Localized electronic states and resonant Raman scattering from localized and quasiresonant phonons in Si-Ge layers

Resonant Raman scattering from localized Si and quasiresonant Ge and Ge-Si optical phonons has been used to study the characteristics of optical transitions at energies near the $E_1$ gap of Ge for structures of ultrathin Ge layers in bulk Si(100) and ultrathin Si layers in bulk Ge(100). Strong enhancements of the Ge-derived Raman scattering at excitation energies near 2.3 eV have been observed for Ge layers as thin as 7 Å. Si layer scattering shows no enhancement at the Ge host resonance. These results show localized electronic states exist in these materials well above the fundamental band edges.