Defect-related photoluminescence in Mg-doped GaN nanostructures

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 ultraviolet (UVL) 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 UVL band appeared as a structureless band with the maximum at about 3.25 eV. There is a possibility that the structureless UVL band and the UVL band with phonon structure have different origin. In addition to the UVL band, the blue luminescence (BL) band peaking at 2.9 eV was observed in samples representing GaN:Mg pyramids on GaN:Si substrate. It is preliminary attributed to transitions from shallow donors to Zn acceptor in GaN:Si substrate.