Abstract
We present optical nonlinearities due to neutral and charged excitons trapped on monomolecular CdTe islands embedded in wide ZnTe–(Zn, Mg)Te quantum wells. These nonlinearities are demonstrated by low-temperature reflectivity and transmission experiments with additional continuous-wave excitation of the sample by different lines of an Ar2+ laser, at various intensities. Such “pumped” transmission measurements show the bleaching and blue-shift of the ground-state heavy-hole exciton, simultaneous to the appearance and strengthening of a lower energy contribution, assigned to a negative trion (X–). These phenomena are explained in terms of (i) space-charge regions in the heterostructure inducing a built-in electric field and (ii) a photo-induced excess of electrons which alters the probability of exciton creation. The experimental results are in good agreement with a simple modeling of the neutralization, by injected carriers, of the initial Stark shift of electronic levels.