Formation Mechanisms of (In,Ga)N Nanoshells Conformally Grown around Pencil-like GaN Nanowires

We present a comprehensive study on the formation mechanisms of (In,Ga)N nanoshells conformally grown around pencil-like GaN nanowires by plasma-assisted molecular beam epitaxy. A detailed growth model is proposed, describing the morphological evolution of the nanoshell tip from an initial truncated pyramid to the final pyramidal form. This transformation is likely driven by the minimization of surface energy of the growing nanocrystal, more precisely, by a change in the preferential semipolar growth plane, from the r-plane (101̅2), for the GaN nanowire core, to the s-plane (101̅1), for the overgrown (In,Ga)N nanoshell. Furthermore, we investigate the facet- and temperature-dependent incorporation of indium, showing that the indium content is higher at the nanowire tip than on the sidewalls and decreases with increasing growth temperature across all facets. Finally, by making simple approximations, we provide quantitative estimations of the indium concentration in the nanoshell, offering partial quantitative insight into the composition profile. These findings contribute to the understanding and more precise control of (In,Ga)N nanoshell growth for employment in nanowire-based optoelectronic devices.