Observation of crystal distortions in SiGeSi superlattice using a new application of large-angle convergent-beam electron diffraction

Cross-sectional specimens of Si0.67Ge0.33Si(001) strained-layer superlattice (SLS) have been employed to detect crystal distortions originated by misfit stresses in strained layers. A large-angle convergent-beam electron diffraction (LACBED) technique has been applied to (110) cross-sectional samples of the superlattice using a small spot size (nanoprobe, size 5) in a Philips EM430 transmission electron microscope at 250 kV. The technique examines displacements in the diffraction contour g = 333 in the dark-field LACBED disc on crossing the interfaces as a function of specimen tilt about the [111] axis. The displacements have been related to the rotation of (111) planes in the superlattice due to the misfit stress, the relative rotation between (111) planes in the Si and SiGe layers being measured as δθ = (1.05 ± 0.03) × 10−2 rad in agreement with a calculated rotation of 1.02 × 10−2 rad.