Abstract
The Raman spectrum from GexSi1−x/Si strained-layer superlattices is critically compared to that from commensurate and incommensurate single layers of the same composition. Our results confirm that the lattice mismatch in commensurate single layers and superlattices is entirely accommodated by a homogeneous tetragonal compression of the alloy layers. The technique is also used to measure absorption coefficients in single layers of GexSi1−x. We studied the Raman cross section of the three alloy peaks as a function of incident laser frequency in the interval 1.8 eV<ℏωL<2.7 eV. The relative cross section (alloy/Si) for superlattice samples exhibits a single peak at a value of ℏωL which lies between the energies of the E1 and E1+Δ1 optical transitions of bulk material for the same composition.
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