Double-crystal x-ray diffraction from Si1−xGex/Si superlattices: Quantification of peak broadening effects

Abstract
Double‐crystal x‐ray diffraction has been successfully used to study dimensional and compositional variations in Si1−x Gex /Si superlattices. For most samples studied an adequate agreement between theoretical and experimental diffraction profiles is obtained by using a theoretical model (kinematical) which assumes uniform superlattices with abrupt interfaces. In some samples, however, the superlattice‐related diffraction peaks reveal an asymmetric broadening which is shown by comparison with dynamical diffraction simulations to be due to a grading in layer compositions and thicknesses throughout the superlattice stack. Detailed analysis of the diffraction data identified a gradual drift of 1.25% in the Ge flux during molecular beam epitaxy (MBE) growth. The MBE system parameters were modified to compensate for this effect and allow the growth of more structurally perfect strained‐layer superlattices.