Ultrafast time-resolved spectroscopy of Si nanocrystals embedded in SiO2 matrix

In this work, we present a comprehensive study of ultrafast transient photoinduced absorption of silicon nanocrystals (NCs) embedded in SiO2 matrix. The samples under investigation are single monolayers of Si-NCs embedded in SiO2. Our investigation gives an important insight of carrier relaxation channels of NCs in the picosecond to femtosecond time scale. Our analysis is based on theoretical predictions, where the coupling between the oxygen-related states and the quantized sublevels plays a crucial role to the relaxation of the confined excitons. We have time-resolved ultrafast relaxation paths of this material and we have compared our observations with recently published results. Finally, we have extracted information about the insertion of modified surface states within the gap that results in an observable pinning of the gap for NC sizes in the strong confinement regime. This study has important implications in the understanding of fundamental optical properties for the studied nanosystem. (C) 2008 Elsevier B.V. All rights reserved.