High pressure fabrication and processing of GaN:Mg

Results on introduction of magnesium to GaN by three methods are presented. They consists of (i) high pressure growth of bulk, single crystals of GaN from Ga+Mg melt, (ii) diffusion of Mg to bulk GaN and to layers of GaN/Al2O3 at high temperatures and high pressures and (iii) implantation of Mg to bulk, single crystals and to layers of GaN/Al2O3 and subsequent high-pressure annealing. Applied pressure is in the range of 10–15 kbar and temperatures between 1200–1500°C. The growth of bulk, highly Mg doped crystals leads to the semi-insulating material with the characteristic blue photoluminescence band at about 3 eV. High pressure annealing of bulk crystals as well as GaN/Al2O3 layers in (N2 +Mg) atmosphere leads to the increase in the Mg incorporation with the highest diffusivity observed for GaN/Al2O3 layers. The performed experiments give an evidence of the importance of the defect (dislocations) in diffusion of Mg in the GaN semiconductor. Moreover, incorporation of Mg impurity appears to be higher on (00.1) Ga-face of the wurtzite GaN crystals than on the (00.−1) N-face. We demonstrate also a strong enhancement of the blue-photoluminescence intensity in high pressure annealed GaN/Al2O3 layers (N2+Mg atmosphere) and Mg-implanted and high pressure annealed GaN crystals and layers.