Abstract
Radiative and non-radiative recombination processes of free excitons in GaN have been investigated in terms of exciton-polariton and bound exciton by using pump-probe technique. The initial non-radiative trapping process ( 40ps) of the resonantly-excited free excitons was attributed to generation of the bound excitons, in good agreement with the coupled rate equations in the four energy levels. As free excitons are released from the bound excitons due to thermal excitation, the activation energy for donor-bound exciton ( Eact = 16.3 ± 5.2 meV) was estimated by temperature-dependent photoluminescence measurements. A comparison of the reflectance spectrum at 4K with the exciton-polariton model enabled us to obtain the exciton-polariton dispersion with oscillator parameters such as resonance energy, polarizibility, and damping linewidth. The radiative recombination time of the activated free excitons ( 305ps) was observed to be comparable to the theoretical exciton-polariton decay time near the bottleneck regime ( 297ps), in which a significant group velocity reduction is seen.
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