Nonlocal resonant optical phonons and the local properties of ultrathin Ge layers on Si(100)

The effect of the degeneracy of the Ge optical modes with the phonons of Si in an epitaxial Ge(100) layer less than 10 thick in Si(100) has been studied by Raman scattering. The interaction of the Ge modes with the Si acoustic phonons produces changes in frequency that are small compared to the shifts due to strain. While the Ge-derived modes are resonances of the Ge-Si system, the weak mixing of the Ge and Si modes means the Raman spectra can still be used to characterize the Ge layers. © 1989 The American Physical Society.