Thin film of GaN:Mg, pyramidal GaN:Mg on GaN, sapphire and AlN substrates were grown in a MOCVD system under same growth conditions and at the same time. In samples with Mg-doped GaN pyramids on GaN:Si template a strong ultra-violet band with few phonon replicas dominated at low temperature and was attributed to transitions from shallow donors to shallow Mg acceptor. In samples grown on sapphire and AlN substrates the ultra-violet band appeared as a structureless band with the maximum at about 3.25eV. There was a possibility that the structureless ultra-violet band and the ultra-violet band with phonon structure have different origin. In addition to the ultra-violet band, the blue luminescence band peaking at 2.9eV was observed in samples representing GaN:Mg pyramids on GaN:Si substrate. It was preliminary attributed to transitions from shallow donors to Zn acceptor in GaN:Si substrate.

Defect-Related Photoluminescence in Mg-Doped GaN Nanostructures. M.A.Reshchikov, F.Shahedipour-Sandvik, B.J.Messer, V.Jindal, N.Tripathi, M.Tungare: Physica B, 2009, 404[23-24], 4903-6