Observation of resonant exciton cooling in GaAs/AlGaAs multiple quantum well structures

In this paper we report detailed low temperature (6 K) photoluminescence excitation spectra of GaAs/AlGaAs multiple quantum well structures while monitoring the intensity of the recombination due to n = 1 electron/heavy hole 1S and 2S excitons. The excitation spectra over the region of interest of the 1S exciton recombination, apart from some previously observed exciton absorption peaks, are flat. Whereas, the excitation spectra of the 2S exciton recombination exhibit some previously unreported decreases in the luminescence intensity. We ascribe these dips to a reduction in the effective 2S exciton temperature and thus the 2S exciton luminescence intensity. The reduction in the 2S exciton temperature at the particular excitation photon energies of the dips is caused by the selective creation of excitons in the continuum and the subsequent emission of one or two LO phonons resulting in 1S excitons with K similar to 0. (C) 1997 Elsevier Science Ltd