Origin of the Q=11 meV bound exciton in GaN

The bound exciton line S with a localization energy of Q=11.5 meV has been studied by power and temperature dependent photoluminescence (PL). High resistivity undoped and Mg doped wurtzite GaN samples grown by MOCVD were analyzed. The experimental data provide strong evidence that line S is due to recombination of excitons bound to ionized shallow donors which is consistent with theoretical expectations. A brief discussion of the coupling strength of different excitons to LO phonons is given.