Study of time-resolved luminescence in GaAs doping superlattices

The time-resolved observation of luminescence in GaAs doping superlattices yields valuable information about the peculiar decay of the excited state in these systems. The luminescence originates from the recombination of photoexcited charge carriers across the tunable effective energy gap. The shift of the luminescence spectrum to lower energies and its associated decrease in intensity after the excitation has ended are due to the increase in superlattice potential associated with the diminishing number of photoexcited charge carriers. Two sets of samples grown by molecular-beam epitaxy with different design parameters were investigated. The relation between energetic position and intensity of the luminescence spectrum was compared with results of self-consistent subband structure calculations, yielding good overall agreement. From the experiments, radiative and total lifetimes were determined as a function of the excitation level. It was found that the lifetimes vary over several orders of magnitude with only moderate changes of carrier concentration, confirming earlier predictions.