X-RAY-DIFFRACTION ANALYSIS OF SI1-XGEX/SI SUPERLATTICES

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.