Ordered arrays of defect-free GaN nanocolumns with very narrow excitonic emission line width

•Ordered arrays of very high quality, defect-free GaN nanocolumns.•Two step process: etching and overgrowth by Molecular Beam Epitaxy.•Effective filtering of dislocations.•GaN nanocolumns with any trace of extended defects.•Very narrow excitonic emission line width.