| Low-dimensional semiconductor heterostructures have been extensively studied because of their potential applications and the unique physical phenomena they exhibit. Quantum dots (QDs) represent the latest innovation in the development of these structures. Due to the three-dimensional confinement of the carriers, semiconductor QD structures are expected not only to lead to the improvement of the device performance but also to limit the device degradation of the II-VI semiconductor-based devices. On the other hand, ZnCdMgSe material system shows potential in fabricating interband and intersubband devices with applications from the UV-visible to infrared range due to their widely adjustable bandgaps. For the first time, single and multi-QDs (MQDs) of CdSe with ZnCdMgSe barriers were successfully grown by self-assembling using molecular beam epitaxy and their properties were characterized. Atomic force microscopy (AFM) measurements showed CdSe QDs in uncapped structures. Control and reproducibility of the QD size leading to light emission throughout the entire visible spectrum was obtained by varying the CdSe deposition time. Based on this, stacked QD structures consisting of three QD layers emitting in the red, green and blue regions of the spectrum were grown. Photoluminescence (PL) measurements exhibited bright white emission that was observed by eye, at 77K or at room temperature, because of the mixing of colors. Preliminary light emitting diodes structures designed to obtain white emission were grown and tested.; Size reduction, higher uniformity, higher density and a blue-shifted PL peak of the QD layer, by increasing Mg concentration in the Zn1-x CdxMg1-x-y Se barrier were demonstrated. Results pointed to Mg as chemical factor that induced QD formation, either by increasing the atomic steps or/and by changing the surface energy of the ZnxCdyMg1-x-ySe. Electronic coupling and polarization of the emitted light from the MQD layers were accomplished by changing the spacer thickness and its MgSe composition. Power dependence studies demonstrated the PL peak position associated with coupled QDs depends on the laser excitation power while the one of the uncoupled QDs remains invariable. Polarized studies consistent with AFM images demonstrated the presence of a spontaneous QD organization for the uncoupled MQDs (wire-like structure). No surface organization was obtained for the coupled case. |
