Evolution of optical phonons in epitaxial Ge1−ySny structures

• Published in: Journal of Raman spectroscopy 2020-11, Vol.51 (11), p.2305-2310
• Main Authors: Kim, Young Chan, Lee, Taegeon, Ryu, Mee‐Yi, Kouvetakis, John, Rho, Heesuk
• Format: Article
• Language: English
• Subjects: Epitaxial growth; Epitaxial layers; Germanium; germanium tin; Inductively coupled plasma; optical phonon; Phonons; polarized Raman spectroscopy; Raman spectra; Raman spectroscopy; Silicon substrates; strain; Strain relaxation; stress; Tin; Wavelengths
• ISSN: 0377-0486; 1097-4555
• DOI: 10.1002/jrs.5986

We report polarized Raman scattering results of Ge1−ySny (0 ≤ y ≤ 0.09) epitaxial layers grown on Ge‐buffered Si substrates. Polarized Raman spectra from the sample surfaces revealed strong Ge–Ge longitudinal optical (LO) phonon responses. The Ge–Ge LO(z) phonon wavenumber decreased systematically as the Sn content increased. Linear fitting results of the Ge–Ge LO(z) phonon wavenumber shifts as a function of Sn content suggested that a partial strain relaxation occurred in the Ge1−ySny layers. Spatially resolved Raman mapping measurements from the cross section of a Ge0.938Sn0.062 samplev showed that the peak wavenumber of the Ge–Ge transverse optical phonon decreased gradually toward the top surface, providing direct evidence that the residual built‐in strain initially formed at the Ge0.938Sn0.062/Ge interface tended to relax gradually along the growth direction. Further, a hydrogen inductively coupled plasma treatment induced a greater homogeneous strain profile in the Ge0.938Sn0.062 layer. We report polarized Raman studies of Ge1−ySny epitaxial layers. The Ge–Ge LO(z) phonon wavenumber shifts as a function of Sn content suggested that a partial strain relaxation occurred in the GeSn layers. Cross‐sectional Raman mapping measurements provided evidence that the residual strain in GeSn tended to relax gradually toward the top surface. Further, hydrogen treatment modified the strain profile.