Simulation and analysis of electron channeling contrast images of threading screw dislocations in 4H-SiC

Abstract

Using methods developed for modeling diffraction contrast of extended defects in thin foils, electron intensity profiles are simulated and found to qualitatively match channeling contrast of threading screw dislocations (TSDs) experimentally recorded by electron channeling contrast imaging (ECCI) using scanning electron microscopy. Plan-view images of TSDs axially penetrating (0001) 4H-SiC surfaces were computed using the Sturkey scattering matrix approach incorporating surface relaxation effects. Simulated diffraction contrast of the TSD allows identification of these threading defects as well as facilitates the determination of the dislocation Burgers vector. The directionality of TSD contrast features, simulated for various Bragg reflections and deviation parameters, is consistent with both ECCI and diffraction contrast imaging by transmission electron microscopy. Topographically enhanced imaging of atomic step spirals, generated by the TSDs, provides a direct determination of the TSD Burgers vector, which is shown to agree with the simulated ECCI contrast. The convergence of the incident electron beam is also shown to influence channeling contrast.