Diffuse X-ray Scattering as a Tool to Characterize Morphology of Multilayered Structures of Ultra-small (Submonolayer) Quantum Dots*

Characterization of submonolayer quantum dots (QDs) (i.e., QDs formed from deposition of less than a monolayer of material) is challenging due to their small size and a low electron density contrast between the embedded QDs and the host. For example, our samples have ZnTe/ZnSe type-II submonolayer QDs grown via migration enhanced epitaxy, in which the contrast between Te- and Se-containing sublattices is very low. We have devised a systematic diffraction analysis to obtain quantitative structural information about such hard-to-image systems. In this procedure, a large portion of the reciprocal space is mapped to acquire both out-of-plane and in-plane information. Vertical self-ordering of QDs is determined from out-of-plane and non-specular reflectivity maps, while diffuse scattering analysis is used to check in-plane correlations. This work greatly enhances the potential for extracting structural information of complex embedded 3D QD structures.