Luminescence of GaN nanocolumns obtained by photon-assisted anodic etching

GaN nanocolumns with transverse dimensions of about 50 nm were obtained by illumination-assisted anodic etching of epilayers grown by metalorganic chemical vapor deposition on sapphire substrates. The photoluminescence spectroscopy characterization shows that the as-grown bulk GaN layers suffer from compressive biaxial strain of 0.5 GPa. The majority of nanocolumns are fully relaxed from strain, and the room-temperature luminescence is free excitonic. The high quality of the columnar nanostructures evidenced by the enhanced intensity of the exciton luminescence and by the decrease of the yellow luminescence is explained by the peculiarities of the anodic etching processing.