Room-temperature photoluminescence bands of wurtzite material, which peaked in the red (1.8eV), yellow (2.2eV) and blue (2.8eV) spectral range, were studied. It was shown that the yellow and blue bands were introduced by Si and Mg doping, respectively, while co-doping with Si and Mg generated the red band. At high doping levels, the yellow and blue bands exhibited marked peak shifts, to higher energies, with increasing power density. This provided very strong evidence for their being due to distant donor-acceptor pair recombination. The deep centers which were involved in donor-acceptor recombination exhibited an electrical activity which was opposite to that of the shallow level of the dopant. They were suggested to arise from self-compensation, and to be vacancy-dopant associates. The self-compensation was found to be weak in the case of Si-doping but was significant for Mg-doping. A recombination model was proposed which accounted for the essential properties of all 3 bands in deliberately doped material. The results also suggested that the yellow and blue bands in nominally undoped samples arose from distant donor-acceptor pairs which involved residual Si and Mg impurities, respectively, as well as their respective vacancy associates.

Origin of defect-related photoluminescence bands in doped and nominally undoped GaN U.Kaufmann, M.Kunzer, H.Obloh, M.Maier, C.Manz, A.Ramakrishnan, B.Santic: Physical Review B, 1999, 59[8], 5561-7