Origin of additional broad peaks in Raman spectra from thin germanium-rich silicon-germanium films

Additional broad peaks in Raman spectra from thin Ge-rich SiGe films were examined in detail. The broad peak on the low-wavenumber side of first-order optical phonon was also present for pure Ge, which indicates that the localized mode is not the reason for the broad peaks. Furthermore, other factors, e.g., strain, defect, phonon confinement effect, Fano effect, and fluorescence from oil, were excluded from the origin of the broad peaks. We assigned the broad peaks to surface optical phonon modes. The dependence of this surface mode on Ge concentration in Ge-rich SiGe was also investigated and the behavior was discussed. (C) 2016 The Japan Society of Applied Physics