Localized biexcitons in AlxGa1-xN ternary alloy epitaxial layers

Excitonic optical properties of AlxGa1-xN ternary alloy epitaxial layers have been studied by means of photoluminescence (PL), time-resolved PL, and PL excitation (PLE) spectroscopy. The luminescence line due to radiative recombination of biexcitons was clearly observed in an Al0.08Ga0.92N epitaxial layer. The PL decay time of excitons and biexcitons was estimated to be 350 and 210 ps, respectively. PLE spectroscopy of biexcitons enabled us to observe a two-photon absorption process of biexcitons. On the basis of the energy separation between exciton resonance and two-photon biexciton resonance, the binding energy of biexcitons in Al0.08Ga0.92N was estimated to be 15 +/- 2 meV. This value was approximately 2.5 times as large as the binding energy of biexcitons in GaN. This value was also found to be comparable to the observed energy separation between the exciton luminescence and the biexciton luminescence, which indicated the strong localization of biexcitons. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.