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

• Published in: IEEE journal of quantum electronics 2015-12, Vol.51 (12), p.1-6
• Main Authors: Ji-Hong Zhao, Chun-Hao Li, Qi-Dai Chen, Bu-Wen Cheng, Hong-Bo Sun
• Format: Article
• Language: English
• Subjects: Femtosecond laser; Metals; Optical surface waves; Rough surfaces; second-harmonic generation; Si1-xGex alloys; Silicon; Silicon germanium; Strain; strain-relaxation; surface defects; Surface roughness
• ISSN: 0018-9197; 1558-1713
• DOI: 10.1109/JQE.2015.2499724

We investigated the strain and surface structural properties of a strain-relaxed Si 1-x Ge x alloy layer with high Ge-content using optical surface second-harmonic generation. Here, the Si 1-x Ge x 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 Si 1-x Ge x alloys were determined using Raman spectroscopy. The SH signals generated from three Si 1-x Ge x 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 Si 1-x Ge x alloy surfaces versus the rotational angle was related with the surface pit defects (densities and sizes) and surface roughness.