Beyond the ensemble average: X-ray microdiffraction analysis of single SiGe islands

X-ray microdiffraction is used to analyze strain and composition profiles in individual micron-sized SiGe islands grown by liquid phase epitaxy on Si(001) substrates. From the variation of the scattered intensity while scanning the sample through a focused x-ray beam of few mu m size, an image of the island distribution on the sample is created. Using this image it is possible to identify particular islands and select them for analysis one by one. The Ge and strain distribution within each island is obtained from the intensity distribution in reciprocal space measured for several individual islands. The detailed shape of each measured island is obtained from scanning electron microscopy. Apart from truncated pyramid-shaped islands, we detect and characterize a small number of flat islands and show that they represent an earlier growth stage of the pyramidal shaped ones. This analysis is only possible by combining the local x-ray diffraction with scanning electron microscopy on exactly the same islands.