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Phonon-assisted photoluminescence in wurtzite GaN epilayer

Photoluminescence of wurztite GaN epilayer was measured in the range of 4K to 300K. At low temperature, the neutral- donor bound exciton emission dominates the spectra, while with increasing temperature, free exciton emissions grow rapidly and finally become the dominant lines. The exciton linewidth due to exciton-phonon interaction was studied.Lo phonon-assisted photoluminescence associated with both the bound exciton and the free exciton were also observed. The temperature dependence of LO phonon-assisted emissions can be well explained by the phonon-assisted free exciton emission theory established for II-VI compound semiconductors. In particular, the study of 2LO phonon replica can provide information of the temperature dependence of the concentration and recombination lifetime of free excitons in GaN.