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 th an or equal to 0.07) gradient crystal, diffraction patterns have been measu red 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 crea tion of new wavefields for strain gradients larger than a critical value is taken into account. In this sense, the crystal behaves like an ideal gradi ent crystal. If the normal absorption is disregarded, for reflection 111 an d 100 keV energy, the full width at half-maximum values and the peak reflec tivities of the diffraction patterns range from 14.6 " and 97%, respectivel y, to 70.9 " and 74%, respectively, for a variation in the Ge concentration from 3.5 to 5.3 at.%.