Optical properties of CdTe/ZnTe quantum dot superlattices

We report on the optical properties of CdTe/ZnTe quantum dot superlattices with different thickness of the spacer between neighboring layers of quantum dots. It is found that for a spacer width larger than 20 monolayers (ML) of ZnTe, only one emission band is observed which is ascribable to excitonic recombination in isolated CdTe islands. On the other hand, if the ZnTe spacer width is smaller than View the MathML source, a second luminescence band evolves on the low energy side of the main PL peak, which we attribute to recombination of excitons in spatially correlated CdTe quantum dots. This additional emission is characterized by a small oscillator strength and by a very long (View the MathML source) decay time, as evidenced by the photoreflectance and the time resolved luminescence spectroscopy. Thus, it is interpreted as being due to a recombination of electrons and holes localized in two spatially separated but neighboring CdTe quantum dots.