Dynamical Formation Process of Electron–Hole Droplets in a GaAs/AlAs Type-II Superlattice

Abstract

We have investigated photoluminescence (PL) dynamics at 10 K in a GaAs/AlAs type-II superlattice from the viewpoint of the dynamical formation of electron–hole droplets (EHDs) from electron–hole plasma (EHP) in a gas phase. From systematic time-resolved PL (TRPL) spectra, we found that only a broad PL band attributed to the EHP is observed in an initial time region within ∼0.4 ns, whereas the exciton- and biexciton-PL bands appear at ∼0.7 ns. The peak energy and width of the broad PL band hardly depend on time after ∼14 ns, associated with the fact that the effective temperature of carriers agrees with that of the excitonic system. This suggests the formation of EHDs in thermal quasi-equilibrium. We estimated the stability energy relative to the biexciton energy to be ∼3.1 meV from the line-shape analysis of the TRPL spectra. This is consistent with the result obtained from the line-shape analysis of the steady-state PL spectrum. Consequently, the above temporal changes of the TRPL spectra demonstrate the...