Atomic scale strain and composition evaluation from high-resolution transmission electron microscopy images

Two methods used to evaluate the composition of ternary sphalerite structure crystals, relied on different sources of information of the high-resolution transmission electron microscopy (HRTEM) micrograph, is discussed. The first procedure is strain-state analysis, which uses the different lattice parameters of layer and substrate/buffer in strained layer heteroepitaxy. The tetragonal distortion of a pseudomorphically grown structure depends on specimen thickness due to the very small values <20 nm that are necessary in HRTEM. The second method is composition evaluation by the lattice fringe analysis (CELFA) procedure. The method uses a (000), (040), and (020) 3-beam imaging condition with the chemically sensitive (020) reflection centered on the optical axis. The CELFA procedure is an efficient and accurate image evaluation tool and is applicable to a whole variety of compound semiconductor systems such as CdxZn1-xSe, InxGa1-xAs, and AlxGa1-xAs.