X-ray optics of in situ synchrotron topography of InGaAs on GaAs

The x-ray optics for high-resolution x-ray topography during in situ molecular beam epitaxial growth of InGaAs on GaAs are critically reviewed. Analysis of dislocation contrast, intensity and geometrical distortion reveals that use of the 224 reflection in the Bragg geometry at a wavelength of 1.48 Angstrom is optimal for such double-crystal topography experiments. We deduce and show experimentally that a 004 channel-cut monochromator is optimal, resulting in significant reduction in exposure times over our present configuration. We present images of misfit dislocations showing evidence for the first time of phase contrast from lattice distortions.