The effect of annealing on photoluminescence from defects in ammonothermal GaN

Ammonothermal GaN samples with the concentration of free electrons of 10(18) and 10(19) cm(-3) were annealed in a wide range of temperatures (T-ann = 300-1400 degrees C) under atmospheric N-2 pressure and under ultra-high N-2 pressure conditions to avoid the GaN decomposition. Photoluminescence (PL) studies reveal the YL2 band with a maximum at 2.3 eV before annealing and two new PL bands after annealing at T-ann > 600 degrees C: the OL3 band with a maximum at 2.1 eV and the RL4 band with a maximum at 1.6-1.7 eV. The ammonothermal GaN samples have high concentrations of complexes containing gallium vacancy (V-Ga), hydrogen, and oxygen. The first-principles calculations suggest that the V-Ga-3H(i) complex is the origin of the YL2 band, while the V-Ga-3O(N) complex is responsible for the RL4 band.