The carrier dynamics in InGaN layers and InGaN multiquantum-well (MQW) structures were studied by employing the degenerate pump and probe, time-resolved photoluminescence (PL), and white-light pump and probe measurements. The results from degenerate pump and probe measurements showed that the internal field existed in undoped in InGaN but then was screened by the electrons supplied by the Si atoms in Si-doped InGaN. The rise time of Pl in InGaN MQW obtained using the upconversion method was very fast, below 1ps, the mechanism of which is due to the carrier-carrier interaction enhanced by the residual electrons. The ΔOD spectra in InGaN MQW observed in white-light pump and probe measurements indicated that the carrier temperature was substantially higher than the lattice temperature even at 40ps after pulsed photo-pumping.
Bound and unbound biexcitons in a free-standing bulk GaN are investigated by time-integrated and spectrally-resolved four-wave mixing measurements, where the formation of hetero-biexcitons that consist of A and B excitons (XXAB) as well as A-biexcitons (XXAA) and their unbound biexciton (XX*AA) are clearly observed. The FWM spectra and delay-time dependence are explained qualitatively and the interaction between A- and B-excitons gives rise to the phase shifts of the quantum beating and the energy shifts of the spectra, which is considered as the effect of the unbound state of XXAB (i.e. XX*AB). The unbound A-biexciton (XX*AA). Is also observed clearly in spectral and temporal domain and is found to play an important role in FWM signals for all polarizations.
Time-integrated and spectrally-resolved four-wave mixing (FWM) has been used to study dephasing dynamics of excitons in a free-standing bulk ZnO. Clear FWM signals due to A〉Γ5- and BΓ5-excitions have been observed. We discuss the dephasing dynamics based on the polariton dispersion and four-particle Coulomb correlations.