Recombination dynamics in GaAs/AlxGa1- xAs quantum well structures

Time-resolved and excitation-dependent photoluminescence of GaAs/AlxGa1-xAs quantum well structures reveal that recombination takes place between free carriers, not excitons, at room temperature for carrier densities at and above the mid -10¹⁶cm^-3level. Other samples show trapping and release of carriers from traps, evidence of dynamic Shockley, Hall, and Read recombination for optically active traps. The traps can be saturated to a large extent. Further studies show that they are associated with interfaces between different materials and that they become active at a temperature around 150 K. Results from all samples indicate that the bimolecular radiative recombination coefficient for quantum wells is no larger than the value of for bulk GaAs, and may in fact be smaller. This is one of the first studies of time-resolved luminescence of impurities in quantum well structures. Impurity decays at low temperatures are found to be quite slow. A spectral line which appeared to be longitudinal optical phonon-shifted emission is shown to be due to an acceptor impurity.