FLA phonons in GexSi1−x/Si strained-layer superlattices

The Raman spectrum due to the folded longitudinal acoustic (FLA) phonons in the Ge x Si 1 i− x /Si (x=0.5) superlattices has been observed. We observed for the first time up to the 9th FLA mode in the sample constituted by Ge x Si 1−x with a layer thickness d 1 =50 A and Si with a layer thickness d 2 =250 A. The observed acoustic modes of various wave vectors were identified by comparing with theoretical calculations. The striking coincidence between theoretical and experimental results indicate that the Rytov model is useful for the large-period Ge x Si 1−x /Si superlattices