Excitonic optical properties of Ga-rich Al_(x)Ga_(1-x)N ternary alloy epitaxial layers (x=0.019, 0.038, 0.057, 0.077, and 0.092) have been studied by means of photoluminescence (PL) and time-resolved PL spectroscopy. The luminescence line due to radiative recombination of biexcitons was clearly observed for all of the five ternary alloy epitaxial layers with different Al compositions. The energy separation between exciton luminescence and biexciton luminescence increased with increasing Al composition, which indicated the increase in the binding energy of biexcitons in ternary alloys.
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