Evolution of Epitaxial Quantum Dots Formed by Volmer–Weber Growth Mechanism

Germanium/silicon systems are among the most promising materials for development of current semiconductor electronics and photonics. Structures with germanium quantum dots on silicon are very interesting from the point of view of the creation of fast-speed transistors, photodetectors, and solar cells. The basic method of the synthesis of nanoislands is their self-organization in the process of molecular beam epitaxy. It was experimentally shown that ultrahigh surface densities (up to 1012–1013 cm–2) of nanometer-sized clusters may be achieved by deposition of germanium on oxidized rather than bare silicon surfaces. Nevertheless, this system with a thin layer of silicon oxide is poorly investigated. In this work, fundamental peculiarities of epitaxial formation and growth of quantum dots by the Volmer–Weber growth mechanism are considered. A kinetic model of nucleation and growth of three-dimensional islands by the Volmer–Weber mechanism based on the general nucleation theory is proposed for the first time. The developed model allows one to evaluate not only equilibrium values of a system with quantum dots (their average size and surface density), but also principally nonequilibrium parameters such as islands nucleation rate, size distribution function, and its time evolution. Dependencies of mean lateral size and surface density of Volmer–Weber quantum dots on the conditions of their synthesis (growth temperature and deposition rate) are obtained. The results of numerical simulations of Volmer–Weber growth for the Ge/SiO2/Si system show very good agreement with experimental data. The proposed theoretical model may be easily applied for other material systems where growth of islands by the Volmer–Weber mechanism is realized.