Analysis of ultrathin Ge layers in Si by large angle convergent beam electron diffraction

Large angle convergent beam electron diffraction (LACBED) has been used to examine thin buried layers (single quantum wells) of Ge in Si which contain self-organized islands 80-200 nm across. Using plan view samples of epitax ially grown Si/GeSi/Si tricrystals, rocking curves for reflections from pla nes inclined to the growth (001) direction are found to be asymmetric. This asymmetry is the result of a normal displacement of atomic planes across t he GeSi layer induced by the lattice mismatch between Si and GeSi. A simple measurement of the asymmetry, using only small values of the deviation par ameter, has been related to the integrated Ge content of the layer by compa rison with two-beam dynamical calculations. Finite element analysis is used to correct for bulk strain relaxation in the Si cladding layers around isl and edges. For comparison electron energy loss spectroscopy (EELS) has been applied in cross-section to measure the composition profile within the lay ers. These results have been found to be in excellent agreement with LACBED . Finally a tentative model for the three-dimensional growth of Ge on Si is proposed.