Abstract
Efficient carrier multiplication has been reported for several semiconductor
nanocrystals: PbSe, PbS, PbTe, CdSe, InAs, and Si. Some of these
reports have been challenged by studies claiming that carrier multiplication
does not occur in CdSe, CdTe, and InAs nanocrystals, thus raising
legitimate doubts concerning the occurrence of carrier multiplication
in the remaining materials. Here, conclusive evidence is given for
its occurrence in PbSe nanocrystals using femtosecond transient photobleaching.
In addition, it is shown that a correct determination of carrier-multiplication
efficiency requires spectral integration over the photobleach feature.
The carrier multiplication efficiency we obtain is significantly
lower than what has been reported previously, and it remains an open
question whether it is higher in nanocrystals than it is in bulk
semiconductors.
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