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-as sisted molecular beam epitaxy were investigated. The optimization of the gr owth conditions was performed referring to reflection high-energy electron diffraction reconstruction patterns during the cooling processes. Three kin ds of surface reconstruction patterns, named (5 x 5), (1 x 2) and (2 x 2), were observed during the cooling processes. Structural, optical and electri cal properties of the GaN films, identified by different reconstruction pat terns, were characterized to determine the optimal growth conditions. It wa s found that high-quality films can be obtained when the films show the (I x 2) pattern. Under this condition, we obtained an electron mobility at roo m temperature of as high as 567 cm(2)/Vs without using a GaN template.