On the Origin of the Yellow Luminescence Band in GaN

The yellow luminescence (YL) band with a maximum at 2.2 eV is the dominant defect-related luminescence in unintentionally doped GaN. The discovery of the mechanism responsible for this luminescence band and related defects in GaN took many years. Eventually, a consensus has been reached that the C-N acceptor is the source of the YL band (the YL1 band) in GaN samples grown by several techniques. Previously suggested candidates, such as V-Ga, VGaON, CNON, and CNSiGa, should be discarded. At the same time, other defects (such as the V-N, Be-Ga, and Ca-Ga) may cause luminescence bands with positions and shapes not much different from the YL1 band. In GaN containing high concentrations of gallium vacancies, oxygen, and hydrogen, complexes containing these species may also contribute in the red-yellow part of the photoluminescence spectrum. The main controversies related to the YL band are resolved.