The self-induced nanostructure formation has numerous advantages compared to both the top-down approach and catalyst-assisted bottom-up synthesis as the defects and impurity induced by the process can be minimized. It was seen that spontaneously grown nanowall network (NwN) of GaN simultaneously exhibit unprecedented optical and electrical properties. However, to engineer such nanostructure it is desirable to understand the growth mechanism. We studied the morphology evolution at the early stage of GaN NwN growth on sapphire substrate using atomic force and scanning electron microscopy. The careful analysis of nucleation and growth of islands at different growth intervals revealed that enhanced growth along the edge of (202 ̅1) facet leading to shape transition from a tetrahedron shaped island to a nanowall network. The first-principle calculation showed that the reduced diffusion barrier towards the edge of (202 ̅1) facet is responsible for the anisotropic growth leading to the formation of NwN. This study suggests that formation of NwN is an archetype example of structure dependent attachment kinetic instability induced shape transition in thin film growth.
Schematic wedge structure depicting the the preferred diffusion of adatoms towards the edge and energy of adsorption at different spatial co-ordinates along  which lead to formation of nanowall network of GaN.
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