Strain and composition of capped Ge/Si self-assembled quantum dots grown by chemical vapor deposition

We have investigated the composition and the strain profile of Ge/Si self-assembled quantum dots. The quantum dots, grown by low-or high-pressure chemical vapor deposition, were covered by a silicon cap layer. The composition and the strain were measured by the selected area transmission electron diffraction of a single quantum dot. The self-assembled quantum dots exhibit a quadratic deformation. No lateral relaxation of the lattice is observed from the main part of the quantum dot. An average composition of Ge around 50% is deduced. The average composition is found dependent on the size of the islands. This composition is correlated to the photoluminescence energy.