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Localization dynamics of biexcitons and electron–hole plasmas in GaN-based mixed crystals



We report time-resolved photoluminescence (PL) spectra in highly excited AlxGa1−xN mixed crystals under band-to-band excitation. The PL dynamics of excitons and biexcitons reveals that the localization of excitons begins within a few picoseconds delay time and almost all the excitons relax into the localized band-tail states within 10 ps delay time after laser excitations. The biexciton formation time of ∼2 ps is extracted from the rise time of the PL intensities of excitons and biexcitons. These results indicate that biexcitons are formed from the free excitons and that the exciton localization, due to the potential fluctuations in the mixed crystals, reduces the exciton–exciton collisions and the formation of free biexcitons.