Exciton-exciton interaction and heterobiexcitons in GaN

Abstract

The formation of not only A biexcitons ${(XX}_{\mathrm{AA}})$ but also heterobiexcitons that consist of A and B excitons ${(XX}_{\mathrm{AB}})$ in a free-standing bulk GaN is identified by polarization-sensitive spectrally resolved FWM measurements. The FWM spectra and delay-time dependence show that the interaction between A and B exciton gives rise to the energy shifts of the spectra and the phase shifts of the quantum beating, which is considered as the effect of the unbound state of ${\mathrm{XX}}_{\mathrm{AB}}$ (i.e., ${\mathrm{XX}}_{\mathrm{AB}}^{*})$ and ${\mathrm{XX}}_{\mathrm{AB}}^{*}$ is found to play an important role in the FWM signals for all polarizations. The unbound A biexciton ${(XX}_{\mathrm{AA}}^{*})$ is also observed clearly in spectral and temporal domains.