is found that the surface morphologies of GaN films are greatly improved by using such kinds of substrates and well-ordered stepped GaN surfaces are realized by RF-MBE growth. The step feature changes from a monolayer step to a multi-layer macro-step morphology, depending on the vicinal angle. High-resolution X-ray diffraction (HRXRD) and photoluminescence results suggest the high structural and optical qualities of the GaN films. Cross-sectional transmission electron microscope observations illustrate the abrupt interface and good periodicity of GaN/AlN SLs, which agree well with the HRXRD results. It is promising that the vicinal substrate is a good choice for the high-quality III-nitride films and their heterostructure growth.