Raman spectra of individual Si thin layers with 4–40 atomic layer thicknesses buried in GaAs (001)

We present a Raman scattering study of 4–40 layer thick Si films grown epitaxially on GaAs (001) and covered by GaAs. The peak shift and the broadening of the optical phonon modes of Si are discussed in terms of the planar biaxially tensile strains in the Si thin layers, the partial lattice relaxation, and the phonon confinement effect in the layers. The extraordinarily broad peaks of the Si phonon modes of the 4–8 layer thick films are not sufficiently explained by the above effects. We propose the three-dimensional confinement effect into the quantum well disks as a candidate of the origin of the peak energy shift and the broadening of the phonons.