Phonon replicas lineshape in GaN epilayers: The A and B exciton contributions

A thorough investigation of the lineshape of phonon-assisted emission in a high-quality c-plane GaN epilayer is presented up to 200K. Before addressing the lineshape analysis, we corrected distortions in the phonon replica spectra due to etaloning effects, by performing photoluminescence and reflectivity measurements. The comparison with existing models for phonon replicas shows that the commonly adopted description of the exciton-phonon interaction involving a single excitonic band leads to a large discrepancy with the experimental data. Only the consideration of the complex nature of the excitonic band in GaN, including A and B exciton contributions, allows accounting for the temperature dependence of phonon replicas lineshape.