X-ray diffraction study of plastic relaxation in Ge-rich SiGe virtual substrates

We report on the experimental and theoretical investigation of the relaxation in Ge-rich SiGe/Ge/Si heterostructures. The experimental x-ray diffraction data are interpreted with the help of a model including both edge and 60${}^{\circ }$ misfit dislocations in the calculated x-ray scattering intensity. Our results show that highly positionally correlated edge dislocations dominate in the relaxation of the compressive strain at the Ge/Si interface, while a smaller tensile strain at the SiGe/Ge interfaces released by uncorrelated/little correlated 60${}^{\circ }$ dislocations.

Figure 1

Geometry of the network of dislocations in a stepped heteroepitaxial system.

Figure 2

(a) A model epitaxial film consisting of two layers with 60${}^{\circ }$ dislocations at the top interface and 90${}^{\circ }$ at the bottom interface. (b)–(e) Transverse scans through symmetrical (004) reflection: (b) and (c) uncorrelated dislocations on both interfaces, (d) and (e) uncorrelated dislocations at the top interface and correlated dislocations at the bottom interface.

Figure 3

The reciprocal space maps of symmetric $\left(004\right)$ and asymmetric $\left(\overline{2}\overline{2}4\right)$ reflections of sample 1. The color intensity distribution are the experimental data, the contour lines present the calculated intensity distribution. The yellow arrow marks the direction from Si$\left(\overline{2}\overline{2}4\right)$ reflection to the origin of the reciprocal lattice.

Figure 4

The longitudinal and transverse scans through the Ge buffer and SiGe top layer peaks of the sample 1.

Figure 5

The reciprocal space maps of symmetric $\left(004\right)$ and asymmetric $\left(\overline{2}\overline{2}4\right)$ reflections of sample 2. The color intensity distribution are the experimental data, the contour lines present the calculated intensity distribution. The yellow arrow marks the direction from Si$\left(\overline{2}\overline{2}4\right)$ reflection to the origin of the reciprocal lattice.

Figure 6

The longitudinal and transverse scans through the Ge buffer and SiGe top layer peaks of the sample 2.