The document summarizes research on the growth of GaN nanocolumns using metalorganic chemical vapor deposition and their coalescence overgrowth. In part 1, MOCVD was used to overgrow MBE-grown GaN nanocolumns. Higher growth temperatures led to better crystal quality in the overgrown layer. In part 2, regularly arranged GaN nanocolumns were grown by MOCVD in a patterned structure and then overgrown. This resulted in reduced dislocation densities and improved optical properties compared to a thin film control sample.