INTERFACE VIBRATIONAL-MODE IN CDSE/ZNTE SUPERLATTICES

We have observed an interface vibrational mode in CdSe/ZnTe superlattices (SL's) by Raman scattering. The frequency of this interface mode lies above the optical-phonon bands of bulk CdSe and ZnTe compounds, and the ion displacements in the mode are sharply localized at the Zn-Se interfaces of the SL's. When the force constants of all four kinds of bonds in the SL's are taken to have thc same values as in the corresponding bulk compounds, the frequency of this interface mode, 222 cm-1, calculated using the linear-chain model is consistent with the experimental result, 222 cm-1. Both the smaller masses and the larger force constants of the interface bonds in the SL's rather than the mass effect alone, suggested previously, favor the appearance of the interface modes.