COMBINED RAMAN HREELS STUDY OF ZNSE-ZNS STRAINED-LAYER SUPERLATTICES

ZnSe-ZnS strained-layer superlattices have been investigated by combining Raman scattering and high-resolution electron energy loss spectroscopy (HREELS). The superlattices were grown on GaAs(001) by MOCVD without a buffer layer. Epitaxial growth of the superlattices was confirmed by the polarization selection rule of Raman scattering. Energy differences between the bulk (ZnS, ZnSe) LO phonons and the superlattice LO phonons indicate that strain is mainly localized in the ZnS layers. In HREELS the loss peak originating from ZnS must be assumed to be appreciably weaker than that from ZnSe. This result does not agree with the theoretical prediction based on the dielectric theory. We conclude that the reduction of the electron scattering intensity results from large strain in the ZnS layers.