ONE-PHONON RAMAN-SCATTERING FROM ARRAYS OF SEMICONDUCTOR NANO-CRYSTALS

We re-consider Raman scattering by LO-type phonons in a small semicond uctor crystal and derive a simple formula taking into account the high er order confined phonon modes, to describe the asymmetric Raman lines hapes observed experimentally. For a single crystalline sphere, we exp licitly calculate the relative contributions of the confined modes wit h different values of the radial quantum number. For arrays of such sp heres, we argue that, apart from a superposition of the above contribu tions from individual scatterers, there exists a collective scattering by a coherent mode which involves many spheres, unless their concentr ation is too small. This collective scattering is determined by an eff ective dielectric function of the composite medium and peaks near the Frohlich frequency. We apply these principles to the analysis and mode lling of Raman spectra taken from CdS doped SiO2 films. (C) 1997 Publi shed by Elsevier Science Ltd.