X-ray diffraction analysis of Si1−xGex/Si superlattices

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Abstract
Si1−xGex/Si strained‐layer superlattices grown by molecular‐beam epitaxy on Si substrates were investigated by x‐ray double‐crystal diffraction and x‐ray grazing incidence diffraction. Both coherent and incoherent interfaces between the two components of the superlattices were observed. By fitting computer‐simulated double‐crystal x‐ray‐diffraction rocking curves to the experimental data, it is determined that there exist graded variations in both the component thickness ratio t1/t2 (t1 and t2 are the thickness of the Si1−xGex and the Si layers, respectively) and the fraction x in one sample. The x‐ray grazing incidence diffraction experiments reveal a lattice strain relaxation of about 27% in another sample. The lattice relaxation and the influence of variations of x and t1/t2 on the rocking curves are discussed.