Different responses of localized and extended excitons to exciton-exciton scattering manifested in excitation density-dependent photoluminescence excitation spectra

Excitation density-dependent photoluminescence excitation (PLE) measurement s are performed for a disordered two-dimensional (2D) In0.40Ga0.60As/GaAs(3 11)B quantum dot superlattice (QDSL) containing localized and extended stat es separated by a mobility edge. For low excitation densities, the PLE spec trum is independent of excitation density. In the extended state region, it takes the shape of the absorption spectrum of the 2D QDSL. With increasing excitation density, the PLE spectral shape is dramatically changed. For ex citation densities at which the state filling can be excluded, it is found that the different responses of localized and extended excitons to exciton- exciton scattering are responsible for the observed change in the PLE spect rum. A qualitative explanation for the evolution of the PLE spectrum is pre sented based on the excitation density-dependent capture, relaxation and re combination times obtained previously in time-resolved photoluminescence (T RPL) experiments. The mobility edge extracted from the modification of the PLE spectrum is in good agreement with that determined by TRPL measurements . To show the effect of coupling strength, a comparison of the excitation d ensity-dependent PLE spectra is made between the 2D QDSL and a weekly coupl ed quantum dot array. It further confirms the existence of highly extended states in the 2D QDSL. (C) 2001 American Institute of Physics.