RAMAN-SPECTRA OF SEMICONDUCTOR NANOPARTICLES - DISORDER-ACTIVATED PHONONS

We present Raman spectra of four semiconductor doped glasses and a sin gle crystal of CdS0.55Se0.45 in the range 30-800 cm(-1) in the backsca ttering geometry. This includes the first-order Raman scattering from the disorder-activated zone-edge phonons and the LO phonons. TO phonon modes are not observed, as in bulk CdS, for the excitation well above the lowest gap. We show that the asymmetric line profile of the LO ph onon structure can be understood as a composite of two phonon modes: t he zone center and the zone edge phonons. Disorder-activated modes in the (30-130)-cm(-1) range and the higher-order Raman spectra are also observed and found to be consistent with this assignment.