Size-dependent optical properties of silicon nanocrystals

We have synthesized green and red luminescent silicon nanocrystals in a SiO 2 matrix by RF co-sputtering on a quartz substrate. The transmission coeffi cient measurements were used to estimate the nanocrystal size distribution. The size distribution reveals peaks in the range 1.1-2.6 nm with a long ta il towards the larger size. As the nanocrystal size reduces photoluminescen ce spectrum shifts from red to green wavelengths. The measured PL emission energy is in agreement with the corrected LDA calculations. With decreasing nanocrystal size, the phonon Raman spectra exhibit softening accompanied w ith increasing asymmetrical broadening. The observed line shape is explaine d by considering phonon confinement in a spherical nanocrystal. The major c ontribution to the phonon line shape comes from those nanocrystals that fav or resonance interaction with either incoming or outgoing photon. (C) 1999 Elsevier Science B.V. All rights reserved.