An investigation was made of the origin of a broad luminescence, which was observed at around 2.7 to 2.9eV in heavily Mg-doped material, by using first-principles pseudopotential calculations. A defect complex was identified which consisted of a Mg interstitial and a N vacancy. This gave rise to optical transition levels at around 2.8eV above the valence band in maximum; thus suggesting that the blue luminescence was caused by deep-donor to valence-band transitions. The formation of the Mgi-VN complex was enhanced by hydrogenation and was more prevalent in p-type samples which were grown under Ga-rich conditions.

Atomic model for blue luminescence in Mg-doped GaN S.G.Lee, K.J.Chang: Semiconductor Science and Technology, 1999, 14[2], 138-42