Self-organized formation processes of CdSe quantum dots studied by reflection high-energy electron diffraction

Initial stages of the growth of CdSe layers on ZnSe and formation processes of CdSe quantum dots (QDs) are studied by in situ reflection high-energy electron diffraction (RHEED). The growth process of the CdSe layer at the initial stage is divided into five stages: (1) stable two-dimensional (2D) growth, (2) metastable 2D growth, (3) metastable growth just before the onset of QD formation, (4) QD formation, and (5) coalescence of QDs. There is a critical growth stage at which the formation of QDs is initiated. It is demonstrated by the RHEED investigation that the formation of the QD is associated with the release of strain energy. Because the strain energy stored in the dislocation-free 2D layer cannot be fully released as long as the surface is flat, in order to decrease the strain energy, the development of the islands occurs, competing with smaller increase of the surface energy.