Cd distribution and defects in single and multilayer CdSe/ZnSe quantum dotstructures

Conventional and high-resolution transmission electron microscopy (TEM) was applied to a study of the Cd distribution and structure of defects in sing le and multiple CdSe layers in a ZnSe matrix, The samples containing nomina l CdSe layer thicknesses t(n) between 1.7 and 3.5 monolayers (ML) were grow n by molecular beam and atomic layer epitaxy under different conditions. In all samples ternary CdZnSe wetting layers with Cd-rich regions with sizes of less than 10 nm (small islands: SIs) and a density of similar to 10(11) cm(-2) are observed, The Cd concentration in the wetting layer and the SIs increase with t(n). In addition, regions with sizes of 20-30 nm (large isla nds: LIs) and Cd concentrations >40% occur in specimens with t(n) > 2.5 ML. In the vicinity of the LIs stacking faults are preferably generated leadin g to a "coffee-bean" contrast in plan-view TEM images. The multilayer struc tures with t(n) approximate to 2.5 ML display a predominant vertical correl ation of the SIs at a ZnSe spacer thickness of 12 ML.