Structural and optical evidence of island correlation in CdTe/ZnTe superlattices

Abstract

The properties of superlattices consisting of 2 monolayer wide CdTe insertions into ZnTe spacer barriers with thickness ranging from 3 to 75 monolayers are investigated by means of transmission electron microscopy and photoluminescence spectroscopy. We show that quasi zero-dimensional CdTe islands form in this highly lattice-mismatched system. For spacer thickness smaller than 25 monolayers, the islands are vertically correlated along the axis tilted by 40° with respect to the growth direction, while for thicker ZnTe spacers no correlation is observed. The electronic coupling between the correlated islands manifests itself by the appearing of an additional emission band at energies lower to those corresponding to uncorrelated dots. The optical spectroscopy data reveal zero-dimensional localization of excitons by the electronically coupled islands. The decay time of the excitonic recombination is found to be over an order of magnitude longer in the case of the coupled islands than in the case of isolated ones.