“…The most common defect-related PL band in high-purity GaN templates is the green luminescence (GL) band with a maximum at about 2.4 eV at low temperatures [5][6][7][8][9]. The GL band is also strong in bulk GaN grown from solution [10,11]. In different undoped GaN layers grown by HVPE, other defect-related PL bands include the red luminescence (RL) band with a maximum at 1.8 eV [9,[13][14][15], the yellow luminescence (YL) band at 2.2 eV [5,8,9,14], the blue luminescence (BL) band at 2.9 eV [14,16], and the ultraviolet luminescence (UVL) band with the main peak at 3.26 eV [5,13,16,17].…”