Two charge states of dominant acceptor in unintentionally doped GaN: Evidence from photoluminescence study

Photoluminescence of the dominant deep-level acceptor in high-purity freestanding GaN is studied over a wide range of excitation intensities. A yellow luminescence (YL) band at about 2.2 eV saturates with increasing excitation intensity, whereas a green luminescence (GL) band at about 2.5 eV increases as a square of the excitation intensity. The YL and GL bands are attributed to two charge states of the same defect, presumably a gallium vacancy-oxygen complex.