Formation and optical properties of stacked CdSe self-assembled quantum dots on ZnxCdyMg1−x−ySe barriers

Abstract

Single layer and stacked CdSe self-assembled quantum dots with ZnCdMgSe barriers for visible and white light emitters J.Multiquantum dot ͑MQD͒ layers of CdSe with Zn x Cd y Mg 1−x−y Se barriers have been grown by self-assembly ͑SA͒ using molecular beam epitaxy on ͑001͒ InP substrates and their optical and structural properties studied by steady state, polarized and power dependence photoluminescence ͑PL͒ studies, x-ray diffraction, and atomic force microscopy ͑AFM͒. Two sets of MQD structures of CdSe SAQDs were grown with different Mg contents in the Zn x Cd y Mg 1−x−y Se. Uncapped structures were also grown. The control of the electronic coupling of CdSe MQDs has been achieved by varying two parameters: the MgSe content on the Zn x Cd y Mg 1−x−y Se barrier and the Zn x Cd y Mg 1−x−y Se spacer thickness. Samples with properties intermediate between those of totally coupled MQDs and uncoupled ones were also grown. Results show that for the edge emission, polarization is mostly TM for the case of coupled QDs, indicating an excitonic delocalization along the growth axis, and TE polarized for the uncoupled QDs. For the surface configuration, the PL emission was slightly TM polarized for the uncoupled case, suggesting a surface organization. AFM images of an uncapped sample grown under the same conditions than the capped one confirmed the formation of connected structures ͑wirelike rather than dotlike͒ in the surface. No surface organization was obtained for the coupled case.

Magnesium effects on CdSe self-assembled quantum dot formation on ZnxCdyMg1−x−ySe layers

“…However, this model describes the direct correlation between an increase of atomic step density and a larger dot density, which was observed experimentally and cannot be directly explained by the thermodynamic model. In addition, the kinetic model is also supported by recent studies of CdSe/ZnCdMgSe stacked dot structures where the formation of connected structures (wirelike instead of dotlike) along the atomic steps has been observed [44]. The formation of these wirelike structures can be interpreted as the limit case for this stepwise model, where the density of the dots is so high that they are aligned consecutively along the step, forming a connected structure instead of individual dots.…”