Abstract
Free-carriers (FC) profoundly impact the performance of silicon nanophotonic devices including amplifiers, modulators, and ring microcavities [1]. Optimizing such devices relies on a good understanding of FC dynamics and how it depends on the FC density (N). This is particularly true in Si nanowaveguides, where surface recombination is important [2] and leads to an N-dependent lifetime [3]. Large density of surface-states enhances the N-dependence as compared to bulk, where recombination is impurity or defect dominated (as described by the Shockley-Read-Hall theory) while for very high N values, Auger process enters the picture [4]. The effect of carrier density on the recombination lifetime has been studied in silicon rib-waveguides [5], where surface effects are reduced somewhat relative to the case of nanowires considered in this paper, since carriers cannot diffuse away from the core region as in the rib. We used a pump-and-probe technique to investigate the recombination rate, and observe carrier lifetimes ranging over almost one order of magnitude for the range of N explored.
© 2017 IEEE
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