Optical properties of self-assembled quantum dots in single and double-layer configurations

We have performed photoluminescence (PL) experiments on CdSe and CdZnSe self-assembled quantum dot (QD) systems in single- and double-layer geometries. The QDs were formed by using molecular beam epitaxy to deposit three monolayers (ML) of either CdSe or CdZnSe. The ZnSe barrier thickness separating the QD layers in the double layer geometry was 20 monolayers (MLs). Strong photoluminescence (PL) peaks were observed for CdSe and CdZnSe QDs in both single- and double-layer QD systems. The intensities of the PL peaks from the QDs exhibited a systematic decrease with increasing temperature. The temperature dependence of the integrated PL revealed that the activation energy of CdSe QDs for PL quenching was significantly different between the two geometries. The observed difference in the activation energies of the CdSe QDs was discussed based on the effective carrier delocalization via neighboring higher-energy CdZnSe QDs in the double-layer QD system.