Nature of the SiGaN antisurfactant layer enabling MOVPE growth of GaN nanowires

Over the past decade, the growth of nanowires via metalorganic vapor phase epitaxy has commonly employed silicon incorporation in high concentration in the gas phase to produce long nanowires (>10 μm) with high aspect ratios (>100). This effect is primarily attributed to the formation of a thin Si-rich antisurfactant layer on the {1−100} sidewalls during growth, which suppresses lateral expansion while facilitating species diffusion along the nanowire's lateral facets. Despite general agreement on the critical role of this antisurfactant layer, its exact structure and composition remain largely uncharacterized, with few, often contradictory, proposals in the literature. In this work, we investigate the layer structure and composition using transmission electron microscopy and complement our findings with density functional theory calculations. Our results confirm that the layer is fully crystalline and operates as an antisurfactant on m-plane GaN, highlighting the importance of Si in the growth of GaN nanowires. Additionally, we demonstrate that once this antisurfactant layer has been used to grow long nanowires, ex situ chemical etching of this layer enables high-quality growth of a shell, which is otherwise hindered by the antisurfactant nature of the SiGaN layer.