Self-assembled growth of Quantum Dots in II-VI semiconductors

The self-assembled formation of II-VI Quantum Dots by MBE opens the possibility to develop Quantum Dot Emitters for the green spectral range, which are needed for new, exciting optoelectronic applications. It can be expected that green Quantum Dot laserdiodes will operate already at small threshold currents and with sufficient light power for the use in future Laser-TV systems. Furthermore, II-VI Quantum Dots as part of semiconductor microcavities allow the development of Polariton-Emitters, which represent a complete new class of devices, which is based on the strong coupling of excitons and photons. The epitaxial growth of self-assembled Quantum Dots is well established and understood for III-V semiconductors since many years. In contrast, the formation mechanism underlying the growth of II-VI Quantum Dots are still an object of research and controversial discussions. The decisive prerequisite for future applications of II-VI Quantum Dots is a detailed knowledge of the kinetic processes of the formation of Quantum Dots, in particular of their structural properties and their interaction with the surrounding barrier material. A comprehensive kinetic and thermodynamic analysis of the formation of CdSe-Quantum Dots on ZnSe will be presented and compared with the behaviour of III-V Quantum Dot systems. The kinetic analysis is based on the experimental determination of the islands density-and island size distribution function. It will be shown that the self-assembled growth of II-VI Quantum Dots unavoidable leads to a bimodal Quantum Dot structure, which has important consequences for the optical properties. The reversibility of the CdSe-Quantum Dot formation will be shown, clearly indicating the Stranski-Krastanow nature of the self-assembled growth process. The dynamics of the lateral redistribution of carriers between different types of Quantum dots of the bimodal structure will be demonstrated.