Phonon structures and Stokes shift in resonantly excited luminescence of silicon nanocrystals

We have studied luminescence Stokes shift and phonon-assisted luminescence in H-terminated and surface-oxidized Si nanocrystals by means of resonant excitation spectroscopy. For resonant excitation at energies within a broad luminescence band, TO- and TA-phonon related structures in luminescence spectra are observed in both H-terminated and surface-oxidized Si nanocrystals. In oxidized Si nanocrystals, the luminescence Stokes shift is large and the phonon-related structures are unclear compared to the case of H-terminated Si nanocrystals. The origin of the luminescence Stokes shift and surface localized states in surface-oxidized Si nanocrystals are discussed.