The effect of Mn on self-assembled CdSe/ZnSe quantum dots

We have studied the fabrication of II-VI-based magnetic self assembled quantum dots (QDs) and the role of Mn atoms in their formation. The QDs involving Mn were grown by molecular beam epitaxy (MBE) using two different growth approaches. One series of QDs was obtained by depositing a CdSe layer on a Mn-passivated ZnSe buffer; and the other was grown by depositing a CdMnSe alloy layer on a bare ZnSe buffer. In photoluminescence (PL) experiments on QDs grown on Mn-passivated surface we observed a red shift of PL energy, indicative of QDs that are larger in size and/or richer in Cd content, as compared to QDs grown without Mn passivation. Furthermore, this QD system shows a significantly better uniformity of the QD size distribution, as manifested by narrower PL linewidth. We ascribe this observation to the nucleating effect of Mn on the formation of QDs. In the case of QDs grown by depositing the CdMnSe alloy directly on ZnSe, we have observed a blue shift in the PL line position relative to reference CdSe QDs. This blue shift results from the increase of the QD band gap. resulting from the incorporation of Mn into the CdMnSe alloy. No evidence of QD seeding was observed in this case. However, both QD systems showed a dramatic increase in the PL intensity and large Zeeman splittings when a magnetic field was applied, clearly demonstrating that the QDs grown by both methods are magnetic.