T. Taliercio et al., Excitons and trions confined on CdTe nano-islands: Optical tuning of the dielectric response, PHYS ST S-B, 220(2), 2000, pp. 875-884
We present optical nonlinearities due to neutral and charged excitons trapp
ed on monomolecular CdTe islands embedded in wide ZnTe-(Zn, Mg)Te quantum w
ells. 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. Su
ch "pumped" transmission measurements show the bleaching and blue-shift of
the ground-state heavy-hole exciton, simultaneous to the appearance and str
engthening of a lower energy contribution, assigned to a negative trion (X-
). These phenomena are explained in terms of (i) space-charge regions in th
e heterostructure inducing a built-in electric field and (ii) a photo-induc
ed excess of electrons which alters the probability of exciton creation. Th
e experimental results are in good agreement with a simple modeling of the
neutralization, by injected carriers, of the initial Stark shift of electro
nic levels.