Speaker
Jeff Krupa
(University of British Columbia)
Description
Ultrafast all-optical switching offers great benefit to communication technologies, as all-optical logic operations can be performed at tremendous (terabit-per-second) data rates. Semiconductors are an obvious choice to perform such switching, given their strong optical nonlinearity, but standard bulk semiconductors suffer from relatively slow recombination—often with nanosecond or microsecond charge-carrier lifetimes. These are unfavorable material characteristics aspects for ultrafast all-optical switching, as the slow recovery impedes the ultimate data rate. To address the demands of ultrafast all-optical switching, the work put forward here investigates semiconductor nanoparticles as a material for ultrafast photoexcitation and recombination. Composite materials comprised of semiconductor nanoparticles in a polymer host are fabricated and investigated. Semiconductor nanoparticles of Si and SiC are employed, with average particle diameters of 20 nm and 50 nm, respectively. An ultrafast pulsed laser system, with 100 fs optical pulses, is used to carry out pump-probe spectroscopy on these materials. For Si, it is found that the photoexcited charge-carriers undergo recombination with a lifetime of 12 ps (being on the order of one thousand times shorter than the 20 ns bulk lifetime). For SiC, it is found that the photoexcited charge-carriers undergo recombination with a lifetime of 2.5 ps (being on the order of one million times shorter than the 22 µs bulk lifetime). A theoretical model is developed to interpret the experimental findings. The model characterizes the ultrafast charge-carrier dynamics within the nanoparticles according to diffusion and recombination processes. It is found that the increased surface-to-volume ratio of the nanoparticles promotes surface recombination, over a picosecond timescale, and this leads to the observed short charge-carrier lifetimes. The enhanced recovery times seen in these materials can be beneficial for future implementations of ultrafast all-optical switching.
Author
Jeff Krupa
(University of British Columbia)
Co-authors
Mr
Brandon Born
(University of British Columbia)
Mr
Christopher M. Collier
(University of British Columbia)
Dr
Jonathan F. Holzman
(University of British Columbia)
Mr
Simon Geoffrey-Gagnon
(University of British Columbia)
