Diffraction of 100 to 200 keV X-rays from an Si1-xGex gradient crystal:: comparison with results from dynamical theory

In a large Czochralski-grown Si1-xGex (0.02 less than or equal to x less than or equal to 0.07) gradient crystal, diffraction patterns have been measured in symmetrical Laue geometry using synchrotron radiation in the energy range 100-200keV. The experimental data are in very good agreement with the results from geometrical optics theory for distorted crystals, if the creation of new wavefields for strain gradients larger than a critical value is taken into account. In this sense, the crystal behaves like an ideal gradient crystal. If the normal absorption is disregarded, for reflection 111 and 100 keV energy, the full width at half-maximum values and the peak reflectivities of the diffraction patterns range from 14.6 " and 97%, respectively, to 70.9 " and 74%, respectively, for a variation in the Ge concentration from 3.5 to 5.3 at.%.