Structural and magneto-optical studies on multiple quantum dots containing magnetic semiconductors

We have fabricated single and multi-layer self-assembled quantum dot (QD) systems based on CdSe/ZnSe combination, including magnetic semiconductors (DMSs). Transmission electron microscopy (TEM) images shows that magnetic QDs are formed within the CdMnSe layer, and they are vertically correlated in multi-layer quantum dot systems. Magneto-optical experiments were also carried out on those structures. The PL energy from multi-layer QDs appears at a lower energy than that emitted by a single QD layer, suggesting that there exists electronic coupling between the QD layers. When an external magnetic field is applied, the PL peaks from QDs both in single-layer and in multi-layer form exhibit a large intensity enhancements and energy shifts, a behavior that is typical for many low dimensional systems involving DMSs. The observed weak PL energy dependence in low magnetic fields can be understood in terms of magnetic polaron formation in these DMS QD systems. We also discuss statistical magnetic fluctuations in these systems, as revealed by PL line narrowing in a magnetic field.