Study of strain in partially relaxed Ge epilayers on Si(100) substrate

Ge epilayers of different thicknesses are grown by molecular-beam epitaxy with Sb as a surfactant on Si(100) substrates. X-ray diffraction illustrates that these Ge thin films are partially strained, and the strains decrease gradually with increasing epilayer thickness. Raman spectra reveal a downward shift of the Ge-Ge mode peak as the epilayer thickness increases. In the regions of high strain, the relationship between the Raman shift of this mode and the strain in the partially relaxed samples is considerably different from the linear relationship reported before, which is mainly attributed to the spatial confinement effect of phonons in a nanocrystal. (C) 1999 American Institute of Physics. [S0003-6951(99)00129-1].