Controlled 1-D to 3-D growth mode transition of GaN nanostructures and their optical properties

► Controlled 1D to 3D growth mode transition in GaN nanostructures. ► The growth directions of 3D nanostructures were polar and nanowires were non-polar. ► Intense yellow and red luminescence was observed from GaN nanowires and polyhedrons, respectively. ► Red luminescence is due to nitrogen vacancies related defect complexes.