Abstrakt
We report in detail on the dynamics of photoexcited charge carriers in size-controlled silicon nanocrystals in silicon nanocrystal/SiO2 superlattices. The samples were prepared using plasma enhanced chemical vapor deposition and subsequent thermally induced phase separation.
This unique approach allows preparation of well-defined Si nanocrystals. Experimental techniques of time-resolved absorption and photoluminescence were used to monitor the carrier dynamics on a wide time scale from picoseconds to milliseconds for a set of samples with different parameters (nanocrystal size, hydrogen annealing).
The initial fast decay (tens of picoseconds) dependent on pump intensity for excitation levels exceeding one electron-hole pair per nanocrystal can be interpreted in terms of the bimolecular recombination with constant B = (2-3) x 10(-10) cm(3) s(-1). The slow pump intensity independent decay (microseconds) can be reproduced well by a stretched-exponential function.
The dependence of stretched-exponential parameters on photoluminescence photon energy and sample properties agrees well with the picture of trapped carriers. (C) 2013 Elsevier B.V. All rights reserved.