The introduction of Mg was carried out by using 3 methods. One of them was the high-pressure growth of bulk single crystals from a Ga+Mg melt. Another was the diffusion of Mg into bulk GaN and into layers of GaN on Al2O3 at high temperatures and high pressures. The third was the implantation of Mg into bulk single crystals and into layers of GaN on Al2O3, followed by high-pressure annealing. The applied pressure was between 10 and 15kbar, and the temperature was between 1200 and 1500C. The growth of bulk highly Mg-doped crystals produced semi-insulating material with a characteristic blue photoluminescence band at about 3eV. High-pressure annealing of bulk crystals, as well as GaN/Al2O3 layers, in N2+Mg atmospheres led to an increase in Mg incorporation; with the highest diffusivity being observed for GaN/Al2O3 layers. The results revealed the importance of dislocations in the diffusion of Mg in GaN semiconductors. Moreover, the incorporation of Mg impurity appeared to be higher at the (00•1)Ga faces of wurtzite-structure crystals than at the (00•1)N faces. It was also demonstrated that there was a marked enhancement of the blue photoluminescence intensity in high-pressure annealed GaN/Al2O3 layers (N2+Mg atmospheres) and Mg-implanted and high-pressure annealed crystals and layers.

High Pressure Fabrication and Processing of GaN:Mg. T.Suski, J.Jun, M.Leszczynski, H.Teisseyre, I.Grzegory, S.Porowski, G.Dollinger, K.Saarinen, T.Laine, J.Nissilá, W.Burkhard, W.Kriegseis, B.K.Meyer: Materials Science and Engineering B, 1999, 59[1-3], 1-5