Raman, photoluminescence and optical absorption studies on nanocrystalline silicon

Raman, photoluminescence (PL) and optical absorption results on silicon nanocrystals in SiO2 matrices prepared by RF sputtering method are presented. The samples have varying Si/SiO2 compositional fraction and are annealed at different temperature and duration. The average size of the nanocrystals is determined by the lineshape analysis of the first-order Raman spectra. Raman results further indicate the existence of a threshold annealing temperature for the formation of nanocrystals and increase in the nanocrystal size with increasing temperature and duration. Size-dependent blue shift of the absorption edge is observed from absorption experiments and is supported by Raman results. Room temperature and temperature dependent PL results are analyzed with the help of a phenomenological model. The PL results in conjunction with the Raman and absorption results indicate the involvement of both the core states and the interfacial states in the luminescence process.