Optimization of GaN Growth with Ga-Polarity by Referring to Surface Reconstruction Reflection High-Energy Electron Diffraction Patterns

GaN films with Ga-polarity on (0001) sapphire substrates grown by plasma-assisted molecular beam epitaxy were investigated. The optimization of the growth conditions was performed referring to reflection high-energy electron diffraction reconstruction patterns during the cooling processes. Three kinds of surface reconstruction patterns, named (5×5), (1×2) and (2×2), were observed during the cooling processes. Structural, optical and electrical properties of the GaN films, identified by different reconstruction patterns, were characterized to determine the optimal growth conditions. It was found that high-quality films can be obtained when the films show the (1×2) pattern. Under this condition, we obtained an electron mobility at room temperature of as high as 567 cm2/Vs without using a GaN template.