Growth evolution of polar-plane-free faceted GaN structures on (11(2)over-bar2) and ((1)over-bar(1)over-bar2(2)over-bar) GaN substrates

We compare the growth evolution of polar-plane-free faceted GaN structures on (11 (2) over bar2) and ((1) over bar(1) over bar2 (2) over bar) planes. The crystal morphologies of the three-dimensional (3D) GaN structures depend on surface orientations. To discuss the underlying mechanism, the temporal developments of the cross-sectional shapes during growth are visualized by periodically inserting AlGaN markers. Quantitative analyses using these markers reveal that as the growth proceeds, the growth rates of the top and inclined facets of the 3D GaN on (11 (2) over bar2) monotonically decrease, whereas those of the 3D GaN on ((1) over bar(1) over bar2 (2) over bar) monotonically increase. The opposite tendencies are attributed to the difference in the surface diffusion of adatoms between the top and inclined facets. Furthermore, it is suggested that the surface bond configuration of each crystallographic plane strongly affects the adatom migration, resulting in distinct 3D GaN morphologies on (11 (2) over bar2) and ((1) over bar(1) over bar2 (2) over bar).