Hole delocalization in CdTe/${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Zn}}_{\mathit{x}}$Te quantum wells

We report on femtosecond pump-probe absorption measurements in CdTe/${\mathrm{Cd}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Zn}}_{\mathit{x}}$Te quantum wells with an unusual distribution of band offset: almost all the band-gap difference between the two constituent materials is found as a conduction-band offset. We have observed a blueshift of the exciton energy due to hard-core repulsion between excitons and an intriguing redshift in the presence of free electron-hole pairs. We evaluate the redshift due to different mechanisms and conclude that the redshift observed is due to hole delocalization throughout the structure resulting from the very shallow valence-band potential wells.