Symmetrically strained Si/Ge superlattices on Si substrates

Abstract

Symmetrically strained Si/Ge superlattices with an overall thickness of 0.2 μm, well above the critical thickness (≅ 10 nm) of unsymmetrically strained superlattices of the same composition, are studied. Strain adjustment is obtained by growing thin homogeneous ${\mathrm{Si}}_{0.4}$ ${\mathrm{Ge}}_{0.6}$ buffer layers (20 nm) on Si substrates. The period lengths vary in the range 0.7-2.8 nm. Raman scattering experiments confirm quantitatively the strain distribution and the superlattice periodicity. Observed zone-folded acoustic-phonon energies agree well with theoretically expected dispersion relations.