Heteroepitaxial growth of cubic GaN on Si(001) coated with thin flat SiC by plasma-assisted molecular-beam epitaxy

High-quality cubic GaN films were grown on Si(001) coated with flat ultrathin SiC under different Ga/N flux ratios. The 2.5-nm-thick cubic SiC film proved to be an effective buffer layer for cubic GaN growth on Si(001). Under a Ga-rich condition, films with local atomically flat surfaces were obtained, and the x-ray diffraction full-width at half maximum of (002) peak was 19 min for a 0.82-μm-thick film. The reduced SiC surface roughness decreased the defect density in the GaN epilayers. Under a N-rich condition, the GaN films showed statistical roughening of the surface and a characteristic columnar structure. Under the Ga-rich condition, the columns grew up and then laterally coalesced, so that an atomically flat surface with flat areas in size from 0.05 to 0.40 μm was formed.