Determination of elastic strains in epitaxial layers by HREM

A new technique is presented to directly measure strains in epitaxial systems from high-resolution electron microscope (HREM) images. This method involves the calculation of the cumulative sum (CUSUM) of deviations from an average lattice fringe spacing value. Even when the variation in individual lattice fringe spacings is large compared to the difference in fringe spacing due to strain, the CUSUM method is capable of providing reliable strain determinations. The CUSUM approach was applied to three samples of semiconductor In 1−xAlxSb/InSb (0≤x≤0.5) bilayer and superlattice systems in [11¯0] zone-axis projection. It was found that the epitaxial strains obtained from the HREM CUSUM method agreed with the bulk X-ray diffraction values when the sample thicknesses were on the order of 80–100 nm. Thinner specimens, on the order of 10–20 nm, displayed significant surface relaxation effects.