Confined and propagating phonons in ultrathin CdTe/ZnTe superlattices

We report the occurrence of confined longitudinal-optical phonons in (CdTe${)}_{\mathit{n}}$(ZnTe${)}_{\mathit{n}}$ (n=2, 3, and 5) short-period superlattices as observed in their Raman spectra, complementing the infrared reflectivity studies in which confined transverse-optical phonons were reported [Phys. Rev. B 47, 1998 (1993)]. The dispersion of ZnTe-LO phonons in these highly strained superlattices, determined from the frequencies of the confined phonons is in agreement with inelastic neutron scattering data on bulk ZnTe. The present study also reveals in these superlattices confined CdTe-LO phonons as well as folded acoustic phonons for n=5.