Investigation of the local Ge concentration in Si/SiGe nanostructures by convergent-beam electron diffraction

SiGe multi quantum well structures were investigated by convergent-beam electron diffraction (CBED) measurements. Detailed layer characterizations were performed by acquiring series of bright field CBED patterns in the form of a line scan across the nanostructures in scanning transmission electron microscopy (STEM) mode. From the higher order Laue zone (HOLZ) lines the local lattice parameters were deduced. The Ge concentration corresponding to these lattice parameters was determined by means of the elasticity theory. In this work it is shown that the lattice constants can be determined locally with an accuracy of about ±0.001 to ±0.003 Å which leads to an accuracy of the corresponding Ge concentration of about 1–2%. The characteristics of the focused electron probe and its influence on the experimental data were used for an estimation of the spatial resolution of the CBED method. For comparison, experimental values regarding the spatial resolution were determined by investigating the abrupt interface between Si(1 1 1) and AlN(0 0 0 1).