Photoluminescence band near 2.9 eV in undoped GaN epitaxial layers

The broad photoluminescence band with a maximum at about 2.9 eV widely observed in undoped epitaxial GaN is studied as a function of temperature and excitation intensity. We attribute the band to transitions from a shallow donor to a deep localized acceptor. The zero-phonon transition for this band is at 3.098 eV as determined from the fine structure at low temperatures. A local vibrational mode in the ground state with an energy of 36 meV is found.