Coupled II-VI semiconductor quantum dots: Manipulation of spin polarization by inter-dot exchange interaction

We have studied self-assembled QDs in the form of single- and double-QD layer systems. The double layers were formed either from CdSe and CdZnSe layers, or from CdSe and CdZnMnSe layers, separated by ZnSe barriers. When a magnetic field is applied to the CdSe/CdZnSe double-QD layer, the intensities of the circularly polarized PL peaks corresponding to the CdSe and CdZnSe layers exhibit significant differences, reflecting correspondingly large differences in the degrees of spin polarization of the CdSe and the CdZnSe QDs. This contrasts with the PL observed on single-layer CdSe or CdZnSe QD reference structures, both of which show nearly identical dependences on the field. The behavior observed on the double-layer QD structures is interpreted in terms of anti-parallel spin interaction between carriers localized in the coupled QD pairs. Such spin interaction is even more pronounced in double-layer structures in which CdZnMnSe QW or QDs are used instead of CdZnSe QDs, reflecting the high potential of magnetic quantum structures in the context of spin-polarized applications.