In situ studies of the role of excess Ga on the growth morphology of thin GaN layers

Homoepitaxial GaN growth and heteroepitaxial growth of GaN on 6H-SiC(0 0 0 1) is studied in situ by low energy electron microscopy and low energy electron diffraction with the goal to elucidate the dominant influence of excess Ga on the growth morphology on substrates with different surface preparation. High-resolution cross-sectional transmission electron microscopy is used to determine the shape and internal structure of the GaN crystals. The results clearly show that (0 0 0 1)-face-terminated growth can be obtained only with Ga-rich conditions and that it is possible with significant excess Ga to reverse the microfaceting appearing in the very early stages of growth. (0 0 0 1)-face-terminated growth is discussed in terms of quasi-liquid phase epitaxy from an adsorbed Ga layer.