Biexciton Emission From Single Quantum-Confined Structures in N-Polar (000-1) InGaN/GaN Multiple Quantum Wells

We report on the observation of biexciton luminescence from single quantum-confined structures in N-polar InGaN/GaN multiple quantum wells (MQWs) grown on c-plane sapphire by metalorganic vapor phase epitaxy. Sharp emission lines are observed at different positions of the sample by micro-photoluminescence (μ-PL) mapping. The density of sharp emission lines is ≈0.3 μm⁻², which is comparable with the inversion domain (ID) density found from transmission electron microscope observation, suggesting that the sharp emission lines originate from single quantum-confined structures formed by the combination of quantum well and IDs in N-polar InGaN/GaN MQWs. It is found from the excitation power dependence of the PL intensity of two adjacent sharp lines that the intensity of biexciton luminescence at the lower energy side shows a quadratic dependence on the excitation power while that of exciton luminescence at the higher energy side increased linearly with increasing excitation power. The biexciton binding energy is found to be 0.8 meV.