Huge binding energy of localized biexcitons in Al-rich AlxGa1−xN ternary alloys

Abstract

Excitonic optical properties of Al-rich AlxGa1−xN ternary alloy epitaxial layers have been studied by means of photoluminescence excitation spectroscopy. On the basis of the energy separation between exciton resonance and two-photon biexciton resonance, the binding energy of biexcitons was estimated to be 56±5 and 48±5 meV for the sample with x=0.81 and 0.89, respectively. The biexciton binding energy of 56 meV was approximately three times as large as the biexciton binding energy of 19 meV in AlN. The large enhancement of the biexciton binding energy resulted from the strong localization of biexcitons due to alloy disorder.