High Sensitivity Convergent Beam Electron Diffraction for the Determination of the Tetragonal Distortion of Epitaxial Films

We have optimized the sensitivity of convergent beam electron diffraction (CBED) by orienting the specimen such that the central (000) diffraction disc shows a pattern of defect lines that are most sensitive to tetragonal distortion. We compare the position of these lines in the experimentally obtained patterns with results from computer simulations, which need to be based on dynamical diffraction theory. In both experimental and simulated patterns the positions of the defect lines are determined by applying a Hough transformation. As a result of this optimized approach, we can measure the tetragonal distortion of a low temperature grown GaAs layer as low as 0.04%.