Investigation of inhomogeneous in-plane strain relaxation in Si/SiGe quantum wires by high resolution x-ray diffraction

The structural properties of Si/SiGe quantum wires, which were grown by local solid source molecular beam epitaxy through a Si3N4/SiO2 wire-like shadow mask, were investigated by means of high resolution x-ray coplanar and x-ray grazing incidence diffraction,as well as by transmission electron microscopy. High resolution x-ray coplanar diffraction was used to obtain the average in-plane strain in Si/SiGe wires before and after removing the Si3N4/SiO2 shadow mask. X-ray grazing incidence diffraction measurements were performed to obtain information on the shape of the wires and on the depth-dependent strain relaxation. A finite element method was used to calculate the strain distribution in the Si/SiGe wires and in the Si substrate which clearly show the influence of the Si3N4/SiO2 shadow masks on the strain status of the Si/SiGe wires in agreement with the experimental data.