“…Since the depth of Mg acceptors is quite high and causing severe problems in devices sensitive to the series resistance of the p-region, such as LEDs or LDs, changes in the structural quality and electronic properties of GaN:Mg occurring as the Mg concentration increases have been looked into in some detail. It turns out that, for high Mg concentrations approaching 10 2 cm À3 , a high density of inversion boundary domains (IBDs), stacking faults (SFs) and dislocations is generated due, as it is thought, to forming of Mg 2 N 3 precipitates limiting the Mg solubility [97][98][99][100][101]. The high density of IBDs causes the inversion of the dominant growth plane mode from Ga-polar at low Mg concentration to N-polar at high Mg concentration [99], with consequent increase in the uptake of Si and O shallow donors and increased compensation [97][98][99].…”