Atomic structure of pyramidal defects in Mg-doped GaN

A detailed transmission electron microscopy study of pyramidal defects appearing in highly Mg-doped GaN is reported. It is shown that these defects are closed pyramidal inversion domains. From a high-resolution microscopy study, we propose atomic models for inversion domain boundaries which consist of Mg₃N₂ building blocks for both the basal and inclined facets of the pyramids. In Mg-doped GaN grown by metalorganics vapor phase epitaxy, these pyramidal inversion domains are a few nanometers wide, and their density is high enough to play a role in the free hole density decrease at high Mg doping.