Resonance Raman scattering in CdTe-ZnTe superlattices

We present a resonance Raman study of strain and excitons in CdTe-ZnTe superlattices. We obtain the strain configuration of the samples from the strain-induced shifts in the Raman frequencies of confined longitudinal optical phonons. We find that CdTe-ZnTe superlattices are not always in a free-standing configuration, as previously suggested. For individual layer thicknesses of the order of 20-30 Å, our superlattices can be grown lattice matched with their Cd_0.1Zn_0.9Te substrates. In resonance with the fundamental gap of the superlattice, we observe an enhancement of the Raman cross section not only for CdTe phonons but also (in the samples with the thinnest layers) for phonons confined in ZnTe. This behavior can be understood in terms of a small valence-band offset.