Photoluminescence dynamics of formation of electron-hole droplets in a GaAs/AlAs type-II superlattice

We report photoluminescence (PL) dynamics at 10 K in a GaAs/AlAs type-II superlattice, in which electrons (holes) are confined in the AlAs (GaAs) layer, focusing on dynamical formation of electron-hole droplets (EHDs) from electronhole plasma (EHP) in a gas phase. It was found from systematic time-resolved PL (TRPL) spectra that only a broad PL band attributed to the EHP is observed in an initial time region within similar to 0.4 ns, whereas the exciton-and biexciton-PL bands appear and grow with time after similar to 0.7 ns. In the time region after similar to 14 ns, the line shape of the broad PL band hardly depends on time; namely photogenerated carriers are in quasi-thermal equilibrium. The stability energy of the EHD was estimated to be similar to 3.1 meV relative to the biexciton energy from the line-shape analysis of the TRPL spectrum at 30 ns. Consequently, the above temporal changes of the line shape of the broad PL band demonstrate the dynamical transition from the EHP to the EHD during the PL decay process. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim