TEM characterization of self-organized CdSe/ZnSe quantum dots

CdSe quantum dots (QDs) grown on ZnSe were investigated by various transmis sion electron microscopy (TEM) techniques including diffraction contrast im aging, high-resolution and analytical transmission electron microscopy both of plan-view as well as cross-section specimens. The size of the QDs range s from about 5-50 nm, where from the contrast features in plan-view imaging two classes can be differentiated. In the features of the smaller dots the re is no inner fine structure resolvable, The larger ones exhibit contrast features of fourfold symmetry as expected for pyramid-like islands. Corresp onding simulations of diffraction contrast images of truncated CdSe pyramid s with the edges of the basal plane orientated parallel to [100] are in rel atively good agreement with this assumption, In TEM diffraction contrast im aging of cross-section samples the locations of the quantum dots are visual ized by additional dark contrast features. The QDs have a distinct larger e xtension in growth direction compared to the almost uniformly thick CdSe we tting layer The presence of the CdSe QDs was also confirmed by energy-dispe rsive X-ray spectroscopy.