Title: Carrier cooling, trapping and recombination processes
and their dynamics in SiNCs: fingerprints for MEG en SSQC

Wieteke de Boer - June 23 2008

Abstract

Si nanocrystals (SiNCs) embedded in a SiO2 matrix are intensively studied as a possible
basis for photovoltaic devices. In spite of that, carrier relaxation and recombination
processes in SiNCs are still not fully understood.
In this thesis optical experiments of electron/hole relaxation in SiNCs are presented. Two
experimental methods were used. In time-resolved (TR) PL experiments we monitor
exciton-related kinetics using time-correlated photon counting detection mode. The
results imply an ultrafast cooling of the system within a ps timescale, which in
contradictory to theoretical predictions. Another important result is the appearance of an
ultrafast (ps) intense PL band in the visible with typical dynamical features which have
not been reported on before.
The fast recombinations and relaxations are investigated further with TR absorption
spectroscopy. From a comparative study between the results obtained with the two
different experimental methods, we draw some important conclusions, which are in
contrast with results reported by other groups. Firstly, we seem to have observed absence
of MEG upon excitation with high photon energy and secondly, we postulate that results
of transient induced absorption cannot be linked with results of TR PL.