Facet Control and Material Redistribution in GaN Growth on Three-Dimensional Structures

In this work, the influence of temperature and ammonia partial pressure on the GaN shell morphology grown on GaN microfin cores is investigated. We demonstrate that GaN overgrowth on 3D structures above a temperature of 1000 °C is determined by the competition between growth and decomposition that results in the redistribution of material between coexisting surfaces due to their different thermal stabilities. By studying the GaN shell growth under different reactor parameters, we show that decomposition processes, often disregarded during planar growth, strongly influence the vertical-to-lateral distribution of material during GaN growth on 3D structures. We observed that GaN shell growth on a-plane microfins at high temperatures and high ammonia fluxes results in an increase of the decomposition rate of the c-plane surfaces and thus, reduces the growth rate in the vertical direction. On the contrary, the lateral growth rate increases due to the diffusion of material from the less stable c-plane facet to the more stable a-plane facet where it reincorporates. Furthermore, under certain growth conditions, the decomposition of the c-plane outweighed the incorporation, reducing the height of the initial 3D structure during growth, while still gradually growing in the lateral direction, which resulted in the development of inclined facets. These findings highlight the high sensitivity of 3D structures to thermal decomposition processes and redistribution of material. Therefore, the understanding of these mechanisms and their interaction is required for controlling and optimizing growth on these architectures.