OBSERVATION OF CRYSTAL DISTORTIONS IN SIGE/SI SUPERLATTICE USING A NEW APPLICATION OF LARGE-ANGLE CONVERGENT-BEAM ELECTRON-DIFFRACTION

Cross-sectional specimens of Si0.67Ge0.33/Si(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 (1 $($) over bar$$ 10) cross-sectional samples of the superlattice using a small spot size (nanoprobe, size 5) in a Philips EM430 transmission electron microscope at 250 kV. The technique examines displacements in the diffraction contour g = 33 $$($) over bar 3 in the dark-field LACBED disc on crossing the interfaces as a function of specimen tilt about the [11 $$($) over bar 1] axis. The displacements have been related to the rotation of (11 $$($) over bar 1) planes in the superlattice due to the misfit stress, the relative rotation between (11 $$($) over bar 1) planes in the Si and SiGe layers being measured as delta theta = (1.05 +/- 0.03) X 10(-2) rad in agreement with a calculated rotation of 1.02 x 10(-2) rad.