Temperature-dependent Raman scattering studies in nanocrystalline silicon and finite-size effects

A comparative study of the temperature-dependent Raman scattering of nanocr ystalline and bulk silicon is presented. The nanocrystalline silicon sample s were made by a cw laser annealing process, and the characteristic dimensi ons were determined with a phenomenological phonon confinement model. Exper imental results indicate a higher degree of anharmonicity in nanocrystals c ompared to that in the bulk. The anharmonic constants are found to be highl y size dependent and increase greatly with decreasing dimensions. The phono n lifetimes have two contributions, one temperature dependent and the other temperature independent, both decreasing rapidly with decreasing nanocryst al size. The temperature-dependent term tau (0) is important for larger nan ocrystals, while the temperature-independent term tau (1) becomes dominant for nanocrystals of sizes less than 4 nm.