Raman spectroscopic characterization of germanium-on-insulator nanolayers

We fabricated Ge-on-insulator monocrystalline nanolayers with thickness H = 1-18 nm using SiO2 substrate and studied their Raman spectra. The spectra display longitudinal optical ( LO) phonon and confined acoustic phonon bands. For H < 5 nm, additional bands due to amorphous-like inclusions appear in the spectra. With a decrease in H, the LO phonon Raman band displays enhancement and downshift. Also, as H decreases, the band homogeneously broadens proportionally to 1/H. We attribute these findings to a reduction in reflectance plus electron quantum size effect, thickness-dependent stress, and surface-disorder-induced phonon lifetime reduction. (C) 2016 AIP Publishing LLC.