Surface Detection of Strain-Relaxed Si1–xGex Alloys With High Ge-Content by Optical Second-Harmonic Generation.

We investigated the strain and surface structural properties of a strain-relaxed Si1–xGex alloy layer with high Ge-content using optical surface second-harmonic generation. Here, the Si1–xGex alloys are heteroepitaxial, and they are deposited onto Si substrates via ultra-high-vacuum-chemical vapor deposition. The in-plane strain and the composition $x$ of the Si1–xGex alloys were determined using Raman spectroscopy. The SH signals generated from three Si1–xGex alloy surfaces versus the rotational angle of the substrate were measured. The SH intensities for the combination of s-input/p-output polarization show fourfold symmetry; however, for s-input/s-output, the SH signals show eightfold symmetry with the rotational angle. Residual strain would induce an enhancement of the isotropic p-output SH component in the Fourier transform coefficient. Finally, the degree of symmetry of the SH signals from these three Si1–xGex alloy surfaces versus the rotational angle was related with the surface pit defects (densities and sizes) and surface roughness. [ABSTRACT FROM AUTHOR]