Transmission electron microscopy investigation of CdSe/ZnSe quantum dot structures

摘要

Different techniques of transmission electron microscopy were applied to study the Cd distribution and the formation of defects in CdSe/ZnSe structures with a nominal CdSe layer thickness t of three monolayers (ML) and different ZnSe cap layer thicknesses which were varied from 20 to 60 nm. The samples were grown by standard molecular-beam epitaxy at 350 degreesC. We report on the configuration of defects which appear in the CdSe/ZnSe structure from a critical thickness t > 2.5 ML. The defects originate in Cd-rich regions close to the CdZnSe layer and consist of stacking fault (SF) pairs on (I I I) crystal planes. The lengths of the dislocation lines and the sizes of the SFs increase with the cap layer thickness. The quantitative measurement of the Cd distribution indicates segregation with an efficiency of R = 0.74 +/- 0.04. [References: 9]