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X-ray optics of in-situ synchrotron topography studies of the early stages of relaxation in epitaxial InGaAs on GaAs

High resolution X-ray topography and diffraction measurements have been made at the Daresbury Synchrotron Radiation Source during in-situ molecular beam epitaxial growth of InGaAs on GaAs. Critical analysis of dislocation contrast, intensity and geometrical distortion reveals that use of the 224 reflection in the Bragg geometry at 1.48 Angstrom wavelength is optimal for such double crystal topography experiments. Examination of the beam-conditioner characteristics and performance had resulted in use of the 333 reflection from a channel-cut silicon crystal as a monochromator. We deduce and show experimentally that a 004 channel-cut monochromator is optimal, resulting in significant reduction in exposure times. We present images of misfit dislocations showing evidence for the first time of phase contrast from lattice distortions.