Photoluminescence from defects in GaN

We present the most recent results of photoluminescence (PL) studies, classification of defects in GaN and their properties. In particular, the yellow luminescence band (labeled YL1) with a maximum at 2.17 eV in undoped GaN grown by most common techniques is unambiguously attributed to the isolated C-N acceptor. From the zero-phonon line (ZPL) at 2.59 eV, the -/0 level of this acceptor is found at 0.916 eV above the valence band. The PL also reveals the 0/+ level of the C-N at 0.33 eV above the valence band, which is responsible for the blue band (BLC), with the ZPL at 3.17 eV. Another yellow band (YL2) with a maximum at 2.3 eV, observed only in GaN grown by the ammonothermal method, is attributed to the V(Ga)3H complex. The nitrogen vacancy (V-N) causes the green luminescence (GL2) band. The V-N also forms complexes with acceptors such as Mg, Be, and Ca. These complexes are responsible for the red luminescence bands (the RL2 family) in high-resistivity GaN. The results from PL studies are compared with theoretical predictions. Uncertainties in the parameters of defects are discussed.