Unveiling the Growth Mode Switching Role of As in the Formation of Dodecagonal/Hexagonal GaN Microrods

Self-assembled III-nitride columnar structures hold promise for enhancing emission efficiency in the UV spectral range. The introduction of As during molecular beam epitaxial growth of GaN leads to the formation of microrods with 12 sidewalls arranged in alternating a- and m-planes. This paper investigates the growth of 12-walled columns to elucidate the nucleation mechanisms, seeding, and the role of As in growth mode switching. We uncover a dual role of As: it induces the formation of Ga droplets, serving as the initiation points for microrod growth, through its antisurfactant effect and by creating an As-containing shell over the droplets. Observation of hybrid hexagonal/dodecagonal microrods reveals the necessity of exposing microrod sidewalls to impinging As for the formation of dodecagonal columns. This is supported by the observed dodecagonal-to-hexagonal growth mode switching upon cessation of As supply during growth.