Phenomenological quantum confinement models for excitons and phonons applied to photoluminescence and Raman spectra of silicon nanocrystals

The photoluminescence and vibrational properties of silicon nanocrystals are studied in a multilayered system elaborated by successive evaporations of SiO and SiO2 layers with controlled thicknesses. The multilayer systems are deposited on a glass substrate (Herasil). The photoluminescence and Raman spectra are fitted by phenomenological exciton and phonon confinement models accounting for the size distribution of the embedded nanocrystals. Contrary to the same study realized with multilayer systems deposited on silicon substrate, the two confinement models (phononic and excitonic) do not lead to the same size distribution. An amorphous silicon phase was also detected in Raman spectroscopy that prevented a good fitting accuracy by the model. Contribution of the substrate to the thermal crystallization process is thus discussed, as well as the origin of the photoluminescence and vibrational properties in terms of quantum confinement or interfacial defects.