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 m ethod involves the calculation of the cumulative sum (CUSUM) of deviat ions from an average lattice fringe spacing value. Even when the varia tion in individual lattice fringe spacings is large compared to the di fference in fringe spacing due to strain, the CUSUM method is capable of providing reliable strain determinations. The CUSUM approach was ap plied to three samples of semiconductor In1-xAlxSb/InSb (0 less than o r equal to x less than or equal to 0.5) bilayer and superlattice syste ms in [1(1) over bar0$] zone-axis projection. It was found that the ep itaxial strains obtained from the HREM CUSUM method agreed with the bu lk X-ray diffraction values when the sample thicknesses were on the or der of 80-100 nm. Thinner specimens, on the order of 10-20 nm, display ed significant surface relaxation effects.