Semiconductor nanostructures receive increasing interest due to their potential for new device concepts, as well as from a scientific point of view. In structures smaller than the DeBroglie wavelength of electrons or holes, quantum confinement effects determine the electronic and optical properties. In typical semiconductor materials, these dimensions are in the order of several nm. Self-assembly is a powerful mechanism to fabricate a large number of nanostructures directly during epitaxial growth.
The properties of self-assembled structures depend sensitively on growth conditions such as substrate temperature, adatom flux, surface miscut etc. For the understanding and finally control of growth in order to fabricate structures with designed properties, structural investigation, i.e., the determination of size, shape, chemical composition and strain state is mandatory. X-ray diffraction is a powerful technique for this purpose. In particular, the strain fields within nanostructures as well as in the surrounding matrix can be determined with high precision. As strain fields depend sensitively on other properties such as size and chemical composition, the latter become accessible, too. With synchrotron radiation, even the distribution of chemical composition within objects with typically several nm height and 10 to 100 nm width can be established. Furthermore, with x-ray diffraction, the non-destructive investigation also of buried structures is possible. The latter is important, as for applications buried structures are needed, and during capping the structural properties may change considerably.
This talk will present scattering techniques sensitive to shape, composition and strain of nanostructures. Results will be presented on the shape and positional correlation of nanostructures in superlattices, and on the composition and strain profile in self-assembled islands on a sample surface. The effects of capping on such islands will be addressed as well.