Recombination dynamics in GaAs/AlxGa1- xAs quantum well structures

Time-resolved and excitation-dependent photoluminescence of GaAs/Al
x
Ga
1-x
As quantum well structures reveal that recombination takes place between free carriers, not excitons, at room temperature for carrier densities at and above the mid -10
¹⁶
cm
^-3
level. 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
B
for quantum wells is no larger than the value of
B
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.