Conventional and high-resolution transmission electron microscopy was used to study the Cd distribution and structures of defects in single and multiple CdSe layers in a ZnSe matrix. The samples involved nominal CdSe layer thicknesses of between 1.7 and 3.5 monolayers, and were grown by molecular beam and atomic layer epitaxy under various conditions. In all of the samples, ternary CdZnSe wetting layers with Cd-rich regions (small islands) having sizes of less than 10nm and a density of about 1011/cm2 were observed. The Cd concentrations in the wetting layers and the small islands increased with the CdSe layer thickness. Regions with sizes of 20 to 30nm (large islands) and Cd concentrations greater than 40% occurred in specimens with CdSe layer thicknesses greater than 2.5 monolayers. In the vicinity of the large islands, stacking faults were generated preferentially; leading to the so-called coffee-bean contrast in plan-view transmission electron microscopic images.

Cd Distribution and Defects in Single and Multilayer CdSe/ZnSe Quantum Dot Structures. D.Litvinov, D.Gerthsen, A.Rosenauer, H.Preis, E.Kurtz, C.Klingshirn: Physica Status Solidi B, 2001, 224[1], 147-51