Below band gap photoreflectance transitions in epitaxial GaN

A photoreflectance (PR) and photoluminescence (PL) study has been performed on a Si-doped epitaxial GaN layer that contains impurity or defect related below band gap features in its PR spectrum. In the 300K PR spectrum, these features appear at energies of 3.26 and 3.33eV, respectively, but below 180K they can no longer be seen. The 3.26eV line evidently corresponds to a donor acceptor pair transition, also seen in PL. The origin of the 3.33eV line is uncertain, but may correspond to a transition involving the nitrogen vacancy.